Make enum variant paths induce trait object lifetime defaults in the enum path segment

Author: fmease

compiler/rustc_hir_analysis/src/collect/resolve_bound_vars.rs

@@ -1691,7 +1691,9 @@ impl<'a, 'tcx> BoundVarContext<'a, 'tcx> {
         // which requires object lifetime defaults.
         let type_def_id = match res {
             Res::Def(DefKind::AssocTy, def_id) if depth == 1 => Some(self.tcx.parent(def_id)),
-            Res::Def(DefKind::Variant, def_id) if depth == 0 => Some(self.tcx.parent(def_id)),
+            Res::Def(DefKind::Variant, def_id) if depth == 0 || depth == 1 => {
+                Some(self.tcx.parent(def_id))
+            }
             Res::Def(
                 DefKind::Struct
                 | DefKind::Union

tests/ui/object-lifetime/object-lifetime-default-enum-variant.rs

@@ -0,0 +1,24 @@
+//@ check-pass
+
+enum Enum<'a, T: 'a + AbideBy<'a> + ?Sized> {
+    Variant,
+
+    Carry(&'a T),
+}
+
+fn scope<'any>() {
+    // We elaborate `dyn Trait` to `dyn Trait + 'any` due to bound `'a` on `T`.
+    let _ = Enum::Variant::<'any, dyn Trait> {};
+
+    // Similarly here.
+    let _ = Enum::<'any, dyn Trait>::Variant {};
+}
+
+trait Trait {}
+
+// We use this to test that a given trait object lifetime bound is
+// *exactly equal* to a given lifetime (not longer, not shorter).
+trait AbideBy<'a> {}
+impl<'a> AbideBy<'a> for dyn Trait + 'a {}
+
+fn main() {}