From 3f97c6be8d4b78c9df55804171c588ebfadcb63e Mon Sep 17 00:00:00 2001
From: Michael Goulet <michael@errs.io>
Date: Fri, 13 Sep 2024 14:00:10 -0400
Subject: [PATCH] Add unwrap_unsafe_binder and wrap_unsafe_binder macro
 operators

---
 compiler/rustc_ast/src/ast.rs                 | 21 +++++++++-
 compiler/rustc_ast/src/mut_visit.rs           |  6 +++
 compiler/rustc_ast/src/util/classify.rs       |  2 +
 compiler/rustc_ast/src/visit.rs               |  4 ++
 compiler/rustc_ast_lowering/src/expr.rs       |  8 ++++
 compiler/rustc_ast_passes/src/feature_gate.rs |  1 +
 .../rustc_ast_pretty/src/pprust/state/expr.rs | 19 +++++++++
 .../src/assert/context.rs                     |  3 +-
 compiler/rustc_feature/src/unstable.rs        |  2 +
 compiler/rustc_hir/src/hir.rs                 | 13 ++++++-
 compiler/rustc_hir/src/intravisit.rs          |  4 ++
 compiler/rustc_hir_pretty/src/lib.rs          | 13 +++++++
 compiler/rustc_hir_typeck/src/expr.rs         | 25 +++++++++++-
 .../rustc_hir_typeck/src/expr_use_visitor.rs  |  7 ++++
 compiler/rustc_lint/src/dangling.rs           |  2 +
 compiler/rustc_lint/src/if_let_rescope.rs     |  1 +
 compiler/rustc_mir_build/src/thir/cx/expr.rs  |  5 +++
 compiler/rustc_parse/src/parser/expr.rs       | 23 ++++++++++-
 compiler/rustc_passes/src/input_stats.rs      | 39 +++++++++++++++++--
 compiler/rustc_passes/src/liveness.rs         |  3 ++
 compiler/rustc_passes/src/naked_functions.rs  |  1 +
 compiler/rustc_span/src/symbol.rs             |  3 ++
 library/core/src/lib.rs                       |  2 +
 library/core/src/unsafe_binder.rs             | 25 ++++++++++++
 library/std/src/lib.rs                        |  2 +
 25 files changed, 222 insertions(+), 12 deletions(-)
 create mode 100644 library/core/src/unsafe_binder.rs

diff --git a/compiler/rustc_ast/src/ast.rs b/compiler/rustc_ast/src/ast.rs
index 5ffad332bcd8..697ee275a9b3 100644
--- a/compiler/rustc_ast/src/ast.rs
+++ b/compiler/rustc_ast/src/ast.rs
@@ -1382,6 +1382,7 @@ impl Expr {
             | ExprKind::Tup(_)
             | ExprKind::Type(..)
             | ExprKind::Underscore
+            | ExprKind::UnsafeBinderCast(..)
             | ExprKind::While(..)
             | ExprKind::Err(_)
             | ExprKind::Dummy => ExprPrecedence::Unambiguous,
@@ -1509,7 +1510,13 @@ pub enum ExprKind {
     /// `'label: for await? pat in iter { block }`
     ///
     /// This is desugared to a combination of `loop` and `match` expressions.
-    ForLoop { pat: P<Pat>, iter: P<Expr>, body: P<Block>, label: Option<Label>, kind: ForLoopKind },
+    ForLoop {
+        pat: P<Pat>,
+        iter: P<Expr>,
+        body: P<Block>,
+        label: Option<Label>,
+        kind: ForLoopKind,
+    },
     /// Conditionless loop (can be exited with `break`, `continue`, or `return`).
     ///
     /// `'label: loop { block }`
@@ -1614,6 +1621,8 @@ pub enum ExprKind {
     /// A `format_args!()` expression.
     FormatArgs(P<FormatArgs>),
 
+    UnsafeBinderCast(UnsafeBinderCastKind, P<Expr>, Option<P<Ty>>),
+
     /// Placeholder for an expression that wasn't syntactically well formed in some way.
     Err(ErrorGuaranteed),
 
@@ -1652,6 +1661,16 @@ impl GenBlockKind {
     }
 }
 
+/// Whether we're unwrapping or wrapping an unsafe binder
+#[derive(Copy, Clone, Debug, PartialEq, Eq)]
+#[derive(Encodable, Decodable, HashStable_Generic)]
+pub enum UnsafeBinderCastKind {
+    // e.g. `&i32` -> `unsafe<'a> &'a i32`
+    Wrap,
+    // e.g. `unsafe<'a> &'a i32` -> `&i32`
+    Unwrap,
+}
+
 /// The explicit `Self` type in a "qualified path". The actual
 /// path, including the trait and the associated item, is stored
 /// separately. `position` represents the index of the associated
diff --git a/compiler/rustc_ast/src/mut_visit.rs b/compiler/rustc_ast/src/mut_visit.rs
index 4105926002d6..d94c392ad118 100644
--- a/compiler/rustc_ast/src/mut_visit.rs
+++ b/compiler/rustc_ast/src/mut_visit.rs
@@ -1780,6 +1780,12 @@ pub fn walk_expr<T: MutVisitor>(vis: &mut T, Expr { kind, id, span, attrs, token
         ExprKind::TryBlock(body) => vis.visit_block(body),
         ExprKind::Lit(_token) => {}
         ExprKind::IncludedBytes(_bytes) => {}
+        ExprKind::UnsafeBinderCast(_kind, expr, ty) => {
+            vis.visit_expr(expr);
+            if let Some(ty) = ty {
+                vis.visit_ty(ty);
+            }
+        }
         ExprKind::Err(_guar) => {}
         ExprKind::Dummy => {}
     }
diff --git a/compiler/rustc_ast/src/util/classify.rs b/compiler/rustc_ast/src/util/classify.rs
index 41ab0f695f10..64f2a98b8a6f 100644
--- a/compiler/rustc_ast/src/util/classify.rs
+++ b/compiler/rustc_ast/src/util/classify.rs
@@ -152,6 +152,7 @@ pub fn leading_labeled_expr(mut expr: &ast::Expr) -> bool {
             | Underscore
             | Yeet(..)
             | Yield(..)
+            | UnsafeBinderCast(..)
             | Err(..)
             | Dummy => return false,
         }
@@ -232,6 +233,7 @@ pub fn expr_trailing_brace(mut expr: &ast::Expr) -> Option<TrailingBrace<'_>> {
             | Paren(_)
             | Try(_)
             | Yeet(None)
+            | UnsafeBinderCast(..)
             | Err(_)
             | Dummy => break None,
         }
diff --git a/compiler/rustc_ast/src/visit.rs b/compiler/rustc_ast/src/visit.rs
index 6b36262bc1f7..7696be92158c 100644
--- a/compiler/rustc_ast/src/visit.rs
+++ b/compiler/rustc_ast/src/visit.rs
@@ -1230,6 +1230,10 @@ pub fn walk_expr<'a, V: Visitor<'a>>(visitor: &mut V, expression: &'a Expr) -> V
         ExprKind::TryBlock(body) => try_visit!(visitor.visit_block(body)),
         ExprKind::Lit(_token) => {}
         ExprKind::IncludedBytes(_bytes) => {}
+        ExprKind::UnsafeBinderCast(_kind, expr, ty) => {
+            try_visit!(visitor.visit_expr(expr));
+            visit_opt!(visitor, visit_ty, ty);
+        }
         ExprKind::Err(_guar) => {}
         ExprKind::Dummy => {}
     }
diff --git a/compiler/rustc_ast_lowering/src/expr.rs b/compiler/rustc_ast_lowering/src/expr.rs
index 2ad0ff3200e7..329058063431 100644
--- a/compiler/rustc_ast_lowering/src/expr.rs
+++ b/compiler/rustc_ast_lowering/src/expr.rs
@@ -379,6 +379,14 @@ impl<'hir> LoweringContext<'_, 'hir> {
                 ExprKind::Yield(opt_expr) => self.lower_expr_yield(e.span, opt_expr.as_deref()),
                 ExprKind::Err(guar) => hir::ExprKind::Err(*guar),
 
+                ExprKind::UnsafeBinderCast(kind, expr, ty) => hir::ExprKind::UnsafeBinderCast(
+                    *kind,
+                    self.lower_expr(expr),
+                    ty.as_ref().map(|ty| {
+                        self.lower_ty(ty, ImplTraitContext::Disallowed(ImplTraitPosition::Cast))
+                    }),
+                ),
+
                 ExprKind::Dummy => {
                     span_bug!(e.span, "lowered ExprKind::Dummy")
                 }
diff --git a/compiler/rustc_ast_passes/src/feature_gate.rs b/compiler/rustc_ast_passes/src/feature_gate.rs
index aa3b772efb15..bd0809652978 100644
--- a/compiler/rustc_ast_passes/src/feature_gate.rs
+++ b/compiler/rustc_ast_passes/src/feature_gate.rs
@@ -565,6 +565,7 @@ pub fn check_crate(krate: &ast::Crate, sess: &Session, features: &Features) {
     gate_all!(return_type_notation, "return type notation is experimental");
     gate_all!(pin_ergonomics, "pinned reference syntax is experimental");
     gate_all!(unsafe_fields, "`unsafe` fields are experimental");
+    gate_all!(unsafe_binders, "unsafe binder types are experimental");
 
     if !visitor.features.never_patterns() {
         if let Some(spans) = spans.get(&sym::never_patterns) {
diff --git a/compiler/rustc_ast_pretty/src/pprust/state/expr.rs b/compiler/rustc_ast_pretty/src/pprust/state/expr.rs
index c239cb249c3c..dce76fb1e770 100644
--- a/compiler/rustc_ast_pretty/src/pprust/state/expr.rs
+++ b/compiler/rustc_ast_pretty/src/pprust/state/expr.rs
@@ -772,6 +772,25 @@ impl<'a> State<'a> {
                 self.word_nbsp("try");
                 self.print_block_with_attrs(blk, attrs)
             }
+            ast::ExprKind::UnsafeBinderCast(kind, expr, ty) => {
+                self.word("builtin # ");
+                match kind {
+                    ast::UnsafeBinderCastKind::Wrap => self.word("wrap_binder"),
+                    ast::UnsafeBinderCastKind::Unwrap => self.word("unwrap_binder"),
+                }
+                self.popen();
+                self.ibox(0);
+                self.print_expr(expr, FixupContext::default());
+
+                if let Some(ty) = ty {
+                    self.word(",");
+                    self.space();
+                    self.print_type(ty);
+                }
+
+                self.end();
+                self.pclose();
+            }
             ast::ExprKind::Err(_) => {
                 self.popen();
                 self.word("/*ERROR*/");
diff --git a/compiler/rustc_builtin_macros/src/assert/context.rs b/compiler/rustc_builtin_macros/src/assert/context.rs
index 70fa4d00c0f3..eb07975d8afd 100644
--- a/compiler/rustc_builtin_macros/src/assert/context.rs
+++ b/compiler/rustc_builtin_macros/src/assert/context.rs
@@ -323,7 +323,8 @@ impl<'cx, 'a> Context<'cx, 'a> {
             | ExprKind::While(_, _, _)
             | ExprKind::Yeet(_)
             | ExprKind::Become(_)
-            | ExprKind::Yield(_) => {}
+            | ExprKind::Yield(_)
+            | ExprKind::UnsafeBinderCast(..) => {}
         }
     }
 
diff --git a/compiler/rustc_feature/src/unstable.rs b/compiler/rustc_feature/src/unstable.rs
index 93a605e197ce..84eab83eb207 100644
--- a/compiler/rustc_feature/src/unstable.rs
+++ b/compiler/rustc_feature/src/unstable.rs
@@ -635,6 +635,8 @@ declare_features! (
     /// Allows creation of instances of a struct by moving fields that have
     /// not changed from prior instances of the same struct (RFC #2528)
     (unstable, type_changing_struct_update, "1.58.0", Some(86555)),
+    /// Allows using `unsafe<'a> &'a T` unsafe binder types.
+    (incomplete, unsafe_binders, "CURRENT_RUSTC_VERSION", Some(130516)),
     /// Allows declaring fields `unsafe`.
     (incomplete, unsafe_fields, "CURRENT_RUSTC_VERSION", Some(132922)),
     /// Allows const generic parameters to be defined with types that
diff --git a/compiler/rustc_hir/src/hir.rs b/compiler/rustc_hir/src/hir.rs
index bd8e660f9f1d..51e637b57485 100644
--- a/compiler/rustc_hir/src/hir.rs
+++ b/compiler/rustc_hir/src/hir.rs
@@ -8,7 +8,7 @@ use rustc_ast::{
 };
 pub use rustc_ast::{
     BinOp, BinOpKind, BindingMode, BorrowKind, BoundConstness, BoundPolarity, ByRef, CaptureBy,
-    ImplPolarity, IsAuto, Movability, Mutability, UnOp,
+    ImplPolarity, IsAuto, Movability, Mutability, UnOp, UnsafeBinderCastKind,
 };
 use rustc_data_structures::fingerprint::Fingerprint;
 use rustc_data_structures::sorted_map::SortedMap;
@@ -1740,6 +1740,7 @@ impl Expr<'_> {
             | ExprKind::Struct(..)
             | ExprKind::Tup(_)
             | ExprKind::Type(..)
+            | ExprKind::UnsafeBinderCast(..)
             | ExprKind::Err(_) => ExprPrecedence::Unambiguous,
 
             ExprKind::DropTemps(ref expr, ..) => expr.precedence(),
@@ -1769,6 +1770,9 @@ impl Expr<'_> {
             // https://github.com/rust-lang/rfcs/blob/master/text/0803-type-ascription.md#type-ascription-and-temporaries
             ExprKind::Type(ref e, _) => e.is_place_expr(allow_projections_from),
 
+            // Unsafe binder cast preserves place-ness of the sub-expression.
+            ExprKind::UnsafeBinderCast(_, e, _) => e.is_place_expr(allow_projections_from),
+
             ExprKind::Unary(UnOp::Deref, _) => true,
 
             ExprKind::Field(ref base, _) | ExprKind::Index(ref base, _, _) => {
@@ -1850,7 +1854,8 @@ impl Expr<'_> {
             | ExprKind::Field(base, _)
             | ExprKind::Index(base, _, _)
             | ExprKind::AddrOf(.., base)
-            | ExprKind::Cast(base, _) => {
+            | ExprKind::Cast(base, _)
+            | ExprKind::UnsafeBinderCast(_, base, _) => {
                 // This isn't exactly true for `Index` and all `Unary`, but we are using this
                 // method exclusively for diagnostics and there's a *cultural* pressure against
                 // them being used only for its side-effects.
@@ -2144,6 +2149,10 @@ pub enum ExprKind<'hir> {
     /// A suspension point for coroutines (i.e., `yield <expr>`).
     Yield(&'hir Expr<'hir>, YieldSource),
 
+    /// Operators which can be used to interconvert `unsafe` binder types.
+    /// e.g. `unsafe<'a> &'a i32` <=> `&i32`.
+    UnsafeBinderCast(UnsafeBinderCastKind, &'hir Expr<'hir>, Option<&'hir Ty<'hir>>),
+
     /// A placeholder for an expression that wasn't syntactically well formed in some way.
     Err(rustc_span::ErrorGuaranteed),
 }
diff --git a/compiler/rustc_hir/src/intravisit.rs b/compiler/rustc_hir/src/intravisit.rs
index 2a49fcde2c09..482940eb5ca7 100644
--- a/compiler/rustc_hir/src/intravisit.rs
+++ b/compiler/rustc_hir/src/intravisit.rs
@@ -857,6 +857,10 @@ pub fn walk_expr<'v, V: Visitor<'v>>(visitor: &mut V, expression: &'v Expr<'v>)
         ExprKind::Yield(ref subexpression, _) => {
             try_visit!(visitor.visit_expr(subexpression));
         }
+        ExprKind::UnsafeBinderCast(_kind, expr, ty) => {
+            try_visit!(visitor.visit_expr(expr));
+            visit_opt!(visitor, visit_ty, ty);
+        }
         ExprKind::Lit(_) | ExprKind::Err(_) => {}
     }
     V::Result::output()
diff --git a/compiler/rustc_hir_pretty/src/lib.rs b/compiler/rustc_hir_pretty/src/lib.rs
index 5782e3e7d3cd..a17b6321ce83 100644
--- a/compiler/rustc_hir_pretty/src/lib.rs
+++ b/compiler/rustc_hir_pretty/src/lib.rs
@@ -1542,6 +1542,19 @@ impl<'a> State<'a> {
 
                 self.word(")");
             }
+            hir::ExprKind::UnsafeBinderCast(kind, expr, ty) => {
+                match kind {
+                    hir::UnsafeBinderCastKind::Wrap => self.word("wrap_binder!("),
+                    hir::UnsafeBinderCastKind::Unwrap => self.word("unwrap_binder!("),
+                }
+                self.print_expr(expr);
+                if let Some(ty) = ty {
+                    self.word(",");
+                    self.space();
+                    self.print_type(ty);
+                }
+                self.word(")");
+            }
             hir::ExprKind::Yield(expr, _) => {
                 self.word_space("yield");
                 self.print_expr_cond_paren(expr, expr.precedence() < ExprPrecedence::Jump);
diff --git a/compiler/rustc_hir_typeck/src/expr.rs b/compiler/rustc_hir_typeck/src/expr.rs
index 569038652777..65345048bfc2 100644
--- a/compiler/rustc_hir_typeck/src/expr.rs
+++ b/compiler/rustc_hir_typeck/src/expr.rs
@@ -329,6 +329,13 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                     // Assignment does call `drop_in_place`, though, but its safety
                     // requirements are not the same.
                     ExprKind::AddrOf(..) | hir::ExprKind::Field(..) => false,
+
+                    // Place-preserving expressions only constitute reads if their
+                    // parent expression constitutes a read.
+                    ExprKind::Type(..) | ExprKind::UnsafeBinderCast(..) => {
+                        self.expr_guaranteed_to_constitute_read_for_never(expr)
+                    }
+
                     ExprKind::Assign(lhs, _, _) => {
                         // Only the LHS does not constitute a read
                         expr.hir_id != lhs.hir_id
@@ -353,7 +360,6 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                     | ExprKind::Binary(_, _, _)
                     | ExprKind::Unary(_, _)
                     | ExprKind::Cast(_, _)
-                    | ExprKind::Type(_, _)
                     | ExprKind::DropTemps(_)
                     | ExprKind::If(_, _, _)
                     | ExprKind::Closure(_)
@@ -564,7 +570,10 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 self.check_expr_index(base, idx, expr, brackets_span)
             }
             ExprKind::Yield(value, _) => self.check_expr_yield(value, expr),
-            hir::ExprKind::Err(guar) => Ty::new_error(tcx, guar),
+            ExprKind::UnsafeBinderCast(kind, expr, ty) => {
+                self.check_expr_unsafe_binder_cast(kind, expr, ty, expected)
+            }
+            ExprKind::Err(guar) => Ty::new_error(tcx, guar),
         }
     }
 
@@ -1634,6 +1643,18 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         }
     }
 
+    fn check_expr_unsafe_binder_cast(
+        &self,
+        _kind: hir::UnsafeBinderCastKind,
+        expr: &'tcx hir::Expr<'tcx>,
+        _hir_ty: Option<&'tcx hir::Ty<'tcx>>,
+        _expected: Expectation<'tcx>,
+    ) -> Ty<'tcx> {
+        let guar =
+            self.dcx().struct_span_err(expr.span, "unsafe binders are not yet implemented").emit();
+        Ty::new_error(self.tcx, guar)
+    }
+
     fn check_expr_array(
         &self,
         args: &'tcx [hir::Expr<'tcx>],
diff --git a/compiler/rustc_hir_typeck/src/expr_use_visitor.rs b/compiler/rustc_hir_typeck/src/expr_use_visitor.rs
index 27ec2e9e0d48..ecbae6ac72fa 100644
--- a/compiler/rustc_hir_typeck/src/expr_use_visitor.rs
+++ b/compiler/rustc_hir_typeck/src/expr_use_visitor.rs
@@ -341,6 +341,10 @@ impl<'tcx, Cx: TypeInformationCtxt<'tcx>, D: Delegate<'tcx>> ExprUseVisitor<'tcx
                 self.walk_expr(subexpr)?;
             }
 
+            hir::ExprKind::UnsafeBinderCast(_, subexpr, _) => {
+                self.walk_expr(subexpr)?;
+            }
+
             hir::ExprKind::Unary(hir::UnOp::Deref, base) => {
                 // *base
                 self.walk_expr(base)?;
@@ -1360,7 +1364,10 @@ impl<'tcx, Cx: TypeInformationCtxt<'tcx>, D: Delegate<'tcx>> ExprUseVisitor<'tcx
                 self.cat_res(expr.hir_id, expr.span, expr_ty, res)
             }
 
+            // both type ascription and unsafe binder casts don't affect
+            // the place-ness of the subexpression.
             hir::ExprKind::Type(e, _) => self.cat_expr(e),
+            hir::ExprKind::UnsafeBinderCast(_, e, _) => self.cat_expr(e),
 
             hir::ExprKind::AddrOf(..)
             | hir::ExprKind::Call(..)
diff --git a/compiler/rustc_lint/src/dangling.rs b/compiler/rustc_lint/src/dangling.rs
index 7e298a9a63c7..10769b57a766 100644
--- a/compiler/rustc_lint/src/dangling.rs
+++ b/compiler/rustc_lint/src/dangling.rs
@@ -192,6 +192,8 @@ fn is_temporary_rvalue(expr: &Expr<'_>) -> bool {
         | ExprKind::DropTemps(..)
         | ExprKind::Let(..) => false,
 
+        ExprKind::UnsafeBinderCast(..) => false,
+
         // Not applicable
         ExprKind::Type(..) | ExprKind::Err(..) => false,
     }
diff --git a/compiler/rustc_lint/src/if_let_rescope.rs b/compiler/rustc_lint/src/if_let_rescope.rs
index 2db229ed133f..1402129195f6 100644
--- a/compiler/rustc_lint/src/if_let_rescope.rs
+++ b/compiler/rustc_lint/src/if_let_rescope.rs
@@ -422,6 +422,7 @@ impl<'tcx, 'a> Visitor<'tcx> for FindSignificantDropper<'tcx, 'a> {
             hir::ExprKind::Unary(_, expr)
             | hir::ExprKind::Cast(expr, _)
             | hir::ExprKind::Type(expr, _)
+            | hir::ExprKind::UnsafeBinderCast(_, expr, _)
             | hir::ExprKind::Yield(expr, _)
             | hir::ExprKind::AddrOf(_, _, expr)
             | hir::ExprKind::Match(expr, _, _)
diff --git a/compiler/rustc_mir_build/src/thir/cx/expr.rs b/compiler/rustc_mir_build/src/thir/cx/expr.rs
index d75f01dfba09..3cbf1e2055c9 100644
--- a/compiler/rustc_mir_build/src/thir/cx/expr.rs
+++ b/compiler/rustc_mir_build/src/thir/cx/expr.rs
@@ -915,6 +915,11 @@ impl<'tcx> Cx<'tcx> {
                     }
                 }
             }
+
+            hir::ExprKind::UnsafeBinderCast(_kind, _source, _ty) => {
+                unreachable!("unsafe binders are not yet implemented")
+            }
+
             hir::ExprKind::DropTemps(source) => ExprKind::Use { source: self.mirror_expr(source) },
             hir::ExprKind::Array(fields) => ExprKind::Array { fields: self.mirror_exprs(fields) },
             hir::ExprKind::Tup(fields) => ExprKind::Tuple { fields: self.mirror_exprs(fields) },
diff --git a/compiler/rustc_parse/src/parser/expr.rs b/compiler/rustc_parse/src/parser/expr.rs
index 0904a42d8a43..4f2e7f466056 100644
--- a/compiler/rustc_parse/src/parser/expr.rs
+++ b/compiler/rustc_parse/src/parser/expr.rs
@@ -15,7 +15,7 @@ use rustc_ast::visit::{Visitor, walk_expr};
 use rustc_ast::{
     self as ast, AnonConst, Arm, AttrStyle, AttrVec, BinOp, BinOpKind, BlockCheckMode, CaptureBy,
     ClosureBinder, DUMMY_NODE_ID, Expr, ExprField, ExprKind, FnDecl, FnRetTy, Label, MacCall,
-    MetaItemLit, Movability, Param, RangeLimits, StmtKind, Ty, TyKind, UnOp,
+    MetaItemLit, Movability, Param, RangeLimits, StmtKind, Ty, TyKind, UnOp, UnsafeBinderCastKind,
 };
 use rustc_ast_pretty::pprust;
 use rustc_data_structures::stack::ensure_sufficient_stack;
@@ -1931,6 +1931,12 @@ impl<'a> Parser<'a> {
             Ok(match ident.name {
                 sym::offset_of => Some(this.parse_expr_offset_of(lo)?),
                 sym::type_ascribe => Some(this.parse_expr_type_ascribe(lo)?),
+                sym::wrap_binder => {
+                    Some(this.parse_expr_unsafe_binder_cast(lo, UnsafeBinderCastKind::Wrap)?)
+                }
+                sym::unwrap_binder => {
+                    Some(this.parse_expr_unsafe_binder_cast(lo, UnsafeBinderCastKind::Unwrap)?)
+                }
                 _ => None,
             })
         })
@@ -2006,6 +2012,17 @@ impl<'a> Parser<'a> {
         Ok(self.mk_expr(span, ExprKind::Type(expr, ty)))
     }
 
+    pub(crate) fn parse_expr_unsafe_binder_cast(
+        &mut self,
+        lo: Span,
+        kind: UnsafeBinderCastKind,
+    ) -> PResult<'a, P<Expr>> {
+        let expr = self.parse_expr()?;
+        let ty = if self.eat(&TokenKind::Comma) { Some(self.parse_ty()?) } else { None };
+        let span = lo.to(self.token.span);
+        Ok(self.mk_expr(span, ExprKind::UnsafeBinderCast(kind, expr, ty)))
+    }
+
     /// Returns a string literal if the next token is a string literal.
     /// In case of error returns `Some(lit)` if the next token is a literal with a wrong kind,
     /// and returns `None` if the next token is not literal at all.
@@ -4019,7 +4036,9 @@ impl MutVisitor for CondChecker<'_> {
                 mut_visit::walk_expr(self, e);
                 self.forbid_let_reason = forbid_let_reason;
             }
-            ExprKind::Cast(ref mut op, _) | ExprKind::Type(ref mut op, _) => {
+            ExprKind::Cast(ref mut op, _)
+            | ExprKind::Type(ref mut op, _)
+            | ExprKind::UnsafeBinderCast(_, ref mut op, _) => {
                 let forbid_let_reason = self.forbid_let_reason;
                 self.forbid_let_reason = Some(OtherForbidden);
                 self.visit_expr(op);
diff --git a/compiler/rustc_passes/src/input_stats.rs b/compiler/rustc_passes/src/input_stats.rs
index d5e6ca491aef..164cbc69595b 100644
--- a/compiler/rustc_passes/src/input_stats.rs
+++ b/compiler/rustc_passes/src/input_stats.rs
@@ -315,9 +315,40 @@ impl<'v> hir_visit::Visitor<'v> for StatCollector<'v> {
 
     fn visit_expr(&mut self, e: &'v hir::Expr<'v>) {
         record_variants!((self, e, e.kind, Some(e.hir_id), hir, Expr, ExprKind), [
-            ConstBlock, Array, Call, MethodCall, Tup, Binary, Unary, Lit, Cast, Type, DropTemps,
-            Let, If, Loop, Match, Closure, Block, Assign, AssignOp, Field, Index, Path, AddrOf,
-            Break, Continue, Ret, Become, InlineAsm, OffsetOf, Struct, Repeat, Yield, Err
+            ConstBlock,
+            Array,
+            Call,
+            MethodCall,
+            Tup,
+            Binary,
+            Unary,
+            Lit,
+            Cast,
+            Type,
+            DropTemps,
+            Let,
+            If,
+            Loop,
+            Match,
+            Closure,
+            Block,
+            Assign,
+            AssignOp,
+            Field,
+            Index,
+            Path,
+            AddrOf,
+            Break,
+            Continue,
+            Ret,
+            Become,
+            InlineAsm,
+            OffsetOf,
+            Struct,
+            Repeat,
+            Yield,
+            UnsafeBinderCast,
+            Err
         ]);
         hir_visit::walk_expr(self, e)
     }
@@ -572,7 +603,7 @@ impl<'v> ast_visit::Visitor<'v> for StatCollector<'v> {
                 If, While, ForLoop, Loop, Match, Closure, Block, Await, TryBlock, Assign,
                 AssignOp, Field, Index, Range, Underscore, Path, AddrOf, Break, Continue, Ret,
                 InlineAsm, FormatArgs, OffsetOf, MacCall, Struct, Repeat, Paren, Try, Yield, Yeet,
-                Become, IncludedBytes, Gen, Err, Dummy
+                Become, IncludedBytes, Gen, UnsafeBinderCast, Err, Dummy
             ]
         );
         ast_visit::walk_expr(self, e)
diff --git a/compiler/rustc_passes/src/liveness.rs b/compiler/rustc_passes/src/liveness.rs
index 09cbb648f9b1..034f7308c4a8 100644
--- a/compiler/rustc_passes/src/liveness.rs
+++ b/compiler/rustc_passes/src/liveness.rs
@@ -447,6 +447,7 @@ impl<'tcx> Visitor<'tcx> for IrMaps<'tcx> {
             | hir::ExprKind::InlineAsm(..)
             | hir::ExprKind::OffsetOf(..)
             | hir::ExprKind::Type(..)
+            | hir::ExprKind::UnsafeBinderCast(..)
             | hir::ExprKind::Err(_)
             | hir::ExprKind::Path(hir::QPath::TypeRelative(..))
             | hir::ExprKind::Path(hir::QPath::LangItem(..)) => {}
@@ -1051,6 +1052,7 @@ impl<'a, 'tcx> Liveness<'a, 'tcx> {
             hir::ExprKind::AddrOf(_, _, ref e)
             | hir::ExprKind::Cast(ref e, _)
             | hir::ExprKind::Type(ref e, _)
+            | hir::ExprKind::UnsafeBinderCast(_, ref e, _)
             | hir::ExprKind::DropTemps(ref e)
             | hir::ExprKind::Unary(_, ref e)
             | hir::ExprKind::Repeat(ref e, _) => self.propagate_through_expr(e, succ),
@@ -1443,6 +1445,7 @@ fn check_expr<'tcx>(this: &mut Liveness<'_, 'tcx>, expr: &'tcx Expr<'tcx>) {
         | hir::ExprKind::Path(_)
         | hir::ExprKind::Yield(..)
         | hir::ExprKind::Type(..)
+        | hir::ExprKind::UnsafeBinderCast(..)
         | hir::ExprKind::Err(_) => {}
     }
 }
diff --git a/compiler/rustc_passes/src/naked_functions.rs b/compiler/rustc_passes/src/naked_functions.rs
index b2f8d7dadff3..766a9e1bdade 100644
--- a/compiler/rustc_passes/src/naked_functions.rs
+++ b/compiler/rustc_passes/src/naked_functions.rs
@@ -186,6 +186,7 @@ impl CheckInlineAssembly {
             | ExprKind::Lit(..)
             | ExprKind::Cast(..)
             | ExprKind::Type(..)
+            | ExprKind::UnsafeBinderCast(..)
             | ExprKind::Loop(..)
             | ExprKind::Match(..)
             | ExprKind::If(..)
diff --git a/compiler/rustc_span/src/symbol.rs b/compiler/rustc_span/src/symbol.rs
index d30b17c9cd8d..99d73c3e4dea 100644
--- a/compiler/rustc_span/src/symbol.rs
+++ b/compiler/rustc_span/src/symbol.rs
@@ -2104,6 +2104,7 @@ symbols! {
         unreachable_macro,
         unrestricted_attribute_tokens,
         unsafe_attributes,
+        unsafe_binders,
         unsafe_block_in_unsafe_fn,
         unsafe_cell,
         unsafe_cell_raw_get,
@@ -2127,6 +2128,7 @@ symbols! {
         unwind_attributes,
         unwind_safe_trait,
         unwrap,
+        unwrap_binder,
         unwrap_or,
         use_extern_macros,
         use_nested_groups,
@@ -2185,6 +2187,7 @@ symbols! {
         windows,
         windows_subsystem,
         with_negative_coherence,
+        wrap_binder,
         wrapping_add,
         wrapping_div,
         wrapping_mul,
diff --git a/library/core/src/lib.rs b/library/core/src/lib.rs
index fde6887c5aba..d45cb01910f6 100644
--- a/library/core/src/lib.rs
+++ b/library/core/src/lib.rs
@@ -354,6 +354,8 @@ pub mod random;
 pub mod range;
 pub mod result;
 pub mod sync;
+#[unstable(feature = "unsafe_binders", issue = "130516")]
+pub mod unsafe_binder;
 
 pub mod fmt;
 pub mod hash;
diff --git a/library/core/src/unsafe_binder.rs b/library/core/src/unsafe_binder.rs
new file mode 100644
index 000000000000..98f53e07d9d8
--- /dev/null
+++ b/library/core/src/unsafe_binder.rs
@@ -0,0 +1,25 @@
+//! Operators used to turn types into unsafe binders and back.
+
+/// Unwrap an unsafe binder into its underlying type.
+#[allow_internal_unstable(builtin_syntax)]
+#[unstable(feature = "unsafe_binders", issue = "130516")]
+pub macro unwrap_binder {
+    ($expr:expr) => {
+        builtin # unwrap_binder ( $expr )
+    },
+    ($expr:expr ; $ty:ty) => {
+        builtin # unwrap_binder ( $expr, $ty )
+    },
+}
+
+/// Wrap a type into an unsafe binder.
+#[allow_internal_unstable(builtin_syntax)]
+#[unstable(feature = "unsafe_binders", issue = "130516")]
+pub macro wrap_binder {
+    ($expr:expr) => {
+        builtin # wrap_binder ( $expr )
+    },
+    ($expr:expr ; $ty:ty) => {
+        builtin # wrap_binder ( $expr, $ty )
+    },
+}
diff --git a/library/std/src/lib.rs b/library/std/src/lib.rs
index 047f5b0c4c58..1cbf51463ea8 100644
--- a/library/std/src/lib.rs
+++ b/library/std/src/lib.rs
@@ -544,6 +544,8 @@ pub use core::u64;
 #[stable(feature = "i128", since = "1.26.0")]
 #[allow(deprecated, deprecated_in_future)]
 pub use core::u128;
+#[unstable(feature = "unsafe_binders", issue = "130516")]
+pub use core::unsafe_binder;
 #[stable(feature = "rust1", since = "1.0.0")]
 #[allow(deprecated, deprecated_in_future)]
 pub use core::usize;