4 files changed, 25 insertions, 16 deletions
diff --git a/compiler/rustc_middle/src/query/mod.rs b/compiler/rustc_middle/src/query/mod.rs
index 49c36a3ff16..3da6c6f5fe1 100644
--- a/compiler/rustc_middle/src/query/mod.rs
+++ b/compiler/rustc_middle/src/query/mod.rs
@@ -1079,21 +1079,9 @@ rustc_queries! {
         desc { |tcx| "comparing impl items against trait for `{}`", tcx.def_path_str(impl_id) }
     }
 
-    /// Given `fn_def_id` of a trait or of an impl that implements a given trait:
-    /// if `fn_def_id` is the def id of a function defined inside a trait, then it creates and returns
-    /// the associated items that correspond to each impl trait in return position for that trait.
-    /// if `fn_def_id` is the def id of a function defined inside an impl that implements a trait, then it
-    /// creates and returns the associated items that correspond to each impl trait in return position
-    /// of the implemented trait.
-    query associated_types_for_impl_traits_in_associated_fn(fn_def_id: DefId) -> &'tcx [DefId] {
-        desc { |tcx| "creating associated items for opaque types returned by `{}`", tcx.def_path_str(fn_def_id) }
-        cache_on_disk_if { fn_def_id.is_local() }
-        separate_provide_extern
-    }
-
-    query associated_types_for_impl_traits_in_trait(trait_id: DefId) -> &'tcx DefIdMap<&'tcx [DefId]> {
+    query associated_types_for_impl_traits_in_trait_or_impl(did: DefId) -> &'tcx ty::AssocTyForImplTraitInTraitOrImpl {
         arena_cache
-        desc { |tcx| "creating associated items for trait `{}`", tcx.def_path_str(trait_id) }
+        desc { |tcx| "creating rpitit for `{}`", tcx.def_path_str(did) }
         separate_provide_extern
     }
 
diff --git a/compiler/rustc_middle/src/ty/assoc.rs b/compiler/rustc_middle/src/ty/assoc.rs
index 344a81f5e24..99714171c72 100644
--- a/compiler/rustc_middle/src/ty/assoc.rs
+++ b/compiler/rustc_middle/src/ty/assoc.rs
@@ -1,4 +1,5 @@
 use rustc_attr_data_structures::{AttributeKind, find_attr};
+use rustc_data_structures::fx::FxIndexMap;
 use rustc_data_structures::sorted_map::SortedIndexMultiMap;
 use rustc_hir as hir;
 use rustc_hir::def::{DefKind, Namespace};
@@ -285,3 +286,23 @@ impl AssocItems {
             .find(|item| tcx.hygienic_eq(ident, item.ident(tcx), parent_def_id))
     }
 }
+
+#[derive(Debug, Clone, PartialEq, Encodable, Decodable, HashStable)]
+pub struct AssocTyForImplTraitInTraitOrImpl(pub FxIndexMap<DefId, Vec<DefId>>);
+
+/// Given an `fn_def_id` of a trait or a trait implementation:
+///
+/// if `fn_def_id` is a function defined inside a trait, then it synthesizes
+/// a new def id corresponding to a new associated type for each return-
+/// position `impl Trait` in the signature.
+///
+/// if `fn_def_id` is a function inside of an impl, then for each synthetic
+/// associated type generated for the corresponding trait function described
+/// above, synthesize a corresponding associated type in the impl.
+pub fn associated_types_for_impl_traits_in_associated_fn(
+    tcx: TyCtxt<'_>,
+    fn_def_id: DefId,
+) -> &'_ [DefId] {
+    let parent_def_id = tcx.parent(fn_def_id);
+    &tcx.associated_types_for_impl_traits_in_trait_or_impl(parent_def_id).0[&fn_def_id]
+}
diff --git a/compiler/rustc_middle/src/ty/mod.rs b/compiler/rustc_middle/src/ty/mod.rs
index 0177a95498b..e1b11e4f54a 100644
--- a/compiler/rustc_middle/src/ty/mod.rs
+++ b/compiler/rustc_middle/src/ty/mod.rs
@@ -2194,8 +2194,7 @@ impl<'tcx> TyCtxt<'tcx> {
             return false;
         };
 
-        return !self
-            .associated_types_for_impl_traits_in_associated_fn(trait_item_def_id)
+        return !associated_types_for_impl_traits_in_associated_fn(self, trait_item_def_id)
             .is_empty();
     }
 }
diff --git a/compiler/rustc_middle/src/ty/parameterized.rs b/compiler/rustc_middle/src/ty/parameterized.rs
index 3858778bfc8..88f6e717af4 100644
--- a/compiler/rustc_middle/src/ty/parameterized.rs
+++ b/compiler/rustc_middle/src/ty/parameterized.rs
@@ -67,6 +67,7 @@ trivially_parameterized_over_tcx! {
     crate::mir::ConstQualifs,
     ty::AsyncDestructor,
     ty::AssocItemContainer,
+    ty::AssocTyForImplTraitInTraitOrImpl,
     ty::Asyncness,
     ty::AnonConstKind,
     ty::DeducedParamAttrs,