Auto merge of #88121 - camelid:better-recursive-alias-error, r=estebank

Improve errors for recursive type aliases

Fixes #17539.

compiler/rustc_query_impl/src/keys.rs

@@ -20,6 +20,12 @@ pub trait Key {
     /// In the event that a cycle occurs, if no explicit span has been
     /// given for a query with key `self`, what span should we use?
     fn default_span(&self, tcx: TyCtxt<'_>) -> Span;
+
+    /// If the key is a [`DefId`] or `DefId`--equivalent, return that `DefId`.
+    /// Otherwise, return `None`.
+    fn key_as_def_id(&self) -> Option<DefId> {
+        None
+    }
 }
 
 impl Key for () {
@@ -95,6 +101,9 @@ impl Key for LocalDefId {
     fn default_span(&self, tcx: TyCtxt<'_>) -> Span {
         self.to_def_id().default_span(tcx)
     }
+    fn key_as_def_id(&self) -> Option<DefId> {
+        Some(self.to_def_id())
+    }
 }
 
 impl Key for DefId {
@@ -105,6 +114,10 @@ impl Key for DefId {
     fn default_span(&self, tcx: TyCtxt<'_>) -> Span {
         tcx.def_span(*self)
     }
+    #[inline(always)]
+    fn key_as_def_id(&self) -> Option<DefId> {
+        Some(*self)
+    }
 }
 
 impl Key for ty::WithOptConstParam<LocalDefId> {
@@ -165,6 +178,10 @@ impl Key for (DefId, Option<Ident>) {
     fn default_span(&self, tcx: TyCtxt<'_>) -> Span {
         tcx.def_span(self.0)
     }
+    #[inline(always)]
+    fn key_as_def_id(&self) -> Option<DefId> {
+        Some(self.0)
+    }
 }
 
 impl Key for (DefId, LocalDefId, Ident) {