Auto merge of #107038 - compiler-errors:dont-wfcheck-non-local-rpit, r=oli-obk

Don't wf-check non-local RPITs

We were using `ty::is_impl_trait_defn(..).is_none()` to check if we need to add WF obligations for an opaque type.

This is *supposed* to be checking if the type is a TAIT, since RPITs' wfness is implied by wf checking its parent item, but since `is_impl_trait_defn` returns `None` for non-local RPIT and async futures, we unnecessarily consider wf predicates for an RPIT if it is coming from a foreign crate.

Fixes #107036

r? `@oli-obk` but feel free to reassign

2 files changed, 12 insertions, 1 deletions

diff --git a/compiler/rustc_hir_analysis/src/astconv/mod.rs b/compiler/rustc_hir_analysis/src/astconv/mod.rs
index 9031c04849d..ce72b78f42f 100644
--- a/compiler/rustc_hir_analysis/src/astconv/mod.rs
+++ b/compiler/rustc_hir_analysis/src/astconv/mod.rs
@@ -2602,7 +2602,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
         match path.res {
             Res::Def(DefKind::OpaqueTy | DefKind::ImplTraitPlaceholder, did) => {
                 // Check for desugared `impl Trait`.
-                assert!(ty::is_impl_trait_defn(tcx, did).is_none());
+                assert!(tcx.is_type_alias_impl_trait(did));
                 let item_segment = path.segments.split_last().unwrap();
                 self.prohibit_generics(item_segment.1.iter(), |err| {
                     err.note("`impl Trait` types can't have type parameters");
diff --git a/compiler/rustc_hir_analysis/src/collect.rs b/compiler/rustc_hir_analysis/src/collect.rs
index 35f47dfc1a5..9be37dbe8c6 100644
--- a/compiler/rustc_hir_analysis/src/collect.rs
+++ b/compiler/rustc_hir_analysis/src/collect.rs
@@ -76,6 +76,7 @@ pub fn provide(providers: &mut Providers) {
         is_foreign_item,
         generator_kind,
         collect_mod_item_types,
+        is_type_alias_impl_trait,
         ..*providers
     };
 }
@@ -1537,3 +1538,13 @@ fn generator_kind(tcx: TyCtxt<'_>, def_id: DefId) -> Option<hir::GeneratorKind>
         _ => bug!("generator_kind applied to non-local def-id {:?}", def_id),
     }
 }
+
+fn is_type_alias_impl_trait<'tcx>(tcx: TyCtxt<'tcx>, def_id: DefId) -> bool {
+    match tcx.hir().get_if_local(def_id) {
+        Some(Node::Item(hir::Item { kind: hir::ItemKind::OpaqueTy(opaque), .. })) => {
+            matches!(opaque.origin, hir::OpaqueTyOrigin::TyAlias)
+        }
+        Some(_) => bug!("tried getting opaque_ty_origin for non-opaque: {:?}", def_id),
+        _ => bug!("tried getting opaque_ty_origin for non-local def-id {:?}", def_id),
+    }
+}