Special case type aliases from impl trait in const/static types

Author: oli-obk

compiler/rustc_ast_lowering/src/item.rs

@@ -342,7 +342,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
                     ty,
                     ImplTraitContext::OtherOpaqueTy {
                         capturable_lifetimes: &mut FxHashSet::default(),
-                        origin: hir::OpaqueTyOrigin::Misc,
+                        origin: hir::OpaqueTyOrigin::TyAlias,
                     },
                 );
                 let generics = self.lower_generics(gen, ImplTraitContext::disallowed());
@@ -918,7 +918,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
                             ty,
                             ImplTraitContext::OtherOpaqueTy {
                                 capturable_lifetimes: &mut FxHashSet::default(),
-                                origin: hir::OpaqueTyOrigin::Misc,
+                                origin: hir::OpaqueTyOrigin::TyAlias,
                             },
                         );
                         hir::ImplItemKind::TyAlias(ty)

compiler/rustc_hir/src/hir.rs

@@ -2291,7 +2291,9 @@ pub enum OpaqueTyOrigin {
     AsyncFn,
     /// `let _: impl Trait = ...`
     Binding,
-    /// Impl trait in type aliases, consts, statics, bounds.
+    /// type aliases: `type Foo = impl Trait;`
+    TyAlias,
+    /// Impl trait consts, statics, bounds.
     Misc,
 }
 

compiler/rustc_trait_selection/src/opaque_types.rs

@@ -422,7 +422,9 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
             }
             // These opaque type inherit all lifetime parameters from their
             // parent, so we have to check them all.
-            hir::OpaqueTyOrigin::Binding | hir::OpaqueTyOrigin::Misc => 0,
+            hir::OpaqueTyOrigin::Binding
+            | hir::OpaqueTyOrigin::TyAlias
+            | hir::OpaqueTyOrigin::Misc => 0,
         };
 
         let span = tcx.def_span(def_id);
@@ -581,6 +583,7 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
             // Otherwise, generate the label we'll use in the error message.
             hir::OpaqueTyOrigin::Binding
             | hir::OpaqueTyOrigin::FnReturn
+            | hir::OpaqueTyOrigin::TyAlias
             | hir::OpaqueTyOrigin::Misc => "impl Trait",
         };
         let msg = format!("ambiguous lifetime bound in `{}`", context_name);

compiler/rustc_typeck/src/check/check.rs

@@ -659,7 +659,8 @@ fn check_opaque_meets_bounds<'tcx>(
         // Checked when type checking the function containing them.
         hir::OpaqueTyOrigin::FnReturn | hir::OpaqueTyOrigin::AsyncFn => return,
         // Can have different predicates to their defining use
-        hir::OpaqueTyOrigin::Binding | hir::OpaqueTyOrigin::Misc => {}
+        hir::OpaqueTyOrigin::Binding | hir::OpaqueTyOrigin::Misc | hir::OpaqueTyOrigin::TyAlias => {
+        }
     }
 
     let hir_id = tcx.hir().local_def_id_to_hir_id(def_id);

compiler/rustc_typeck/src/check/writeback.rs

@@ -497,7 +497,8 @@ impl<'cx, 'tcx> WritebackCx<'cx, 'tcx> {
             let mut skip_add = false;
 
             if let ty::Opaque(defin_ty_def_id, _substs) = *definition_ty.kind() {
-                if let hir::OpaqueTyOrigin::Misc = opaque_defn.origin {
+                if let hir::OpaqueTyOrigin::Misc | hir::OpaqueTyOrigin::TyAlias = opaque_defn.origin
+                {
                     if def_id == defin_ty_def_id {
                         debug!(
                             "skipping adding concrete definition for opaque type {:?} {:?}",