Add opt_rpitit_info query

compiler/rustc_middle/src/hir/mod.rs

@@ -177,6 +177,7 @@ 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

@@ -1144,6 +1144,14 @@ rustc_queries! {
         separate_provide_extern
     }
 
+    /// 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/mod.rs

@@ -2071,6 +2071,12 @@ pub enum ImplOverlapKind {
     Issue33140,
 }
 
+#[derive(Clone, Copy, Debug, PartialEq, Eq, Hash, TyEncodable, TyDecodable, HashStable)]
+pub enum ImplTraitInTraitData {
+    Trait { fn_def_id: DefId, opaque_def_id: DefId },
+    Impl { fn_def_id: DefId },
+}
+
 impl<'tcx> TyCtxt<'tcx> {
     pub fn typeck_body(self, body: hir::BodyId) -> &'tcx TypeckResults<'tcx> {
         self.typeck(self.hir().body_owner_def_id(body))