Account for impl/trait difference

Author: estebank

compiler/rustc_trait_selection/src/error_reporting/infer/need_type_info.rs

@@ -833,9 +833,18 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
 
             // We're at the `impl` level, but we want to get the same method we
             // called *on this `impl`*, in order to get the right DefId and args.
-            let Some(assoc) = assocs.filter_by_name_unhygienic(name).next() else {
-                // The method isn't in this `impl`? Not useful to us then.
+            let assoc = if let Some(assoc) = assocs.filter_by_name_unhygienic(name).next() {
+                // Method in the `impl`.
+                assoc
+            } else {
+                let assocs = tcx.associated_items(trait_def_id);
+                if let Some(assoc) = assocs.filter_by_name_unhygienic(name).next() {
+                    // Method in the `trait`.
+                    assoc
+                } else {
+                    // The method isn't in this `impl` or `trait`? Not useful to us then.
                 return;
+                }
             };
             let Some(trait_assoc_item) = assoc.trait_item_def_id else {
                 return;

tests/ui/inference/issue-80816.stderr

@@ -21,8 +21,8 @@ LL | impl<T, A: Access<T>, P: Deref<Target = A>> Access<T> for P {
    |            unsatisfied trait bound introduced here
 help: try using a fully qualified path to specify the expected types
    |
-LL |     let guard: Guard<Arc<usize>> = <Arc<ArcSwapAny<Arc<usize>>> as Access<T>>::load(&s);
-   |                                    ++++++++++++++++++++++++++++++++++++++++++++++++++ ~
+LL |     let guard: Guard<Arc<usize>> = <_ as Access<_>>::load(&s);
+   |                                    ++++++++++++++++++++++++ ~
 
 error: aborting due to 1 previous error