Tweak feature error, add test

Author: compiler-errors

compiler/rustc_ast_lowering/src/lib.rs

@@ -312,7 +312,7 @@ impl std::fmt::Display for ImplTraitPosition {
  }
 }
 
-#[derive(Debug)]
+#[derive(Debug, PartialEq, Eq)]
 enum FnDeclKind {
  Fn,
  Inherent,
@@ -1373,6 +1373,18 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
  }
  path
  }
+ ImplTraitContext::Disallowed(
+ position @ (ImplTraitPosition::TraitReturn | ImplTraitPosition::ImplReturn),
+ ) => {
+ self.tcx.sess.create_feature_err(
+ MisplacedImplTrait {
+ span: t.span,
+ position: DiagnosticArgFromDisplay(&position),
+ },
+ sym::return_position_impl_trait_in_trait,
+ ).emit();
+ hir::TyKind::Err
+ }
  ImplTraitContext::Disallowed(position) => {
  self.tcx.sess.emit_err(MisplacedImplTrait {
  span: t.span,
@@ -1717,13 +1729,17 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
  }
  _ => {
  if !kind.impl_trait_return_allowed(self.tcx) {
- self.tcx
- .sess
- .create_feature_err(
- TraitFnAsync { fn_span, span },
- sym::return_position_impl_trait_in_trait,
- )
- .emit();
+ if kind == FnDeclKind::Impl {
+ self.tcx
+ .sess
+ .create_feature_err(
+ TraitFnAsync { fn_span, span },
+ sym::return_position_impl_trait_in_trait,
+ )
+ .emit();
+ } else {
+ self.tcx.sess.emit_err(TraitFnAsync { fn_span, span });
+ }
  }
  self.lower_async_fn_ret_ty(
  &decl.output,

src/test/ui/async-await/async-trait-fn.stderr

@@ -62,7 +62,7 @@ LL | async fn bar(&self) {}
 LL | pub const fn from_generator<T>(gen: T) -> impl Future<Output = T::Return>
  | ------------------------------- the found opaque type
  |
- = note: expected associated type `<Self as T>::bar::{opaque#0}`
+ = note: expected associated type `<Self as T>::bar::{opaque#0}<'_>`
  found opaque type `impl Future<Output = ()>`
 
 error[E0308]: mismatched types

src/test/ui/feature-gates/feature-gate-return_position_impl_trait_in_trait.stderr

@@ -3,6 +3,9 @@ error[E0562]: `impl Trait` only allowed in function and inherent method return t
  |
 LL | fn bar() -> impl Sized;
  | ^^^^^^^^^^
+ |
+ = note: see issue #91611 <https://github.com/rust-lang/rust/issues/91611> for more information
+ = help: add `#![feature(return_position_impl_trait_in_trait)]` to the crate attributes to enable
 
 error: aborting due to previous error
 

src/test/ui/impl-trait/in-trait/reveal.rs

@@ -0,0 +1,18 @@
+// check-pass
+
+#![feature(return_position_impl_trait_in_trait)]
+#![allow(incomplete_features)]
+
+trait Foo {
+ fn f() -> Box<impl Sized>;
+}
+
+impl Foo for () {
+ fn f() -> Box<String> {
+ Box::new(String::new())
+ }
+}
+
+fn main() {
+ let x: Box<String> = <() as Foo>::f();
+}

src/test/ui/impl-trait/where-allowed.stderr

@@ -162,12 +162,18 @@ error[E0562]: `impl Trait` only allowed in function and inherent method return t
  |
 LL | fn in_return() -> impl Debug;
  | ^^^^^^^^^^
+ |
+ = note: see issue #91611 <https://github.com/rust-lang/rust/issues/91611> for more information
+ = help: add `#![feature(return_position_impl_trait_in_trait)]` to the crate attributes to enable
 
 error[E0562]: `impl Trait` only allowed in function and inherent method return types, not in `impl` method return
  --> $DIR/where-allowed.rs:125:34
  |
 LL | fn in_trait_impl_return() -> impl Debug { () }
  | ^^^^^^^^^^
+ |
+ = note: see issue #91611 <https://github.com/rust-lang/rust/issues/91611> for more information
+ = help: add `#![feature(return_position_impl_trait_in_trait)]` to the crate attributes to enable
 
 error[E0562]: `impl Trait` only allowed in function and inherent method return types, not in `extern fn` param
  --> $DIR/where-allowed.rs:138:33