Tweak #[rustc_object_lifetime_default]

* print `Empty` as it's called in code, otherwise it's unnecessarily confusing
* go through the middle::ty Generics instead of the HIR ones, so we can dump the
  default for the implicit `Self` type parameter of traits, too
* allow the attribute on more targets (it used to be allowed anywhere for the
  longest time but someone must've incorrectly restricted it during the
  migration to the new attribute parsing API)

Author: fmease

compiler/rustc_attr_parsing/src/attributes/rustc_internal.rs

@@ -46,7 +46,14 @@ impl<S: Stage> SingleAttributeParser<S> for RustcObjectLifetimeDefaultParser {
     const PATH: &[rustc_span::Symbol] = &[sym::rustc_object_lifetime_default];
     const ATTRIBUTE_ORDER: AttributeOrder = AttributeOrder::KeepInnermost;
     const ON_DUPLICATE: OnDuplicate<S> = OnDuplicate::Error;
-    const ALLOWED_TARGETS: AllowedTargets = AllowedTargets::AllowList(&[Allow(Target::Struct)]);
+    const ALLOWED_TARGETS: AllowedTargets = AllowedTargets::AllowList(&[
+        Allow(Target::Struct),
+        Allow(Target::Enum),
+        Allow(Target::Union),
+        Allow(Target::Trait),
+        Allow(Target::TyAlias),
+        Allow(Target::AssocTy),
+    ]);
     const TEMPLATE: AttributeTemplate = template!(Word);
 
     fn convert(cx: &mut AcceptContext<'_, '_, S>, args: &ArgParser<'_>) -> Option<AttributeKind> {

compiler/rustc_passes/src/check_attr.rs

@@ -649,20 +649,18 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
     /// Debugging aid for `object_lifetime_default` query.
     fn check_object_lifetime_default(&self, hir_id: HirId) {
         let tcx = self.tcx;
-        if let Some(owner_id) = hir_id.as_owner()
-            && let Some(generics) = tcx.hir_get_generics(owner_id.def_id)
-        {
-            for p in generics.params {
-                let hir::GenericParamKind::Type { .. } = p.kind else { continue };
-                let default = tcx.object_lifetime_default(p.def_id);
-                let repr = match default {
-                    ObjectLifetimeDefault::Empty => "BaseDefault".to_owned(),
-                    ObjectLifetimeDefault::Static => "'static".to_owned(),
-                    ObjectLifetimeDefault::Param(def_id) => tcx.item_name(def_id).to_string(),
-                    ObjectLifetimeDefault::Ambiguous => "Ambiguous".to_owned(),
-                };
-                tcx.dcx().emit_err(errors::ObjectLifetimeErr { span: p.span, repr });
-            }
+        let Some(owner_id) = hir_id.as_owner() else { return };
+        for param in &tcx.generics_of(owner_id.def_id).own_params {
+            let ty::GenericParamDefKind::Type { .. } = param.kind else { continue };
+            let default = tcx.object_lifetime_default(param.def_id);
+            let repr = match default {
+                ObjectLifetimeDefault::Empty => "Empty".to_owned(),
+                ObjectLifetimeDefault::Static => "'static".to_owned(),
+                ObjectLifetimeDefault::Param(def_id) => tcx.item_name(def_id).to_string(),
+                ObjectLifetimeDefault::Ambiguous => "Ambiguous".to_owned(),
+            };
+            tcx.dcx()
+                .emit_err(errors::ObjectLifetimeErr { span: tcx.def_span(param.def_id), repr });
         }
     }
     /// Checks if `#[collapse_debuginfo]` is applied to a macro.

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

@@ -2,13 +2,13 @@
 
 #[rustc_object_lifetime_default]
 struct A<
-    T, //~ ERROR BaseDefault
+    T, //~ ERROR Empty
 >(T);
 
 #[rustc_object_lifetime_default]
 struct B<
     'a,
-    T, //~ ERROR BaseDefault
+    T, //~ ERROR Empty
 >(&'a (), T);
 
 #[rustc_object_lifetime_default]
@@ -47,4 +47,12 @@ struct G<
     U: 'a + 'b, //~ ERROR Ambiguous
 >(&'a T, &'b U);
 
+// Check that we also dump the default for the implicit `Self` type param of traits.
+#[rustc_object_lifetime_default]
+trait H< //~ ERROR 'a
+    'a,
+    'b,
+    T: 'b, //~ ERROR 'b
+>: 'a {}
+
 fn main() {}

tests/ui/object-lifetime/object-lifetime-default.stderr

@@ -1,10 +1,10 @@
-error: BaseDefault
+error: Empty
   --> $DIR/object-lifetime-default.rs:5:5
    |
 LL |     T,
    |     ^
 
-error: BaseDefault
+error: Empty
   --> $DIR/object-lifetime-default.rs:11:5
    |
 LL |     T,
@@ -52,5 +52,21 @@ error: Ambiguous
 LL |     U: 'a + 'b,
    |     ^
 
-error: aborting due to 9 previous errors
+error: 'a
+  --> $DIR/object-lifetime-default.rs:52:1
+   |
+LL | / trait H<
+LL | |     'a,
+LL | |     'b,
+LL | |     T: 'b,
+LL | | >: 'a {}
+   | |_____^
+
+error: 'b
+  --> $DIR/object-lifetime-default.rs:55:5
+   |
+LL |     T: 'b,
+   |     ^
+
+error: aborting due to 11 previous errors