Note that type aliases cannot be recursive

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> {

compiler/rustc_query_impl/src/lib.rs

@@ -51,6 +51,8 @@ pub use on_disk_cache::OnDiskCache;
 mod profiling_support;
 pub use self::profiling_support::alloc_self_profile_query_strings;
 
+mod util;
+
 rustc_query_append! { [define_queries!][<'tcx>] }
 
 impl<'tcx> Queries<'tcx> {

compiler/rustc_query_impl/src/plumbing.rs

@@ -337,6 +337,11 @@ macro_rules! define_queries {
                 } else {
                     Some(key.default_span(*tcx))
                 };
+                let def_id = key.key_as_def_id();
+                let def_kind = def_id.map(|def_id| {
+                    let def_kind = tcx.def_kind(def_id);
+                    $crate::util::def_kind_to_simple_def_kind(def_kind)
+                });
                 let hash = || {
                     let mut hcx = tcx.create_stable_hashing_context();
                     let mut hasher = StableHasher::new();
@@ -345,7 +350,7 @@ macro_rules! define_queries {
                     hasher.finish::<u64>()
                 };
 
-                QueryStackFrame::new(name, description, span, hash)
+                QueryStackFrame::new(name, description, span, def_kind, hash)
             })*
         }
 

compiler/rustc_query_impl/src/util.rs

@@ -0,0 +1,18 @@
+use rustc_hir::def::DefKind;
+use rustc_query_system::query::SimpleDefKind;
+
+/// Convert a [`DefKind`] to a [`SimpleDefKind`].
+///
+/// *See [`SimpleDefKind`]'s docs for more information.*
+pub(crate) fn def_kind_to_simple_def_kind(def_kind: DefKind) -> SimpleDefKind {
+    match def_kind {
+        DefKind::Struct => SimpleDefKind::Struct,
+        DefKind::Enum => SimpleDefKind::Enum,
+        DefKind::Union => SimpleDefKind::Union,
+        DefKind::Trait => SimpleDefKind::Trait,
+        DefKind::TyAlias => SimpleDefKind::TyAlias,
+        DefKind::TraitAlias => SimpleDefKind::TraitAlias,
+
+        _ => SimpleDefKind::Other,
+    }
+}