resolve: Simplify some diagnostic code to avoid an ICE

compiler/rustc_resolve/src/late/diagnostics.rs

@@ -696,14 +696,7 @@ impl<'a: 'ast, 'ast> LateResolutionVisitor<'a, '_, 'ast> {
         ) = &bounded_ty.kind
         {
             // use this to verify that ident is a type param.
-            let Ok(Some(partial_res)) = self.resolve_qpath_anywhere(
-                None,
-                &Segment::from_path(path),
-                Namespace::TypeNS,
-                span,
-                true,
-                Finalize::No,
-            ) else {
+            let Some(partial_res) = self.r.partial_res_map.get(&bounded_ty.id) else {
                 return false;
             };
             if !(matches!(
@@ -718,16 +711,10 @@ impl<'a: 'ast, 'ast> LateResolutionVisitor<'a, '_, 'ast> {
             return false;
         };
 
-        if let ast::TyKind::Path(None, type_param_path) = &ty.peel_refs().kind {
+        let peeled_ty = ty.peel_refs();
+        if let ast::TyKind::Path(None, type_param_path) = &peeled_ty.kind {
             // Confirm that the `SelfTy` is a type parameter.
-            let Ok(Some(partial_res)) = self.resolve_qpath_anywhere(
-                None,
-                &Segment::from_path(type_param_path),
-                Namespace::TypeNS,
-                span,
-                true,
-                Finalize::No,
-            ) else {
+            let Some(partial_res) = self.r.partial_res_map.get(&peeled_ty.id) else {
                 return false;
             };
             if !(matches!(

src/test/ui/traits/associated_type_bound/assoc_type_bound_with_struct.rs

@@ -16,4 +16,8 @@ fn foo<T: Bar>(_: T) where <T as Bar>::Baz: String { //~ ERROR expected trait, f
 fn qux<'a, T: Bar>(_: &'a T) where <&'a T as Bar>::Baz: String { //~ ERROR expected trait, found
 }
 
+fn issue_95327() where <u8 as Unresolved>::Assoc: String {}
+//~^ ERROR expected trait, found struct
+//~| ERROR use of undeclared type `Unresolved`
+
 fn main() {}

src/test/ui/traits/associated_type_bound/assoc_type_bound_with_struct.stderr

@@ -1,3 +1,9 @@
+error[E0433]: failed to resolve: use of undeclared type `Unresolved`
+  --> $DIR/assoc_type_bound_with_struct.rs:19:31
+   |
+LL | fn issue_95327() where <u8 as Unresolved>::Assoc: String {}
+   |                               ^^^^^^^^^^ use of undeclared type `Unresolved`
+
 error[E0404]: expected trait, found struct `String`
   --> $DIR/assoc_type_bound_with_struct.rs:5:46
    |
@@ -78,6 +84,18 @@ help: a trait with a similar name exists
 LL | fn qux<'a, T: Bar>(_: &'a T) where <&'a T as Bar>::Baz: ToString {
    |                                                         ~~~~~~~~
 
-error: aborting due to 4 previous errors
+error[E0404]: expected trait, found struct `String`
+  --> $DIR/assoc_type_bound_with_struct.rs:19:51
+   |
+LL | fn issue_95327() where <u8 as Unresolved>::Assoc: String {}
+   |                                                   ^^^^^^ help: a trait with a similar name exists: `ToString`
+   |
+  ::: $SRC_DIR/alloc/src/string.rs:LL:COL
+   |
+LL | pub trait ToString {
+   | ------------------ similarly named trait `ToString` defined here
+
+error: aborting due to 6 previous errors
 
-For more information about this error, try `rustc --explain E0404`.
+Some errors have detailed explanations: E0404, E0433.
+For more information about an error, try `rustc --explain E0404`.