Rollup merge of #149667 - Shinonn23:fix-ice-constblock-148138, r=dianne

Fix ICE by rejecting const blocks in patterns during AST lowering (closes #148138)

This PR fixes the ICE reported in rust-lang/rust#148138.

The root cause is that `const` blocks aren’t allowed in pattern position, but the AST lowering logic still attempted to create `PatExprKind::ConstBlock`, allowing invalid HIR to reach type checking and trigger a `span_bug!`.

Following the discussion in the issue, this patch removes the `ConstBlock` lowering path from `lower_expr_within_pat`. Any `ExprKind::ConstBlock` inside a pattern is now handled consistently with other invalid pattern expressions.

A new UI test is included to ensure the compiler reports a proper error and to prevent regressions.

Closes rust-lang/rust#148138.

compiler/rustc_ast_lowering/messages.ftl

@@ -6,6 +6,7 @@ ast_lowering_abi_specified_multiple_times =
 ast_lowering_arbitrary_expression_in_pattern =
     arbitrary expressions aren't allowed in patterns
     .pattern_from_macro_note = the `expr` fragment specifier forces the metavariable's content to be an expression
+    .const_block_in_pattern_help = use a named `const`-item or an `if`-guard (`x if x == const {"{ ... }"}`) instead
 
 ast_lowering_argument = argument
 

compiler/rustc_ast_lowering/src/errors.rs

@@ -357,6 +357,8 @@ pub(crate) struct ArbitraryExpressionInPattern {
     pub span: Span,
     #[note(ast_lowering_pattern_from_macro_note)]
     pub pattern_from_macro_note: bool,
+    #[help(ast_lowering_const_block_in_pattern_help)]
+    pub const_block_in_pattern_help: bool,
 }
 
 #[derive(Diagnostic)]

compiler/rustc_ast_lowering/src/pat.rs

@@ -399,7 +399,6 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
             ExprKind::Lit(lit) => {
                 hir::PatExprKind::Lit { lit: self.lower_lit(lit, span), negated: false }
             }
-            ExprKind::ConstBlock(c) => hir::PatExprKind::ConstBlock(self.lower_const_block(c)),
             ExprKind::IncludedBytes(byte_sym) => hir::PatExprKind::Lit {
                 lit: respan(span, LitKind::ByteStr(*byte_sym, StrStyle::Cooked)),
                 negated: false,
@@ -419,10 +418,12 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                 hir::PatExprKind::Lit { lit: self.lower_lit(lit, span), negated: true }
             }
             _ => {
+                let is_const_block = matches!(expr.kind, ExprKind::ConstBlock(_));
                 let pattern_from_macro = expr.is_approximately_pattern();
                 let guar = self.dcx().emit_err(ArbitraryExpressionInPattern {
                     span,
                     pattern_from_macro_note: pattern_from_macro,
+                    const_block_in_pattern_help: is_const_block,
                 });
                 err(guar)
             }

compiler/rustc_hir/src/hir.rs

@@ -1944,7 +1944,6 @@ pub enum PatExprKind<'hir> {
         // once instead of matching on unop neg expressions everywhere.
         negated: bool,
     },
-    ConstBlock(ConstBlock),
     /// A path pattern for a unit struct/variant or a (maybe-associated) constant.
     Path(QPath<'hir>),
 }

compiler/rustc_hir/src/intravisit.rs

@@ -792,7 +792,6 @@ pub fn walk_pat_expr<'v, V: Visitor<'v>>(visitor: &mut V, expr: &'v PatExpr<'v>)
     try_visit!(visitor.visit_id(*hir_id));
     match kind {
         PatExprKind::Lit { lit, negated } => visitor.visit_lit(*hir_id, *lit, *negated),
-        PatExprKind::ConstBlock(c) => visitor.visit_inline_const(c),
         PatExprKind::Path(qpath) => visitor.visit_qpath(qpath, *hir_id, *span),
     }
 }

compiler/rustc_hir_pretty/src/lib.rs

@@ -1880,7 +1880,6 @@ impl<'a> State<'a> {
                 }
                 self.print_literal(lit);
             }
-            hir::PatExprKind::ConstBlock(c) => self.print_inline_const(c),
             hir::PatExprKind::Path(qpath) => self.print_qpath(qpath, true),
         }
     }

compiler/rustc_hir_typeck/src/pat.rs

@@ -925,9 +925,6 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 }
                 ty
             }
-            rustc_hir::PatExprKind::ConstBlock(c) => {
-                self.check_expr_const_block(c, Expectation::NoExpectation)
-            }
             rustc_hir::PatExprKind::Path(qpath) => {
                 let (res, opt_ty, segments) =
                     self.resolve_ty_and_res_fully_qualified_call(qpath, lt.hir_id, lt.span);

compiler/rustc_mir_build/src/thir/pattern/mod.rs

@@ -13,14 +13,13 @@ use rustc_hir::def::{CtorOf, DefKind, Res};
 use rustc_hir::pat_util::EnumerateAndAdjustIterator;
 use rustc_hir::{self as hir, LangItem, RangeEnd};
 use rustc_index::Idx;
-use rustc_infer::infer::TyCtxtInferExt;
 use rustc_middle::mir::interpret::LitToConstInput;
 use rustc_middle::thir::{
     Ascription, DerefPatBorrowMode, FieldPat, LocalVarId, Pat, PatKind, PatRange, PatRangeBoundary,
 };
 use rustc_middle::ty::adjustment::{PatAdjust, PatAdjustment};
 use rustc_middle::ty::layout::IntegerExt;
-use rustc_middle::ty::{self, CanonicalUserTypeAnnotation, Ty, TyCtxt, TypingMode};
+use rustc_middle::ty::{self, CanonicalUserTypeAnnotation, Ty, TyCtxt};
 use rustc_middle::{bug, span_bug};
 use rustc_span::def_id::DefId;
 use rustc_span::{ErrorGuaranteed, Span};
@@ -613,54 +612,8 @@ impl<'tcx> PatCtxt<'tcx> {
         pattern
     }
 
-    /// Lowers an inline const block (e.g. `const { 1 + 1 }`) to a pattern.
-    fn lower_inline_const(
-        &mut self,
-        block: &'tcx hir::ConstBlock,
-        id: hir::HirId,
-        span: Span,
-    ) -> PatKind<'tcx> {
-        let tcx = self.tcx;
-        let def_id = block.def_id;
-        let ty = tcx.typeck(def_id).node_type(block.hir_id);
-
-        let typeck_root_def_id = tcx.typeck_root_def_id(def_id.to_def_id());
-        let parent_args = ty::GenericArgs::identity_for_item(tcx, typeck_root_def_id);
-        let args = ty::InlineConstArgs::new(tcx, ty::InlineConstArgsParts { parent_args, ty }).args;
-
-        let ct = ty::UnevaluatedConst { def: def_id.to_def_id(), args };
-        let c = ty::Const::new_unevaluated(self.tcx, ct);
-        let pattern = self.const_to_pat(c, ty, id, span);
-
-        // Apply a type ascription for the inline constant.
-        let annotation = {
-            let infcx = tcx.infer_ctxt().build(TypingMode::non_body_analysis());
-            let args = ty::InlineConstArgs::new(
-                tcx,
-                ty::InlineConstArgsParts { parent_args, ty: infcx.next_ty_var(span) },
-            )
-            .args;
-            infcx.canonicalize_user_type_annotation(ty::UserType::new(ty::UserTypeKind::TypeOf(
-                def_id.to_def_id(),
-                ty::UserArgs { args, user_self_ty: None },
-            )))
-        };
-        let annotation =
-            CanonicalUserTypeAnnotation { user_ty: Box::new(annotation), span, inferred_ty: ty };
-        PatKind::AscribeUserType {
-            subpattern: pattern,
-            ascription: Ascription {
-                annotation,
-                // Note that we use `Contravariant` here. See the `variance` field documentation
-                // for details.
-                variance: ty::Contravariant,
-            },
-        }
-    }
-
     /// Lowers the kinds of "expression" that can appear in a HIR pattern:
     /// - Paths (e.g. `FOO`, `foo::BAR`, `Option::None`)
-    /// - Inline const blocks (e.g. `const { 1 + 1 }`)
     /// - Literals, possibly negated (e.g. `-128u8`, `"hello"`)
     fn lower_pat_expr(
         &mut self,
@@ -669,9 +622,6 @@ impl<'tcx> PatCtxt<'tcx> {
     ) -> PatKind<'tcx> {
         match &expr.kind {
             hir::PatExprKind::Path(qpath) => self.lower_path(qpath, expr.hir_id, expr.span).kind,
-            hir::PatExprKind::ConstBlock(anon_const) => {
-                self.lower_inline_const(anon_const, expr.hir_id, expr.span)
-            }
             hir::PatExprKind::Lit { lit, negated } => {
                 // We handle byte string literal patterns by using the pattern's type instead of the
                 // literal's type in `const_to_pat`: if the literal `b"..."` matches on a slice reference,

compiler/rustc_parse/src/parser/expr.rs

@@ -1521,7 +1521,7 @@ impl<'a> Parser<'a> {
                     },
                 )
             } else if this.check_inline_const(0) {
-                this.parse_const_block(lo, false)
+                this.parse_const_block(lo)
             } else if this.may_recover() && this.is_do_catch_block() {
                 this.recover_do_catch()
             } else if this.is_try_block() {

compiler/rustc_parse/src/parser/mod.rs

@@ -1317,7 +1317,7 @@ impl<'a> Parser<'a> {
     }
 
     /// Parses inline const expressions.
-    fn parse_const_block(&mut self, span: Span, pat: bool) -> PResult<'a, Box<Expr>> {
+    fn parse_const_block(&mut self, span: Span) -> PResult<'a, Box<Expr>> {
         self.expect_keyword(exp!(Const))?;
         let (attrs, blk) = self.parse_inner_attrs_and_block(None)?;
         let anon_const = AnonConst {
@@ -1326,18 +1326,7 @@ impl<'a> Parser<'a> {
             mgca_disambiguation: MgcaDisambiguation::AnonConst,
         };
         let blk_span = anon_const.value.span;
-        let kind = if pat {
-            let guar = self
-                .dcx()
-                .struct_span_err(blk_span, "const blocks cannot be used as patterns")
-                .with_help(
-                    "use a named `const`-item or an `if`-guard (`x if x == const { ... }`) instead",
-                )
-                .emit();
-            ExprKind::Err(guar)
-        } else {
-            ExprKind::ConstBlock(anon_const)
-        };
+        let kind = ExprKind::ConstBlock(anon_const);
         Ok(self.mk_expr_with_attrs(span.to(blk_span), kind, attrs))
     }
 

compiler/rustc_parse/src/parser/pat.rs

@@ -785,8 +785,10 @@ impl<'a> Parser<'a> {
         } else if self.eat_keyword(exp!(Box)) {
             self.parse_pat_box()?
         } else if self.check_inline_const(0) {
-            // Parse `const pat`
-            let const_expr = self.parse_const_block(lo.to(self.token.span), true)?;
+            // Parse `const pat`.
+            // NOTE: This will always error later during AST lowering because
+            // inline const cannot be used as patterns.
+            let const_expr = self.parse_const_block(lo.to(self.token.span))?;
 
             if let Some(re) = self.parse_range_end() {
                 self.parse_pat_range_begin_with(const_expr, re)?
@@ -1281,7 +1283,7 @@ impl<'a> Parser<'a> {
             .then_some(self.prev_token.span);
 
         let bound = if self.check_inline_const(0) {
-            self.parse_const_block(self.token.span, true)
+            self.parse_const_block(self.token.span)
         } else if self.check_path() {
             let lo = self.token.span;
             let (qself, path) = if self.eat_lt() {

src/tools/clippy/clippy_lints/src/utils/author.rs

@@ -724,7 +724,6 @@ impl<'a, 'tcx> PrintVisitor<'a, 'tcx> {
                 kind!("Lit {{ ref {lit}, {negated} }}");
                 self.lit(lit);
             },
-            PatExprKind::ConstBlock(_) => kind!("ConstBlock(_)"),
             PatExprKind::Path(_) => self.maybe_path(pat),
         }
     }

src/tools/clippy/clippy_utils/src/consts.rs

@@ -578,7 +578,6 @@ impl<'tcx> ConstEvalCtxt<'tcx> {
                     Some(val)
                 }
             },
-            PatExprKind::ConstBlock(ConstBlock { body, .. }) => self.expr(self.tcx.hir_body(*body).value),
             PatExprKind::Path(qpath) => self.qpath(qpath, pat_expr.hir_id),
         }
     }

src/tools/clippy/clippy_utils/src/hir_utils.rs

@@ -705,9 +705,8 @@ impl HirEqInterExpr<'_, '_, '_> {
                     negated: right_neg,
                 },
             ) => left_neg == right_neg && left.node == right.node,
-            (PatExprKind::ConstBlock(left), PatExprKind::ConstBlock(right)) => self.eq_body(left.body, right.body),
             (PatExprKind::Path(left), PatExprKind::Path(right)) => self.eq_qpath(left, right),
-            (PatExprKind::Lit { .. } | PatExprKind::ConstBlock(..) | PatExprKind::Path(..), _) => false,
+            (PatExprKind::Lit { .. } | PatExprKind::Path(..), _) => false,
         }
     }
 
@@ -1312,7 +1311,6 @@ impl<'a, 'tcx> SpanlessHash<'a, 'tcx> {
                 lit.node.hash(&mut self.s);
                 negated.hash(&mut self.s);
             },
-            PatExprKind::ConstBlock(c) => self.hash_body(c.body),
             PatExprKind::Path(qpath) => self.hash_qpath(qpath),
         }
     }

tests/ui/inline-const/in-pat-recovery.rs

@@ -4,8 +4,63 @@
 fn main() {
     match 1 {
         const { 1 + 7 } => {}
-        //~^ ERROR const blocks cannot be used as patterns
+        //~^ ERROR arbitrary expressions aren't allowed in patterns
         2 => {}
         _ => {}
     }
+
+    match 5 {
+        const { 1 } ..= 10 => {}
+        //~^ ERROR arbitrary expressions aren't allowed in patterns
+        _ => {}
+    }
+
+    match 5 {
+        1 ..= const { 10 } => {}
+        //~^ ERROR arbitrary expressions aren't allowed in patterns
+        _ => {}
+    }
+
+    match 5 {
+        const { 1 } ..= const { 10 } => {}
+        //~^ ERROR arbitrary expressions aren't allowed in patterns
+        //~| ERROR arbitrary expressions aren't allowed in patterns
+        _ => {}
+    }
+
+    match 5 {
+        const { 1 } .. 10 => {}
+        //~^ ERROR arbitrary expressions aren't allowed in patterns
+        _ => {}
+    }
+
+    match 5 {
+        1 .. const { 10 } => {}
+        //~^ ERROR arbitrary expressions aren't allowed in patterns
+        _ => {}
+    }
+
+    match 5 {
+        const { 1 + 2 } ..= 10 => {}
+        //~^ ERROR arbitrary expressions aren't allowed in patterns
+        _ => {}
+    }
+
+    match 5 {
+        1 ..= const { 5 + 5 } => {}
+        //~^ ERROR arbitrary expressions aren't allowed in patterns
+        _ => {}
+    }
+
+    match 5 {
+        const { 3 } .. => {}
+        //~^ ERROR arbitrary expressions aren't allowed in patterns
+        _ => {}
+    }
+
+    match 5 {
+        ..= const { 7 } => {}
+        //~^ ERROR arbitrary expressions aren't allowed in patterns
+        _ => {}
+    }
 }

tests/ui/inline-const/in-pat-recovery.stderr

@@ -1,10 +1,90 @@
-error: const blocks cannot be used as patterns
-  --> $DIR/in-pat-recovery.rs:6:15
+error: arbitrary expressions aren't allowed in patterns
+  --> $DIR/in-pat-recovery.rs:6:9
    |
 LL |         const { 1 + 7 } => {}
-   |               ^^^^^^^^^
+   |         ^^^^^^^^^^^^^^^
    |
    = help: use a named `const`-item or an `if`-guard (`x if x == const { ... }`) instead
 
-error: aborting due to 1 previous error
+error: arbitrary expressions aren't allowed in patterns
+  --> $DIR/in-pat-recovery.rs:13:9
+   |
+LL |         const { 1 } ..= 10 => {}
+   |         ^^^^^^^^^^^
+   |
+   = help: use a named `const`-item or an `if`-guard (`x if x == const { ... }`) instead
+
+error: arbitrary expressions aren't allowed in patterns
+  --> $DIR/in-pat-recovery.rs:19:15
+   |
+LL |         1 ..= const { 10 } => {}
+   |               ^^^^^^^^^^^^
+   |
+   = help: use a named `const`-item or an `if`-guard (`x if x == const { ... }`) instead
+
+error: arbitrary expressions aren't allowed in patterns
+  --> $DIR/in-pat-recovery.rs:25:9
+   |
+LL |         const { 1 } ..= const { 10 } => {}
+   |         ^^^^^^^^^^^
+   |
+   = help: use a named `const`-item or an `if`-guard (`x if x == const { ... }`) instead
+
+error: arbitrary expressions aren't allowed in patterns
+  --> $DIR/in-pat-recovery.rs:25:25
+   |
+LL |         const { 1 } ..= const { 10 } => {}
+   |                         ^^^^^^^^^^^^
+   |
+   = help: use a named `const`-item or an `if`-guard (`x if x == const { ... }`) instead
+
+error: arbitrary expressions aren't allowed in patterns
+  --> $DIR/in-pat-recovery.rs:32:9
+   |
+LL |         const { 1 } .. 10 => {}
+   |         ^^^^^^^^^^^
+   |
+   = help: use a named `const`-item or an `if`-guard (`x if x == const { ... }`) instead
+
+error: arbitrary expressions aren't allowed in patterns
+  --> $DIR/in-pat-recovery.rs:38:14
+   |
+LL |         1 .. const { 10 } => {}
+   |              ^^^^^^^^^^^^
+   |
+   = help: use a named `const`-item or an `if`-guard (`x if x == const { ... }`) instead
+
+error: arbitrary expressions aren't allowed in patterns
+  --> $DIR/in-pat-recovery.rs:44:9
+   |
+LL |         const { 1 + 2 } ..= 10 => {}
+   |         ^^^^^^^^^^^^^^^
+   |
+   = help: use a named `const`-item or an `if`-guard (`x if x == const { ... }`) instead
+
+error: arbitrary expressions aren't allowed in patterns
+  --> $DIR/in-pat-recovery.rs:50:15
+   |
+LL |         1 ..= const { 5 + 5 } => {}
+   |               ^^^^^^^^^^^^^^^
+   |
+   = help: use a named `const`-item or an `if`-guard (`x if x == const { ... }`) instead
+
+error: arbitrary expressions aren't allowed in patterns
+  --> $DIR/in-pat-recovery.rs:56:9
+   |
+LL |         const { 3 } .. => {}
+   |         ^^^^^^^^^^^
+   |
+   = help: use a named `const`-item or an `if`-guard (`x if x == const { ... }`) instead
+
+error: arbitrary expressions aren't allowed in patterns
+  --> $DIR/in-pat-recovery.rs:62:13
+   |
+LL |         ..= const { 7 } => {}
+   |             ^^^^^^^^^^^
+   |
+   = help: use a named `const`-item or an `if`-guard (`x if x == const { ... }`) instead
+
+error: aborting due to 11 previous errors
 

tests/ui/pattern/deref-patterns/ice-adjust-mode-unimplemented-for-constblock.rs

@@ -0,0 +1,10 @@
+#![feature(deref_patterns)]
+#![expect(incomplete_features)]
+
+fn main() {
+    let vec![const { vec![] }]: Vec<usize> = vec![];
+    //~^ ERROR expected a pattern, found a function call
+    //~| ERROR usage of qualified paths in this context is experimental
+    //~| ERROR expected tuple struct or tuple variant
+    //~| ERROR arbitrary expressions aren't allowed in patterns
+}

tests/ui/pattern/deref-patterns/ice-adjust-mode-unimplemented-for-constblock.stderr

@@ -0,0 +1,41 @@
+error[E0532]: expected a pattern, found a function call
+  --> $DIR/ice-adjust-mode-unimplemented-for-constblock.rs:5:9
+   |
+LL |     let vec![const { vec![] }]: Vec<usize> = vec![];
+   |         ^^^^^^^^^^^^^^^^^^^^^^ not a tuple struct or tuple variant
+   |
+   = note: function calls are not allowed in patterns: <https://doc.rust-lang.org/book/ch19-00-patterns.html>
+   = note: this error originates in the macro `vec` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0658]: usage of qualified paths in this context is experimental
+  --> $DIR/ice-adjust-mode-unimplemented-for-constblock.rs:5:9
+   |
+LL |     let vec![const { vec![] }]: Vec<usize> = vec![];
+   |         ^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #86935 <https://github.com/rust-lang/rust/issues/86935> for more information
+   = help: add `#![feature(more_qualified_paths)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+   = note: this error originates in the macro `vec` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error: arbitrary expressions aren't allowed in patterns
+  --> $DIR/ice-adjust-mode-unimplemented-for-constblock.rs:5:14
+   |
+LL |     let vec![const { vec![] }]: Vec<usize> = vec![];
+   |              ^^^^^^^^^^^^^^^^
+   |
+   = help: use a named `const`-item or an `if`-guard (`x if x == const { ... }`) instead
+
+error[E0164]: expected tuple struct or tuple variant, found associated function `<[_]>::into_vec`
+  --> $DIR/ice-adjust-mode-unimplemented-for-constblock.rs:5:9
+   |
+LL |     let vec![const { vec![] }]: Vec<usize> = vec![];
+   |         ^^^^^^^^^^^^^^^^^^^^^^ `fn` calls are not allowed in patterns
+   |
+   = help: for more information, visit https://doc.rust-lang.org/book/ch19-00-patterns.html
+   = note: this error originates in the macro `vec` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error: aborting due to 4 previous errors
+
+Some errors have detailed explanations: E0164, E0532, E0658.
+For more information about an error, try `rustc --explain E0164`.