From be55ad53a1da73203e73ad3ff8ef0bad6c955e6c Mon Sep 17 00:00:00 2001
From: Michael Goulet <michael@errs.io>
Date: Tue, 17 Jan 2023 22:12:23 +0000
Subject: [PATCH] Remove default trait RPITIT candidates

---
 .../src/traits/project.rs                     | 36 ++-----------------
 1 file changed, 3 insertions(+), 33 deletions(-)

diff --git a/compiler/rustc_trait_selection/src/traits/project.rs b/compiler/rustc_trait_selection/src/traits/project.rs
index 9b3249e58e8..1c66fb257eb 100644
--- a/compiler/rustc_trait_selection/src/traits/project.rs
+++ b/compiler/rustc_trait_selection/src/traits/project.rs
@@ -90,15 +90,7 @@ enum ProjectionCandidate<'tcx> {
     /// From an "impl" (or a "pseudo-impl" returned by select)
     Select(Selection<'tcx>),
 
-    ImplTraitInTrait(ImplTraitInTraitCandidate<'tcx>),
-}
-
-#[derive(PartialEq, Eq, Debug)]
-enum ImplTraitInTraitCandidate<'tcx> {
-    // The `impl Trait` from a trait function's default body
-    Trait,
-    // A concrete type provided from a trait's `impl Trait` from an impl
-    Impl(ImplSourceUserDefinedData<'tcx, PredicateObligation<'tcx>>),
+    ImplTraitInTrait(ImplSourceUserDefinedData<'tcx, PredicateObligation<'tcx>>),
 }
 
 enum ProjectionCandidateSet<'tcx> {
@@ -1292,17 +1284,6 @@ fn assemble_candidate_for_impl_trait_in_trait<'cx, 'tcx>(
     let tcx = selcx.tcx();
     if tcx.def_kind(obligation.predicate.def_id) == DefKind::ImplTraitPlaceholder {
         let trait_fn_def_id = tcx.impl_trait_in_trait_parent(obligation.predicate.def_id);
-        // If we are trying to project an RPITIT with trait's default `Self` parameter,
-        // then we must be within a default trait body.
-        if obligation.predicate.self_ty()
-            == ty::InternalSubsts::identity_for_item(tcx, obligation.predicate.def_id).type_at(0)
-            && tcx.associated_item(trait_fn_def_id).defaultness(tcx).has_value()
-        {
-            candidate_set.push_candidate(ProjectionCandidate::ImplTraitInTrait(
-                ImplTraitInTraitCandidate::Trait,
-            ));
-            return;
-        }
 
         let trait_def_id = tcx.parent(trait_fn_def_id);
         let trait_substs =
@@ -1313,9 +1294,7 @@ fn assemble_candidate_for_impl_trait_in_trait<'cx, 'tcx>(
         let _ = selcx.infcx.commit_if_ok(|_| {
             match selcx.select(&obligation.with(tcx, trait_predicate)) {
                 Ok(Some(super::ImplSource::UserDefined(data))) => {
-                    candidate_set.push_candidate(ProjectionCandidate::ImplTraitInTrait(
-                        ImplTraitInTraitCandidate::Impl(data),
-                    ));
+                    candidate_set.push_candidate(ProjectionCandidate::ImplTraitInTrait(data));
                     Ok(())
                 }
                 Ok(None) => {
@@ -1777,18 +1756,9 @@ fn confirm_candidate<'cx, 'tcx>(
         ProjectionCandidate::Select(impl_source) => {
             confirm_select_candidate(selcx, obligation, impl_source)
         }
-        ProjectionCandidate::ImplTraitInTrait(ImplTraitInTraitCandidate::Impl(data)) => {
+        ProjectionCandidate::ImplTraitInTrait(data) => {
             confirm_impl_trait_in_trait_candidate(selcx, obligation, data)
         }
-        // If we're projecting an RPITIT for a default trait body, that's just
-        // the same def-id, but as an opaque type (with regular RPIT semantics).
-        ProjectionCandidate::ImplTraitInTrait(ImplTraitInTraitCandidate::Trait) => Progress {
-            term: selcx
-                .tcx()
-                .mk_opaque(obligation.predicate.def_id, obligation.predicate.substs)
-                .into(),
-            obligations: vec![],
-        },
     };
 
     // When checking for cycle during evaluation, we compare predicates with