Add associated_items_for_impl_trait_in_trait query

compiler/rustc_middle/src/hir/map/mod.rs

@@ -849,6 +849,13 @@ impl<'hir> Map<'hir> {
         }
     }
 
+    pub fn get_fn_output(self, def_id: LocalDefId) -> Option<&'hir FnRetTy<'hir>> {
+        match self.tcx.hir_owner(OwnerId { def_id }) {
+            Some(Owner { node, .. }) => node.fn_decl().map(|fn_decl| &fn_decl.output),
+            _ => None,
+        }
+    }
+
     pub fn expect_variant(self, id: HirId) -> &'hir Variant<'hir> {
         match self.find(id) {
             Some(Node::Variant(variant)) => variant,

compiler/rustc_middle/src/query/mod.rs

@@ -767,6 +767,13 @@ rustc_queries! {
         desc { |tcx| "comparing impl items against trait for `{}`", tcx.def_path_str(impl_id) }
     }
 
+    /// Given an `fn_def_id`, create and return the associated items for that function.
+    query associated_items_for_impl_trait_in_trait(fn_def_id: DefId) -> &'tcx [DefId] {
+        desc { |tcx| "creating associated items for impl trait in trait returned by `{}`", tcx.def_path_str(fn_def_id) }
+        cache_on_disk_if { fn_def_id.is_local() }
+        separate_provide_extern
+    }
+
     /// Given an `impl_id`, return the trait it implements.
     /// Return `None` if this is an inherent impl.
     query impl_trait_ref(impl_id: DefId) -> Option<ty::EarlyBinder<ty::TraitRef<'tcx>>> {