Tweak logic to account for methods implemented on trait

Author: estebank

compiler/rustc_borrowck/src/diagnostics/region_errors.rs

@@ -634,11 +634,26 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
             return;
         };
         let def_id = instance.def_id();
-        let parent = tcx.parent(def_id);
-        let hir::def::DefKind::Impl { .. } = tcx.def_kind(parent) else {
-            return;
-        };
-        let ty = tcx.type_of(parent).instantiate(tcx, instance.args);
+        let mut parent = tcx.parent(def_id);
+        match tcx.def_kind(parent) {
+            hir::def::DefKind::Impl { .. } => {}
+            hir::def::DefKind::Trait => {
+                let Some(ty) = args.get(0).and_then(|arg| arg.as_type()) else {
+                    return;
+                };
+                let mut impls = vec![];
+                tcx.for_each_relevant_impl(parent, ty, |id| { impls.push(id); });
+                if let [def_id] = impls[..] {
+                    // The method we have is on the trait, but for `parent` we want to analyze the
+                    // relevant impl instead.
+                    parent = def_id;
+                } else {
+                    return;
+                };
+            }
+            _ => return,
+        }
+        let ty = tcx.type_of(parent).instantiate_identity();
         if self.to_error_region(outlived_fr) != Some(tcx.lifetimes.re_static) {
             return;
         }
@@ -719,9 +734,7 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
                     ..
                 }),
             ..
-        })) = tcx.hir().get_if_local(parent)
-            && let Some(hir::Node::ImplItem(hir::ImplItem { .. })) = tcx.hir().get_if_local(def_id)
-        {
+        })) = tcx.hir().get_if_local(parent) {
             let suggestion = match lt.res {
                 hir::LifetimeName::ImplicitObjectLifetimeDefault if predicates.is_empty() => {
                     // `impl dyn Trait {}`

tests/ui/suggestions/impl-on-dyn-trait-with-implicit-static-bound.stderr

@@ -69,6 +69,10 @@ LL |         fn use_self(&self) -> &() { panic!() }
 ...
 LL |     impl MyTrait for dyn ObjectTrait {}
    |                          ^^^^^^^^^^^ this has an implicit `'static` lifetime requirement
+help: consider relaxing the implicit `'static` requirement on the impl
+   |
+LL |     impl MyTrait for dyn ObjectTrait + '_ {}
+   |                                      ++++
 
 error[E0521]: borrowed data escapes outside of function
   --> $DIR/impl-on-dyn-trait-with-implicit-static-bound.rs:112:9
@@ -91,6 +95,10 @@ LL |         fn use_self(&self) -> &() { panic!() }
 ...
 LL |     impl MyTrait for dyn ObjectTrait {}
    |                          ^^^^^^^^^^^ this has an implicit `'static` lifetime requirement
+help: consider relaxing the implicit `'static` requirement on the impl
+   |
+LL |     impl MyTrait for dyn ObjectTrait + '_ {}
+   |                                      ++++
 
 error[E0521]: borrowed data escapes outside of function
   --> $DIR/impl-on-dyn-trait-with-implicit-static-bound.rs:38:9