Auto merge of #3384 - rust-lang:rustup-2024-03-17, r=RalfJung

Automatic Rustup

.github/workflows/dependencies.yml

@@ -6,6 +6,8 @@ on:
   schedule:
     # Run weekly
     - cron: '0 0 * * Sun'
+    # Re-bump deps every 4 hours
+    - cron: '0 */4 * * *'
   workflow_dispatch:
     # Needed so we can run it manually
 permissions:
@@ -135,8 +137,8 @@ jobs:
           gh pr edit cargo_update --title "${PR_TITLE}" --body-file body.md --repo $GITHUB_REPOSITORY
 
       - name: open new pull request
-        # Only run if there wasn't an existing PR
-        if: steps.edit.outcome != 'success'
+        # Only run if there wasn't an existing PR and if this is the weekly run
+        if: steps.edit.outcome != 'success' && github.event.schedule == '0 0 * * Sun'
         env:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
         run: gh pr create --title "${PR_TITLE}" --body-file body.md --repo $GITHUB_REPOSITORY

Cargo.lock

@@ -4400,6 +4400,7 @@ dependencies = [
  "rustc_lexer",
  "rustc_macros",
  "rustc_middle",
+ "rustc_privacy",
  "rustc_session",
  "rustc_span",
  "rustc_target",
@@ -6279,12 +6280,14 @@ dependencies = [
 
 [[package]]
 name = "windows-bindgen"
-version = "0.52.0"
+version = "0.55.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "970efb0b6849eb8a87a898f586af7cc167567b070014c7434514c0bde0ca341c"
+checksum = "073ff8a486ebad239d557809d2cd5fe5e04ee1de29e09c6cd83fb0bae19b8a4c"
 dependencies = [
  "proc-macro2",
  "rayon",
+ "serde",
+ "serde_json",
  "syn 2.0.52",
  "windows-metadata",
 ]
@@ -6300,9 +6303,9 @@ dependencies = [
 
 [[package]]
 name = "windows-metadata"
-version = "0.52.0"
+version = "0.55.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "218fd59201e26acdbb894fa2b302d1de84bf3eec7d0eb894ac8e9c5a854ee4ef"
+checksum = "b602635050172a1fc57a35040d4d225baefc6098fefd97094919921d95961a7d"
 
 [[package]]
 name = "windows-sys"

compiler/rustc_ast/src/util/literal.rs

@@ -276,8 +276,10 @@ fn filtered_float_lit(
         Some(suffix) => LitKind::Float(
             symbol,
             ast::LitFloatType::Suffixed(match suffix {
+                sym::f16 => ast::FloatTy::F16,
                 sym::f32 => ast::FloatTy::F32,
                 sym::f64 => ast::FloatTy::F64,
+                sym::f128 => ast::FloatTy::F128,
                 _ => return Err(LitError::InvalidFloatSuffix(suffix)),
             }),
         ),

compiler/rustc_ast_lowering/src/item.rs

@@ -373,6 +373,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
                         (trait_ref, lowered_ty)
                     });
 
+                self.is_in_trait_impl = trait_ref.is_some();
                 let new_impl_items = self
                     .arena
                     .alloc_from_iter(impl_items.iter().map(|item| self.lower_impl_item_ref(item)));
@@ -978,13 +979,6 @@ impl<'hir> LoweringContext<'_, 'hir> {
     }
 
     fn lower_impl_item_ref(&mut self, i: &AssocItem) -> hir::ImplItemRef {
-        let trait_item_def_id = self
-            .resolver
-            .get_partial_res(i.id)
-            .map(|r| r.expect_full_res().opt_def_id())
-            .unwrap_or(None);
-        self.is_in_trait_impl = trait_item_def_id.is_some();
-
         hir::ImplItemRef {
             id: hir::ImplItemId { owner_id: hir::OwnerId { def_id: self.local_def_id(i.id) } },
             ident: self.lower_ident(i.ident),
@@ -1000,7 +994,11 @@ impl<'hir> LoweringContext<'_, 'hir> {
                 },
                 AssocItemKind::MacCall(..) => unimplemented!(),
             },
-            trait_item_def_id,
+            trait_item_def_id: self
+                .resolver
+                .get_partial_res(i.id)
+                .map(|r| r.expect_full_res().opt_def_id())
+                .unwrap_or(None),
         }
     }
 

compiler/rustc_ast_passes/src/ast_validation.rs

@@ -1527,6 +1527,7 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
                     generics,
                     body.as_deref(),
                 );
+                walk_list!(self, visit_attribute, &item.attrs);
                 self.visit_fn(kind, item.span, item.id);
             }
             AssocItemKind::Type(_) => {

compiler/rustc_ast_passes/src/feature_gate.rs

@@ -1,7 +1,7 @@
 use rustc_ast as ast;
 use rustc_ast::visit::{self, AssocCtxt, FnCtxt, FnKind, Visitor};
 use rustc_ast::{attr, AssocConstraint, AssocConstraintKind, NodeId};
-use rustc_ast::{PatKind, RangeEnd};
+use rustc_ast::{token, PatKind, RangeEnd};
 use rustc_feature::{AttributeGate, BuiltinAttribute, Features, GateIssue, BUILTIN_ATTRIBUTE_MAP};
 use rustc_session::parse::{feature_err, feature_err_issue, feature_warn};
 use rustc_session::Session;
@@ -378,6 +378,17 @@ impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
             ast::ExprKind::TryBlock(_) => {
                 gate!(&self, try_blocks, e.span, "`try` expression is experimental");
             }
+            ast::ExprKind::Lit(token::Lit { kind: token::LitKind::Float, suffix, .. }) => {
+                match suffix {
+                    Some(sym::f16) => {
+                        gate!(&self, f16, e.span, "the type `f16` is unstable")
+                    }
+                    Some(sym::f128) => {
+                        gate!(&self, f128, e.span, "the type `f128` is unstable")
+                    }
+                    _ => (),
+                }
+            }
             _ => {}
         }
         visit::walk_expr(self, e)

compiler/rustc_borrowck/messages.ftl

@@ -16,6 +16,9 @@ borrowck_borrow_due_to_use_closure =
 borrowck_borrow_due_to_use_coroutine =
     borrow occurs due to use in coroutine
 
+borrowck_calling_operator_moves =
+    calling this operator moves the value
+
 borrowck_calling_operator_moves_lhs =
     calling this operator moves the left-hand side
 

compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs

@@ -12,7 +12,6 @@ use rustc_hir::def::{DefKind, Res};
 use rustc_hir::intravisit::{walk_block, walk_expr, Visitor};
 use rustc_hir::{CoroutineDesugaring, PatField};
 use rustc_hir::{CoroutineKind, CoroutineSource, LangItem};
-use rustc_infer::traits::ObligationCause;
 use rustc_middle::hir::nested_filter::OnlyBodies;
 use rustc_middle::mir::tcx::PlaceTy;
 use rustc_middle::mir::{
@@ -21,16 +20,21 @@ use rustc_middle::mir::{
     PlaceRef, ProjectionElem, Rvalue, Statement, StatementKind, Terminator, TerminatorKind,
     VarBindingForm,
 };
-use rustc_middle::ty::{self, suggest_constraining_type_params, PredicateKind, Ty, TyCtxt};
+use rustc_middle::ty::{
+    self, suggest_constraining_type_params, PredicateKind, ToPredicate, Ty, TyCtxt,
+    TypeSuperVisitable, TypeVisitor,
+};
 use rustc_middle::util::CallKind;
 use rustc_mir_dataflow::move_paths::{InitKind, MoveOutIndex, MovePathIndex};
+use rustc_span::def_id::DefId;
 use rustc_span::def_id::LocalDefId;
 use rustc_span::hygiene::DesugaringKind;
 use rustc_span::symbol::{kw, sym, Ident};
 use rustc_span::{BytePos, Span, Symbol};
 use rustc_trait_selection::infer::InferCtxtExt;
+use rustc_trait_selection::traits::error_reporting::suggestions::TypeErrCtxtExt;
 use rustc_trait_selection::traits::error_reporting::FindExprBySpan;
-use rustc_trait_selection::traits::ObligationCtxt;
+use rustc_trait_selection::traits::{Obligation, ObligationCause, ObligationCtxt};
 use std::iter;
 
 use crate::borrow_set::TwoPhaseActivation;
@@ -39,7 +43,7 @@ use crate::diagnostics::conflict_errors::StorageDeadOrDrop::LocalStorageDead;
 use crate::diagnostics::{find_all_local_uses, CapturedMessageOpt};
 use crate::{
     borrow_set::BorrowData, diagnostics::Instance, prefixes::IsPrefixOf,
-    InitializationRequiringAction, MirBorrowckCtxt, PrefixSet, WriteKind,
+    InitializationRequiringAction, MirBorrowckCtxt, WriteKind,
 };
 
 use super::{
@@ -114,7 +118,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
             self.buffer_error(err);
         } else {
             if let Some((reported_place, _)) = self.has_move_error(&move_out_indices) {
-                if self.prefixes(*reported_place, PrefixSet::All).any(|p| p == used_place) {
+                if used_place.is_prefix_of(*reported_place) {
                     debug!(
                         "report_use_of_moved_or_uninitialized place: error suppressed mois={:?}",
                         move_out_indices
@@ -283,7 +287,8 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                 // something that already has `Fn`-like bounds (or is a closure), so we can't
                 // restrict anyways.
             } else {
-                self.suggest_adding_copy_bounds(&mut err, ty, span);
+                let copy_did = self.infcx.tcx.require_lang_item(LangItem::Copy, Some(span));
+                self.suggest_adding_bounds(&mut err, ty, copy_did, span);
             }
 
             if needs_note {
@@ -422,8 +427,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                     (None, &[][..], 0)
                 };
                 if let Some(def_id) = def_id
-                    && let node =
-                        self.infcx.tcx.hir_node(self.infcx.tcx.local_def_id_to_hir_id(def_id))
+                    && let node = self.infcx.tcx.hir_node_by_def_id(def_id)
                     && let Some(fn_sig) = node.fn_sig()
                     && let Some(ident) = node.ident()
                     && let Some(pos) = args.iter().position(|arg| arg.hir_id == expr.hir_id)
@@ -775,7 +779,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
         }
     }
 
-    fn suggest_adding_copy_bounds(&self, err: &mut Diag<'_>, ty: Ty<'tcx>, span: Span) {
+    fn suggest_adding_bounds(&self, err: &mut Diag<'_>, ty: Ty<'tcx>, def_id: DefId, span: Span) {
         let tcx = self.infcx.tcx;
         let generics = tcx.generics_of(self.mir_def_id());
 
@@ -788,10 +792,9 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
         };
         // Try to find predicates on *generic params* that would allow copying `ty`
         let ocx = ObligationCtxt::new(self.infcx);
-        let copy_did = tcx.require_lang_item(LangItem::Copy, Some(span));
         let cause = ObligationCause::misc(span, self.mir_def_id());
 
-        ocx.register_bound(cause, self.param_env, ty, copy_did);
+        ocx.register_bound(cause, self.param_env, ty, def_id);
         let errors = ocx.select_all_or_error();
 
         // Only emit suggestion if all required predicates are on generic
@@ -877,6 +880,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                 Some(borrow_span),
                 None,
             );
+        self.suggest_copy_for_type_in_cloned_ref(&mut err, place);
         self.buffer_error(err);
     }
 
@@ -1215,10 +1219,104 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
         );
 
         self.suggest_using_local_if_applicable(&mut err, location, issued_borrow, explanation);
+        self.suggest_copy_for_type_in_cloned_ref(&mut err, place);
 
         err
     }
 
+    fn suggest_copy_for_type_in_cloned_ref(&self, err: &mut Diag<'tcx>, place: Place<'tcx>) {
+        let tcx = self.infcx.tcx;
+        let hir = tcx.hir();
+        let Some(body_id) = tcx.hir_node(self.mir_hir_id()).body_id() else { return };
+        struct FindUselessClone<'hir> {
+            pub clones: Vec<&'hir hir::Expr<'hir>>,
+        }
+        impl<'hir> FindUselessClone<'hir> {
+            pub fn new() -> Self {
+                Self { clones: vec![] }
+            }
+        }
+
+        impl<'v> Visitor<'v> for FindUselessClone<'v> {
+            fn visit_expr(&mut self, ex: &'v hir::Expr<'v>) {
+                // FIXME: use `lookup_method_for_diagnostic`?
+                if let hir::ExprKind::MethodCall(segment, _rcvr, args, _span) = ex.kind
+                    && segment.ident.name == sym::clone
+                    && args.len() == 0
+                {
+                    self.clones.push(ex);
+                }
+                hir::intravisit::walk_expr(self, ex);
+            }
+        }
+        let mut expr_finder = FindUselessClone::new();
+
+        let body = hir.body(body_id).value;
+        expr_finder.visit_expr(body);
+
+        pub struct Holds<'tcx> {
+            ty: Ty<'tcx>,
+            holds: bool,
+        }
+
+        impl<'tcx> TypeVisitor<TyCtxt<'tcx>> for Holds<'tcx> {
+            type Result = std::ops::ControlFlow<()>;
+
+            fn visit_ty(&mut self, t: Ty<'tcx>) -> Self::Result {
+                if t == self.ty {
+                    self.holds = true;
+                }
+                t.super_visit_with(self)
+            }
+        }
+
+        let mut types_to_constrain = FxIndexSet::default();
+
+        let local_ty = self.body.local_decls[place.local].ty;
+        let typeck_results = tcx.typeck(self.mir_def_id());
+        let clone = tcx.require_lang_item(LangItem::Clone, Some(body.span));
+        for expr in expr_finder.clones {
+            if let hir::ExprKind::MethodCall(_, rcvr, _, span) = expr.kind
+                && let Some(rcvr_ty) = typeck_results.node_type_opt(rcvr.hir_id)
+                && let Some(ty) = typeck_results.node_type_opt(expr.hir_id)
+                && rcvr_ty == ty
+                && let ty::Ref(_, inner, _) = rcvr_ty.kind()
+                && let inner = inner.peel_refs()
+                && let mut v = (Holds { ty: inner, holds: false })
+                && let _ = v.visit_ty(local_ty)
+                && v.holds
+                && let None = self.infcx.type_implements_trait_shallow(clone, inner, self.param_env)
+            {
+                err.span_label(
+                    span,
+                    format!(
+                        "this call doesn't do anything, the result is still `{rcvr_ty}` \
+                             because `{inner}` doesn't implement `Clone`",
+                    ),
+                );
+                types_to_constrain.insert(inner);
+            }
+        }
+        for ty in types_to_constrain {
+            self.suggest_adding_bounds(err, ty, clone, body.span);
+            if let ty::Adt(..) = ty.kind() {
+                // The type doesn't implement Clone.
+                let trait_ref = ty::Binder::dummy(ty::TraitRef::new(self.infcx.tcx, clone, [ty]));
+                let obligation = Obligation::new(
+                    self.infcx.tcx,
+                    ObligationCause::dummy(),
+                    self.param_env,
+                    trait_ref,
+                );
+                self.infcx.err_ctxt().suggest_derive(
+                    &obligation,
+                    err,
+                    trait_ref.to_predicate(self.infcx.tcx),
+                );
+            }
+        }
+    }
+
     #[instrument(level = "debug", skip(self, err))]
     fn suggest_using_local_if_applicable(
         &self,
@@ -1995,21 +2093,14 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
         kind: Option<WriteKind>,
     ) {
         let drop_span = place_span.1;
-        let root_place =
-            self.prefixes(borrow.borrowed_place.as_ref(), PrefixSet::All).last().unwrap();
+        let borrowed_local = borrow.borrowed_place.local;
 
         let borrow_spans = self.retrieve_borrow_spans(borrow);
         let borrow_span = borrow_spans.var_or_use_path_span();
 
-        assert!(root_place.projection.is_empty());
-        let proper_span = self.body.local_decls[root_place.local].source_info.span;
+        let proper_span = self.body.local_decls[borrowed_local].source_info.span;
 
-        let root_place_projection = self.infcx.tcx.mk_place_elems(root_place.projection);
-
-        if self.access_place_error_reported.contains(&(
-            Place { local: root_place.local, projection: root_place_projection },
-            borrow_span,
-        )) {
+        if self.access_place_error_reported.contains(&(Place::from(borrowed_local), borrow_span)) {
             debug!(
                 "suppressing access_place error when borrow doesn't live long enough for {:?}",
                 borrow_span
@@ -2017,12 +2108,8 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
             return;
         }
 
-        self.access_place_error_reported.insert((
-            Place { local: root_place.local, projection: root_place_projection },
-            borrow_span,
-        ));
+        self.access_place_error_reported.insert((Place::from(borrowed_local), borrow_span));
 
-        let borrowed_local = borrow.borrowed_place.local;
         if self.body.local_decls[borrowed_local].is_ref_to_thread_local() {
             let err =
                 self.report_thread_local_value_does_not_live_long_enough(drop_span, borrow_span);
@@ -2544,9 +2631,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
             };
             (format!("{local_kind}`{place_desc}`"), format!("`{place_desc}` is borrowed here"))
         } else {
-            let root_place =
-                self.prefixes(borrow.borrowed_place.as_ref(), PrefixSet::All).last().unwrap();
-            let local = root_place.local;
+            let local = borrow.borrowed_place.local;
             match self.body.local_kind(local) {
                 LocalKind::Arg => (
                     "function parameter".to_string(),

compiler/rustc_borrowck/src/diagnostics/mod.rs

@@ -1050,7 +1050,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                     );
                     err.subdiagnostic(self.dcx(), CaptureReasonNote::FnOnceMoveInCall { var_span });
                 }
-                CallKind::Operator { self_arg, .. } => {
+                CallKind::Operator { self_arg, trait_id, .. } => {
                     let self_arg = self_arg.unwrap();
                     err.subdiagnostic(
                         self.dcx(),
@@ -1062,9 +1062,16 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                         },
                     );
                     if self.fn_self_span_reported.insert(fn_span) {
+                        let lang = self.infcx.tcx.lang_items();
                         err.subdiagnostic(
                             self.dcx(),
-                            CaptureReasonNote::LhsMoveByOperator { span: self_arg.span },
+                            if [lang.not_trait(), lang.deref_trait(), lang.neg_trait()]
+                                .contains(&Some(trait_id))
+                            {
+                                CaptureReasonNote::UnOpMoveByOperator { span: self_arg.span }
+                            } else {
+                                CaptureReasonNote::LhsMoveByOperator { span: self_arg.span }
+                            },
                         );
                     }
                 }
@@ -1226,20 +1233,20 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                             {
                                 let msg = match &errors[..] {
                                     [] => "you can `clone` the value and consume it, but this \
-                                            might not be your desired behavior"
+                                           might not be your desired behavior"
                                         .to_string(),
                                     [error] => {
                                         format!(
-                                            "you could `clone` the value and consume it, if \
-                                                the `{}` trait bound could be satisfied",
+                                            "you could `clone` the value and consume it, if the \
+                                             `{}` trait bound could be satisfied",
                                             error.obligation.predicate,
                                         )
                                     }
                                     [errors @ .., last] => {
                                         format!(
-                                            "you could `clone` the value and consume it, if \
-                                                the following trait bounds could be satisfied: {} \
-                                                and `{}`",
+                                            "you could `clone` the value and consume it, if the \
+                                             following trait bounds could be satisfied: \
+                                             {} and `{}`",
                                             errors
                                                 .iter()
                                                 .map(|e| format!("`{}`", e.obligation.predicate))

compiler/rustc_borrowck/src/diagnostics/mutability_errors.rs

@@ -672,11 +672,8 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
         };
         (
             true,
-            td.as_local().and_then(|tld| match self.infcx.tcx.opt_hir_node_by_def_id(tld) {
-                Some(Node::Item(hir::Item {
-                    kind: hir::ItemKind::Trait(_, _, _, _, items),
-                    ..
-                })) => {
+            td.as_local().and_then(|tld| match self.infcx.tcx.hir_node_by_def_id(tld) {
+                Node::Item(hir::Item { kind: hir::ItemKind::Trait(_, _, _, _, items), .. }) => {
                     let mut f_in_trait_opt = None;
                     for hir::TraitItemRef { id: fi, kind: k, .. } in *items {
                         let hi = fi.hir_id();
@@ -1475,11 +1472,9 @@ fn get_mut_span_in_struct_field<'tcx>(
     if let ty::Ref(_, ty, _) = ty.kind()
         && let ty::Adt(def, _) = ty.kind()
         && let field = def.all_fields().nth(field.index())?
-        // Use the HIR types to construct the diagnostic message.
-        && let node = tcx.opt_hir_node_by_def_id(field.did.as_local()?)?
         // Now we're dealing with the actual struct that we're going to suggest a change to,
         // we can expect a field that is an immutable reference to a type.
-        && let hir::Node::Field(field) = node
+        && let hir::Node::Field(field) = tcx.hir_node_by_def_id(field.did.as_local()?)
         && let hir::TyKind::Ref(lt, hir::MutTy { mutbl: hir::Mutability::Not, ty }) = field.ty.kind
     {
         return Some(lt.ident.span.between(ty.span));

compiler/rustc_borrowck/src/prefixes.rs

@@ -1,7 +1,4 @@
-//! From the NLL RFC: "The deep [aka 'supporting'] prefixes for an
-//! place are formed by stripping away fields and derefs, except that
-//! we stop when we reach the deref of a shared reference. [...] "
-//!
+//! From the NLL RFC:
 //! "Shallow prefixes are found by stripping away fields, but stop at
 //! any dereference. So: writing a path like `a` is illegal if `a.b`
 //! is borrowed. But: writing `a` is legal if `*a` is borrowed,
@@ -9,9 +6,7 @@
 
 use super::MirBorrowckCtxt;
 
-use rustc_hir as hir;
-use rustc_middle::mir::{Body, PlaceRef, ProjectionElem};
-use rustc_middle::ty::{self, TyCtxt};
+use rustc_middle::mir::{PlaceRef, ProjectionElem};
 
 pub trait IsPrefixOf<'tcx> {
     fn is_prefix_of(&self, other: PlaceRef<'tcx>) -> bool;
@@ -25,9 +20,7 @@ impl<'tcx> IsPrefixOf<'tcx> for PlaceRef<'tcx> {
     }
 }
 
-pub(super) struct Prefixes<'cx, 'tcx> {
-    body: &'cx Body<'tcx>,
-    tcx: TyCtxt<'tcx>,
+pub(super) struct Prefixes<'tcx> {
     kind: PrefixSet,
     next: Option<PlaceRef<'tcx>>,
 }
@@ -39,24 +32,18 @@ pub(super) enum PrefixSet {
     All,
     /// Stops at any dereference.
     Shallow,
-    /// Stops at the deref of a shared reference.
-    Supporting,
 }
 
 impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
     /// Returns an iterator over the prefixes of `place`
     /// (inclusive) from longest to smallest, potentially
     /// terminating the iteration early based on `kind`.
-    pub(super) fn prefixes(
-        &self,
-        place_ref: PlaceRef<'tcx>,
-        kind: PrefixSet,
-    ) -> Prefixes<'cx, 'tcx> {
-        Prefixes { next: Some(place_ref), kind, body: self.body, tcx: self.infcx.tcx }
+    pub(super) fn prefixes(&self, place_ref: PlaceRef<'tcx>, kind: PrefixSet) -> Prefixes<'tcx> {
+        Prefixes { next: Some(place_ref), kind }
     }
 }
 
-impl<'cx, 'tcx> Iterator for Prefixes<'cx, 'tcx> {
+impl<'tcx> Iterator for Prefixes<'tcx> {
     type Item = PlaceRef<'tcx>;
     fn next(&mut self) -> Option<Self::Item> {
         let mut cursor = self.next?;
@@ -91,57 +78,23 @@ impl<'cx, 'tcx> Iterator for Prefixes<'cx, 'tcx> {
                             panic!("Subtype projection is not allowed before borrow check")
                         }
                         ProjectionElem::Deref => {
-                            // (handled below)
+                            match self.kind {
+                                PrefixSet::Shallow => {
+                                    // Shallow prefixes are found by stripping away
+                                    // fields, but stop at *any* dereference.
+                                    // So we can just stop the traversal now.
+                                    self.next = None;
+                                    return Some(cursor);
+                                }
+                                PrefixSet::All => {
+                                    // All prefixes: just blindly enqueue the base
+                                    // of the projection.
+                                    self.next = Some(cursor_base);
+                                    return Some(cursor);
+                                }
+                            }
                         }
                     }
-
-                    assert_eq!(elem, ProjectionElem::Deref);
-
-                    match self.kind {
-                        PrefixSet::Shallow => {
-                            // Shallow prefixes are found by stripping away
-                            // fields, but stop at *any* dereference.
-                            // So we can just stop the traversal now.
-                            self.next = None;
-                            return Some(cursor);
-                        }
-                        PrefixSet::All => {
-                            // All prefixes: just blindly enqueue the base
-                            // of the projection.
-                            self.next = Some(cursor_base);
-                            return Some(cursor);
-                        }
-                        PrefixSet::Supporting => {
-                            // Fall through!
-                        }
-                    }
-
-                    assert_eq!(self.kind, PrefixSet::Supporting);
-                    // Supporting prefixes: strip away fields and
-                    // derefs, except we stop at the deref of a shared
-                    // reference.
-
-                    let ty = cursor_base.ty(self.body, self.tcx).ty;
-                    match ty.kind() {
-                        ty::RawPtr(_) | ty::Ref(_ /*rgn*/, _ /*ty*/, hir::Mutability::Not) => {
-                            // don't continue traversing over derefs of raw pointers or shared
-                            // borrows.
-                            self.next = None;
-                            return Some(cursor);
-                        }
-
-                        ty::Ref(_ /*rgn*/, _ /*ty*/, hir::Mutability::Mut) => {
-                            self.next = Some(cursor_base);
-                            return Some(cursor);
-                        }
-
-                        ty::Adt(..) if ty.is_box() => {
-                            self.next = Some(cursor_base);
-                            return Some(cursor);
-                        }
-
-                        _ => panic!("unknown type fed to Projection Deref."),
-                    }
                 }
             }
         }

compiler/rustc_borrowck/src/session_diagnostics.rs

@@ -368,6 +368,11 @@ pub(crate) enum CaptureReasonNote {
         #[primary_span]
         var_span: Span,
     },
+    #[note(borrowck_calling_operator_moves)]
+    UnOpMoveByOperator {
+        #[primary_span]
+        span: Span,
+    },
     #[note(borrowck_calling_operator_moves_lhs)]
     LhsMoveByOperator {
         #[primary_span]

compiler/rustc_codegen_cranelift/.github/workflows/main.yml

@@ -44,10 +44,9 @@ jobs:
             env:
               TARGET_TRIPLE: x86_64-apple-darwin
           # cross-compile from Linux to Windows using mingw
-          # FIXME The wine version in Ubuntu 22.04 is missing ProcessPrng
-          #- os: ubuntu-latest
-          #  env:
-          #    TARGET_TRIPLE: x86_64-pc-windows-gnu
+          - os: ubuntu-latest
+            env:
+              TARGET_TRIPLE: x86_64-pc-windows-gnu
           - os: ubuntu-latest
             env:
               TARGET_TRIPLE: aarch64-unknown-linux-gnu
@@ -81,11 +80,11 @@ jobs:
       if: matrix.os == 'windows-latest' && matrix.env.TARGET_TRIPLE == 'x86_64-pc-windows-gnu'
       run: rustup set default-host x86_64-pc-windows-gnu
 
-    #- name: Install MinGW toolchain and wine
-    #  if: matrix.os == 'ubuntu-latest' && matrix.env.TARGET_TRIPLE == 'x86_64-pc-windows-gnu'
-    #  run: |
-    #    sudo apt-get update
-    #    sudo apt-get install -y gcc-mingw-w64-x86-64 wine-stable
+    - name: Install MinGW toolchain and wine
+      if: matrix.os == 'ubuntu-latest' && matrix.env.TARGET_TRIPLE == 'x86_64-pc-windows-gnu'
+      run: |
+        sudo apt-get update
+        sudo apt-get install -y gcc-mingw-w64-x86-64 wine-stable
 
     - name: Install AArch64 toolchain and qemu
       if: matrix.os == 'ubuntu-latest' && matrix.env.TARGET_TRIPLE == 'aarch64-unknown-linux-gnu'
@@ -108,6 +107,15 @@ jobs:
     - name: Prepare dependencies
       run: ./y.sh prepare
 
+    # The Wine version shipped with Ubuntu 22.04 doesn't implement bcryptprimitives.dll
+    - name: Build bcryptprimitives.dll shim for Wine
+      if: matrix.os == 'ubuntu-latest' && matrix.env.TARGET_TRIPLE == 'x86_64-pc-windows-gnu'
+      run: |
+        rustup target add x86_64-pc-windows-gnu
+        mkdir wine_shims
+        rustc patches/bcryptprimitives.rs -Copt-level=3 -Clto=fat --out-dir wine_shims --target x86_64-pc-windows-gnu
+        echo "WINEPATH=$(pwd)/wine_shims" >> $GITHUB_ENV
+
     - name: Build
       run: ./y.sh build --sysroot none
 
@@ -234,11 +242,11 @@ jobs:
       if: matrix.os == 'windows-latest' && matrix.env.TARGET_TRIPLE == 'x86_64-pc-windows-gnu'
       run: rustup set default-host x86_64-pc-windows-gnu
 
-    - name: Install MinGW toolchain and wine
+    - name: Install MinGW toolchain
       if: matrix.os == 'ubuntu-latest' && matrix.env.TARGET_TRIPLE == 'x86_64-pc-windows-gnu'
       run: |
         sudo apt-get update
-        sudo apt-get install -y gcc-mingw-w64-x86-64 wine-stable
+        sudo apt-get install -y gcc-mingw-w64-x86-64
 
     - name: Prepare dependencies
       run: ./y.sh prepare

compiler/rustc_codegen_cranelift/example/std_example.rs

@@ -167,6 +167,14 @@ fn main() {
     transmute_fat_pointer();
 
     rust_call_abi();
+
+    const fn no_str() -> Option<Box<str>> {
+        None
+    }
+
+    static STATIC_WITH_MAYBE_NESTED_BOX: &Option<Box<str>> = &no_str();
+
+    println!("{:?}", STATIC_WITH_MAYBE_NESTED_BOX);
 }
 
 fn panic(_: u128) {

compiler/rustc_codegen_cranelift/patches/bcryptprimitives.rs

@@ -0,0 +1,22 @@
+// Shim for bcryptprimitives.dll. The Wine version shipped with Ubuntu 22.04
+// doesn't support it yet. Authored by @ChrisDenton
+
+#![crate_type = "cdylib"]
+#![allow(nonstandard_style)]
+
+#[no_mangle]
+pub unsafe extern "system" fn ProcessPrng(mut pbData: *mut u8, mut cbData: usize) -> i32 {
+    while cbData > 0 {
+        let size = core::cmp::min(cbData, u32::MAX as usize);
+        RtlGenRandom(pbData, size as u32);
+        cbData -= size;
+        pbData = pbData.add(size);
+    }
+    1
+}
+
+#[link(name = "advapi32")]
+extern "system" {
+    #[link_name = "SystemFunction036"]
+    pub fn RtlGenRandom(RandomBuffer: *mut u8, RandomBufferLength: u32) -> u8;
+}

compiler/rustc_codegen_cranelift/patches/stdlib-lock.toml

@@ -42,12 +42,9 @@ checksum = "0942ffc6dcaadf03badf6e6a2d0228460359d5e34b57ccdc720b7382dfbd5ec5"
 
 [[package]]
 name = "cc"
-version = "1.0.83"
+version = "1.0.90"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "f1174fb0b6ec23863f8b971027804a42614e347eafb0a95bf0b12cdae21fc4d0"
-dependencies = [
- "libc",
-]
+checksum = "8cd6604a82acf3039f1144f54b8eb34e91ffba622051189e71b781822d5ee1f5"
 
 [[package]]
 name = "cfg-if"

compiler/rustc_codegen_cranelift/rust-toolchain

@@ -1,3 +1,3 @@
 [toolchain]
-channel = "nightly-2024-03-08"
+channel = "nightly-2024-03-16"
 components = ["rust-src", "rustc-dev", "llvm-tools"]

compiler/rustc_codegen_cranelift/scripts/test_rustc_tests.sh

@@ -83,6 +83,7 @@ rm -r tests/run-make/symbols-include-type-name # --emit=asm not supported
 rm -r tests/run-make/target-specs # i686 not supported by Cranelift
 rm -r tests/run-make/mismatching-target-triples # same
 rm tests/ui/asm/x86_64/issue-96797.rs # const and sym inline asm operands don't work entirely correctly
+rm tests/ui/asm/x86_64/goto.rs # inline asm labels not supported
 
 # requires LTO
 rm -r tests/run-make/cdylib
@@ -121,6 +122,7 @@ rm -r tests/run-make/optimization-remarks-dir # remarks are LLVM specific
 rm tests/ui/mir/mir_misc_casts.rs # depends on deduplication of constants
 rm tests/ui/mir/mir_raw_fat_ptr.rs # same
 rm tests/ui/consts/issue-33537.rs # same
+rm tests/ui/consts/const-mut-refs-crate.rs # same
 
 # rustdoc-clif passes extra args, suppressing the help message when no args are passed
 rm -r tests/run-make/issue-88756-default-output

compiler/rustc_codegen_cranelift/src/constant.rs

@@ -53,7 +53,11 @@ pub(crate) fn codegen_tls_ref<'tcx>(
         let call = fx.bcx.ins().call(func_ref, &[]);
         fx.bcx.func.dfg.first_result(call)
     } else {
-        let data_id = data_id_for_static(fx.tcx, fx.module, def_id, false);
+        let data_id = data_id_for_static(
+            fx.tcx, fx.module, def_id, false,
+            // For a declaration the stated mutability doesn't matter.
+            false,
+        );
         let local_data_id = fx.module.declare_data_in_func(data_id, &mut fx.bcx.func);
         if fx.clif_comments.enabled() {
             fx.add_comment(local_data_id, format!("tls {:?}", def_id));
@@ -164,7 +168,11 @@ pub(crate) fn codegen_const_value<'tcx>(
                     }
                     GlobalAlloc::Static(def_id) => {
                         assert!(fx.tcx.is_static(def_id));
-                        let data_id = data_id_for_static(fx.tcx, fx.module, def_id, false);
+                        let data_id = data_id_for_static(
+                            fx.tcx, fx.module, def_id, false,
+                            // For a declaration the stated mutability doesn't matter.
+                            false,
+                        );
                         let local_data_id =
                             fx.module.declare_data_in_func(data_id, &mut fx.bcx.func);
                         if fx.clif_comments.enabled() {
@@ -232,21 +240,19 @@ fn data_id_for_static(
     module: &mut dyn Module,
     def_id: DefId,
     definition: bool,
+    definition_writable: bool,
 ) -> DataId {
     let attrs = tcx.codegen_fn_attrs(def_id);
 
     let instance = Instance::mono(tcx, def_id).polymorphize(tcx);
     let symbol_name = tcx.symbol_name(instance).name;
-    let ty = instance.ty(tcx, ParamEnv::reveal_all());
-    let is_mutable = if tcx.is_mutable_static(def_id) {
-        true
-    } else {
-        !ty.is_freeze(tcx, ParamEnv::reveal_all())
-    };
-    let align = tcx.layout_of(ParamEnv::reveal_all().and(ty)).unwrap().align.pref.bytes();
 
     if let Some(import_linkage) = attrs.import_linkage {
         assert!(!definition);
+        assert!(!tcx.is_mutable_static(def_id));
+
+        let ty = instance.ty(tcx, ParamEnv::reveal_all());
+        let align = tcx.layout_of(ParamEnv::reveal_all().and(ty)).unwrap().align.pref.bytes();
 
         let linkage = if import_linkage == rustc_middle::mir::mono::Linkage::ExternalWeak
             || import_linkage == rustc_middle::mir::mono::Linkage::WeakAny
@@ -259,7 +265,7 @@ fn data_id_for_static(
         let data_id = match module.declare_data(
             symbol_name,
             linkage,
-            is_mutable,
+            false,
             attrs.flags.contains(CodegenFnAttrFlags::THREAD_LOCAL),
         ) {
             Ok(data_id) => data_id,
@@ -307,7 +313,7 @@ fn data_id_for_static(
     let data_id = match module.declare_data(
         symbol_name,
         linkage,
-        is_mutable,
+        definition_writable,
         attrs.flags.contains(CodegenFnAttrFlags::THREAD_LOCAL),
     ) {
         Ok(data_id) => data_id,
@@ -341,7 +347,13 @@ fn define_all_allocs(tcx: TyCtxt<'_>, module: &mut dyn Module, cx: &mut Constant
 
                 let alloc = tcx.eval_static_initializer(def_id).unwrap();
 
-                let data_id = data_id_for_static(tcx, module, def_id, true);
+                let data_id = data_id_for_static(
+                    tcx,
+                    module,
+                    def_id,
+                    true,
+                    alloc.inner().mutability == Mutability::Mut,
+                );
                 (data_id, alloc, section_name)
             }
         };
@@ -421,7 +433,11 @@ fn define_all_allocs(tcx: TyCtxt<'_>, module: &mut dyn Module, cx: &mut Constant
                     // Don't push a `TodoItem::Static` here, as it will cause statics used by
                     // multiple crates to be duplicated between them. It isn't necessary anyway,
                     // as it will get pushed by `codegen_static` when necessary.
-                    data_id_for_static(tcx, module, def_id, false)
+                    data_id_for_static(
+                        tcx, module, def_id, false,
+                        // For a declaration the stated mutability doesn't matter.
+                        false,
+                    )
                 }
             };
 

compiler/rustc_codegen_ssa/src/back/link.rs

@@ -1216,20 +1216,29 @@ fn add_sanitizer_libraries(
     crate_type: CrateType,
     linker: &mut dyn Linker,
 ) {
+    if sess.target.is_like_android {
+        // Sanitizer runtime libraries are provided dynamically on Android
+        // targets.
+        return;
+    }
+
+    if sess.opts.unstable_opts.external_clangrt {
+        // Linking against in-tree sanitizer runtimes is disabled via
+        // `-Z external-clangrt`
+        return;
+    }
+
+    if matches!(crate_type, CrateType::Rlib | CrateType::Staticlib) {
+        return;
+    }
+
     // On macOS and Windows using MSVC the runtimes are distributed as dylibs
     // which should be linked to both executables and dynamic libraries.
     // Everywhere else the runtimes are currently distributed as static
     // libraries which should be linked to executables only.
-    let needs_runtime = !sess.target.is_like_android
-        && match crate_type {
-            CrateType::Executable => true,
-            CrateType::Dylib | CrateType::Cdylib | CrateType::ProcMacro => {
-                sess.target.is_like_osx || sess.target.is_like_msvc
-            }
-            CrateType::Rlib | CrateType::Staticlib => false,
-        };
-
-    if !needs_runtime {
+    if matches!(crate_type, CrateType::Dylib | CrateType::Cdylib | CrateType::ProcMacro)
+        && !(sess.target.is_like_osx || sess.target.is_like_msvc)
+    {
         return;
     }
 

compiler/rustc_codegen_ssa/src/back/linker.rs

@@ -929,6 +929,15 @@ impl<'a> Linker for MsvcLinker<'a> {
                 // from the CodeView line tables in the object files.
                 self.cmd.arg("/DEBUG");
 
+                // Default to emitting only the file name of the PDB file into
+                // the binary instead of the full path. Emitting the full path
+                // may leak private information (such as user names).
+                // See https://github.com/rust-lang/rust/issues/87825.
+                //
+                // This default behavior can be overridden by explicitly passing
+                // `-Clink-arg=/PDBALTPATH:...` to rustc.
+                self.cmd.arg("/PDBALTPATH:%_PDB%");
+
                 // This will cause the Microsoft linker to embed .natvis info into the PDB file
                 let natvis_dir_path = self.sess.sysroot.join("lib\\rustlib\\etc");
                 if let Ok(natvis_dir) = fs::read_dir(&natvis_dir_path) {

compiler/rustc_const_eval/src/interpret/memory.rs

@@ -949,6 +949,8 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
     /// Runs the close in "validation" mode, which means the machine's memory read hooks will be
     /// suppressed. Needless to say, this must only be set with great care! Cannot be nested.
     pub(super) fn run_for_validation<R>(&self, f: impl FnOnce() -> R) -> R {
+        // This deliberately uses `==` on `bool` to follow the pattern
+        // `assert!(val.replace(new) == old)`.
         assert!(
             self.memory.validation_in_progress.replace(true) == false,
             "`validation_in_progress` was already set"

compiler/rustc_data_structures/src/memmap.rs

@@ -18,8 +18,14 @@ impl Mmap {
     /// However in practice most callers do not ensure this, so uses of this function are likely unsound.
     #[inline]
     pub unsafe fn map(file: File) -> io::Result<Self> {
-        // Safety: the caller must ensure that this is safe.
-        unsafe { memmap2::Mmap::map(&file).map(Mmap) }
+        // By default, memmap2 creates shared mappings, implying that we could see updates to the
+        // file through the mapping. That would violate our precondition; so by requesting a
+        // map_copy_read_only we do not lose anything.
+        // This mapping mode also improves our support for filesystems such as cacheless virtiofs.
+        // For more details see https://github.com/rust-lang/rust/issues/122262
+        //
+        // SAFETY: The caller must ensure that this is safe.
+        unsafe { memmap2::MmapOptions::new().map_copy_read_only(&file).map(Mmap) }
     }
 }
 

compiler/rustc_feature/src/builtin_attrs.rs

@@ -580,6 +580,13 @@ pub const BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
         "`may_dangle` has unstable semantics and may be removed in the future",
     ),
 
+    rustc_attr!(
+        rustc_never_type_mode, Normal, template!(NameValueStr: "fallback_to_unit|fallback_to_niko|fallback_to_never|no_fallback"), ErrorFollowing,
+        @only_local: true,
+        "`rustc_never_type_fallback` is used to experiment with never type fallback and work on \
+         never type stabilization, and will never be stable"
+    ),
+
     // ==========================================================================
     // Internal attributes: Runtime related:
     // ==========================================================================

compiler/rustc_feature/src/unstable.rs

@@ -463,6 +463,10 @@ declare_features! (
     (unstable, extended_varargs_abi_support, "1.65.0", Some(100189)),
     /// Allows defining `extern type`s.
     (unstable, extern_types, "1.23.0", Some(43467)),
+    /// Allow using 128-bit (quad precision) floating point numbers.
+    (unstable, f128, "CURRENT_RUSTC_VERSION", Some(116909)),
+    /// Allow using 16-bit (half precision) floating point numbers.
+    (unstable, f16, "CURRENT_RUSTC_VERSION", Some(116909)),
     /// Allows the use of `#[ffi_const]` on foreign functions.
     (unstable, ffi_const, "1.45.0", Some(58328)),
     /// Allows the use of `#[ffi_pure]` on foreign functions.

compiler/rustc_hir/src/hir.rs

@@ -2444,7 +2444,7 @@ pub enum PrimTy {
 
 impl PrimTy {
     /// All of the primitive types
-    pub const ALL: [Self; 17] = [
+    pub const ALL: [Self; 19] = [
         // any changes here should also be reflected in `PrimTy::from_name`
         Self::Int(IntTy::I8),
         Self::Int(IntTy::I16),
@@ -2458,9 +2458,10 @@ impl PrimTy {
         Self::Uint(UintTy::U64),
         Self::Uint(UintTy::U128),
         Self::Uint(UintTy::Usize),
+        Self::Float(FloatTy::F16),
         Self::Float(FloatTy::F32),
         Self::Float(FloatTy::F64),
-        // FIXME(f16_f128): add these when enabled below
+        Self::Float(FloatTy::F128),
         Self::Bool,
         Self::Char,
         Self::Str,
@@ -2508,12 +2509,10 @@ impl PrimTy {
             sym::u64 => Self::Uint(UintTy::U64),
             sym::u128 => Self::Uint(UintTy::U128),
             sym::usize => Self::Uint(UintTy::Usize),
+            sym::f16 => Self::Float(FloatTy::F16),
             sym::f32 => Self::Float(FloatTy::F32),
             sym::f64 => Self::Float(FloatTy::F64),
-            // FIXME(f16_f128): enabling these will open the gates of f16 and f128 being
-            // understood by rustc.
-            // sym::f16 => Self::Float(FloatTy::F16),
-            // sym::f128 => Self::Float(FloatTy::F128),
+            sym::f128 => Self::Float(FloatTy::F128),
             sym::bool => Self::Bool,
             sym::char => Self::Char,
             sym::str => Self::Str,

compiler/rustc_hir_analysis/messages.ftl

@@ -351,6 +351,7 @@ hir_analysis_rpitit_refined = impl trait in impl method signature does not match
     .label = return type from trait method defined here
     .unmatched_bound_label = this bound is stronger than that defined on the trait
     .note = add `#[allow(refining_impl_trait)]` if it is intended for this to be part of the public API of this crate
+    .feedback_note = we are soliciting feedback, see issue #121718 <https://github.com/rust-lang/rust/issues/121718> for more information
 
 hir_analysis_self_in_impl_self =
     `Self` is not valid in the self type of an impl block

compiler/rustc_hir_analysis/src/astconv/bounds.rs

@@ -149,7 +149,6 @@ impl<'tcx> dyn AstConv<'tcx> + '_ {
                         polarity,
                         param_ty,
                         bounds,
-                        false,
                         only_self_bounds,
                     );
                 }
@@ -231,14 +230,13 @@ impl<'tcx> dyn AstConv<'tcx> + '_ {
     /// **A note on binders:** given something like `T: for<'a> Iterator<Item = &'a u32>`, the
     /// `trait_ref` here will be `for<'a> T: Iterator`. The `binding` data however is from *inside*
     /// the binder (e.g., `&'a u32`) and hence may reference bound regions.
-    #[instrument(level = "debug", skip(self, bounds, speculative, dup_bindings, path_span))]
+    #[instrument(level = "debug", skip(self, bounds, dup_bindings, path_span))]
     pub(super) fn add_predicates_for_ast_type_binding(
         &self,
         hir_ref_id: hir::HirId,
         trait_ref: ty::PolyTraitRef<'tcx>,
         binding: &hir::TypeBinding<'tcx>,
         bounds: &mut Bounds<'tcx>,
-        speculative: bool,
         dup_bindings: &mut FxIndexMap<DefId, Span>,
         path_span: Span,
         only_self_bounds: OnlySelfBounds,
@@ -317,19 +315,17 @@ impl<'tcx> dyn AstConv<'tcx> + '_ {
         }
         tcx.check_stability(assoc_item.def_id, Some(hir_ref_id), binding.span, None);
 
-        if !speculative {
-            dup_bindings
-                .entry(assoc_item.def_id)
-                .and_modify(|prev_span| {
-                    tcx.dcx().emit_err(errors::ValueOfAssociatedStructAlreadySpecified {
-                        span: binding.span,
-                        prev_span: *prev_span,
-                        item_name: binding.ident,
-                        def_path: tcx.def_path_str(assoc_item.container_id(tcx)),
-                    });
-                })
-                .or_insert(binding.span);
-        }
+        dup_bindings
+            .entry(assoc_item.def_id)
+            .and_modify(|prev_span| {
+                tcx.dcx().emit_err(errors::ValueOfAssociatedStructAlreadySpecified {
+                    span: binding.span,
+                    prev_span: *prev_span,
+                    item_name: binding.ident,
+                    def_path: tcx.def_path_str(assoc_item.container_id(tcx)),
+                });
+            })
+            .or_insert(binding.span);
 
         let projection_ty = if let ty::AssocKind::Fn = assoc_kind {
             let mut emitted_bad_param_err = None;
@@ -433,9 +429,8 @@ impl<'tcx> dyn AstConv<'tcx> + '_ {
             });
 
             // Provide the resolved type of the associated constant to `type_of(AnonConst)`.
-            if !speculative
-                && let hir::TypeBindingKind::Equality { term: hir::Term::Const(anon_const) } =
-                    binding.kind
+            if let hir::TypeBindingKind::Equality { term: hir::Term::Const(anon_const) } =
+                binding.kind
             {
                 let ty = alias_ty.map_bound(|ty| tcx.type_of(ty.def_id).instantiate(tcx, ty.args));
                 // Since the arguments passed to the alias type above may contain early-bound
@@ -463,42 +458,40 @@ impl<'tcx> dyn AstConv<'tcx> + '_ {
                     hir::Term::Const(ct) => ty::Const::from_anon_const(tcx, ct.def_id).into(),
                 };
 
-                if !speculative {
-                    // Find any late-bound regions declared in `ty` that are not
-                    // declared in the trait-ref or assoc_item. These are not well-formed.
-                    //
-                    // Example:
-                    //
-                    //     for<'a> <T as Iterator>::Item = &'a str // <-- 'a is bad
-                    //     for<'a> <T as FnMut<(&'a u32,)>>::Output = &'a str // <-- 'a is ok
-                    let late_bound_in_projection_ty =
-                        tcx.collect_constrained_late_bound_regions(projection_ty);
-                    let late_bound_in_term =
-                        tcx.collect_referenced_late_bound_regions(trait_ref.rebind(term));
-                    debug!(?late_bound_in_projection_ty);
-                    debug!(?late_bound_in_term);
+                // Find any late-bound regions declared in `ty` that are not
+                // declared in the trait-ref or assoc_item. These are not well-formed.
+                //
+                // Example:
+                //
+                //     for<'a> <T as Iterator>::Item = &'a str // <-- 'a is bad
+                //     for<'a> <T as FnMut<(&'a u32,)>>::Output = &'a str // <-- 'a is ok
+                let late_bound_in_projection_ty =
+                    tcx.collect_constrained_late_bound_regions(projection_ty);
+                let late_bound_in_term =
+                    tcx.collect_referenced_late_bound_regions(trait_ref.rebind(term));
+                debug!(?late_bound_in_projection_ty);
+                debug!(?late_bound_in_term);
 
-                    // FIXME: point at the type params that don't have appropriate lifetimes:
-                    // struct S1<F: for<'a> Fn(&i32, &i32) -> &'a i32>(F);
-                    //                         ----  ----     ^^^^^^^
-                    // NOTE(associated_const_equality): This error should be impossible to trigger
-                    //                                  with associated const equality bounds.
-                    self.validate_late_bound_regions(
-                        late_bound_in_projection_ty,
-                        late_bound_in_term,
-                        |br_name| {
-                            struct_span_code_err!(
-                                tcx.dcx(),
-                                binding.span,
-                                E0582,
-                                "binding for associated type `{}` references {}, \
-                                 which does not appear in the trait input types",
-                                binding.ident,
-                                br_name
-                            )
-                        },
-                    );
-                }
+                // FIXME: point at the type params that don't have appropriate lifetimes:
+                // struct S1<F: for<'a> Fn(&i32, &i32) -> &'a i32>(F);
+                //                         ----  ----     ^^^^^^^
+                // NOTE(associated_const_equality): This error should be impossible to trigger
+                //                                  with associated const equality bounds.
+                self.validate_late_bound_regions(
+                    late_bound_in_projection_ty,
+                    late_bound_in_term,
+                    |br_name| {
+                        struct_span_code_err!(
+                            tcx.dcx(),
+                            binding.span,
+                            E0582,
+                            "binding for associated type `{}` references {}, \
+                                which does not appear in the trait input types",
+                            binding.ident,
+                            br_name
+                        )
+                    },
+                );
 
                 // "Desugar" a constraint like `T: Iterator<Item = u32>` this to
                 // the "projection predicate" for:

compiler/rustc_hir_analysis/src/astconv/errors.rs

@@ -22,7 +22,7 @@ use rustc_span::symbol::{sym, Ident};
 use rustc_span::{Span, Symbol, DUMMY_SP};
 use rustc_trait_selection::traits::object_safety_violations_for_assoc_item;
 
-impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
+impl<'tcx> dyn AstConv<'tcx> + '_ {
     /// On missing type parameters, emit an E0393 error and provide a structured suggestion using
     /// the type parameter's name as a placeholder.
     pub(crate) fn complain_about_missing_type_params(
@@ -349,6 +349,118 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
         })
     }
 
+    pub(super) fn report_ambiguous_associated_type(
+        &self,
+        span: Span,
+        types: &[String],
+        traits: &[String],
+        name: Symbol,
+    ) -> ErrorGuaranteed {
+        let mut err =
+            struct_span_code_err!(self.tcx().dcx(), span, E0223, "ambiguous associated type");
+        if self
+            .tcx()
+            .resolutions(())
+            .confused_type_with_std_module
+            .keys()
+            .any(|full_span| full_span.contains(span))
+        {
+            err.span_suggestion_verbose(
+                span.shrink_to_lo(),
+                "you are looking for the module in `std`, not the primitive type",
+                "std::",
+                Applicability::MachineApplicable,
+            );
+        } else {
+            let mut types = types.to_vec();
+            types.sort();
+            let mut traits = traits.to_vec();
+            traits.sort();
+            match (&types[..], &traits[..]) {
+                ([], []) => {
+                    err.span_suggestion_verbose(
+                        span,
+                        format!(
+                            "if there were a type named `Type` that implements a trait named \
+                             `Trait` with associated type `{name}`, you could use the \
+                             fully-qualified path",
+                        ),
+                        format!("<Type as Trait>::{name}"),
+                        Applicability::HasPlaceholders,
+                    );
+                }
+                ([], [trait_str]) => {
+                    err.span_suggestion_verbose(
+                        span,
+                        format!(
+                            "if there were a type named `Example` that implemented `{trait_str}`, \
+                             you could use the fully-qualified path",
+                        ),
+                        format!("<Example as {trait_str}>::{name}"),
+                        Applicability::HasPlaceholders,
+                    );
+                }
+                ([], traits) => {
+                    err.span_suggestions(
+                        span,
+                        format!(
+                            "if there were a type named `Example` that implemented one of the \
+                             traits with associated type `{name}`, you could use the \
+                             fully-qualified path",
+                        ),
+                        traits
+                            .iter()
+                            .map(|trait_str| format!("<Example as {trait_str}>::{name}"))
+                            .collect::<Vec<_>>(),
+                        Applicability::HasPlaceholders,
+                    );
+                }
+                ([type_str], []) => {
+                    err.span_suggestion_verbose(
+                        span,
+                        format!(
+                            "if there were a trait named `Example` with associated type `{name}` \
+                             implemented for `{type_str}`, you could use the fully-qualified path",
+                        ),
+                        format!("<{type_str} as Example>::{name}"),
+                        Applicability::HasPlaceholders,
+                    );
+                }
+                (types, []) => {
+                    err.span_suggestions(
+                        span,
+                        format!(
+                            "if there were a trait named `Example` with associated type `{name}` \
+                             implemented for one of the types, you could use the fully-qualified \
+                             path",
+                        ),
+                        types
+                            .into_iter()
+                            .map(|type_str| format!("<{type_str} as Example>::{name}")),
+                        Applicability::HasPlaceholders,
+                    );
+                }
+                (types, traits) => {
+                    let mut suggestions = vec![];
+                    for type_str in types {
+                        for trait_str in traits {
+                            suggestions.push(format!("<{type_str} as {trait_str}>::{name}"));
+                        }
+                    }
+                    err.span_suggestions(
+                        span,
+                        "use fully-qualified syntax",
+                        suggestions,
+                        Applicability::MachineApplicable,
+                    );
+                }
+            }
+        }
+        let reported = err.emit();
+        self.set_tainted_by_errors(reported);
+        reported
+    }
+
     pub(crate) fn complain_about_ambiguous_inherent_assoc_type(
         &self,
         name: Ident,

compiler/rustc_hir_analysis/src/astconv/generics.rs

@@ -409,15 +409,12 @@ pub fn check_generic_arg_count_for_call(
     seg: &hir::PathSegment<'_>,
     is_method_call: IsMethodCall,
 ) -> GenericArgCountResult {
-    let empty_args = hir::GenericArgs::none();
-    let gen_args = seg.args.unwrap_or(&empty_args);
     let gen_pos = match is_method_call {
         IsMethodCall::Yes => GenericArgPosition::MethodCall,
         IsMethodCall::No => GenericArgPosition::Value,
     };
     let has_self = generics.parent.is_none() && generics.has_self;
-
-    check_generic_arg_count(tcx, def_id, seg, generics, gen_args, gen_pos, has_self, seg.infer_args)
+    check_generic_arg_count(tcx, def_id, seg, generics, gen_pos, has_self)
 }
 
 /// Checks that the correct number of generic arguments have been provided.
@@ -428,11 +425,10 @@ pub(crate) fn check_generic_arg_count(
     def_id: DefId,
     seg: &hir::PathSegment<'_>,
     gen_params: &ty::Generics,
-    gen_args: &hir::GenericArgs<'_>,
     gen_pos: GenericArgPosition,
     has_self: bool,
-    infer_args: bool,
 ) -> GenericArgCountResult {
+    let gen_args = seg.args();
     let default_counts = gen_params.own_defaults();
     let param_counts = gen_params.own_counts();
 
@@ -453,7 +449,7 @@ pub(crate) fn check_generic_arg_count(
         .count();
     let named_const_param_count = param_counts.consts - synth_const_param_count;
     let infer_lifetimes =
-        (gen_pos != GenericArgPosition::Type || infer_args) && !gen_args.has_lifetime_params();
+        (gen_pos != GenericArgPosition::Type || seg.infer_args) && !gen_args.has_lifetime_params();
 
     if gen_pos != GenericArgPosition::Type
         && let Some(b) = gen_args.bindings.first()
@@ -586,7 +582,7 @@ pub(crate) fn check_generic_arg_count(
     };
 
     let args_correct = {
-        let expected_min = if infer_args {
+        let expected_min = if seg.infer_args {
             0
         } else {
             param_counts.consts + named_type_param_count

compiler/rustc_hir_analysis/src/astconv/lint.rs

@@ -8,7 +8,7 @@ use rustc_trait_selection::traits::error_reporting::suggestions::NextTypeParamNa
 
 use super::AstConv;
 
-impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
+impl<'tcx> dyn AstConv<'tcx> + '_ {
     /// Make sure that we are in the condition to suggest the blanket implementation.
     pub(super) fn maybe_lint_blanket_trait_impl<G: EmissionGuarantee>(
         &self,

compiler/rustc_hir_analysis/src/astconv/mod.rs

@@ -214,7 +214,7 @@ pub trait CreateInstantiationsForGenericArgsCtxt<'a, 'tcx> {
     ) -> ty::GenericArg<'tcx>;
 }
 
-impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
+impl<'tcx> dyn AstConv<'tcx> + '_ {
     #[instrument(level = "debug", skip(self), ret)]
     pub fn ast_region_to_region(
         &self,
@@ -284,8 +284,6 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
             def_id,
             &[],
             item_segment,
-            item_segment.args(),
-            item_segment.infer_args,
             None,
             ty::BoundConstness::NotConst,
         );
@@ -330,14 +328,12 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
     /// type itself: `['a]`. The returned `GenericArgsRef` concatenates these two
     /// lists: `[Vec<u8>, u8, 'a]`.
     #[instrument(level = "debug", skip(self, span), ret)]
-    fn create_args_for_ast_path<'a>(
+    fn create_args_for_ast_path(
         &self,
         span: Span,
         def_id: DefId,
         parent_args: &[ty::GenericArg<'tcx>],
-        seg: &hir::PathSegment<'_>,
-        generic_args: &'a hir::GenericArgs<'tcx>,
-        infer_args: bool,
+        segment: &hir::PathSegment<'tcx>,
         self_ty: Option<Ty<'tcx>>,
         constness: ty::BoundConstness,
     ) -> (GenericArgsRef<'tcx>, GenericArgCountResult) {
@@ -365,12 +361,10 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
         let mut arg_count = check_generic_arg_count(
             tcx,
             def_id,
-            seg,
+            segment,
             generics,
-            generic_args,
             GenericArgPosition::Type,
             self_ty.is_some(),
-            infer_args,
         );
 
         if let Err(err) = &arg_count.correct
@@ -388,7 +382,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
         }
 
         struct InstantiationsForAstPathCtxt<'a, 'tcx> {
-            astconv: &'a (dyn AstConv<'tcx> + 'a),
+            astconv: &'a dyn AstConv<'tcx>,
             def_id: DefId,
             generic_args: &'a GenericArgs<'tcx>,
             span: Span,
@@ -547,9 +541,9 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
             astconv: self,
             def_id,
             span,
-            generic_args,
+            generic_args: segment.args(),
             inferred_params: vec![],
-            infer_args,
+            infer_args: segment.infer_args,
         };
         if let ty::BoundConstness::Const | ty::BoundConstness::ConstIfConst = constness
             && generics.has_self
@@ -592,8 +586,6 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
             item_def_id,
             parent_args,
             item_segment,
-            item_segment.args(),
-            item_segment.infer_args,
             None,
             ty::BoundConstness::NotConst,
         );
@@ -647,7 +639,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
     /// where `'a` is a bound region at depth 0. Similarly, the `poly_trait_ref` would be
     /// `Bar<'a>`. The returned poly-trait-ref will have this binder instantiated explicitly,
     /// however.
-    #[instrument(level = "debug", skip(self, span, constness, bounds, speculative))]
+    #[instrument(level = "debug", skip(self, span, constness, bounds))]
     pub(crate) fn instantiate_poly_trait_ref(
         &self,
         trait_ref: &hir::TraitRef<'tcx>,
@@ -656,12 +648,10 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
         polarity: ty::ImplPolarity,
         self_ty: Ty<'tcx>,
         bounds: &mut Bounds<'tcx>,
-        speculative: bool,
         only_self_bounds: OnlySelfBounds,
     ) -> GenericArgCountResult {
         let trait_def_id = trait_ref.trait_def_id().unwrap_or_else(|| FatalError.raise());
         let trait_segment = trait_ref.path.segments.last().unwrap();
-        let args = trait_segment.args();
 
         self.prohibit_generics(trait_ref.path.segments.split_last().unwrap().1.iter(), |_| {});
         self.complain_about_internal_fn_trait(span, trait_def_id, trait_segment, false);
@@ -671,8 +661,6 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
             trait_def_id,
             &[],
             trait_segment,
-            args,
-            trait_segment.infer_args,
             Some(self_ty),
             constness,
         );
@@ -690,7 +678,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
         bounds.push_trait_bound(tcx, poly_trait_ref, span, polarity);
 
         let mut dup_bindings = FxIndexMap::default();
-        for binding in args.bindings {
+        for binding in trait_segment.args().bindings {
             // Don't register additional associated type bounds for negative bounds,
             // since we should have emitten an error for them earlier, and they will
             // not be well-formed!
@@ -708,7 +696,6 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                 poly_trait_ref,
                 binding,
                 bounds,
-                speculative,
                 &mut dup_bindings,
                 binding.span,
                 only_self_bounds,
@@ -729,12 +716,14 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
         // FIXME(effects) move all host param things in astconv to hir lowering
         constness: ty::BoundConstness,
     ) -> ty::TraitRef<'tcx> {
-        let (generic_args, _) = self.create_args_for_ast_trait_ref(
+        self.complain_about_internal_fn_trait(span, trait_def_id, trait_segment, is_impl);
+
+        let (generic_args, _) = self.create_args_for_ast_path(
             span,
             trait_def_id,
-            self_ty,
+            &[],
             trait_segment,
-            is_impl,
+            Some(self_ty),
             constness,
         );
         if let Some(b) = trait_segment.args().bindings.first() {
@@ -743,30 +732,6 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
         ty::TraitRef::new(self.tcx(), trait_def_id, generic_args)
     }
 
-    #[instrument(level = "debug", skip(self, span))]
-    fn create_args_for_ast_trait_ref<'a>(
-        &self,
-        span: Span,
-        trait_def_id: DefId,
-        self_ty: Ty<'tcx>,
-        trait_segment: &'a hir::PathSegment<'tcx>,
-        is_impl: bool,
-        constness: ty::BoundConstness,
-    ) -> (GenericArgsRef<'tcx>, GenericArgCountResult) {
-        self.complain_about_internal_fn_trait(span, trait_def_id, trait_segment, is_impl);
-
-        self.create_args_for_ast_path(
-            span,
-            trait_def_id,
-            &[],
-            trait_segment,
-            trait_segment.args(),
-            trait_segment.infer_args,
-            Some(self_ty),
-            constness,
-        )
-    }
-
     fn trait_defines_associated_item_named(
         &self,
         trait_def_id: DefId,
@@ -801,115 +766,6 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
         }
     }
 
-    fn report_ambiguous_associated_type(
-        &self,
-        span: Span,
-        types: &[String],
-        traits: &[String],
-        name: Symbol,
-    ) -> ErrorGuaranteed {
-        let mut err =
-            struct_span_code_err!(self.tcx().dcx(), span, E0223, "ambiguous associated type");
-        if self
-            .tcx()
-            .resolutions(())
-            .confused_type_with_std_module
-            .keys()
-            .any(|full_span| full_span.contains(span))
-        {
-            err.span_suggestion_verbose(
-                span.shrink_to_lo(),
-                "you are looking for the module in `std`, not the primitive type",
-                "std::",
-                Applicability::MachineApplicable,
-            );
-        } else {
-            let mut types = types.to_vec();
-            types.sort();
-            let mut traits = traits.to_vec();
-            traits.sort();
-            match (&types[..], &traits[..]) {
-                ([], []) => {
-                    err.span_suggestion_verbose(
-                        span,
-                        format!(
-                            "if there were a type named `Type` that implements a trait named \
-                             `Trait` with associated type `{name}`, you could use the \
-                             fully-qualified path",
-                        ),
-                        format!("<Type as Trait>::{name}"),
-                        Applicability::HasPlaceholders,
-                    );
-                }
-                ([], [trait_str]) => {
-                    err.span_suggestion_verbose(
-                        span,
-                        format!(
-                            "if there were a type named `Example` that implemented `{trait_str}`, \
-                             you could use the fully-qualified path",
-                        ),
-                        format!("<Example as {trait_str}>::{name}"),
-                        Applicability::HasPlaceholders,
-                    );
-                }
-                ([], traits) => {
-                    err.span_suggestions(
-                        span,
-                        format!(
-                            "if there were a type named `Example` that implemented one of the \
-                             traits with associated type `{name}`, you could use the \
-                             fully-qualified path",
-                        ),
-                        traits.iter().map(|trait_str| format!("<Example as {trait_str}>::{name}")),
-                        Applicability::HasPlaceholders,
-                    );
-                }
-                ([type_str], []) => {
-                    err.span_suggestion_verbose(
-                        span,
-                        format!(
-                            "if there were a trait named `Example` with associated type `{name}` \
-                             implemented for `{type_str}`, you could use the fully-qualified path",
-                        ),
-                        format!("<{type_str} as Example>::{name}"),
-                        Applicability::HasPlaceholders,
-                    );
-                }
-                (types, []) => {
-                    err.span_suggestions(
-                        span,
-                        format!(
-                            "if there were a trait named `Example` with associated type `{name}` \
-                             implemented for one of the types, you could use the fully-qualified \
-                             path",
-                        ),
-                        types
-                            .into_iter()
-                            .map(|type_str| format!("<{type_str} as Example>::{name}")),
-                        Applicability::HasPlaceholders,
-                    );
-                }
-                (types, traits) => {
-                    let mut suggestions = vec![];
-                    for type_str in types {
-                        for trait_str in traits {
-                            suggestions.push(format!("<{type_str} as {trait_str}>::{name}"));
-                        }
-                    }
-                    err.span_suggestions(
-                        span,
-                        "use fully-qualified syntax",
-                        suggestions,
-                        Applicability::MachineApplicable,
-                    );
-                }
-            }
-        }
-        let reported = err.emit();
-        self.set_tainted_by_errors(reported);
-        reported
-    }
-
     // Search for a bound on a type parameter which includes the associated item
     // given by `assoc_name`. `ty_param_def_id` is the `DefId` of the type parameter
     // This function will fail if there are no suitable bounds or there is
@@ -2471,8 +2327,6 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                     def_id,
                     &[],
                     &hir::PathSegment::invalid(),
-                    &GenericArgs::none(),
-                    true,
                     None,
                     ty::BoundConstness::NotConst,
                 );
@@ -2552,9 +2406,9 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
 
     pub fn ty_of_arg(&self, ty: &hir::Ty<'tcx>, expected_ty: Option<Ty<'tcx>>) -> Ty<'tcx> {
         match ty.kind {
-            hir::TyKind::Infer if expected_ty.is_some() => {
-                self.record_ty(ty.hir_id, expected_ty.unwrap(), ty.span);
-                expected_ty.unwrap()
+            hir::TyKind::Infer if let Some(expected_ty) = expected_ty => {
+                self.record_ty(ty.hir_id, expected_ty, ty.span);
+                expected_ty
             }
             _ => self.ast_ty_to_ty(ty),
         }

compiler/rustc_hir_analysis/src/astconv/object_safety.rs

@@ -17,7 +17,7 @@ use smallvec::{smallvec, SmallVec};
 
 use super::AstConv;
 
-impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
+impl<'tcx> dyn AstConv<'tcx> + '_ {
     pub(super) fn conv_object_ty_poly_trait_ref(
         &self,
         span: Span,
@@ -44,7 +44,6 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                 ty::ImplPolarity::Positive,
                 dummy_self,
                 &mut bounds,
-                false,
                 // True so we don't populate `bounds` with associated type bounds, even
                 // though they're disallowed from object types.
                 OnlySelfBounds(true),

compiler/rustc_hir_analysis/src/check/compare_impl_item/refine.rs

@@ -2,7 +2,7 @@ use rustc_data_structures::fx::FxIndexSet;
 use rustc_hir as hir;
 use rustc_hir::def_id::DefId;
 use rustc_infer::infer::{outlives::env::OutlivesEnvironment, TyCtxtInferExt};
-use rustc_lint_defs::builtin::REFINING_IMPL_TRAIT;
+use rustc_lint_defs::builtin::{REFINING_IMPL_TRAIT_INTERNAL, REFINING_IMPL_TRAIT_REACHABLE};
 use rustc_middle::traits::{ObligationCause, Reveal};
 use rustc_middle::ty::{
     self, Ty, TyCtxt, TypeFoldable, TypeFolder, TypeSuperVisitable, TypeVisitable, TypeVisitor,
@@ -23,26 +23,23 @@ pub(super) fn check_refining_return_position_impl_trait_in_trait<'tcx>(
     if !tcx.impl_method_has_trait_impl_trait_tys(impl_m.def_id) {
         return;
     }
+
     // unreachable traits don't have any library guarantees, there's no need to do this check.
-    if trait_m
+    let is_internal = trait_m
         .container_id(tcx)
         .as_local()
         .is_some_and(|trait_def_id| !tcx.effective_visibilities(()).is_reachable(trait_def_id))
-    {
-        return;
-    }
+        // If a type in the trait ref is private, then there's also no reason to do this check.
+        || impl_trait_ref.args.iter().any(|arg| {
+            if let Some(ty) = arg.as_type()
+                && let Some(self_visibility) = type_visibility(tcx, ty)
+            {
+                return !self_visibility.is_public();
+            }
+            false
+        });
 
-    // If a type in the trait ref is private, then there's also no reason to do this check.
     let impl_def_id = impl_m.container_id(tcx);
-    for arg in impl_trait_ref.args {
-        if let Some(ty) = arg.as_type()
-            && let Some(self_visibility) = type_visibility(tcx, ty)
-            && !self_visibility.is_public()
-        {
-            return;
-        }
-    }
-
     let impl_m_args = ty::GenericArgs::identity_for_item(tcx, impl_m.def_id);
     let trait_m_to_impl_m_args = impl_m_args.rebase_onto(tcx, impl_def_id, impl_trait_ref.args);
     let bound_trait_m_sig = tcx.fn_sig(trait_m.def_id).instantiate(tcx, trait_m_to_impl_m_args);
@@ -85,6 +82,7 @@ pub(super) fn check_refining_return_position_impl_trait_in_trait<'tcx>(
                 trait_m.def_id,
                 impl_m.def_id,
                 None,
+                is_internal,
             );
             return;
         };
@@ -104,6 +102,7 @@ pub(super) fn check_refining_return_position_impl_trait_in_trait<'tcx>(
                 trait_m.def_id,
                 impl_m.def_id,
                 None,
+                is_internal,
             );
             return;
         }
@@ -198,6 +197,7 @@ pub(super) fn check_refining_return_position_impl_trait_in_trait<'tcx>(
                 trait_m.def_id,
                 impl_m.def_id,
                 Some(span),
+                is_internal,
             );
             return;
         }
@@ -235,6 +235,7 @@ fn report_mismatched_rpitit_signature<'tcx>(
     trait_m_def_id: DefId,
     impl_m_def_id: DefId,
     unmatched_bound: Option<Span>,
+    is_internal: bool,
 ) {
     let mapping = std::iter::zip(
         tcx.fn_sig(trait_m_def_id).skip_binder().bound_vars(),
@@ -287,7 +288,7 @@ fn report_mismatched_rpitit_signature<'tcx>(
 
     let span = unmatched_bound.unwrap_or(span);
     tcx.emit_node_span_lint(
-        REFINING_IMPL_TRAIT,
+        if is_internal { REFINING_IMPL_TRAIT_INTERNAL } else { REFINING_IMPL_TRAIT_REACHABLE },
         tcx.local_def_id_to_hir_id(impl_m_def_id.expect_local()),
         span,
         crate::errors::ReturnPositionImplTraitInTraitRefined {

compiler/rustc_hir_analysis/src/check/entry.rs

@@ -42,8 +42,7 @@ fn check_main_fn_ty(tcx: TyCtxt<'_>, main_def_id: DefId) {
         if !def_id.is_local() {
             return None;
         }
-        let hir_id = tcx.local_def_id_to_hir_id(def_id.expect_local());
-        match tcx.hir_node(hir_id) {
+        match tcx.hir_node_by_def_id(def_id.expect_local()) {
             Node::Item(hir::Item { kind: hir::ItemKind::Fn(_, generics, _), .. }) => {
                 generics.params.is_empty().not().then_some(generics.span)
             }
@@ -57,8 +56,7 @@ fn check_main_fn_ty(tcx: TyCtxt<'_>, main_def_id: DefId) {
         if !def_id.is_local() {
             return None;
         }
-        let hir_id = tcx.local_def_id_to_hir_id(def_id.expect_local());
-        match tcx.hir_node(hir_id) {
+        match tcx.hir_node_by_def_id(def_id.expect_local()) {
             Node::Item(hir::Item { kind: hir::ItemKind::Fn(_, generics, _), .. }) => {
                 Some(generics.where_clause_span)
             }
@@ -79,8 +77,7 @@ fn check_main_fn_ty(tcx: TyCtxt<'_>, main_def_id: DefId) {
         if !def_id.is_local() {
             return None;
         }
-        let hir_id = tcx.local_def_id_to_hir_id(def_id.expect_local());
-        match tcx.hir_node(hir_id) {
+        match tcx.hir_node_by_def_id(def_id.expect_local()) {
             Node::Item(hir::Item { kind: hir::ItemKind::Fn(fn_sig, _, _), .. }) => {
                 Some(fn_sig.decl.output.span())
             }

compiler/rustc_hir_analysis/src/check/mod.rs

@@ -130,7 +130,7 @@ fn get_owner_return_paths(
 ) -> Option<(LocalDefId, ReturnsVisitor<'_>)> {
     let hir_id = tcx.local_def_id_to_hir_id(def_id);
     let parent_id = tcx.hir().get_parent_item(hir_id).def_id;
-    tcx.opt_hir_node_by_def_id(parent_id).and_then(|node| node.body_id()).map(|body_id| {
+    tcx.hir_node_by_def_id(parent_id).body_id().map(|body_id| {
         let body = tcx.hir().body(body_id);
         let mut visitor = ReturnsVisitor::default();
         visitor.visit_body(body);

compiler/rustc_hir_analysis/src/check/wfcheck.rs

@@ -1969,13 +1969,10 @@ impl<'tcx> WfCheckingCtxt<'_, 'tcx> {
             // Match the existing behavior.
             if pred.is_global() && !pred.has_type_flags(TypeFlags::HAS_BINDER_VARS) {
                 let pred = self.normalize(span, None, pred);
-                let hir_node = tcx.opt_hir_node_by_def_id(self.body_def_id);
 
                 // only use the span of the predicate clause (#90869)
-
-                if let Some(hir::Generics { predicates, .. }) =
-                    hir_node.and_then(|node| node.generics())
-                {
+                let hir_node = tcx.hir_node_by_def_id(self.body_def_id);
+                if let Some(hir::Generics { predicates, .. }) = hir_node.generics() {
                     span = predicates
                         .iter()
                         // There seems to be no better way to find out which predicate we are in

compiler/rustc_hir_analysis/src/collect.rs

@@ -595,12 +595,14 @@ fn convert_item(tcx: TyCtxt<'_>, item_id: hir::ItemId) {
             tcx.ensure().type_of(def_id);
             tcx.ensure().impl_trait_header(def_id);
             tcx.ensure().predicates_of(def_id);
+            tcx.ensure().associated_items(def_id);
         }
         hir::ItemKind::Trait(..) => {
             tcx.ensure().generics_of(def_id);
             tcx.ensure().trait_def(def_id);
             tcx.at(it.span).super_predicates_of(def_id);
             tcx.ensure().predicates_of(def_id);
+            tcx.ensure().associated_items(def_id);
         }
         hir::ItemKind::TraitAlias(..) => {
             tcx.ensure().generics_of(def_id);

compiler/rustc_hir_analysis/src/collect/predicates_of.rs

@@ -609,10 +609,8 @@ pub(super) fn implied_predicates_with_filter(
         return tcx.super_predicates_of(trait_def_id);
     };
 
-    let trait_hir_id = tcx.local_def_id_to_hir_id(trait_def_id);
-
-    let Node::Item(item) = tcx.hir_node(trait_hir_id) else {
-        bug!("trait_node_id {} is not an item", trait_hir_id);
+    let Node::Item(item) = tcx.hir_node_by_def_id(trait_def_id) else {
+        bug!("trait_def_id {trait_def_id:?} is not an item");
     };
 
     let (generics, bounds) = match item.kind {

compiler/rustc_hir_analysis/src/collect/type_of.rs

@@ -108,8 +108,7 @@ fn anon_const_type_of<'tcx>(tcx: TyCtxt<'tcx>, def_id: LocalDefId) -> Ty<'tcx> {
                 .unwrap()
                 .0
                 .def_id;
-            let item_ctxt = &ItemCtxt::new(tcx, item_def_id) as &dyn crate::astconv::AstConv<'_>;
-            let ty = item_ctxt.ast_ty_to_ty(hir_ty);
+            let ty = ItemCtxt::new(tcx, item_def_id).to_ty(hir_ty);
 
             // Iterate through the generics of the projection to find the one that corresponds to
             // the def_id that this query was called with. We filter to only type and const args here

compiler/rustc_hir_analysis/src/collect/type_of/opaque.rs

@@ -371,11 +371,10 @@ pub(super) fn find_opaque_ty_constraints_for_rpit<'tcx>(
             return mir_opaque_ty.ty;
         }
 
-        let scope = tcx.local_def_id_to_hir_id(owner_def_id);
-        debug!(?scope);
+        debug!(?owner_def_id);
         let mut locator = RpitConstraintChecker { def_id, tcx, found: mir_opaque_ty };
 
-        match tcx.hir_node(scope) {
+        match tcx.hir_node_by_def_id(owner_def_id) {
             Node::Item(it) => intravisit::walk_item(&mut locator, it),
             Node::ImplItem(it) => intravisit::walk_impl_item(&mut locator, it),
             Node::TraitItem(it) => intravisit::walk_trait_item(&mut locator, it),

compiler/rustc_hir_analysis/src/errors.rs

@@ -1072,6 +1072,7 @@ pub struct UnusedAssociatedTypeBounds {
 #[derive(LintDiagnostic)]
 #[diag(hir_analysis_rpitit_refined)]
 #[note]
+#[note(hir_analysis_feedback_note)]
 pub(crate) struct ReturnPositionImplTraitInTraitRefined<'tcx> {
     #[suggestion(applicability = "maybe-incorrect", code = "{pre}{return_ty}{post}")]
     pub impl_return_span: Span,

compiler/rustc_hir_analysis/src/lib.rs

@@ -100,19 +100,16 @@ mod variance;
 
 use rustc_errors::ErrorGuaranteed;
 use rustc_hir as hir;
+use rustc_hir::def::DefKind;
 use rustc_middle::middle;
 use rustc_middle::query::Providers;
-use rustc_middle::ty::{self, Ty, TyCtxt};
+use rustc_middle::ty::{Ty, TyCtxt};
 use rustc_middle::util;
 use rustc_session::parse::feature_err;
-use rustc_span::{symbol::sym, Span, DUMMY_SP};
+use rustc_span::{symbol::sym, Span};
 use rustc_target::spec::abi::Abi;
 use rustc_trait_selection::traits;
 
-use astconv::{AstConv, OnlySelfBounds};
-use bounds::Bounds;
-use rustc_hir::def::DefKind;
-
 rustc_fluent_macro::fluent_messages! { "../messages.ftl" }
 
 fn require_c_abi_if_c_variadic(tcx: TyCtxt<'_>, decl: &hir::FnDecl<'_>, abi: Abi, span: Span) {
@@ -222,31 +219,5 @@ pub fn hir_ty_to_ty<'tcx>(tcx: TyCtxt<'tcx>, hir_ty: &hir::Ty<'tcx>) -> Ty<'tcx>
     // def-ID that will be used to determine the traits/predicates in
     // scope. This is derived from the enclosing item-like thing.
     let env_def_id = tcx.hir().get_parent_item(hir_ty.hir_id);
-    let item_cx = self::collect::ItemCtxt::new(tcx, env_def_id.def_id);
-    item_cx.astconv().ast_ty_to_ty(hir_ty)
-}
-
-pub fn hir_trait_to_predicates<'tcx>(
-    tcx: TyCtxt<'tcx>,
-    hir_trait: &hir::TraitRef<'tcx>,
-    self_ty: Ty<'tcx>,
-) -> Bounds<'tcx> {
-    // In case there are any projections, etc., find the "environment"
-    // def-ID that will be used to determine the traits/predicates in
-    // scope. This is derived from the enclosing item-like thing.
-    let env_def_id = tcx.hir().get_parent_item(hir_trait.hir_ref_id);
-    let item_cx = self::collect::ItemCtxt::new(tcx, env_def_id.def_id);
-    let mut bounds = Bounds::default();
-    let _ = &item_cx.astconv().instantiate_poly_trait_ref(
-        hir_trait,
-        DUMMY_SP,
-        ty::BoundConstness::NotConst,
-        ty::ImplPolarity::Positive,
-        self_ty,
-        &mut bounds,
-        true,
-        OnlySelfBounds(false),
-    );
-
-    bounds
+    collect::ItemCtxt::new(tcx, env_def_id.def_id).to_ty(hir_ty)
 }

compiler/rustc_hir_typeck/src/_match.rs

@@ -234,11 +234,8 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         }
 
         // Next, make sure that we have no type expectation.
-        let Some(ret) = self
-            .tcx
-            .opt_hir_node_by_def_id(self.body_id)
-            .and_then(|owner| owner.fn_decl())
-            .map(|decl| decl.output.span())
+        let Some(ret) =
+            self.tcx.hir_node_by_def_id(self.body_id).fn_decl().map(|decl| decl.output.span())
         else {
             return;
         };

compiler/rustc_hir_typeck/src/closure.rs

@@ -780,7 +780,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         decl: &hir::FnDecl<'tcx>,
         closure_kind: hir::ClosureKind,
     ) -> ty::PolyFnSig<'tcx> {
-        let astconv: &dyn AstConv<'_> = self;
+        let astconv = self.astconv();
 
         trace!("decl = {:#?}", decl);
         debug!(?closure_kind);
@@ -985,7 +985,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         decl: &hir::FnDecl<'tcx>,
         guar: ErrorGuaranteed,
     ) -> ty::PolyFnSig<'tcx> {
-        let astconv: &dyn AstConv<'_> = self;
+        let astconv = self.astconv();
         let err_ty = Ty::new_error(self.tcx, guar);
 
         let supplied_arguments = decl.inputs.iter().map(|a| {

compiler/rustc_hir_typeck/src/demand.rs

@@ -1071,7 +1071,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                     err.span_suggestion_verbose(
                         *span,
                         "use the type name directly",
-                        self.tcx.value_path_str_with_args(*alias_to, e_args),
+                        self.tcx.value_path_str_with_args(e_def.did(), e_args),
                         Applicability::MaybeIncorrect,
                     );
                 }

compiler/rustc_hir_typeck/src/expr.rs

@@ -890,21 +890,19 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 
         let encl_item_id = self.tcx.hir().get_parent_item(expr.hir_id);
 
-        if let Some(hir::Node::Item(hir::Item {
-            kind: hir::ItemKind::Fn(..),
-            span: encl_fn_span,
-            ..
-        }))
-        | Some(hir::Node::TraitItem(hir::TraitItem {
+        if let hir::Node::Item(hir::Item {
+            kind: hir::ItemKind::Fn(..), span: encl_fn_span, ..
+        })
+        | hir::Node::TraitItem(hir::TraitItem {
             kind: hir::TraitItemKind::Fn(_, hir::TraitFn::Provided(_)),
             span: encl_fn_span,
             ..
-        }))
-        | Some(hir::Node::ImplItem(hir::ImplItem {
+        })
+        | hir::Node::ImplItem(hir::ImplItem {
             kind: hir::ImplItemKind::Fn(..),
             span: encl_fn_span,
             ..
-        })) = self.tcx.opt_hir_node_by_def_id(encl_item_id.def_id)
+        }) = self.tcx.hir_node_by_def_id(encl_item_id.def_id)
         {
             // We are inside a function body, so reporting "return statement
             // outside of function body" needs an explanation.

compiler/rustc_hir_typeck/src/fallback.rs

@@ -4,8 +4,22 @@ use rustc_data_structures::{
     graph::{iterate::DepthFirstSearch, vec_graph::VecGraph},
     unord::{UnordBag, UnordMap, UnordSet},
 };
+use rustc_hir::def_id::CRATE_DEF_ID;
 use rustc_infer::infer::{DefineOpaqueTypes, InferOk};
 use rustc_middle::ty::{self, Ty};
+use rustc_span::sym;
+
+enum DivergingFallbackBehavior {
+    /// Always fallback to `()` (aka "always spontaneous decay")
+    FallbackToUnit,
+    /// Sometimes fallback to `!`, but mainly fallback to `()` so that most of the crates are not broken.
+    FallbackToNiko,
+    /// Always fallback to `!` (which should be equivalent to never falling back + not making
+    /// never-to-any coercions unless necessary)
+    FallbackToNever,
+    /// Don't fallback at all
+    NoFallback,
+}
 
 impl<'tcx> FnCtxt<'_, 'tcx> {
     /// Performs type inference fallback, setting `FnCtxt::fallback_has_occurred`
@@ -64,7 +78,9 @@ impl<'tcx> FnCtxt<'_, 'tcx> {
             return false;
         }
 
-        let diverging_fallback = self.calculate_diverging_fallback(&unresolved_variables);
+        let diverging_behavior = self.diverging_fallback_behavior();
+        let diverging_fallback =
+            self.calculate_diverging_fallback(&unresolved_variables, diverging_behavior);
 
         // We do fallback in two passes, to try to generate
         // better error messages.
@@ -78,6 +94,32 @@ impl<'tcx> FnCtxt<'_, 'tcx> {
         fallback_occurred
     }
 
+    fn diverging_fallback_behavior(&self) -> DivergingFallbackBehavior {
+        let Some((mode, span)) = self
+            .tcx
+            .get_attr(CRATE_DEF_ID, sym::rustc_never_type_mode)
+            .map(|attr| (attr.value_str().unwrap(), attr.span))
+        else {
+            if self.tcx.features().never_type_fallback {
+                return DivergingFallbackBehavior::FallbackToNiko;
+            }
+
+            return DivergingFallbackBehavior::FallbackToUnit;
+        };
+
+        match mode {
+            sym::fallback_to_unit => DivergingFallbackBehavior::FallbackToUnit,
+            sym::fallback_to_niko => DivergingFallbackBehavior::FallbackToNiko,
+            sym::fallback_to_never => DivergingFallbackBehavior::FallbackToNever,
+            sym::no_fallback => DivergingFallbackBehavior::NoFallback,
+            _ => {
+                self.tcx.dcx().span_err(span, format!("unknown never type mode: `{mode}` (supported: `fallback_to_unit`, `fallback_to_niko`, `fallback_to_never` and `no_fallback`)"));
+
+                DivergingFallbackBehavior::FallbackToUnit
+            }
+        }
+    }
+
     fn fallback_effects(&self) -> bool {
         let unsolved_effects = self.unsolved_effects();
 
@@ -232,6 +274,7 @@ impl<'tcx> FnCtxt<'_, 'tcx> {
     fn calculate_diverging_fallback(
         &self,
         unresolved_variables: &[Ty<'tcx>],
+        behavior: DivergingFallbackBehavior,
     ) -> UnordMap<Ty<'tcx>, Ty<'tcx>> {
         debug!("calculate_diverging_fallback({:?})", unresolved_variables);
 
@@ -345,39 +388,61 @@ impl<'tcx> FnCtxt<'_, 'tcx> {
                 output: infer_var_infos.items().any(|info| info.output),
             };
 
-            if found_infer_var_info.self_in_trait && found_infer_var_info.output {
-                // This case falls back to () to ensure that the code pattern in
-                // tests/ui/never_type/fallback-closure-ret.rs continues to
-                // compile when never_type_fallback is enabled.
-                //
-                // This rule is not readily explainable from first principles,
-                // but is rather intended as a patchwork fix to ensure code
-                // which compiles before the stabilization of never type
-                // fallback continues to work.
-                //
-                // Typically this pattern is encountered in a function taking a
-                // closure as a parameter, where the return type of that closure
-                // (checked by `relationship.output`) is expected to implement
-                // some trait (checked by `relationship.self_in_trait`). This
-                // can come up in non-closure cases too, so we do not limit this
-                // rule to specifically `FnOnce`.
-                //
-                // When the closure's body is something like `panic!()`, the
-                // return type would normally be inferred to `!`. However, it
-                // needs to fall back to `()` in order to still compile, as the
-                // trait is specifically implemented for `()` but not `!`.
-                //
-                // For details on the requirements for these relationships to be
-                // set, see the relationship finding module in
-                // compiler/rustc_trait_selection/src/traits/relationships.rs.
-                debug!("fallback to () - found trait and projection: {:?}", diverging_vid);
-                diverging_fallback.insert(diverging_ty, self.tcx.types.unit);
-            } else if can_reach_non_diverging {
-                debug!("fallback to () - reached non-diverging: {:?}", diverging_vid);
-                diverging_fallback.insert(diverging_ty, self.tcx.types.unit);
-            } else {
-                debug!("fallback to ! - all diverging: {:?}", diverging_vid);
-                diverging_fallback.insert(diverging_ty, Ty::new_diverging_default(self.tcx));
+            use DivergingFallbackBehavior::*;
+            match behavior {
+                FallbackToUnit => {
+                    debug!("fallback to () - legacy: {:?}", diverging_vid);
+                    diverging_fallback.insert(diverging_ty, self.tcx.types.unit);
+                }
+                FallbackToNiko => {
+                    if found_infer_var_info.self_in_trait && found_infer_var_info.output {
+                        // This case falls back to () to ensure that the code pattern in
+                        // tests/ui/never_type/fallback-closure-ret.rs continues to
+                        // compile when never_type_fallback is enabled.
+                        //
+                        // This rule is not readily explainable from first principles,
+                        // but is rather intended as a patchwork fix to ensure code
+                        // which compiles before the stabilization of never type
+                        // fallback continues to work.
+                        //
+                        // Typically this pattern is encountered in a function taking a
+                        // closure as a parameter, where the return type of that closure
+                        // (checked by `relationship.output`) is expected to implement
+                        // some trait (checked by `relationship.self_in_trait`). This
+                        // can come up in non-closure cases too, so we do not limit this
+                        // rule to specifically `FnOnce`.
+                        //
+                        // When the closure's body is something like `panic!()`, the
+                        // return type would normally be inferred to `!`. However, it
+                        // needs to fall back to `()` in order to still compile, as the
+                        // trait is specifically implemented for `()` but not `!`.
+                        //
+                        // For details on the requirements for these relationships to be
+                        // set, see the relationship finding module in
+                        // compiler/rustc_trait_selection/src/traits/relationships.rs.
+                        debug!("fallback to () - found trait and projection: {:?}", diverging_vid);
+                        diverging_fallback.insert(diverging_ty, self.tcx.types.unit);
+                    } else if can_reach_non_diverging {
+                        debug!("fallback to () - reached non-diverging: {:?}", diverging_vid);
+                        diverging_fallback.insert(diverging_ty, self.tcx.types.unit);
+                    } else {
+                        debug!("fallback to ! - all diverging: {:?}", diverging_vid);
+                        diverging_fallback.insert(diverging_ty, self.tcx.types.never);
+                    }
+                }
+                FallbackToNever => {
+                    debug!(
+                        "fallback to ! - `rustc_never_type_mode = \"fallback_to_never\")`: {:?}",
+                        diverging_vid
+                    );
+                    diverging_fallback.insert(diverging_ty, self.tcx.types.never);
+                }
+                NoFallback => {
+                    debug!(
+                        "no fallback - `rustc_never_type_mode = \"no_fallback\"`: {:?}",
+                        diverging_vid
+                    );
+                }
             }
         }
 

compiler/rustc_hir_typeck/src/fn_ctxt/checks.rs

@@ -2172,16 +2172,11 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 // Try to find earlier invocations of this closure to find if the type mismatch
                 // is because of inference. If we find one, point at them.
                 let mut call_finder = FindClosureArg { tcx: self.tcx, calls: vec![] };
-                let node = self
-                    .tcx
-                    .opt_local_def_id_to_hir_id(
-                        self.tcx.hir().get_parent_item(call_expr.hir_id).def_id,
-                    )
-                    .map(|hir_id| self.tcx.hir_node(hir_id));
-                match node {
-                    Some(hir::Node::Item(item)) => call_finder.visit_item(item),
-                    Some(hir::Node::TraitItem(item)) => call_finder.visit_trait_item(item),
-                    Some(hir::Node::ImplItem(item)) => call_finder.visit_impl_item(item),
+                let parent_def_id = self.tcx.hir().get_parent_item(call_expr.hir_id).def_id;
+                match self.tcx.hir_node_by_def_id(parent_def_id) {
+                    hir::Node::Item(item) => call_finder.visit_item(item),
+                    hir::Node::TraitItem(item) => call_finder.visit_trait_item(item),
+                    hir::Node::ImplItem(item) => call_finder.visit_impl_item(item),
                     _ => {}
                 }
                 let typeck = self.typeck_results.borrow();

compiler/rustc_infer/src/infer/error_reporting/mod.rs

@@ -2126,8 +2126,8 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
         let TypeError::FixedArraySize(sz) = terr else {
             return None;
         };
-        let tykind = match self.tcx.opt_hir_node_by_def_id(trace.cause.body_id) {
-            Some(hir::Node::Item(hir::Item { kind: hir::ItemKind::Fn(_, _, body_id), .. })) => {
+        let tykind = match self.tcx.hir_node_by_def_id(trace.cause.body_id) {
+            hir::Node::Item(hir::Item { kind: hir::ItemKind::Fn(_, _, body_id), .. }) => {
                 let body = hir.body(*body_id);
                 struct LetVisitor {
                     span: Span,
@@ -2156,7 +2156,7 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
                 }
                 LetVisitor { span }.visit_body(body).break_value()
             }
-            Some(hir::Node::Item(hir::Item { kind: hir::ItemKind::Const(ty, _, _), .. })) => {
+            hir::Node::Item(hir::Item { kind: hir::ItemKind::Const(ty, _, _), .. }) => {
                 Some(&ty.peel_refs().kind)
             }
             _ => None,
@@ -2527,15 +2527,14 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
                     .filter(|p| matches!(p.kind, ty::GenericParamDefKind::Lifetime))
                     .map(|p| p.name)
                     .collect::<Vec<_>>();
-            if let Some(hir_id) = self.tcx.opt_local_def_id_to_hir_id(lifetime_scope) {
-                // consider late-bound lifetimes ...
-                used_names.extend(self.tcx.late_bound_vars(hir_id).into_iter().filter_map(|p| {
-                    match p {
-                        ty::BoundVariableKind::Region(lt) => lt.get_name(),
-                        _ => None,
-                    }
-                }))
-            }
+            let hir_id = self.tcx.local_def_id_to_hir_id(lifetime_scope);
+            // consider late-bound lifetimes ...
+            used_names.extend(self.tcx.late_bound_vars(hir_id).into_iter().filter_map(
+                |p| match p {
+                    ty::BoundVariableKind::Region(lt) => lt.get_name(),
+                    _ => None,
+                },
+            ));
             (b'a'..=b'z')
                 .map(|c| format!("'{}", c as char))
                 .find(|candidate| !used_names.iter().any(|e| e.as_str() == candidate))

compiler/rustc_infer/src/infer/error_reporting/nice_region_error/static_impl_trait.rs

@@ -459,7 +459,7 @@ impl<'a, 'tcx> NiceRegionError<'a, 'tcx> {
                 tcx.hir().trait_impls(trait_did).iter().find_map(|&impl_did| {
                     if let Node::Item(Item {
                         kind: ItemKind::Impl(hir::Impl { self_ty, .. }), ..
-                    }) = tcx.opt_hir_node_by_def_id(impl_did)?
+                    }) = tcx.hir_node_by_def_id(impl_did)
                         && trait_objects.iter().all(|did| {
                             // FIXME: we should check `self_ty` against the receiver
                             // type in the `UnifyReceiver` context, but for now, use

compiler/rustc_infer/src/infer/error_reporting/note_and_explain.rs

@@ -804,23 +804,22 @@ fn foo(&self) -> Self::T { String::new() }
     ) -> bool {
         let tcx = self.tcx;
 
-        let Some(hir_id) = body_owner_def_id.as_local() else {
-            return false;
-        };
-        let Some(hir_id) = tcx.opt_local_def_id_to_hir_id(hir_id) else {
+        let Some(def_id) = body_owner_def_id.as_local() else {
             return false;
         };
+
         // When `body_owner` is an `impl` or `trait` item, look in its associated types for
         // `expected` and point at it.
+        let hir_id = tcx.local_def_id_to_hir_id(def_id);
         let parent_id = tcx.hir().get_parent_item(hir_id);
-        let item = tcx.opt_hir_node_by_def_id(parent_id.def_id);
+        let item = tcx.hir_node_by_def_id(parent_id.def_id);
 
         debug!("expected_projection parent item {:?}", item);
 
         let param_env = tcx.param_env(body_owner_def_id);
 
         match item {
-            Some(hir::Node::Item(hir::Item { kind: hir::ItemKind::Trait(.., items), .. })) => {
+            hir::Node::Item(hir::Item { kind: hir::ItemKind::Trait(.., items), .. }) => {
                 // FIXME: account for `#![feature(specialization)]`
                 for item in &items[..] {
                     match item.kind {
@@ -845,10 +844,10 @@ fn foo(&self) -> Self::T { String::new() }
                     }
                 }
             }
-            Some(hir::Node::Item(hir::Item {
+            hir::Node::Item(hir::Item {
                 kind: hir::ItemKind::Impl(hir::Impl { items, .. }),
                 ..
-            })) => {
+            }) => {
                 for item in &items[..] {
                     if let hir::AssocItemKind::Type = item.kind {
                         let assoc_ty = tcx.type_of(item.id.owner_id).instantiate_identity();

compiler/rustc_lint/src/builtin.rs

@@ -2468,6 +2468,8 @@ impl<'tcx> LateLintPass<'tcx> for InvalidValue {
             ty: Ty<'tcx>,
             init: InitKind,
         ) -> Option<InitError> {
+            let ty = cx.tcx.try_normalize_erasing_regions(cx.param_env, ty).unwrap_or(ty);
+
             use rustc_type_ir::TyKind::*;
             match ty.kind() {
                 // Primitive types that don't like 0 as a value.

compiler/rustc_lint/src/lib.rs

@@ -313,6 +313,12 @@ fn register_builtins(store: &mut LintStore) {
                                        // MACRO_USE_EXTERN_CRATE
     );
 
+    add_lint_group!(
+        "refining_impl_trait",
+        REFINING_IMPL_TRAIT_REACHABLE,
+        REFINING_IMPL_TRAIT_INTERNAL
+    );
+
     // Register renamed and removed lints.
     store.register_renamed("single_use_lifetime", "single_use_lifetimes");
     store.register_renamed("elided_lifetime_in_path", "elided_lifetimes_in_paths");

compiler/rustc_lint/src/types.rs

@@ -561,10 +561,11 @@ fn lint_literal<'tcx>(
         ty::Float(t) => {
             let is_infinite = match lit.node {
                 ast::LitKind::Float(v, _) => match t {
-                    ty::FloatTy::F16 => unimplemented!("f16_f128"),
+                    // FIXME(f16_f128): add this check once we have library support
+                    ty::FloatTy::F16 => Ok(false),
                     ty::FloatTy::F32 => v.as_str().parse().map(f32::is_infinite),
                     ty::FloatTy::F64 => v.as_str().parse().map(f64::is_infinite),
-                    ty::FloatTy::F128 => unimplemented!("f16_f128"),
+                    ty::FloatTy::F128 => Ok(false),
                 },
                 _ => bug!(),
             };
@@ -984,7 +985,14 @@ pub fn transparent_newtype_field<'a, 'tcx>(
 }
 
 /// Is type known to be non-null?
-fn ty_is_known_nonnull<'tcx>(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>, mode: CItemKind) -> bool {
+fn ty_is_known_nonnull<'tcx>(
+    tcx: TyCtxt<'tcx>,
+    param_env: ty::ParamEnv<'tcx>,
+    ty: Ty<'tcx>,
+    mode: CItemKind,
+) -> bool {
+    let ty = tcx.try_normalize_erasing_regions(param_env, ty).unwrap_or(ty);
+
     match ty.kind() {
         ty::FnPtr(_) => true,
         ty::Ref(..) => true,
@@ -1004,7 +1012,7 @@ fn ty_is_known_nonnull<'tcx>(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>, mode: CItemKind) -
             def.variants()
                 .iter()
                 .filter_map(|variant| transparent_newtype_field(tcx, variant))
-                .any(|field| ty_is_known_nonnull(tcx, field.ty(tcx, args), mode))
+                .any(|field| ty_is_known_nonnull(tcx, param_env, field.ty(tcx, args), mode))
         }
         _ => false,
     }
@@ -1012,7 +1020,13 @@ fn ty_is_known_nonnull<'tcx>(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>, mode: CItemKind) -
 
 /// Given a non-null scalar (or transparent) type `ty`, return the nullable version of that type.
 /// If the type passed in was not scalar, returns None.
-fn get_nullable_type<'tcx>(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>) -> Option<Ty<'tcx>> {
+fn get_nullable_type<'tcx>(
+    tcx: TyCtxt<'tcx>,
+    param_env: ty::ParamEnv<'tcx>,
+    ty: Ty<'tcx>,
+) -> Option<Ty<'tcx>> {
+    let ty = tcx.try_normalize_erasing_regions(param_env, ty).unwrap_or(ty);
+
     Some(match *ty.kind() {
         ty::Adt(field_def, field_args) => {
             let inner_field_ty = {
@@ -1028,22 +1042,19 @@ fn get_nullable_type<'tcx>(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>) -> Option<Ty<'tcx>>
                     .expect("No non-zst fields in transparent type.")
                     .ty(tcx, field_args)
             };
-            return get_nullable_type(tcx, inner_field_ty);
+            return get_nullable_type(tcx, param_env, inner_field_ty);
         }
         ty::Int(ty) => Ty::new_int(tcx, ty),
         ty::Uint(ty) => Ty::new_uint(tcx, ty),
         ty::RawPtr(ty_mut) => Ty::new_ptr(tcx, ty_mut),
         // As these types are always non-null, the nullable equivalent of
-        // Option<T> of these types are their raw pointer counterparts.
+        // `Option<T>` of these types are their raw pointer counterparts.
         ty::Ref(_region, ty, mutbl) => Ty::new_ptr(tcx, ty::TypeAndMut { ty, mutbl }),
-        ty::FnPtr(..) => {
-            // There is no nullable equivalent for Rust's function pointers -- you
-            // must use an Option<fn(..) -> _> to represent it.
-            ty
-        }
-
-        // We should only ever reach this case if ty_is_known_nonnull is extended
-        // to other types.
+        // There is no nullable equivalent for Rust's function pointers,
+        // you must use an `Option<fn(..) -> _>` to represent it.
+        ty::FnPtr(..) => ty,
+        // We should only ever reach this case if `ty_is_known_nonnull` is
+        // extended to other types.
         ref unhandled => {
             debug!(
                 "get_nullable_type: Unhandled scalar kind: {:?} while checking {:?}",
@@ -1056,7 +1067,7 @@ fn get_nullable_type<'tcx>(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>) -> Option<Ty<'tcx>>
 
 /// Check if this enum can be safely exported based on the "nullable pointer optimization". If it
 /// can, return the type that `ty` can be safely converted to, otherwise return `None`.
-/// Currently restricted to function pointers, boxes, references, `core::num::NonZero*`,
+/// Currently restricted to function pointers, boxes, references, `core::num::NonZero`,
 /// `core::ptr::NonNull`, and `#[repr(transparent)]` newtypes.
 /// FIXME: This duplicates code in codegen.
 pub(crate) fn repr_nullable_ptr<'tcx>(
@@ -1075,7 +1086,7 @@ pub(crate) fn repr_nullable_ptr<'tcx>(
             _ => return None,
         };
 
-        if !ty_is_known_nonnull(tcx, field_ty, ckind) {
+        if !ty_is_known_nonnull(tcx, param_env, field_ty, ckind) {
             return None;
         }
 
@@ -1099,10 +1110,10 @@ pub(crate) fn repr_nullable_ptr<'tcx>(
                 WrappingRange { start: 0, end }
                     if end == field_ty_scalar.size(&tcx).unsigned_int_max() - 1 =>
                 {
-                    return Some(get_nullable_type(tcx, field_ty).unwrap());
+                    return Some(get_nullable_type(tcx, param_env, field_ty).unwrap());
                 }
                 WrappingRange { start: 1, .. } => {
-                    return Some(get_nullable_type(tcx, field_ty).unwrap());
+                    return Some(get_nullable_type(tcx, param_env, field_ty).unwrap());
                 }
                 WrappingRange { start, end } => {
                     unreachable!("Unhandled start and end range: ({}, {})", start, end)

compiler/rustc_lint_defs/src/builtin.rs

@@ -79,7 +79,8 @@ declare_lint_pass! {
         PROC_MACRO_BACK_COMPAT,
         PROC_MACRO_DERIVE_RESOLUTION_FALLBACK,
         PUB_USE_OF_PRIVATE_EXTERN_CRATE,
-        REFINING_IMPL_TRAIT,
+        REFINING_IMPL_TRAIT_INTERNAL,
+        REFINING_IMPL_TRAIT_REACHABLE,
         RENAMED_AND_REMOVED_LINTS,
         REPR_TRANSPARENT_EXTERNAL_PRIVATE_FIELDS,
         RUST_2021_INCOMPATIBLE_CLOSURE_CAPTURES,
@@ -130,6 +131,7 @@ declare_lint_pass! {
         UNUSED_VARIABLES,
         USELESS_DEPRECATED,
         WARNINGS,
+        WASM_C_ABI,
         WHERE_CLAUSES_OBJECT_SAFETY,
         WRITES_THROUGH_IMMUTABLE_POINTER,
         // tidy-alphabetical-end
@@ -4401,8 +4403,10 @@ declare_lint! {
 }
 
 declare_lint! {
-    /// The `refining_impl_trait` lint detects usages of return-position impl
-    /// traits in trait signatures which are refined by implementations.
+    /// The `refining_impl_trait_reachable` lint detects `impl Trait` return
+    /// types in method signatures that are refined by a publically reachable
+    /// trait implementation, meaning the implementation adds information about
+    /// the return type that is not present in the trait.
     ///
     /// ### Example
     ///
@@ -4424,7 +4428,7 @@ declare_lint! {
     /// fn main() {
     ///     // users can observe that the return type of
     ///     // `<&str as AsDisplay>::as_display()` is `&str`.
-    ///     let x: &str = "".as_display();
+    ///     let _x: &str = "".as_display();
     /// }
     /// ```
     ///
@@ -4432,13 +4436,80 @@ declare_lint! {
     ///
     /// ### Explanation
     ///
-    /// Return-position impl trait in traits (RPITITs) desugar to associated types,
-    /// and callers of methods for types where the implementation is known are
+    /// Callers of methods for types where the implementation is known are
     /// able to observe the types written in the impl signature. This may be
-    /// intended behavior, but may also pose a semver hazard for authors of libraries
-    /// who do not wish to make stronger guarantees about the types than what is
-    /// written in the trait signature.
-    pub REFINING_IMPL_TRAIT,
+    /// intended behavior, but may also lead to implementation details being
+    /// revealed unintentionally. In particular, it may pose a semver hazard
+    /// for authors of libraries who do not wish to make stronger guarantees
+    /// about the types than what is written in the trait signature.
+    ///
+    /// `refining_impl_trait` is a lint group composed of two lints:
+    ///
+    /// * `refining_impl_trait_reachable`, for refinements that are publically
+    ///   reachable outside a crate, and
+    /// * `refining_impl_trait_internal`, for refinements that are only visible
+    ///    within a crate.
+    ///
+    /// We are seeking feedback on each of these lints; see issue
+    /// [#121718](https://github.com/rust-lang/rust/issues/121718) for more
+    /// information.
+    pub REFINING_IMPL_TRAIT_REACHABLE,
+    Warn,
+    "impl trait in impl method signature does not match trait method signature",
+}
+
+declare_lint! {
+    /// The `refining_impl_trait_internal` lint detects `impl Trait` return
+    /// types in method signatures that are refined by a trait implementation,
+    /// meaning the implementation adds information about the return type that
+    /// is not present in the trait.
+    ///
+    /// ### Example
+    ///
+    /// ```rust,compile_fail
+    /// #![deny(refining_impl_trait)]
+    ///
+    /// use std::fmt::Display;
+    ///
+    /// trait AsDisplay {
+    ///     fn as_display(&self) -> impl Display;
+    /// }
+    ///
+    /// impl<'s> AsDisplay for &'s str {
+    ///     fn as_display(&self) -> Self {
+    ///         *self
+    ///     }
+    /// }
+    ///
+    /// fn main() {
+    ///     // users can observe that the return type of
+    ///     // `<&str as AsDisplay>::as_display()` is `&str`.
+    ///     let _x: &str = "".as_display();
+    /// }
+    /// ```
+    ///
+    /// {{produces}}
+    ///
+    /// ### Explanation
+    ///
+    /// Callers of methods for types where the implementation is known are
+    /// able to observe the types written in the impl signature. This may be
+    /// intended behavior, but may also lead to implementation details being
+    /// revealed unintentionally. In particular, it may pose a semver hazard
+    /// for authors of libraries who do not wish to make stronger guarantees
+    /// about the types than what is written in the trait signature.
+    ///
+    /// `refining_impl_trait` is a lint group composed of two lints:
+    ///
+    /// * `refining_impl_trait_reachable`, for refinements that are publically
+    ///   reachable outside a crate, and
+    /// * `refining_impl_trait_internal`, for refinements that are only visible
+    ///    within a crate.
+    ///
+    /// We are seeking feedback on each of these lints; see issue
+    /// [#121718](https://github.com/rust-lang/rust/issues/121718) for more
+    /// information.
+    pub REFINING_IMPL_TRAIT_INTERNAL,
     Warn,
     "impl trait in impl method signature does not match trait method signature",
 }
@@ -4564,3 +4635,41 @@ declare_lint! {
         reference: "issue #120192 <https://github.com/rust-lang/rust/issues/120192>",
     };
 }
+
+declare_lint! {
+    /// The `wasm_c_abi` lint detects crate dependencies that are incompatible
+    /// with future versions of Rust that will emit spec-compliant C ABI.
+    ///
+    /// ### Example
+    ///
+    /// ```rust,ignore (needs extern crate)
+    /// #![deny(wasm_c_abi)]
+    /// ```
+    ///
+    /// This will produce:
+    ///
+    /// ```text
+    /// error: the following packages contain code that will be rejected by a future version of Rust: wasm-bindgen v0.2.87
+    ///   |
+    /// note: the lint level is defined here
+    ///  --> src/lib.rs:1:9
+    ///   |
+    /// 1 | #![deny(wasm_c_abi)]
+    ///   |         ^^^^^^^^^^
+    /// ```
+    ///
+    /// ### Explanation
+    ///
+    /// Rust has historically emitted non-spec-compliant C ABI. This has caused
+    /// incompatibilities between other compilers and Wasm targets. In a future
+    /// version of Rust this will be fixed and therefore dependencies relying
+    /// on the non-spec-compliant C ABI will stop functioning.
+    pub WASM_C_ABI,
+    Warn,
+    "detects dependencies that are incompatible with the Wasm C ABI",
+    @future_incompatible = FutureIncompatibleInfo {
+        reason: FutureIncompatibilityReason::FutureReleaseErrorReportInDeps,
+        reference: "issue #71871 <https://github.com/rust-lang/rust/issues/71871>",
+    };
+    crate_level_only
+}

compiler/rustc_metadata/messages.ftl

@@ -281,6 +281,8 @@ metadata_unsupported_abi =
 metadata_unsupported_abi_i686 =
     ABI not supported by `#[link(kind = "raw-dylib")]` on i686
 
+metadata_wasm_c_abi =
+    older versions of the `wasm-bindgen` crate will be incompatible with future versions of Rust; please update to `wasm-bindgen` v0.2.88
 metadata_wasm_import_form =
     wasm import module must be of the form `wasm_import_module = "string"`
 

compiler/rustc_metadata/src/creader.rs

@@ -31,8 +31,9 @@ use proc_macro::bridge::client::ProcMacro;
 use std::error::Error;
 use std::ops::Fn;
 use std::path::Path;
+use std::str::FromStr;
 use std::time::Duration;
-use std::{cmp, iter};
+use std::{cmp, env, iter};
 
 /// The backend's way to give the crate store access to the metadata in a library.
 /// Note that it returns the raw metadata bytes stored in the library file, whether
@@ -397,7 +398,8 @@ impl<'a, 'tcx> CrateLoader<'a, 'tcx> {
         name: Symbol,
         private_dep: Option<bool>,
     ) -> Result<CrateNum, CrateError> {
-        let _prof_timer = self.sess.prof.generic_activity("metadata_register_crate");
+        let _prof_timer =
+            self.sess.prof.generic_activity_with_arg("metadata_register_crate", name.as_str());
 
         let Library { source, metadata } = lib;
         let crate_root = metadata.get_root();
@@ -985,6 +987,44 @@ impl<'a, 'tcx> CrateLoader<'a, 'tcx> {
         }
     }
 
+    fn report_future_incompatible_deps(&self, krate: &ast::Crate) {
+        let name = self.tcx.crate_name(LOCAL_CRATE);
+
+        if name.as_str() == "wasm_bindgen" {
+            let major = env::var("CARGO_PKG_VERSION_MAJOR")
+                .ok()
+                .and_then(|major| u64::from_str(&major).ok());
+            let minor = env::var("CARGO_PKG_VERSION_MINOR")
+                .ok()
+                .and_then(|minor| u64::from_str(&minor).ok());
+            let patch = env::var("CARGO_PKG_VERSION_PATCH")
+                .ok()
+                .and_then(|patch| u64::from_str(&patch).ok());
+
+            match (major, minor, patch) {
+                // v1 or bigger is valid.
+                (Some(1..), _, _) => return,
+                // v0.3 or bigger is valid.
+                (Some(0), Some(3..), _) => return,
+                // v0.2.88 or bigger is valid.
+                (Some(0), Some(2), Some(88..)) => return,
+                // Not using Cargo.
+                (None, None, None) => return,
+                _ => (),
+            }
+
+            // Make a point span rather than covering the whole file
+            let span = krate.spans.inner_span.shrink_to_lo();
+
+            self.sess.psess.buffer_lint(
+                lint::builtin::WASM_C_ABI,
+                span,
+                ast::CRATE_NODE_ID,
+                crate::fluent_generated::metadata_wasm_c_abi,
+            );
+        }
+    }
+
     pub fn postprocess(&mut self, krate: &ast::Crate) {
         self.inject_forced_externs();
         self.inject_profiler_runtime(krate);
@@ -992,6 +1032,7 @@ impl<'a, 'tcx> CrateLoader<'a, 'tcx> {
         self.inject_panic_runtime(krate);
 
         self.report_unused_deps(krate);
+        self.report_future_incompatible_deps(krate);
 
         info!("{:?}", CrateDump(self.cstore));
     }

compiler/rustc_metadata/src/rmeta/encoder.rs

@@ -1339,8 +1339,8 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
             is_doc_hidden: false,
         };
         let attr_iter = tcx
-            .opt_local_def_id_to_hir_id(def_id)
-            .map_or(Default::default(), |hir_id| tcx.hir().attrs(hir_id))
+            .hir()
+            .attrs(tcx.local_def_id_to_hir_id(def_id))
             .iter()
             .filter(|attr| analyze_attr(attr, &mut state));
 

compiler/rustc_middle/src/hir/map/mod.rs

@@ -158,12 +158,6 @@ impl<'tcx> TyCtxt<'tcx> {
         self.hir_owner_nodes(owner_id).node()
     }
 
-    /// Retrieves the `hir::Node` corresponding to `id`, returning `None` if cannot be found.
-    #[inline]
-    pub fn opt_hir_node_by_def_id(self, id: LocalDefId) -> Option<Node<'tcx>> {
-        Some(self.hir_node_by_def_id(id))
-    }
-
     /// Retrieves the `hir::Node` corresponding to `id`.
     pub fn hir_node(self, id: HirId) -> Node<'tcx> {
         self.hir_owner_nodes(id.owner).nodes[id.local_id].node
@@ -239,8 +233,7 @@ impl<'hir> Map<'hir> {
     }
 
     pub fn get_if_local(self, id: DefId) -> Option<Node<'hir>> {
-        id.as_local()
-            .and_then(|id| Some(self.tcx.hir_node(self.tcx.opt_local_def_id_to_hir_id(id)?)))
+        id.as_local().map(|id| self.tcx.hir_node_by_def_id(id))
     }
 
     pub fn get_generics(self, id: LocalDefId) -> Option<&'hir Generics<'hir>> {
@@ -304,7 +297,7 @@ impl<'hir> Map<'hir> {
     /// Given a `LocalDefId`, returns the `BodyId` associated with it,
     /// if the node is a body owner, otherwise returns `None`.
     pub fn maybe_body_owned_by(self, id: LocalDefId) -> Option<BodyId> {
-        let node = self.tcx.opt_hir_node_by_def_id(id)?;
+        let node = self.tcx.hir_node_by_def_id(id);
         let (_, body_id) = associated_body(node)?;
         Some(body_id)
     }

compiler/rustc_middle/src/mir/interpret/value.rs

@@ -3,7 +3,7 @@ use std::fmt;
 use either::{Either, Left, Right};
 
 use rustc_apfloat::{
-    ieee::{Double, Single},
+    ieee::{Double, Half, Quad, Single},
     Float,
 };
 use rustc_macros::HashStable;
@@ -201,6 +201,11 @@ impl<Prov> Scalar<Prov> {
         Self::from_int(i, cx.data_layout().pointer_size)
     }
 
+    #[inline]
+    pub fn from_f16(f: Half) -> Self {
+        Scalar::Int(f.into())
+    }
+
     #[inline]
     pub fn from_f32(f: Single) -> Self {
         Scalar::Int(f.into())
@@ -211,6 +216,11 @@ impl<Prov> Scalar<Prov> {
         Scalar::Int(f.into())
     }
 
+    #[inline]
+    pub fn from_f128(f: Quad) -> Self {
+        Scalar::Int(f.into())
+    }
+
     /// This is almost certainly not the method you want!  You should dispatch on the type
     /// and use `to_{u8,u16,...}`/`scalar_to_ptr` to perform ptr-to-int / int-to-ptr casts as needed.
     ///
@@ -422,6 +432,11 @@ impl<'tcx, Prov: Provenance> Scalar<Prov> {
         Ok(F::from_bits(self.to_bits(Size::from_bits(F::BITS))?))
     }
 
+    #[inline]
+    pub fn to_f16(self) -> InterpResult<'tcx, Half> {
+        self.to_float()
+    }
+
     #[inline]
     pub fn to_f32(self) -> InterpResult<'tcx, Single> {
         self.to_float()
@@ -431,4 +446,9 @@ impl<'tcx, Prov: Provenance> Scalar<Prov> {
     pub fn to_f64(self) -> InterpResult<'tcx, Double> {
         self.to_float()
     }
+
+    #[inline]
+    pub fn to_f128(self) -> InterpResult<'tcx, Quad> {
+        self.to_float()
+    }
 }

compiler/rustc_middle/src/thir.rs

@@ -321,9 +321,13 @@ pub enum ExprKind<'tcx> {
     Cast {
         source: ExprId,
     },
+    /// Forces its contents to be treated as a value expression, not a place
+    /// expression. This is inserted in some places where an operation would
+    /// otherwise be erased completely (e.g. some no-op casts), but we still
+    /// need to ensure that its operand is treated as a value and not a place.
     Use {
         source: ExprId,
-    }, // Use a lexpr to get a vexpr.
+    },
     /// A coercion from `!` to any type.
     NeverToAny {
         source: ExprId,
@@ -338,6 +342,13 @@ pub enum ExprKind<'tcx> {
     Loop {
         body: ExprId,
     },
+    /// Special expression representing the `let` part of an `if let` or similar construct
+    /// (including `if let` guards in match arms, and let-chains formed by `&&`).
+    ///
+    /// This isn't considered a real expression in surface Rust syntax, so it can
+    /// only appear in specific situations, such as within the condition of an `if`.
+    ///
+    /// (Not to be confused with [`StmtKind::Let`], which is a normal `let` statement.)
     Let {
         expr: ExprId,
         pat: Box<Pat<'tcx>>,

compiler/rustc_middle/src/ty/consts/int.rs

@@ -1,4 +1,4 @@
-use rustc_apfloat::ieee::{Double, Single};
+use rustc_apfloat::ieee::{Double, Half, Quad, Single};
 use rustc_apfloat::Float;
 use rustc_errors::{DiagArgValue, IntoDiagArg};
 use rustc_serialize::{Decodable, Decoder, Encodable, Encoder};
@@ -369,6 +369,11 @@ impl ScalarInt {
         Ok(F::from_bits(self.to_bits(Size::from_bits(F::BITS))?))
     }
 
+    #[inline]
+    pub fn try_to_f16(self) -> Result<Half, Size> {
+        self.try_to_float()
+    }
+
     #[inline]
     pub fn try_to_f32(self) -> Result<Single, Size> {
         self.try_to_float()
@@ -378,6 +383,11 @@ impl ScalarInt {
     pub fn try_to_f64(self) -> Result<Double, Size> {
         self.try_to_float()
     }
+
+    #[inline]
+    pub fn try_to_f128(self) -> Result<Quad, Size> {
+        self.try_to_float()
+    }
 }
 
 macro_rules! from {
@@ -450,6 +460,22 @@ impl TryFrom<ScalarInt> for char {
     }
 }
 
+impl From<Half> for ScalarInt {
+    #[inline]
+    fn from(f: Half) -> Self {
+        // We trust apfloat to give us properly truncated data.
+        Self { data: f.to_bits(), size: NonZero::new((Half::BITS / 8) as u8).unwrap() }
+    }
+}
+
+impl TryFrom<ScalarInt> for Half {
+    type Error = Size;
+    #[inline]
+    fn try_from(int: ScalarInt) -> Result<Self, Size> {
+        int.to_bits(Size::from_bytes(2)).map(Self::from_bits)
+    }
+}
+
 impl From<Single> for ScalarInt {
     #[inline]
     fn from(f: Single) -> Self {
@@ -482,6 +508,22 @@ impl TryFrom<ScalarInt> for Double {
     }
 }
 
+impl From<Quad> for ScalarInt {
+    #[inline]
+    fn from(f: Quad) -> Self {
+        // We trust apfloat to give us properly truncated data.
+        Self { data: f.to_bits(), size: NonZero::new((Quad::BITS / 8) as u8).unwrap() }
+    }
+}
+
+impl TryFrom<ScalarInt> for Quad {
+    type Error = Size;
+    #[inline]
+    fn try_from(int: ScalarInt) -> Result<Self, Size> {
+        int.to_bits(Size::from_bytes(16)).map(Self::from_bits)
+    }
+}
+
 impl fmt::Debug for ScalarInt {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         // Dispatch to LowerHex below.

compiler/rustc_middle/src/ty/context.rs

@@ -1265,11 +1265,9 @@ impl<'tcx> TyCtxt<'tcx> {
             break (scope, ty::BrNamed(def_id.into(), self.item_name(def_id.into())));
         };
 
-        let is_impl_item = match self.opt_hir_node_by_def_id(suitable_region_binding_scope) {
-            Some(Node::Item(..) | Node::TraitItem(..)) => false,
-            Some(Node::ImplItem(..)) => {
-                self.is_bound_region_in_impl_item(suitable_region_binding_scope)
-            }
+        let is_impl_item = match self.hir_node_by_def_id(suitable_region_binding_scope) {
+            Node::Item(..) | Node::TraitItem(..) => false,
+            Node::ImplItem(..) => self.is_bound_region_in_impl_item(suitable_region_binding_scope),
             _ => false,
         };
 
@@ -2355,10 +2353,6 @@ impl<'tcx> TyCtxt<'tcx> {
         self.intrinsic_raw(def_id)
     }
 
-    pub fn opt_local_def_id_to_hir_id(self, local_def_id: LocalDefId) -> Option<HirId> {
-        Some(self.local_def_id_to_hir_id(local_def_id))
-    }
-
     pub fn next_trait_solver_globally(self) -> bool {
         self.sess.opts.unstable_opts.next_solver.map_or(false, |c| c.globally)
     }

compiler/rustc_mir_build/messages.ftl

@@ -24,7 +24,7 @@ mir_build_borrow_of_layout_constrained_field_requires_unsafe_unsafe_op_in_unsafe
 
 mir_build_borrow_of_moved_value = borrow of moved value
     .label = value moved into `{$name}` here
-    .occurs_because_label = move occurs because `{$name}` has type `{$ty}` which does not implement the `Copy` trait
+    .occurs_because_label = move occurs because `{$name}` has type `{$ty}`, which does not implement the `Copy` trait
     .value_borrowed_label = value borrowed here after move
     .suggestion = borrow this binding in the pattern to avoid moving the value
 

compiler/rustc_mir_build/src/build/mod.rs

@@ -1,7 +1,7 @@
 use crate::build::expr::as_place::PlaceBuilder;
 use crate::build::scope::DropKind;
 use itertools::Itertools;
-use rustc_apfloat::ieee::{Double, Single};
+use rustc_apfloat::ieee::{Double, Half, Quad, Single};
 use rustc_apfloat::Float;
 use rustc_ast::attr;
 use rustc_data_structures::fx::FxHashMap;
@@ -1060,7 +1060,8 @@ pub(crate) fn parse_float_into_scalar(
 ) -> Option<Scalar> {
     let num = num.as_str();
     match float_ty {
-        ty::FloatTy::F16 => unimplemented!("f16_f128"),
+        // FIXME(f16_f128): When available, compare to the library parser as with `f32` and `f64`
+        ty::FloatTy::F16 => num.parse::<Half>().ok().map(Scalar::from_f16),
         ty::FloatTy::F32 => {
             let Ok(rust_f) = num.parse::<f32>() else { return None };
             let mut f = num
@@ -1107,7 +1108,8 @@ pub(crate) fn parse_float_into_scalar(
 
             Some(Scalar::from_f64(f))
         }
-        ty::FloatTy::F128 => unimplemented!("f16_f128"),
+        // FIXME(f16_f128): When available, compare to the library parser as with `f32` and `f64`
+        ty::FloatTy::F128 => num.parse::<Quad>().ok().map(Scalar::from_f128),
     }
 }
 

compiler/rustc_mir_transform/src/dataflow_const_prop.rs

@@ -393,7 +393,9 @@ impl<'a, 'tcx> ConstAnalysis<'a, 'tcx> {
                 }
             }
             Operand::Constant(box constant) => {
-                if let Ok(constant) = self.ecx.eval_mir_constant(&constant.const_, None, None) {
+                if let Ok(constant) =
+                    self.ecx.eval_mir_constant(&constant.const_, Some(constant.span), None)
+                {
                     self.assign_constant(state, place, constant, &[]);
                 }
             }

compiler/rustc_mir_transform/src/jump_threading.rs

@@ -416,7 +416,8 @@ impl<'tcx, 'a> TOFinder<'tcx, 'a> {
         match rhs {
             // If we expect `lhs ?= A`, we have an opportunity if we assume `constant == A`.
             Operand::Constant(constant) => {
-                let constant = self.ecx.eval_mir_constant(&constant.const_, None, None).ok()?;
+                let constant =
+                    self.ecx.eval_mir_constant(&constant.const_, Some(constant.span), None).ok()?;
                 self.process_constant(bb, lhs, constant, state);
             }
             // Transfer the conditions on the copied rhs.

compiler/rustc_monomorphize/src/collector.rs

@@ -828,14 +828,17 @@ impl<'a, 'tcx> MirVisitor<'tcx> for MirUsedCollector<'a, 'tcx> {
         // a codegen-time error). rustc stops after collection if there was an error, so this
         // ensures codegen never has to worry about failing consts.
         // (codegen relies on this and ICEs will happen if this is violated.)
-        let val = match const_.eval(self.tcx, param_env, None) {
+        let val = match const_.eval(self.tcx, param_env, Some(constant.span)) {
             Ok(v) => v,
-            Err(ErrorHandled::Reported(..)) => return,
             Err(ErrorHandled::TooGeneric(..)) => span_bug!(
                 self.body.source_info(location).span,
                 "collection encountered polymorphic constant: {:?}",
                 const_
             ),
+            Err(err @ ErrorHandled::Reported(..)) => {
+                err.emit_note(self.tcx);
+                return;
+            }
         };
         collect_const_value(self.tcx, val, self.output);
         MirVisitor::visit_ty(self, const_.ty(), TyContext::Location(location));

compiler/rustc_passes/Cargo.toml

@@ -18,6 +18,7 @@ rustc_index = { path = "../rustc_index" }
 rustc_lexer = { path = "../rustc_lexer" }
 rustc_macros = { path = "../rustc_macros" }
 rustc_middle = { path = "../rustc_middle" }
+rustc_privacy = { path = "../rustc_privacy" }
 rustc_session = { path = "../rustc_session" }
 rustc_span = { path = "../rustc_span" }
 rustc_target = { path = "../rustc_target" }

compiler/rustc_passes/src/dead.rs

@@ -33,15 +33,13 @@ use crate::errors::{
 // may need to be marked as live.
 fn should_explore(tcx: TyCtxt<'_>, def_id: LocalDefId) -> bool {
     matches!(
-        tcx.opt_hir_node_by_def_id(def_id),
-        Some(
-            Node::Item(..)
-                | Node::ImplItem(..)
-                | Node::ForeignItem(..)
-                | Node::TraitItem(..)
-                | Node::Variant(..)
-                | Node::AnonConst(..)
-        )
+        tcx.hir_node_by_def_id(def_id),
+        Node::Item(..)
+            | Node::ImplItem(..)
+            | Node::ForeignItem(..)
+            | Node::TraitItem(..)
+            | Node::Variant(..)
+            | Node::AnonConst(..)
     )
 }
 
@@ -316,33 +314,31 @@ impl<'tcx> MarkSymbolVisitor<'tcx> {
             // tuple struct constructor function
             let id = self.struct_constructors.get(&id).copied().unwrap_or(id);
 
-            if let Some(node) = self.tcx.opt_hir_node_by_def_id(id) {
-                // When using `#[allow]` or `#[expect]` of `dead_code`, we do a QOL improvement
-                // by declaring fn calls, statics, ... within said items as live, as well as
-                // the item itself, although technically this is not the case.
-                //
-                // This means that the lint for said items will never be fired.
-                //
-                // This doesn't make any difference for the item declared with `#[allow]`, as
-                // the lint firing will be a nop, as it will be silenced by the `#[allow]` of
-                // the item.
-                //
-                // However, for `#[expect]`, the presence or absence of the lint is relevant,
-                // so we don't add it to the list of live symbols when it comes from a
-                // `#[expect]`. This means that we will correctly report an item as live or not
-                // for the `#[expect]` case.
-                //
-                // Note that an item can and will be duplicated on the worklist with different
-                // `ComesFromAllowExpect`, particularly if it was added from the
-                // `effective_visibilities` query or from the `#[allow]`/`#[expect]` checks,
-                // this "duplication" is essential as otherwise a function with `#[expect]`
-                // called from a `pub fn` may be falsely reported as not live, falsely
-                // triggering the `unfulfilled_lint_expectations` lint.
-                if comes_from_allow_expect != ComesFromAllowExpect::Yes {
-                    self.live_symbols.insert(id);
-                }
-                self.visit_node(node);
+            // When using `#[allow]` or `#[expect]` of `dead_code`, we do a QOL improvement
+            // by declaring fn calls, statics, ... within said items as live, as well as
+            // the item itself, although technically this is not the case.
+            //
+            // This means that the lint for said items will never be fired.
+            //
+            // This doesn't make any difference for the item declared with `#[allow]`, as
+            // the lint firing will be a nop, as it will be silenced by the `#[allow]` of
+            // the item.
+            //
+            // However, for `#[expect]`, the presence or absence of the lint is relevant,
+            // so we don't add it to the list of live symbols when it comes from a
+            // `#[expect]`. This means that we will correctly report an item as live or not
+            // for the `#[expect]` case.
+            //
+            // Note that an item can and will be duplicated on the worklist with different
+            // `ComesFromAllowExpect`, particularly if it was added from the
+            // `effective_visibilities` query or from the `#[allow]`/`#[expect]` checks,
+            // this "duplication" is essential as otherwise a function with `#[expect]`
+            // called from a `pub fn` may be falsely reported as not live, falsely
+            // triggering the `unfulfilled_lint_expectations` lint.
+            if comes_from_allow_expect != ComesFromAllowExpect::Yes {
+                self.live_symbols.insert(id);
             }
+            self.visit_node(self.tcx.hir_node_by_def_id(id));
         }
     }
 
@@ -739,8 +735,8 @@ fn check_item<'tcx>(
             for local_def_id in local_def_ids {
                 // check the function may construct Self
                 let mut may_construct_self = true;
-                if let Some(hir_id) = tcx.opt_local_def_id_to_hir_id(local_def_id)
-                    && let Some(fn_sig) = tcx.hir().fn_sig_by_hir_id(hir_id)
+                if let Some(fn_sig) =
+                    tcx.hir().fn_sig_by_hir_id(tcx.local_def_id_to_hir_id(local_def_id))
                 {
                     may_construct_self =
                         matches!(fn_sig.decl.implicit_self, hir::ImplicitSelfKind::None);

compiler/rustc_passes/src/entry.rs

@@ -127,7 +127,7 @@ fn configure_main(tcx: TyCtxt<'_>, visitor: &EntryContext<'_>) -> Option<(DefId,
         {
             // non-local main imports are handled below
             if let Some(def_id) = def_id.as_local()
-                && matches!(tcx.opt_hir_node_by_def_id(def_id), Some(Node::ForeignItem(_)))
+                && matches!(tcx.hir_node_by_def_id(def_id), Node::ForeignItem(_))
             {
                 tcx.dcx().emit_err(ExternMain { span: tcx.def_span(def_id) });
                 return None;

compiler/rustc_passes/src/reachable.rs

@@ -6,6 +6,7 @@
 // reachable as well.
 
 use hir::def_id::LocalDefIdSet;
+use rustc_data_structures::stack::ensure_sufficient_stack;
 use rustc_hir as hir;
 use rustc_hir::def::{DefKind, Res};
 use rustc_hir::def_id::{DefId, LocalDefId};
@@ -15,7 +16,8 @@ use rustc_middle::middle::codegen_fn_attrs::{CodegenFnAttrFlags, CodegenFnAttrs}
 use rustc_middle::middle::privacy::{self, Level};
 use rustc_middle::mir::interpret::{ConstAllocation, GlobalAlloc};
 use rustc_middle::query::Providers;
-use rustc_middle::ty::{self, TyCtxt};
+use rustc_middle::ty::{self, ExistentialTraitRef, TyCtxt};
+use rustc_privacy::DefIdVisitor;
 use rustc_session::config::CrateType;
 use rustc_target::spec::abi::Abi;
 
@@ -65,23 +67,8 @@ impl<'tcx> Visitor<'tcx> for ReachableContext<'tcx> {
             _ => None,
         };
 
-        if let Some(res) = res
-            && let Some(def_id) = res.opt_def_id().and_then(|el| el.as_local())
-        {
-            if self.def_id_represents_local_inlined_item(def_id.to_def_id()) {
-                self.worklist.push(def_id);
-            } else {
-                match res {
-                    // Reachable constants and reachable statics can have their contents inlined
-                    // into other crates. Mark them as reachable and recurse into their body.
-                    Res::Def(DefKind::Const | DefKind::AssocConst | DefKind::Static { .. }, _) => {
-                        self.worklist.push(def_id);
-                    }
-                    _ => {
-                        self.reachable_symbols.insert(def_id);
-                    }
-                }
-            }
+        if let Some(res) = res {
+            self.propagate_item(res);
         }
 
         intravisit::walk_expr(self, expr)
@@ -116,26 +103,25 @@ impl<'tcx> ReachableContext<'tcx> {
             return false;
         };
 
-        match self.tcx.opt_hir_node_by_def_id(def_id) {
-            Some(Node::Item(item)) => match item.kind {
+        match self.tcx.hir_node_by_def_id(def_id) {
+            Node::Item(item) => match item.kind {
                 hir::ItemKind::Fn(..) => item_might_be_inlined(self.tcx, def_id.into()),
                 _ => false,
             },
-            Some(Node::TraitItem(trait_method)) => match trait_method.kind {
+            Node::TraitItem(trait_method) => match trait_method.kind {
                 hir::TraitItemKind::Const(_, ref default) => default.is_some(),
                 hir::TraitItemKind::Fn(_, hir::TraitFn::Provided(_)) => true,
                 hir::TraitItemKind::Fn(_, hir::TraitFn::Required(_))
                 | hir::TraitItemKind::Type(..) => false,
             },
-            Some(Node::ImplItem(impl_item)) => match impl_item.kind {
+            Node::ImplItem(impl_item) => match impl_item.kind {
                 hir::ImplItemKind::Const(..) => true,
                 hir::ImplItemKind::Fn(..) => {
                     item_might_be_inlined(self.tcx, impl_item.hir_id().owner.to_def_id())
                 }
                 hir::ImplItemKind::Type(_) => false,
             },
-            Some(_) => false,
-            None => false, // This will happen for default methods.
+            _ => false,
         }
     }
 
@@ -147,9 +133,7 @@ impl<'tcx> ReachableContext<'tcx> {
                 continue;
             }
 
-            if let Some(ref item) = self.tcx.opt_hir_node_by_def_id(search_item) {
-                self.propagate_node(item, search_item);
-            }
+            self.propagate_node(&self.tcx.hir_node_by_def_id(search_item), search_item);
         }
     }
 
@@ -201,17 +185,9 @@ impl<'tcx> ReachableContext<'tcx> {
                     hir::ItemKind::Const(_, _, init) => {
                         self.visit_nested_body(init);
                     }
-
-                    // Reachable statics are inlined if read from another constant or static
-                    // in other crates. Additionally anonymous nested statics may be created
-                    // when evaluating a static, so preserve those, too.
-                    hir::ItemKind::Static(_, _, init) => {
-                        // FIXME(oli-obk): remove this body walking and instead walk the evaluated initializer
-                        // to find nested items that end up in the final value instead of also marking symbols
-                        // as reachable that are only needed for evaluation.
-                        self.visit_nested_body(init);
+                    hir::ItemKind::Static(..) => {
                         if let Ok(alloc) = self.tcx.eval_static_initializer(item.owner_id.def_id) {
-                            self.propagate_statics_from_alloc(item.owner_id.def_id, alloc);
+                            self.propagate_from_alloc(alloc);
                         }
                     }
 
@@ -282,28 +258,89 @@ impl<'tcx> ReachableContext<'tcx> {
         }
     }
 
-    /// Finds anonymous nested statics created for nested allocations and adds them to `reachable_symbols`.
-    fn propagate_statics_from_alloc(&mut self, root: LocalDefId, alloc: ConstAllocation<'tcx>) {
+    /// Finds things to add to `reachable_symbols` within allocations.
+    /// In contrast to visit_nested_body this ignores things that were only needed to evaluate
+    /// the allocation.
+    fn propagate_from_alloc(&mut self, alloc: ConstAllocation<'tcx>) {
         if !self.any_library {
             return;
         }
         for (_, prov) in alloc.0.provenance().ptrs().iter() {
             match self.tcx.global_alloc(prov.alloc_id()) {
                 GlobalAlloc::Static(def_id) => {
-                    if let Some(def_id) = def_id.as_local()
-                        && self.tcx.local_parent(def_id) == root
-                        // This is the main purpose of this function: add the def_id we find
-                        // to `reachable_symbols`.
-                        && self.reachable_symbols.insert(def_id)
-                        && let Ok(alloc) = self.tcx.eval_static_initializer(def_id)
-                    {
-                        self.propagate_statics_from_alloc(root, alloc);
+                    self.propagate_item(Res::Def(self.tcx.def_kind(def_id), def_id))
+                }
+                GlobalAlloc::Function(instance) => {
+                    // Manually visit to actually see the instance's `DefId`. Type visitors won't see it
+                    self.propagate_item(Res::Def(
+                        self.tcx.def_kind(instance.def_id()),
+                        instance.def_id(),
+                    ));
+                    self.visit(instance.args);
+                }
+                GlobalAlloc::VTable(ty, trait_ref) => {
+                    self.visit(ty);
+                    // Manually visit to actually see the trait's `DefId`. Type visitors won't see it
+                    if let Some(trait_ref) = trait_ref {
+                        let ExistentialTraitRef { def_id, args } = trait_ref.skip_binder();
+                        self.visit_def_id(def_id, "", &"");
+                        self.visit(args);
                     }
                 }
-                GlobalAlloc::Function(_) | GlobalAlloc::VTable(_, _) | GlobalAlloc::Memory(_) => {}
+                GlobalAlloc::Memory(alloc) => self.propagate_from_alloc(alloc),
             }
         }
     }
+
+    fn propagate_item(&mut self, res: Res) {
+        let Res::Def(kind, def_id) = res else { return };
+        let Some(def_id) = def_id.as_local() else { return };
+        match kind {
+            DefKind::Static { nested: true, .. } => {
+                // This is the main purpose of this function: add the def_id we find
+                // to `reachable_symbols`.
+                if self.reachable_symbols.insert(def_id) {
+                    if let Ok(alloc) = self.tcx.eval_static_initializer(def_id) {
+                        // This cannot cause infinite recursion, because we abort by inserting into the
+                        // work list once we hit a normal static. Nested statics, even if they somehow
+                        // become recursive, are also not infinitely recursing, because of the
+                        // `reachable_symbols` check above.
+                        // We still need to protect against stack overflow due to deeply nested statics.
+                        ensure_sufficient_stack(|| self.propagate_from_alloc(alloc));
+                    }
+                }
+            }
+            // Reachable constants and reachable statics can have their contents inlined
+            // into other crates. Mark them as reachable and recurse into their body.
+            DefKind::Const | DefKind::AssocConst | DefKind::Static { .. } => {
+                self.worklist.push(def_id);
+            }
+            _ => {
+                if self.def_id_represents_local_inlined_item(def_id.to_def_id()) {
+                    self.worklist.push(def_id);
+                } else {
+                    self.reachable_symbols.insert(def_id);
+                }
+            }
+        }
+    }
+}
+
+impl<'tcx> DefIdVisitor<'tcx> for ReachableContext<'tcx> {
+    type Result = ();
+
+    fn tcx(&self) -> TyCtxt<'tcx> {
+        self.tcx
+    }
+
+    fn visit_def_id(
+        &mut self,
+        def_id: DefId,
+        _kind: &str,
+        _descr: &dyn std::fmt::Display,
+    ) -> Self::Result {
+        self.propagate_item(Res::Def(self.tcx.def_kind(def_id), def_id))
+    }
 }
 
 fn check_item<'tcx>(

compiler/rustc_privacy/src/lib.rs

@@ -67,7 +67,7 @@ impl<'tcx> fmt::Display for LazyDefPathStr<'tcx> {
 /// First, it doesn't have overridable `fn visit_trait_ref`, so we have to catch trait `DefId`s
 /// manually. Second, it doesn't visit some type components like signatures of fn types, or traits
 /// in `impl Trait`, see individual comments in `DefIdVisitorSkeleton::visit_ty`.
-trait DefIdVisitor<'tcx> {
+pub trait DefIdVisitor<'tcx> {
     type Result: VisitorResult = ();
     const SHALLOW: bool = false;
     const SKIP_ASSOC_TYS: bool = false;
@@ -98,7 +98,7 @@ trait DefIdVisitor<'tcx> {
     }
 }
 
-struct DefIdVisitorSkeleton<'v, 'tcx, V: ?Sized> {
+pub struct DefIdVisitorSkeleton<'v, 'tcx, V: ?Sized> {
     def_id_visitor: &'v mut V,
     visited_opaque_tys: FxHashSet<DefId>,
     dummy: PhantomData<TyCtxt<'tcx>>,

compiler/rustc_resolve/src/ident.rs

@@ -5,8 +5,10 @@ use rustc_middle::bug;
 use rustc_middle::ty;
 use rustc_session::lint::builtin::PROC_MACRO_DERIVE_RESOLUTION_FALLBACK;
 use rustc_session::lint::BuiltinLintDiag;
+use rustc_session::parse::feature_err;
 use rustc_span::def_id::LocalDefId;
 use rustc_span::hygiene::{ExpnId, ExpnKind, LocalExpnId, MacroKind, SyntaxContext};
+use rustc_span::sym;
 use rustc_span::symbol::{kw, Ident};
 use rustc_span::Span;
 
@@ -598,7 +600,35 @@ impl<'a, 'tcx> Resolver<'a, 'tcx> {
                         result
                     }
                     Scope::BuiltinTypes => match this.builtin_types_bindings.get(&ident.name) {
-                        Some(binding) => Ok((*binding, Flags::empty())),
+                        Some(binding) => {
+                            if matches!(ident.name, sym::f16)
+                                && !this.tcx.features().f16
+                                && !ident.span.allows_unstable(sym::f16)
+                                && finalize.is_some()
+                            {
+                                feature_err(
+                                    this.tcx.sess,
+                                    sym::f16,
+                                    ident.span,
+                                    "the type `f16` is unstable",
+                                )
+                                .emit();
+                            }
+                            if matches!(ident.name, sym::f128)
+                                && !this.tcx.features().f128
+                                && !ident.span.allows_unstable(sym::f128)
+                                && finalize.is_some()
+                            {
+                                feature_err(
+                                    this.tcx.sess,
+                                    sym::f128,
+                                    ident.span,
+                                    "the type `f128` is unstable",
+                                )
+                                .emit();
+                            }
+                            Ok((*binding, Flags::empty()))
+                        }
                         None => Err(Determinacy::Determined),
                     },
                 };

compiler/rustc_resolve/src/late.rs

@@ -27,6 +27,7 @@ use rustc_middle::middle::resolve_bound_vars::Set1;
 use rustc_middle::{bug, span_bug};
 use rustc_session::config::{CrateType, ResolveDocLinks};
 use rustc_session::lint;
+use rustc_session::parse::feature_err;
 use rustc_span::source_map::{respan, Spanned};
 use rustc_span::symbol::{kw, sym, Ident, Symbol};
 use rustc_span::{BytePos, Span, SyntaxContext};
@@ -4138,6 +4139,25 @@ impl<'a: 'ast, 'b, 'ast, 'tcx> LateResolutionVisitor<'a, 'b, 'ast, 'tcx> {
                     && PrimTy::from_name(path[0].ident.name).is_some() =>
             {
                 let prim = PrimTy::from_name(path[0].ident.name).unwrap();
+                let tcx = self.r.tcx();
+
+                let gate_err_sym_msg = match prim {
+                    PrimTy::Float(FloatTy::F16) if !tcx.features().f16 => {
+                        Some((sym::f16, "the type `f16` is unstable"))
+                    }
+                    PrimTy::Float(FloatTy::F128) if !tcx.features().f128 => {
+                        Some((sym::f128, "the type `f128` is unstable"))
+                    }
+                    _ => None,
+                };
+
+                if let Some((sym, msg)) = gate_err_sym_msg {
+                    let span = path[0].ident.span;
+                    if !span.allows_unstable(sym) {
+                        feature_err(tcx.sess, sym, span, msg).emit();
+                    }
+                };
+
                 PartialRes::with_unresolved_segments(Res::PrimTy(prim), path.len() - 1)
             }
             PathResult::Module(ModuleOrUniformRoot::Module(module)) => {

compiler/rustc_resolve/src/rustdoc.rs

@@ -167,12 +167,13 @@ pub fn unindent_doc_fragments(docs: &mut [DocFragment]) {
 ///
 /// Note: remove the trailing newline where appropriate
 pub fn add_doc_fragment(out: &mut String, frag: &DocFragment) {
-    let s = frag.doc.as_str();
-    let mut iter = s.lines();
-    if s.is_empty() {
+    if frag.doc == kw::Empty {
         out.push('\n');
         return;
     }
+    let s = frag.doc.as_str();
+    let mut iter = s.lines();
+
     while let Some(line) = iter.next() {
         if line.chars().any(|c| !c.is_whitespace()) {
             assert!(line.len() >= frag.indent);

compiler/rustc_session/src/options.rs

@@ -1645,6 +1645,8 @@ options! {
         "emit the bc module with thin LTO info (default: yes)"),
     export_executable_symbols: bool = (false, parse_bool, [TRACKED],
         "export symbols from executables, as if they were dynamic libraries"),
+    external_clangrt: bool = (false, parse_bool, [UNTRACKED],
+        "rely on user specified linker commands to find clangrt"),
     extra_const_ub_checks: bool = (false, parse_bool, [TRACKED],
         "turns on more checks to detect const UB, which can be slow (default: no)"),
     #[rustc_lint_opt_deny_field_access("use `Session::fewer_names` instead of this field")]

compiler/rustc_smir/src/rustc_smir/builder.rs

@@ -56,7 +56,7 @@ impl<'tcx> MutVisitor<'tcx> for BodyBuilder<'tcx> {
 
     fn visit_constant(&mut self, constant: &mut mir::ConstOperand<'tcx>, location: mir::Location) {
         let const_ = self.monomorphize(constant.const_);
-        let val = match const_.eval(self.tcx, ty::ParamEnv::reveal_all(), None) {
+        let val = match const_.eval(self.tcx, ty::ParamEnv::reveal_all(), Some(constant.span)) {
             Ok(v) => v,
             Err(mir::interpret::ErrorHandled::Reported(..)) => return,
             Err(mir::interpret::ErrorHandled::TooGeneric(..)) => {

compiler/rustc_span/src/symbol.rs

@@ -815,6 +815,9 @@ symbols! {
         fadd_algebraic,
         fadd_fast,
         fake_variadic,
+        fallback_to_never,
+        fallback_to_niko,
+        fallback_to_unit,
         fdiv_algebraic,
         fdiv_fast,
         feature,
@@ -1233,6 +1236,7 @@ symbols! {
         no_crate_inject,
         no_debug,
         no_default_passes,
+        no_fallback,
         no_implicit_prelude,
         no_inline,
         no_link,
@@ -1551,6 +1555,7 @@ symbols! {
         rustc_mir,
         rustc_must_implement_one_of,
         rustc_never_returns_null_ptr,
+        rustc_never_type_mode,
         rustc_no_mir_inline,
         rustc_nonnull_optimization_guaranteed,
         rustc_nounwind,

compiler/rustc_trait_selection/src/traits/error_reporting/on_unimplemented.rs

@@ -91,7 +91,7 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
     /// Used to set on_unimplemented's `ItemContext`
     /// to be the enclosing (async) block/function/closure
     fn describe_enclosure(&self, def_id: LocalDefId) -> Option<&'static str> {
-        match self.tcx.opt_hir_node_by_def_id(def_id)? {
+        match self.tcx.hir_node_by_def_id(def_id) {
             hir::Node::Item(hir::Item { kind: hir::ItemKind::Fn(..), .. }) => Some("a function"),
             hir::Node::TraitItem(hir::TraitItem { kind: hir::TraitItemKind::Fn(..), .. }) => {
                 Some("a trait method")

compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs

@@ -261,7 +261,8 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
 
         // FIXME: Add check for trait bound that is already present, particularly `?Sized` so we
         //        don't suggest `T: Sized + ?Sized`.
-        while let Some(node) = self.tcx.opt_hir_node_by_def_id(body_id) {
+        loop {
+            let node = self.tcx.hir_node_by_def_id(body_id);
             match node {
                 hir::Node::Item(hir::Item {
                     ident,
@@ -987,10 +988,6 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
             else {
                 return false;
             };
-            let arg_node = self.tcx.hir_node(*arg_hir_id);
-            let Node::Expr(Expr { kind: hir::ExprKind::Path(_), .. }) = arg_node else {
-                return false;
-            };
 
             let clone_trait = self.tcx.require_lang_item(LangItem::Clone, None);
             let has_clone = |ty| {
@@ -998,6 +995,39 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
                     .must_apply_modulo_regions()
             };
 
+            let existing_clone_call = match self.tcx.hir_node(*arg_hir_id) {
+                // It's just a variable. Propose cloning it.
+                Node::Expr(Expr { kind: hir::ExprKind::Path(_), .. }) => None,
+                // It's already a call to `clone()`. We might be able to suggest
+                // adding a `+ Clone` bound, though.
+                Node::Expr(Expr {
+                    kind:
+                        hir::ExprKind::MethodCall(
+                            hir::PathSegment { ident, .. },
+                            _receiver,
+                            &[],
+                            call_span,
+                        ),
+                    hir_id,
+                    ..
+                }) if ident.name == sym::clone
+                    && !call_span.from_expansion()
+                    && !has_clone(*inner_ty) =>
+                {
+                    // We only care about method calls corresponding to the real `Clone` trait.
+                    let Some(typeck_results) = self.typeck_results.as_ref() else { return false };
+                    let Some((DefKind::AssocFn, did)) = typeck_results.type_dependent_def(*hir_id)
+                    else {
+                        return false;
+                    };
+                    if self.tcx.trait_of_item(did) != Some(clone_trait) {
+                        return false;
+                    }
+                    Some(ident.span)
+                }
+                _ => return false,
+            };
+
             let new_obligation = self.mk_trait_obligation_with_new_self_ty(
                 obligation.param_env,
                 trait_pred.map_bound(|trait_pred| (trait_pred, *inner_ty)),
@@ -1015,12 +1045,23 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
                         None,
                     );
                 }
-                err.span_suggestion_verbose(
-                    obligation.cause.span.shrink_to_hi(),
-                    "consider using clone here",
-                    ".clone()".to_string(),
-                    Applicability::MaybeIncorrect,
-                );
+                if let Some(existing_clone_call) = existing_clone_call {
+                    err.span_note(
+                        existing_clone_call,
+                        format!(
+                            "this `clone()` copies the reference, \
+                            which does not do anything, \
+                            because `{inner_ty}` does not implement `Clone`"
+                        ),
+                    );
+                } else {
+                    err.span_suggestion_verbose(
+                        obligation.cause.span.shrink_to_hi(),
+                        "consider using clone here",
+                        ".clone()".to_string(),
+                        Applicability::MaybeIncorrect,
+                    );
+                }
                 return true;
             }
             false
@@ -1685,8 +1726,8 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
         trait_pred: ty::PolyTraitPredicate<'tcx>,
     ) -> bool {
         let hir = self.tcx.hir();
-        let node = self.tcx.opt_hir_node_by_def_id(obligation.cause.body_id);
-        if let Some(hir::Node::Item(hir::Item { kind: hir::ItemKind::Fn(sig, _, body_id), .. })) = node
+        let node = self.tcx.hir_node_by_def_id(obligation.cause.body_id);
+        if let hir::Node::Item(hir::Item { kind: hir::ItemKind::Fn(sig, _, body_id), .. }) = node
             && let hir::ExprKind::Block(blk, _) = &hir.body(*body_id).value.kind
             && sig.decl.output.span().overlaps(span)
             && blk.expr.is_none()
@@ -1720,8 +1761,8 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
     }
 
     fn return_type_span(&self, obligation: &PredicateObligation<'tcx>) -> Option<Span> {
-        let Some(hir::Node::Item(hir::Item { kind: hir::ItemKind::Fn(sig, ..), .. })) =
-            self.tcx.opt_hir_node_by_def_id(obligation.cause.body_id)
+        let hir::Node::Item(hir::Item { kind: hir::ItemKind::Fn(sig, ..), .. }) =
+            self.tcx.hir_node_by_def_id(obligation.cause.body_id)
         else {
             return None;
         };
@@ -1813,10 +1854,8 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
         }
 
         let hir = self.tcx.hir();
-        let node = self.tcx.opt_hir_node_by_def_id(obligation.cause.body_id);
-        if let Some(hir::Node::Item(hir::Item { kind: hir::ItemKind::Fn(_, _, body_id), .. })) =
-            node
-        {
+        let node = self.tcx.hir_node_by_def_id(obligation.cause.body_id);
+        if let hir::Node::Item(hir::Item { kind: hir::ItemKind::Fn(_, _, body_id), .. }) = node {
             let body = hir.body(*body_id);
             // Point at all the `return`s in the function as they have failed trait bounds.
             let mut visitor = ReturnsVisitor::default();
@@ -4450,7 +4489,7 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
             }
             return;
         };
-        let Some(hir::Node::TraitItem(item)) = self.tcx.opt_hir_node_by_def_id(fn_def_id) else {
+        let hir::Node::TraitItem(item) = self.tcx.hir_node_by_def_id(fn_def_id) else {
             return;
         };
 

compiler/rustc_trait_selection/src/traits/error_reporting/type_err_ctxt_ext.rs

@@ -2497,11 +2497,11 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
                         err.code(E0790);
 
                         if let Some(local_def_id) = data.trait_ref.def_id.as_local()
-                            && let Some(hir::Node::Item(hir::Item {
+                            && let hir::Node::Item(hir::Item {
                                 ident: trait_name,
                                 kind: hir::ItemKind::Trait(_, _, _, _, trait_item_refs),
                                 ..
-                            })) = self.tcx.opt_hir_node_by_def_id(local_def_id)
+                            }) = self.tcx.hir_node_by_def_id(local_def_id)
                             && let Some(method_ref) = trait_item_refs
                                 .iter()
                                 .find(|item_ref| item_ref.ident == *assoc_item_name)
@@ -3073,29 +3073,29 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
                 let src = trait_ref.args.type_at(1);
                 let err_msg = format!("`{src}` cannot be safely transmuted into `{dst}`");
                 let safe_transmute_explanation = match reason {
-                    rustc_transmute::Reason::SrcIsUnspecified => {
-                        format!("`{src}` does not have a well-specified layout")
+                    rustc_transmute::Reason::SrcIsNotYetSupported => {
+                        format!("analyzing the transmutability of `{src}` is not yet supported.")
                     }
 
-                    rustc_transmute::Reason::DstIsUnspecified => {
-                        format!("`{dst}` does not have a well-specified layout")
+                    rustc_transmute::Reason::DstIsNotYetSupported => {
+                        format!("analyzing the transmutability of `{dst}` is not yet supported.")
                     }
 
                     rustc_transmute::Reason::DstIsBitIncompatible => {
-                        format!("At least one value of `{src}` isn't a bit-valid value of `{dst}`")
+                        format!("at least one value of `{src}` isn't a bit-valid value of `{dst}`")
                     }
 
                     rustc_transmute::Reason::DstMayHaveSafetyInvariants => {
                         format!("`{dst}` may carry safety invariants")
                     }
                     rustc_transmute::Reason::DstIsTooBig => {
-                        format!("The size of `{src}` is smaller than the size of `{dst}`")
+                        format!("the size of `{src}` is smaller than the size of `{dst}`")
                     }
                     rustc_transmute::Reason::DstRefIsTooBig { src, dst } => {
                         let src_size = src.size;
                         let dst_size = dst.size;
                         format!(
-                            "The referent size of `{src}` ({src_size} bytes) is smaller than that of `{dst}` ({dst_size} bytes)"
+                            "the referent size of `{src}` ({src_size} bytes) is smaller than that of `{dst}` ({dst_size} bytes)"
                         )
                     }
                     rustc_transmute::Reason::SrcSizeOverflow => {
@@ -3113,7 +3113,7 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
                         dst_min_align,
                     } => {
                         format!(
-                            "The minimum alignment of `{src}` ({src_min_align}) should be greater than that of `{dst}` ({dst_min_align})"
+                            "the minimum alignment of `{src}` ({src_min_align}) should be greater than that of `{dst}` ({dst_min_align})"
                         )
                     }
                     rustc_transmute::Reason::DstIsMoreUnique => {

compiler/rustc_trait_selection/src/traits/wf.rs

@@ -164,7 +164,7 @@ pub fn clause_obligations<'tcx>(
             wf.compute(ty.into());
         }
         ty::ClauseKind::Projection(t) => {
-            wf.compute_projection(t.projection_ty);
+            wf.compute_alias(t.projection_ty);
             wf.compute(match t.term.unpack() {
                 ty::TermKind::Ty(ty) => ty.into(),
                 ty::TermKind::Const(c) => c.into(),
@@ -436,9 +436,9 @@ impl<'a, 'tcx> WfPredicates<'a, 'tcx> {
         }
     }
 
-    /// Pushes the obligations required for `trait_ref::Item` to be WF
+    /// Pushes the obligations required for an alias (except inherent) to be WF
     /// into `self.out`.
-    fn compute_projection(&mut self, data: ty::AliasTy<'tcx>) {
+    fn compute_alias(&mut self, data: ty::AliasTy<'tcx>) {
         // A projection is well-formed if
         //
         // (a) its predicates hold (*)
@@ -466,6 +466,9 @@ impl<'a, 'tcx> WfPredicates<'a, 'tcx> {
         self.compute_projection_args(data.args);
     }
 
+    /// Pushes the obligations required for an inherent alias to be WF
+    /// into `self.out`.
+    // FIXME(inherent_associated_types): Merge this function with `fn compute_alias`.
     fn compute_inherent_projection(&mut self, data: ty::AliasTy<'tcx>) {
         // An inherent projection is well-formed if
         //
@@ -688,8 +691,8 @@ impl<'a, 'tcx> TypeVisitor<TyCtxt<'tcx>> for WfPredicates<'a, 'tcx> {
                 // Simple cases that are WF if their type args are WF.
             }
 
-            ty::Alias(ty::Projection, data) => {
-                self.compute_projection(data);
+            ty::Alias(ty::Projection | ty::Opaque | ty::Weak, data) => {
+                self.compute_alias(data);
                 return; // Subtree handled by compute_projection.
             }
             ty::Alias(ty::Inherent, data) => {
@@ -791,21 +794,6 @@ impl<'a, 'tcx> TypeVisitor<TyCtxt<'tcx>> for WfPredicates<'a, 'tcx> {
                 // types appearing in the fn signature.
             }
 
-            ty::Alias(ty::Opaque, ty::AliasTy { def_id, args, .. }) => {
-                // All of the requirements on type parameters
-                // have already been checked for `impl Trait` in
-                // return position. We do need to check type-alias-impl-trait though.
-                if self.tcx().is_type_alias_impl_trait(def_id) {
-                    let obligations = self.nominal_obligations(def_id, args);
-                    self.out.extend(obligations);
-                }
-            }
-
-            ty::Alias(ty::Weak, ty::AliasTy { def_id, args, .. }) => {
-                let obligations = self.nominal_obligations(def_id, args);
-                self.out.extend(obligations);
-            }
-
             ty::Dynamic(data, r, _) => {
                 // WfObject
                 //

compiler/rustc_transmute/src/layout/tree.rs

@@ -186,8 +186,8 @@ pub(crate) mod rustc {
 
     #[derive(Debug, Copy, Clone)]
     pub(crate) enum Err {
-        /// The layout of the type is unspecified.
-        Unspecified,
+        /// The layout of the type is not yet supported.
+        NotYetSupported,
         /// This error will be surfaced elsewhere by rustc, so don't surface it.
         UnknownLayout,
         /// Overflow size
@@ -288,14 +288,14 @@ pub(crate) mod rustc {
                     if members.len() == 0 {
                         Ok(Tree::unit())
                     } else {
-                        Err(Err::Unspecified)
+                        Err(Err::NotYetSupported)
                     }
                 }
 
                 ty::Array(ty, len) => {
                     let len = len
                         .try_eval_target_usize(tcx, ParamEnv::reveal_all())
-                        .ok_or(Err::Unspecified)?;
+                        .ok_or(Err::NotYetSupported)?;
                     let elt = Tree::from_ty(*ty, tcx)?;
                     Ok(std::iter::repeat(elt)
                         .take(len as usize)
@@ -307,7 +307,7 @@ pub(crate) mod rustc {
 
                     // If the layout is ill-specified, halt.
                     if !(adt_def.repr().c() || adt_def.repr().int.is_some()) {
-                        return Err(Err::Unspecified);
+                        return Err(Err::NotYetSupported);
                     }
 
                     // Compute a summary of the type's layout.
@@ -348,7 +348,7 @@ pub(crate) mod rustc {
                         AdtKind::Union => {
                             // is the layout well-defined?
                             if !adt_def.repr().c() {
-                                return Err(Err::Unspecified);
+                                return Err(Err::NotYetSupported);
                             }
 
                             let ty_layout = layout_of(tcx, ty)?;
@@ -384,7 +384,7 @@ pub(crate) mod rustc {
                     }))
                 }
 
-                _ => Err(Err::Unspecified),
+                _ => Err(Err::NotYetSupported),
             }
         }
 

compiler/rustc_transmute/src/lib.rs

@@ -43,10 +43,10 @@ pub enum Condition<R> {
 /// Answers "why wasn't the source type transmutable into the destination type?"
 #[derive(Debug, Hash, Eq, PartialEq, PartialOrd, Ord, Clone)]
 pub enum Reason<T> {
-    /// The layout of the source type is unspecified.
-    SrcIsUnspecified,
-    /// The layout of the destination type is unspecified.
-    DstIsUnspecified,
+    /// The layout of the source type is not yet supported.
+    SrcIsNotYetSupported,
+    /// The layout of the destination type is not yet supported.
+    DstIsNotYetSupported,
     /// The layout of the destination type is bit-incompatible with the source type.
     DstIsBitIncompatible,
     /// The destination type may carry safety invariants.

compiler/rustc_transmute/src/maybe_transmutable/mod.rs

@@ -56,8 +56,8 @@ mod rustc {
                 }
                 (Err(Err::UnknownLayout), _) => Answer::No(Reason::SrcLayoutUnknown),
                 (_, Err(Err::UnknownLayout)) => Answer::No(Reason::DstLayoutUnknown),
-                (Err(Err::Unspecified), _) => Answer::No(Reason::SrcIsUnspecified),
-                (_, Err(Err::Unspecified)) => Answer::No(Reason::DstIsUnspecified),
+                (Err(Err::NotYetSupported), _) => Answer::No(Reason::SrcIsNotYetSupported),
+                (_, Err(Err::NotYetSupported)) => Answer::No(Reason::DstIsNotYetSupported),
                 (Err(Err::SizeOverflow), _) => Answer::No(Reason::SrcSizeOverflow),
                 (_, Err(Err::SizeOverflow)) => Answer::No(Reason::DstSizeOverflow),
                 (Ok(src), Ok(dst)) => MaybeTransmutableQuery { src, dst, assume, context }.answer(),

compiler/rustc_ty_utils/src/assoc.rs

@@ -325,11 +325,7 @@ fn associated_type_for_impl_trait_in_impl(
 ) -> LocalDefId {
     let impl_local_def_id = tcx.local_parent(impl_fn_def_id);
 
-    let decl = tcx
-        .opt_hir_node_by_def_id(impl_fn_def_id)
-        .expect("expected item")
-        .fn_decl()
-        .expect("expected decl");
+    let decl = tcx.hir_node_by_def_id(impl_fn_def_id).fn_decl().expect("expected decl");
     let span = match decl.output {
         hir::FnRetTy::DefaultReturn(_) => tcx.def_span(impl_fn_def_id),
         hir::FnRetTy::Return(ty) => ty.span,

library/core/src/num/nonzero.rs

@@ -4,23 +4,15 @@ use crate::cmp::Ordering;
 use crate::fmt;
 use crate::hash::{Hash, Hasher};
 use crate::intrinsics;
-use crate::marker::StructuralPartialEq;
+use crate::marker::{Freeze, StructuralPartialEq};
 use crate::ops::{BitOr, BitOrAssign, Div, Neg, Rem};
+use crate::panic::{RefUnwindSafe, UnwindSafe};
+use crate::ptr;
 use crate::str::FromStr;
 
 use super::from_str_radix;
 use super::{IntErrorKind, ParseIntError};
 
-mod private {
-    #[unstable(
-        feature = "nonzero_internals",
-        reason = "implementation detail which may disappear or be replaced at any time",
-        issue = "none"
-    )]
-    #[const_trait]
-    pub trait Sealed {}
-}
-
 /// A marker trait for primitive types which can be zero.
 ///
 /// This is an implementation detail for <code>[NonZero]\<T></code> which may disappear or be replaced at any time.
@@ -34,38 +26,70 @@ mod private {
     issue = "none"
 )]
 #[const_trait]
-pub unsafe trait ZeroablePrimitive: Sized + Copy + private::Sealed {}
+pub unsafe trait ZeroablePrimitive: Sized + Copy + private::Sealed {
+    #[doc(hidden)]
+    type NonZeroInner: Sized + Copy;
+}
 
 macro_rules! impl_zeroable_primitive {
-    ($primitive:ty) => {
-        #[unstable(
-            feature = "nonzero_internals",
-            reason = "implementation detail which may disappear or be replaced at any time",
-            issue = "none"
-        )]
-        impl const private::Sealed for $primitive {}
+    ($($NonZeroInner:ident ( $primitive:ty )),+ $(,)?) => {
+        mod private {
+            #[unstable(
+                feature = "nonzero_internals",
+                reason = "implementation detail which may disappear or be replaced at any time",
+                issue = "none"
+            )]
+            #[const_trait]
+            pub trait Sealed {}
 
-        #[unstable(
-            feature = "nonzero_internals",
-            reason = "implementation detail which may disappear or be replaced at any time",
-            issue = "none"
-        )]
-        unsafe impl const ZeroablePrimitive for $primitive {}
+            $(
+                #[derive(Debug, Clone, Copy, PartialEq)]
+                #[repr(transparent)]
+                #[rustc_layout_scalar_valid_range_start(1)]
+                #[rustc_nonnull_optimization_guaranteed]
+                #[unstable(
+                    feature = "nonzero_internals",
+                    reason = "implementation detail which may disappear or be replaced at any time",
+                    issue = "none"
+                )]
+                pub struct $NonZeroInner($primitive);
+            )+
+        }
+
+        $(
+            #[unstable(
+                feature = "nonzero_internals",
+                reason = "implementation detail which may disappear or be replaced at any time",
+                issue = "none"
+            )]
+            impl const private::Sealed for $primitive {}
+
+            #[unstable(
+                feature = "nonzero_internals",
+                reason = "implementation detail which may disappear or be replaced at any time",
+                issue = "none"
+            )]
+            unsafe impl const ZeroablePrimitive for $primitive {
+                type NonZeroInner = private::$NonZeroInner;
+            }
+        )+
     };
 }
 
-impl_zeroable_primitive!(u8);
-impl_zeroable_primitive!(u16);
-impl_zeroable_primitive!(u32);
-impl_zeroable_primitive!(u64);
-impl_zeroable_primitive!(u128);
-impl_zeroable_primitive!(usize);
-impl_zeroable_primitive!(i8);
-impl_zeroable_primitive!(i16);
-impl_zeroable_primitive!(i32);
-impl_zeroable_primitive!(i64);
-impl_zeroable_primitive!(i128);
-impl_zeroable_primitive!(isize);
+impl_zeroable_primitive!(
+    NonZeroU8Inner(u8),
+    NonZeroU16Inner(u16),
+    NonZeroU32Inner(u32),
+    NonZeroU64Inner(u64),
+    NonZeroU128Inner(u128),
+    NonZeroUsizeInner(usize),
+    NonZeroI8Inner(i8),
+    NonZeroI16Inner(i16),
+    NonZeroI32Inner(i32),
+    NonZeroI64Inner(i64),
+    NonZeroI128Inner(i128),
+    NonZeroIsizeInner(isize),
+);
 
 /// A value that is known not to equal zero.
 ///
@@ -80,10 +104,9 @@ impl_zeroable_primitive!(isize);
 /// ```
 #[unstable(feature = "generic_nonzero", issue = "120257")]
 #[repr(transparent)]
-#[rustc_layout_scalar_valid_range_start(1)]
 #[rustc_nonnull_optimization_guaranteed]
 #[rustc_diagnostic_item = "NonZero"]
-pub struct NonZero<T: ZeroablePrimitive>(T);
+pub struct NonZero<T: ZeroablePrimitive>(T::NonZeroInner);
 
 macro_rules! impl_nonzero_fmt {
     ($Trait:ident) => {
@@ -107,6 +130,26 @@ impl_nonzero_fmt!(Octal);
 impl_nonzero_fmt!(LowerHex);
 impl_nonzero_fmt!(UpperHex);
 
+macro_rules! impl_nonzero_auto_trait {
+    (unsafe $Trait:ident) => {
+        #[stable(feature = "nonzero", since = "1.28.0")]
+        unsafe impl<T> $Trait for NonZero<T> where T: ZeroablePrimitive + $Trait {}
+    };
+    ($Trait:ident) => {
+        #[stable(feature = "nonzero", since = "1.28.0")]
+        impl<T> $Trait for NonZero<T> where T: ZeroablePrimitive + $Trait {}
+    };
+}
+
+// Implement auto-traits manually based on `T` to avoid docs exposing
+// the `ZeroablePrimitive::NonZeroInner` implementation detail.
+impl_nonzero_auto_trait!(unsafe Freeze);
+impl_nonzero_auto_trait!(RefUnwindSafe);
+impl_nonzero_auto_trait!(unsafe Send);
+impl_nonzero_auto_trait!(unsafe Sync);
+impl_nonzero_auto_trait!(Unpin);
+impl_nonzero_auto_trait!(UnwindSafe);
+
 #[stable(feature = "nonzero", since = "1.28.0")]
 impl<T> Clone for NonZero<T>
 where
@@ -114,8 +157,7 @@ where
 {
     #[inline]
     fn clone(&self) -> Self {
-        // SAFETY: The contained value is non-zero.
-        unsafe { Self(self.0) }
+        Self(self.0)
     }
 }
 
@@ -188,19 +230,19 @@ where
     #[inline]
     fn max(self, other: Self) -> Self {
         // SAFETY: The maximum of two non-zero values is still non-zero.
-        unsafe { Self(self.get().max(other.get())) }
+        unsafe { Self::new_unchecked(self.get().max(other.get())) }
     }
 
     #[inline]
     fn min(self, other: Self) -> Self {
         // SAFETY: The minimum of two non-zero values is still non-zero.
-        unsafe { Self(self.get().min(other.get())) }
+        unsafe { Self::new_unchecked(self.get().min(other.get())) }
     }
 
     #[inline]
     fn clamp(self, min: Self, max: Self) -> Self {
         // SAFETY: A non-zero value clamped between two non-zero values is still non-zero.
-        unsafe { Self(self.get().clamp(min.get(), max.get())) }
+        unsafe { Self::new_unchecked(self.get().clamp(min.get(), max.get())) }
     }
 }
 
@@ -240,7 +282,7 @@ where
     #[inline]
     fn bitor(self, rhs: Self) -> Self::Output {
         // SAFETY: Bitwise OR of two non-zero values is still non-zero.
-        unsafe { Self(self.get() | rhs.get()) }
+        unsafe { Self::new_unchecked(self.get() | rhs.get()) }
     }
 }
 
@@ -254,7 +296,7 @@ where
     #[inline]
     fn bitor(self, rhs: T) -> Self::Output {
         // SAFETY: Bitwise OR of a non-zero value with anything is still non-zero.
-        unsafe { Self(self.get() | rhs) }
+        unsafe { Self::new_unchecked(self.get() | rhs) }
     }
 }
 
@@ -268,7 +310,7 @@ where
     #[inline]
     fn bitor(self, rhs: NonZero<T>) -> Self::Output {
         // SAFETY: Bitwise OR of anything with a non-zero value is still non-zero.
-        unsafe { NonZero(self | rhs.get()) }
+        unsafe { NonZero::new_unchecked(self | rhs.get()) }
     }
 }
 
@@ -346,7 +388,7 @@ where
     pub fn from_mut(n: &mut T) -> Option<&mut Self> {
         // SAFETY: Memory layout optimization guarantees that `Option<NonZero<T>>` has
         //         the same layout and size as `T`, with `0` representing `None`.
-        let opt_n = unsafe { &mut *(n as *mut T as *mut Option<Self>) };
+        let opt_n = unsafe { &mut *(ptr::from_mut(n).cast::<Option<Self>>()) };
 
         opt_n.as_mut()
     }
@@ -390,12 +432,17 @@ where
         // memory somewhere. If the value of `self` was from by-value argument
         // of some not-inlined function, LLVM don't have range metadata
         // to understand that the value cannot be zero.
-        match Self::new(self.0) {
-            Some(Self(n)) => n,
+        //
+        // SAFETY: `Self` is guaranteed to have the same layout as `Option<Self>`.
+        match unsafe { intrinsics::transmute_unchecked(self) } {
             None => {
                 // SAFETY: `NonZero` is guaranteed to only contain non-zero values, so this is unreachable.
                 unsafe { intrinsics::unreachable() }
             }
+            Some(Self(inner)) => {
+                // SAFETY: `T::NonZeroInner` is guaranteed to have the same layout as `T`.
+                unsafe { intrinsics::transmute_unchecked(inner) }
+            }
         }
     }
 }

library/core/src/ptr/mod.rs

@@ -1114,7 +1114,7 @@ const unsafe fn swap_nonoverlapping_simple_untyped<T>(x: *mut T, y: *mut T, coun
 #[stable(feature = "rust1", since = "1.0.0")]
 #[rustc_const_unstable(feature = "const_replace", issue = "83164")]
 #[rustc_diagnostic_item = "ptr_replace"]
-pub const unsafe fn replace<T>(dst: *mut T, mut src: T) -> T {
+pub const unsafe fn replace<T>(dst: *mut T, src: T) -> T {
     // SAFETY: the caller must guarantee that `dst` is valid to be
     // cast to a mutable reference (valid for writes, aligned, initialized),
     // and cannot overlap `src` since `dst` must point to a distinct
@@ -1128,9 +1128,8 @@ pub const unsafe fn replace<T>(dst: *mut T, mut src: T) -> T {
                 align: usize = align_of::<T>(),
             ) => is_aligned_and_not_null(addr, align)
         );
-        mem::swap(&mut *dst, &mut src); // cannot overlap
+        mem::replace(&mut *dst, src)
     }
-    src
 }
 
 /// Reads the value from `src` without moving it. This leaves the

library/std/src/fs/tests.rs

@@ -1782,6 +1782,7 @@ fn windows_unix_socket_exists() {
         }
         let mut addr = c::SOCKADDR_UN { sun_family: c::AF_UNIX, sun_path: mem::zeroed() };
         let bytes = socket_path.as_os_str().as_encoded_bytes();
+        let bytes = core::slice::from_raw_parts(bytes.as_ptr().cast::<i8>(), bytes.len());
         addr.sun_path[..bytes.len()].copy_from_slice(bytes);
         let len = mem::size_of_val(&addr) as i32;
         let result = c::bind(socket, ptr::addr_of!(addr).cast::<c::SOCKADDR>(), len);

library/std/src/io/cursor.rs

@@ -51,6 +51,8 @@ use crate::io::{self, BorrowedCursor, ErrorKind, IoSlice, IoSliceMut, SeekFrom};
 /// // We might want to use a BufReader here for efficiency, but let's
 /// // keep this example focused.
 /// let mut file = File::create("foo.txt")?;
+/// // First, we need to allocate 10 bytes to be able to write into.
+/// file.set_len(10)?;
 ///
 /// write_ten_bytes_at_end(&mut file)?;
 /// # Ok(())

library/std/src/keyword_docs.rs

@@ -48,7 +48,7 @@ mod as_keyword {}
 
 #[doc(keyword = "break")]
 //
-/// Exit early from a loop.
+/// Exit early from a loop or labelled block.
 ///
 /// When `break` is encountered, execution of the associated loop body is
 /// immediately terminated.

library/std/src/sys/thread_local/fast_local.rs

@@ -13,22 +13,21 @@ pub macro thread_local_inner {
     (@key $t:ty, const $init:expr) => {{
         #[inline]
         #[deny(unsafe_op_in_unsafe_fn)]
-        // FIXME: Use `SyncUnsafeCell` instead of allowing `static_mut_refs` lint
-        #[cfg_attr(bootstrap, allow(static_mut_ref))]
-        #[cfg_attr(not(bootstrap), allow(static_mut_refs))]
         unsafe fn __getit(
             _init: $crate::option::Option<&mut $crate::option::Option<$t>>,
         ) -> $crate::option::Option<&'static $t> {
             const INIT_EXPR: $t = $init;
             // If the platform has support for `#[thread_local]`, use it.
             #[thread_local]
-            static mut VAL: $t = INIT_EXPR;
+            // We use `UnsafeCell` here instead of `static mut` to ensure any generated TLS shims
+            // have a nonnull attribute on their return value.
+            static VAL: $crate::cell::UnsafeCell<$t> = $crate::cell::UnsafeCell::new(INIT_EXPR);
 
             // If a dtor isn't needed we can do something "very raw" and
             // just get going.
             if !$crate::mem::needs_drop::<$t>() {
                 unsafe {
-                    return $crate::option::Option::Some(&VAL)
+                    return $crate::option::Option::Some(&*VAL.get())
                 }
             }
 
@@ -55,15 +54,15 @@ pub macro thread_local_inner {
                     //   so now.
                     0 => {
                         $crate::thread::local_impl::Key::<$t>::register_dtor(
-                            $crate::ptr::addr_of_mut!(VAL) as *mut $crate::primitive::u8,
+                            VAL.get() as *mut $crate::primitive::u8,
                             destroy,
                         );
                         STATE.set(1);
-                        $crate::option::Option::Some(&VAL)
+                        $crate::option::Option::Some(&*VAL.get())
                     }
                     // 1 == the destructor is registered and the value
                     //   is valid, so return the pointer.
-                    1 => $crate::option::Option::Some(&VAL),
+                    1 => $crate::option::Option::Some(&*VAL.get()),
                     // otherwise the destructor has already run, so we
                     // can't give access.
                     _ => $crate::option::Option::None,

src/bootstrap/configure.py

@@ -131,6 +131,8 @@ v("musl-root-riscv32gc", "target.riscv32gc-unknown-linux-musl.musl-root",
   "riscv32gc-unknown-linux-musl install directory")
 v("musl-root-riscv64gc", "target.riscv64gc-unknown-linux-musl.musl-root",
   "riscv64gc-unknown-linux-musl install directory")
+v("musl-root-loongarch64", "target.loongarch64-unknown-linux-musl.musl-root",
+  "loongarch64-unknown-linux-musl install directory")
 v("qemu-armhf-rootfs", "target.arm-unknown-linux-gnueabihf.qemu-rootfs",
   "rootfs in qemu testing, you probably don't want to use this")
 v("qemu-aarch64-rootfs", "target.aarch64-unknown-linux-gnu.qemu-rootfs",

src/bootstrap/src/bin/main.rs

@@ -7,6 +7,7 @@
 
 use std::io::Write;
 use std::process;
+use std::str::FromStr;
 use std::{
     env,
     fs::{self, OpenOptions},
@@ -136,16 +137,25 @@ fn check_version(config: &Config) -> Option<String> {
     let latest_change_id = CONFIG_CHANGE_HISTORY.last().unwrap().change_id;
     let warned_id_path = config.out.join("bootstrap").join(".last-warned-change-id");
 
-    if let Some(id) = config.change_id {
+    if let Some(mut id) = config.change_id {
         if id == latest_change_id {
             return None;
         }
 
-        if let Ok(last_warned_id) = fs::read_to_string(&warned_id_path) {
-            if latest_change_id.to_string() == last_warned_id {
-                return None;
+        // Always try to use `change-id` from .last-warned-change-id first. If it doesn't exist,
+        // then use the one from the config.toml. This way we never show the same warnings
+        // more than once.
+        if let Ok(t) = fs::read_to_string(&warned_id_path) {
+            let last_warned_id =
+                usize::from_str(&t).expect(&format!("{} is corrupted.", warned_id_path.display()));
+
+            // We only use the last_warned_id if it exists in `CONFIG_CHANGE_HISTORY`.
+            // Otherwise, we may retrieve all the changes if it's not the highest value.
+            // For better understanding, refer to `change_tracker::find_recent_config_change_ids`.
+            if CONFIG_CHANGE_HISTORY.iter().any(|config| config.change_id == last_warned_id) {
+                id = last_warned_id;
             }
-        }
+        };
 
         let changes = find_recent_config_change_ids(id);
 

src/bootstrap/src/core/build_steps/compile.rs

@@ -231,7 +231,7 @@ impl Step for Std {
                 let target_sysroot_bin =
                     builder.sysroot_libdir(compiler, target).parent().unwrap().join("bin");
                 t!(fs::create_dir_all(&target_sysroot_bin));
-                builder.cp_r(&src_sysroot_bin, &target_sysroot_bin);
+                builder.cp_link_r(&src_sysroot_bin, &target_sysroot_bin);
             }
         }
 
@@ -307,7 +307,7 @@ fn copy_and_stamp(
     dependency_type: DependencyType,
 ) {
     let target = libdir.join(name);
-    builder.copy(&sourcedir.join(name), &target);
+    builder.copy_link(&sourcedir.join(name), &target);
 
     target_deps.push((target, dependency_type));
 }
@@ -316,7 +316,7 @@ fn copy_llvm_libunwind(builder: &Builder<'_>, target: TargetSelection, libdir: &
     let libunwind_path = builder.ensure(llvm::Libunwind { target });
     let libunwind_source = libunwind_path.join("libunwind.a");
     let libunwind_target = libdir.join("libunwind.a");
-    builder.copy(&libunwind_source, &libunwind_target);
+    builder.copy_link(&libunwind_source, &libunwind_target);
     libunwind_target
 }
 
@@ -385,7 +385,7 @@ fn copy_self_contained_objects(
         for &obj in &["crtbegin.o", "crtbeginS.o", "crtend.o", "crtendS.o"] {
             let src = crt_path.join(obj);
             let target = libdir_self_contained.join(obj);
-            builder.copy(&src, &target);
+            builder.copy_link(&src, &target);
             target_deps.push((target, DependencyType::TargetSelfContained));
         }
 
@@ -418,7 +418,7 @@ fn copy_self_contained_objects(
         for obj in ["crt2.o", "dllcrt2.o"].iter() {
             let src = compiler_file(builder, &builder.cc(target), target, CLang::C, obj);
             let target = libdir_self_contained.join(obj);
-            builder.copy(&src, &target);
+            builder.copy_link(&src, &target);
             target_deps.push((target, DependencyType::TargetSelfContained));
         }
     }
@@ -637,7 +637,7 @@ impl Step for StdLink {
             let stage0_bin_dir = builder.out.join(host).join("stage0/bin");
             let sysroot_bin_dir = sysroot.join("bin");
             t!(fs::create_dir_all(&sysroot_bin_dir));
-            builder.cp_r(&stage0_bin_dir, &sysroot_bin_dir);
+            builder.cp_link_r(&stage0_bin_dir, &sysroot_bin_dir);
 
             // Copy all *.so files from stage0/lib to stage0-sysroot/lib
             let stage0_lib_dir = builder.out.join(host).join("stage0/lib");
@@ -646,7 +646,8 @@ impl Step for StdLink {
                     let file = t!(file);
                     let path = file.path();
                     if path.is_file() && is_dylib(&file.file_name().into_string().unwrap()) {
-                        builder.copy(&path, &sysroot.join("lib").join(path.file_name().unwrap()));
+                        builder
+                            .copy_link(&path, &sysroot.join("lib").join(path.file_name().unwrap()));
                     }
                 }
             }
@@ -661,7 +662,7 @@ impl Step for StdLink {
                 .join(host)
                 .join("codegen-backends");
             if stage0_codegen_backends.exists() {
-                builder.cp_r(&stage0_codegen_backends, &sysroot_codegen_backends);
+                builder.cp_link_r(&stage0_codegen_backends, &sysroot_codegen_backends);
             }
         }
     }
@@ -684,7 +685,7 @@ fn copy_sanitizers(
 
     for runtime in &runtimes {
         let dst = libdir.join(&runtime.name);
-        builder.copy(&runtime.path, &dst);
+        builder.copy_link(&runtime.path, &dst);
 
         // The `aarch64-apple-ios-macabi` and `x86_64-apple-ios-macabi` are also supported for
         // sanitizers, but they share a sanitizer runtime with `${arch}-apple-darwin`, so we do
@@ -790,7 +791,7 @@ impl Step for StartupObjects {
             }
 
             let target = sysroot_dir.join((*file).to_string() + ".o");
-            builder.copy(dst_file, &target);
+            builder.copy_link(dst_file, &target);
             target_deps.push((target, DependencyType::Target));
         }
 
@@ -812,7 +813,7 @@ fn cp_rustc_component_to_ci_sysroot(
         if src.is_dir() {
             t!(fs::create_dir_all(dst));
         } else {
-            builder.copy(&src, &dst);
+            builder.copy_link(&src, &dst);
         }
     }
 }
@@ -1443,7 +1444,7 @@ fn copy_codegen_backends_to_sysroot(
             let dot = filename.find('.').unwrap();
             format!("{}-{}{}", &filename[..dash], builder.rust_release(), &filename[dot..])
         };
-        builder.copy(file, &dst.join(target_filename));
+        builder.copy_link(file, &dst.join(target_filename));
     }
 }
 
@@ -1599,7 +1600,7 @@ impl Step for Sysroot {
                 OsStr::new(std::env::consts::DLL_EXTENSION),
             ];
             let ci_rustc_dir = builder.config.ci_rustc_dir();
-            builder.cp_filtered(&ci_rustc_dir, &sysroot, &|path| {
+            builder.cp_link_filtered(&ci_rustc_dir, &sysroot, &|path| {
                 if path.extension().map_or(true, |ext| !filtered_extensions.contains(&ext)) {
                     return true;
                 }
@@ -1791,7 +1792,7 @@ impl Step for Assemble {
             let filename = f.file_name().into_string().unwrap();
             if (is_dylib(&filename) || is_debug_info(&filename)) && !proc_macros.contains(&filename)
             {
-                builder.copy(&f.path(), &rustc_libdir.join(&filename));
+                builder.copy_link(&f.path(), &rustc_libdir.join(&filename));
             }
         }
 
@@ -1805,7 +1806,7 @@ impl Step for Assemble {
         if let Some(lld_install) = lld_install {
             let src_exe = exe("lld", target_compiler.host);
             let dst_exe = exe("rust-lld", target_compiler.host);
-            builder.copy(&lld_install.join("bin").join(src_exe), &libdir_bin.join(dst_exe));
+            builder.copy_link(&lld_install.join("bin").join(src_exe), &libdir_bin.join(dst_exe));
             let self_contained_lld_dir = libdir_bin.join("gcc-ld");
             t!(fs::create_dir_all(&self_contained_lld_dir));
             let lld_wrapper_exe = builder.ensure(crate::core::build_steps::tool::LldWrapper {
@@ -1813,7 +1814,7 @@ impl Step for Assemble {
                 target: target_compiler.host,
             });
             for name in crate::LLD_FILE_NAMES {
-                builder.copy(
+                builder.copy_link(
                     &lld_wrapper_exe,
                     &self_contained_lld_dir.join(exe(name, target_compiler.host)),
                 );
@@ -1838,7 +1839,7 @@ impl Step for Assemble {
                     // When using `download-ci-llvm`, some of the tools
                     // may not exist, so skip trying to copy them.
                     if src_path.exists() {
-                        builder.copy(&src_path, &libdir_bin.join(&tool_exe));
+                        builder.copy_link(&src_path, &libdir_bin.join(&tool_exe));
                     }
                 }
             }
@@ -1851,7 +1852,7 @@ impl Step for Assemble {
                 extra_features: vec![],
             });
             let tool_exe = exe("llvm-bitcode-linker", target_compiler.host);
-            builder.copy(&src_path, &libdir_bin.join(&tool_exe));
+            builder.copy_link(&src_path, &libdir_bin.join(&tool_exe));
         }
 
         // Ensure that `libLLVM.so` ends up in the newly build compiler directory,
@@ -1865,7 +1866,7 @@ impl Step for Assemble {
         let bindir = sysroot.join("bin");
         t!(fs::create_dir_all(bindir));
         let compiler = builder.rustc(target_compiler);
-        builder.copy(&rustc, &compiler);
+        builder.copy_link(&rustc, &compiler);
 
         target_compiler
     }
@@ -1891,7 +1892,7 @@ pub fn add_to_sysroot(
             DependencyType::Target => sysroot_dst,
             DependencyType::TargetSelfContained => self_contained_dst,
         };
-        builder.copy(&path, &dst.join(path.file_name().unwrap()));
+        builder.copy_link(&path, &dst.join(path.file_name().unwrap()));
     }
 }
 

src/bootstrap/src/core/build_steps/dist.rs

@@ -272,7 +272,7 @@ fn make_win_dist(
     let dist_bin_dir = rust_root.join("bin/");
     fs::create_dir_all(&dist_bin_dir).expect("creating dist_bin_dir failed");
     for src in rustc_dlls {
-        builder.copy_to_folder(&src, &dist_bin_dir);
+        builder.copy_link_to_folder(&src, &dist_bin_dir);
     }
 
     //Copy platform tools to platform-specific bin directory
@@ -284,7 +284,7 @@ fn make_win_dist(
         .join("self-contained");
     fs::create_dir_all(&target_bin_dir).expect("creating target_bin_dir failed");
     for src in target_tools {
-        builder.copy_to_folder(&src, &target_bin_dir);
+        builder.copy_link_to_folder(&src, &target_bin_dir);
     }
 
     // Warn windows-gnu users that the bundled GCC cannot compile C files
@@ -304,7 +304,7 @@ fn make_win_dist(
         .join("self-contained");
     fs::create_dir_all(&target_lib_dir).expect("creating target_lib_dir failed");
     for src in target_libs {
-        builder.copy_to_folder(&src, &target_lib_dir);
+        builder.copy_link_to_folder(&src, &target_lib_dir);
     }
 }
 
@@ -400,7 +400,7 @@ impl Step for Rustc {
 
             // Copy rustc binary
             t!(fs::create_dir_all(image.join("bin")));
-            builder.cp_r(&src.join("bin"), &image.join("bin"));
+            builder.cp_link_r(&src.join("bin"), &image.join("bin"));
 
             // If enabled, copy rustdoc binary
             if builder
@@ -458,13 +458,13 @@ impl Step for Rustc {
             if builder.config.lld_enabled {
                 let src_dir = builder.sysroot_libdir(compiler, host).parent().unwrap().join("bin");
                 let rust_lld = exe("rust-lld", compiler.host);
-                builder.copy(&src_dir.join(&rust_lld), &dst_dir.join(&rust_lld));
+                builder.copy_link(&src_dir.join(&rust_lld), &dst_dir.join(&rust_lld));
                 let self_contained_lld_src_dir = src_dir.join("gcc-ld");
                 let self_contained_lld_dst_dir = dst_dir.join("gcc-ld");
                 t!(fs::create_dir(&self_contained_lld_dst_dir));
                 for name in crate::LLD_FILE_NAMES {
                     let exe_name = exe(name, compiler.host);
-                    builder.copy(
+                    builder.copy_link(
                         &self_contained_lld_src_dir.join(&exe_name),
                         &self_contained_lld_dst_dir.join(&exe_name),
                     );
@@ -609,9 +609,9 @@ fn copy_target_libs(builder: &Builder<'_>, target: TargetSelection, image: &Path
     t!(fs::create_dir_all(&self_contained_dst));
     for (path, dependency_type) in builder.read_stamp_file(stamp) {
         if dependency_type == DependencyType::TargetSelfContained {
-            builder.copy(&path, &self_contained_dst.join(path.file_name().unwrap()));
+            builder.copy_link(&path, &self_contained_dst.join(path.file_name().unwrap()));
         } else if dependency_type == DependencyType::Target || builder.config.build == target {
-            builder.copy(&path, &dst.join(path.file_name().unwrap()));
+            builder.copy_link(&path, &dst.join(path.file_name().unwrap()));
         }
     }
 }
@@ -865,7 +865,8 @@ fn copy_src_dirs(
     for item in src_dirs {
         let dst = &dst_dir.join(item);
         t!(fs::create_dir_all(dst));
-        builder.cp_filtered(&base.join(item), dst, &|path| filter_fn(exclude_dirs, item, path));
+        builder
+            .cp_link_filtered(&base.join(item), dst, &|path| filter_fn(exclude_dirs, item, path));
     }
 }
 
@@ -923,7 +924,7 @@ impl Step for Src {
             &dst_src,
         );
         for file in src_files.iter() {
-            builder.copy(&builder.src.join(file), &dst_src.join(file));
+            builder.copy_link(&builder.src.join(file), &dst_src.join(file));
         }
 
         tarball.generate()
@@ -979,7 +980,7 @@ impl Step for PlainSourceTarball {
 
         // Copy the files normally
         for item in &src_files {
-            builder.copy(&builder.src.join(item), &plain_dst_src.join(item));
+            builder.copy_link(&builder.src.join(item), &plain_dst_src.join(item));
         }
 
         // Create the version file
@@ -1608,7 +1609,7 @@ impl Step for Extended {
 
             let prepare = |name: &str| {
                 builder.create_dir(&pkg.join(name));
-                builder.cp_r(
+                builder.cp_link_r(
                     &work.join(format!("{}-{}", pkgname(builder, name), target.triple)),
                     &pkg.join(name),
                 );
@@ -1672,7 +1673,7 @@ impl Step for Extended {
                 } else {
                     name.to_string()
                 };
-                builder.cp_r(
+                builder.cp_link_r(
                     &work.join(format!("{}-{}", pkgname(builder, name), target.triple)).join(dir),
                     &exe.join(name),
                 );
@@ -2040,7 +2041,7 @@ fn install_llvm_file(
         if install_symlink {
             // For download-ci-llvm, also install the symlink, to match what LLVM does. Using a
             // symlink is fine here, as this is not a rustup component.
-            builder.copy(&source, &full_dest);
+            builder.copy_link(&source, &full_dest);
         } else {
             // Otherwise, replace the symlink with an equivalent linker script. This is used when
             // projects like miri link against librustc_driver.so. We don't use a symlink, as

src/bootstrap/src/core/build_steps/doc.rs

@@ -520,7 +520,10 @@ impl Step for SharedAssets {
             t!(fs::write(&version_info, info));
         }
 
-        builder.copy(&builder.src.join("src").join("doc").join("rust.css"), &out.join("rust.css"));
+        builder.copy_link(
+            &builder.src.join("src").join("doc").join("rust.css"),
+            &out.join("rust.css"),
+        );
 
         SharedAssetsPaths { version_info }
     }
@@ -718,7 +721,7 @@ fn doc_std(
     let _guard = builder.msg_doc(compiler, description, target);
 
     builder.run(&mut cargo.into());
-    builder.cp_r(&out_dir, out);
+    builder.cp_link_r(&out_dir, out);
 }
 
 #[derive(Debug, Clone, Hash, PartialEq, Eq)]
@@ -1151,7 +1154,7 @@ impl Step for RustcBook {
         let out_base = builder.md_doc_out(self.target).join("rustc");
         t!(fs::create_dir_all(&out_base));
         let out_listing = out_base.join("src/lints");
-        builder.cp_r(&builder.src.join("src/doc/rustc"), &out_base);
+        builder.cp_link_r(&builder.src.join("src/doc/rustc"), &out_base);
         builder.info(&format!("Generating lint docs ({})", self.target));
 
         let rustc = builder.rustc(self.compiler);