Detect bare blocks with type ascription that were meant to be a `struct` literal

Address part of #34255.

Potential improvement: silence the other knock down errors in
`issue-34255-1.rs`.

2 files changed, 9 insertions, 1 deletions

diff --git a/compiler/rustc_ast/src/ast.rs b/compiler/rustc_ast/src/ast.rs
index 0632d937c4c..5e154805644 100644
--- a/compiler/rustc_ast/src/ast.rs
+++ b/compiler/rustc_ast/src/ast.rs
@@ -565,6 +565,14 @@ pub struct Block {
     pub rules: BlockCheckMode,
     pub span: Span,
     pub tokens: Option<LazyTokenStream>,
+    /// The following *isn't* a parse error, but will cause multiple errors in following stages.
+    /// ```
+    /// let x = {
+    ///     foo: var
+    /// };
+    /// ```
+    /// #34255
+    pub could_be_bare_literal: bool,
 }
 
 /// A match pattern.
diff --git a/compiler/rustc_ast/src/mut_visit.rs b/compiler/rustc_ast/src/mut_visit.rs
index 368a23e3429..4d9fc6554e7 100644
--- a/compiler/rustc_ast/src/mut_visit.rs
+++ b/compiler/rustc_ast/src/mut_visit.rs
@@ -949,7 +949,7 @@ pub fn noop_visit_mt<T: MutVisitor>(MutTy { ty, mutbl: _ }: &mut MutTy, vis: &mu
 }
 
 pub fn noop_visit_block<T: MutVisitor>(block: &mut P<Block>, vis: &mut T) {
-    let Block { id, stmts, rules: _, span, tokens } = block.deref_mut();
+    let Block { id, stmts, rules: _, span, tokens, could_be_bare_literal: _ } = block.deref_mut();
     vis.visit_id(id);
     stmts.flat_map_in_place(|stmt| vis.flat_map_stmt(stmt));
     vis.visit_span(span);