Don't opt_rpitit_info as a separate query

compiler/rustc_middle/src/hir/mod.rs

@@ -177,7 +177,6 @@ pub fn provide(providers: &mut Providers) {
         }
     };
     providers.opt_def_kind = |tcx, def_id| tcx.hir().opt_def_kind(def_id.expect_local());
-    providers.opt_rpitit_info = |_, _| None;
     providers.all_local_trait_impls = |tcx, ()| &tcx.resolutions(()).trait_impls;
     providers.expn_that_defined = |tcx, id| {
         let id = id.expect_local();

compiler/rustc_middle/src/query/mod.rs

@@ -1161,14 +1161,6 @@ rustc_queries! {
         feedable
     }
 
-    /// The `opt_rpitit_info` query returns the pair of the def id of the function where the RPIT
-    /// is defined and the opaque def id if any.
-    query opt_rpitit_info(def_id: DefId) -> Option<ty::ImplTraitInTraitData> {
-        desc { |tcx| "opt_rpitit_info `{}`", tcx.def_path_str(def_id) }
-        cache_on_disk_if { def_id.is_local() }
-        feedable
-    }
-
     /// Gets the span for the definition.
     query def_span(def_id: DefId) -> Span {
         desc { |tcx| "looking up span for `{}`", tcx.def_path_str(def_id) }

compiler/rustc_middle/src/ty/assoc.rs

@@ -30,6 +30,11 @@ pub struct AssocItem {
     /// Whether this is a method with an explicit self
     /// as its first parameter, allowing method calls.
     pub fn_has_self_parameter: bool,
+
+    /// `Some` if the associated item (an associated type) comes from the
+    /// return-position `impl Trait` in trait desugaring. The `ImplTraitInTraitData`
+    /// provides additional information about its source.
+    pub opt_rpitit_info: Option<ty::ImplTraitInTraitData>,
 }
 
 impl AssocItem {

compiler/rustc_middle/src/ty/context.rs

@@ -2452,7 +2452,7 @@ impl<'tcx> TyCtxt<'tcx> {
 
     pub fn is_impl_trait_in_trait(self, def_id: DefId) -> bool {
         if self.lower_impl_trait_in_trait_to_assoc_ty() {
-            self.def_kind(def_id) == DefKind::AssocTy && self.opt_rpitit_info(def_id).is_some()
+            self.opt_rpitit_info(def_id).is_some()
         } else {
             self.def_kind(def_id) == DefKind::ImplTraitPlaceholder
         }

compiler/rustc_middle/src/ty/mod.rs

@@ -2070,7 +2070,9 @@ pub enum ImplOverlapKind {
     Issue33140,
 }
 
-#[derive(Clone, Copy, Debug, PartialEq, Eq, Hash, TyEncodable, TyDecodable, HashStable)]
+/// Useful source information about where a desugared associated type for an
+/// RPITIT originated from.
+#[derive(Clone, Copy, Debug, PartialEq, Eq, Hash, Encodable, Decodable, HashStable)]
 pub enum ImplTraitInTraitData {
     Trait { fn_def_id: DefId, opaque_def_id: DefId },
     Impl { fn_def_id: DefId },
@@ -2213,6 +2215,17 @@ impl<'tcx> TyCtxt<'tcx> {
         }
     }
 
+    /// If the def-id is an associated type that was desugared from a
+    /// return-position `impl Trait` from a trait, then provide the source info
+    /// about where that RPITIT came from.
+    pub fn opt_rpitit_info(self, def_id: DefId) -> Option<ImplTraitInTraitData> {
+        if let DefKind::AssocTy = self.def_kind(def_id) {
+            self.associated_item(def_id).opt_rpitit_info
+        } else {
+            None
+        }
+    }
+
     pub fn find_field_index(self, ident: Ident, variant: &VariantDef) -> Option<usize> {
         variant
             .fields