bail in collect_trait_impl_trait_tys if signatures reference errors

compiler/rustc_hir_analysis/src/check/compare_method.rs

@@ -373,6 +373,7 @@ pub fn collect_trait_impl_trait_tys<'tcx>(
             tcx.fn_sig(impl_m.def_id),
         ),
     );
+    impl_sig.error_reported()?;
     let impl_return_ty = impl_sig.output();
 
     // Normalize the trait signature with liberated bound vars, passing it through
@@ -387,6 +388,7 @@ pub fn collect_trait_impl_trait_tys<'tcx>(
         )
         .fold_with(&mut collector);
     let trait_sig = ocx.normalize(&norm_cause, param_env, unnormalized_trait_sig);
+    trait_sig.error_reported()?;
     let trait_return_ty = trait_sig.output();
 
     let wf_tys = FxIndexSet::from_iter(

src/test/ui/async-await/in-trait/bad-signatures.rs

@@ -0,0 +1,16 @@
+// edition:2021
+
+#![feature(async_fn_in_trait)]
+//~^ WARN the feature `async_fn_in_trait` is incomplete
+
+trait MyTrait {
+    async fn bar(&abc self);
+    //~^ ERROR expected identifier, found keyword `self`
+    //~| ERROR expected one of `:`, `@`, or `|`, found keyword `self`
+}
+
+impl MyTrait for () {
+    async fn bar(&self) {}
+}
+
+fn main() {}

src/test/ui/async-await/in-trait/bad-signatures.stderr

@@ -0,0 +1,26 @@
+error: expected identifier, found keyword `self`
+  --> $DIR/bad-signatures.rs:7:23
+   |
+LL |     async fn bar(&abc self);
+   |                       ^^^^ expected identifier, found keyword
+
+error: expected one of `:`, `@`, or `|`, found keyword `self`
+  --> $DIR/bad-signatures.rs:7:23
+   |
+LL |     async fn bar(&abc self);
+   |                  -----^^^^
+   |                  |    |
+   |                  |    expected one of `:`, `@`, or `|`
+   |                  help: declare the type after the parameter binding: `<identifier>: <type>`
+
+warning: the feature `async_fn_in_trait` is incomplete and may not be safe to use and/or cause compiler crashes
+  --> $DIR/bad-signatures.rs:3:12
+   |
+LL | #![feature(async_fn_in_trait)]
+   |            ^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #91611 <https://github.com/rust-lang/rust/issues/91611> for more information
+   = note: `#[warn(incomplete_features)]` on by default
+
+error: aborting due to 2 previous errors; 1 warning emitted
+