Don't proceed into parent bodies when collecting stmts for possible return suggestion

Author: compiler-errors

Diff for: compiler/rustc_hir_typeck/src/fn_ctxt/checks.rs

@@ -2016,12 +2016,16 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         for (span, code) in errors_causecode {
             self.dcx().try_steal_modify_and_emit_err(span, StashKey::MaybeForgetReturn, |err| {
                 if let Some(fn_sig) = self.body_fn_sig()
-                    && let ExprBindingObligation(_, _, hir_id, ..) = code
+                    && let ExprBindingObligation(_, _, binding_hir_id, ..) = code
                     && !fn_sig.output().is_unit()
                 {
                     let mut block_num = 0;
                     let mut found_semi = false;
-                    for (_, node) in self.tcx.hir().parent_iter(hir_id) {
+                    for (hir_id, node) in self.tcx.hir().parent_iter(binding_hir_id) {
+                        // Don't proceed into parent bodies
+                        if hir_id.owner != binding_hir_id.owner {
+                            break;
+                        }
                         match node {
                             hir::Node::Stmt(stmt) => {
                                 if let hir::StmtKind::Semi(expr) = stmt.kind {

Diff for: tests/ui/inference/dont-collect-stmts-from-parent-body.rs

@@ -0,0 +1,15 @@
+// issue: rust-lang/rust#124022
+
+struct Type<T>;
+//~^ ERROR type parameter `T` is never used
+
+fn main() {
+    {
+        impl<T> Type<T> {
+            fn new() -> Type<T> {
+                Type
+                //~^ ERROR type annotations needed
+            }
+        }
+    };
+}

Diff for: tests/ui/inference/dont-collect-stmts-from-parent-body.stderr

@@ -0,0 +1,24 @@
+error[E0392]: type parameter `T` is never used
+  --> $DIR/dont-collect-stmts-from-parent-body.rs:3:13
+   |
+LL | struct Type<T>;
+   |             ^ unused type parameter
+   |
+   = help: consider removing `T`, referring to it in a field, or using a marker such as `PhantomData`
+   = help: if you intended `T` to be a const parameter, use `const T: /* Type */` instead
+
+error[E0282]: type annotations needed
+  --> $DIR/dont-collect-stmts-from-parent-body.rs:10:17
+   |
+LL |                 Type
+   |                 ^^^^ cannot infer type of the type parameter `T` declared on the struct `Type`
+   |
+help: consider specifying the generic argument
+   |
+LL |                 Type::<T>
+   |                     +++++
+
+error: aborting due to 2 previous errors
+
+Some errors have detailed explanations: E0282, E0392.
+For more information about an error, try `rustc --explain E0282`.