Pre-populate MIR with opaques, prefer subst-relate candidate

2 files changed, 25 insertions, 28 deletions

diff --git a/compiler/rustc_trait_selection/src/solve/mod.rs b/compiler/rustc_trait_selection/src/solve/mod.rs
index 1427268f829..26ace28f5fd 100644
--- a/compiler/rustc_trait_selection/src/solve/mod.rs
+++ b/compiler/rustc_trait_selection/src/solve/mod.rs
@@ -239,34 +239,34 @@ impl<'a, 'tcx> EvalCtxt<'a, 'tcx> {
                     evaluate_normalizes_to(self, alias_rhs, lhs, direction, Invert::Yes).ok(),
                 );
                 // Relate via substs
-                candidates.extend(
-                    self.probe(|ecx| {
-                        let span = tracing::span!(
-                            tracing::Level::DEBUG,
-                            "compute_alias_relate_goal(relate_via_substs)",
-                            ?alias_lhs,
-                            ?alias_rhs,
-                            ?direction
-                        );
-                        let _enter = span.enter();
-
-                        match direction {
-                            ty::AliasRelationDirection::Equate => {
-                                ecx.eq(goal.param_env, alias_lhs, alias_rhs)?;
-                            }
-                            ty::AliasRelationDirection::Subtype => {
-                                ecx.sub(goal.param_env, alias_lhs, alias_rhs)?;
-                            }
+                let subst_relate_response = self.probe(|ecx| {
+                    let span = tracing::span!(
+                        tracing::Level::DEBUG,
+                        "compute_alias_relate_goal(relate_via_substs)",
+                        ?alias_lhs,
+                        ?alias_rhs,
+                        ?direction
+                    );
+                    let _enter = span.enter();
+
+                    match direction {
+                        ty::AliasRelationDirection::Equate => {
+                            ecx.eq(goal.param_env, alias_lhs, alias_rhs)?;
+                        }
+                        ty::AliasRelationDirection::Subtype => {
+                            ecx.sub(goal.param_env, alias_lhs, alias_rhs)?;
                         }
+                    }
 
-                        ecx.evaluate_added_goals_and_make_canonical_response(Certainty::Yes)
-                    })
-                    .ok(),
-                );
+                    ecx.evaluate_added_goals_and_make_canonical_response(Certainty::Yes)
+                });
+                candidates.extend(subst_relate_response);
                 debug!(?candidates);
 
                 if let Some(merged) = self.try_merge_responses(&candidates) {
                     Ok(merged)
+                } else if let Ok(subst_relate_response) = subst_relate_response {
+                    Ok(subst_relate_response)
                 } else {
                     self.flounder(&candidates)
                 }
diff --git a/compiler/rustc_trait_selection/src/solve/opaques.rs b/compiler/rustc_trait_selection/src/solve/opaques.rs
index 1d5bb46450c..f97f54e760e 100644
--- a/compiler/rustc_trait_selection/src/solve/opaques.rs
+++ b/compiler/rustc_trait_selection/src/solve/opaques.rs
@@ -1,6 +1,6 @@
 use rustc_middle::traits::query::NoSolution;
 use rustc_middle::traits::solve::{Certainty, Goal, QueryResult};
-use rustc_middle::traits::{ObligationCause, Reveal};
+use rustc_middle::traits::Reveal;
 use rustc_middle::ty;
 use rustc_middle::ty::util::NotUniqueParam;
 
@@ -37,11 +37,8 @@ impl<'tcx> EvalCtxt<'_, 'tcx> {
                         Ok(()) => {}
                     }
                     // Prefer opaques registered already.
-                    let matches = self.unify_existing_opaque_tys(
-                        goal.param_env,
-                        opaque_ty,
-                        expected
-                    );
+                    let matches =
+                        self.unify_existing_opaque_tys(goal.param_env, opaque_ty, expected);
                     if !matches.is_empty() {
                         if let Some(response) = self.try_merge_responses(&matches) {
                             return Ok(response);