do not use the global solver cache for proof trees

doing so requires overwriting global cache entries and
generally adds significant complexity to the solver. This is
also only ever done for root goals, so it feels easier to wrap
the `evaluate_canonical_goal` in an ordinary query if
necessary.

1 files changed, 3 insertions, 7 deletions

diff --git a/compiler/rustc_trait_selection/src/solve/inspect/analyse.rs b/compiler/rustc_trait_selection/src/solve/inspect/analyse.rs
index e8de8457440..4e4022830d4 100644
--- a/compiler/rustc_trait_selection/src/solve/inspect/analyse.rs
+++ b/compiler/rustc_trait_selection/src/solve/inspect/analyse.rs
@@ -332,13 +332,9 @@ impl<'a, 'tcx> InspectGoal<'a, 'tcx> {
 
     pub fn candidates(&'a self) -> Vec<InspectCandidate<'a, 'tcx>> {
         let mut candidates = vec![];
-        let last_eval_step = match self.evaluation_kind {
-            inspect::CanonicalGoalEvaluationKind::Overflow
-            | inspect::CanonicalGoalEvaluationKind::CycleInStack
-            | inspect::CanonicalGoalEvaluationKind::ProvisionalCacheHit => {
-                warn!("unexpected root evaluation: {:?}", self.evaluation_kind);
-                return vec![];
-            }
+        let last_eval_step = match &self.evaluation_kind {
+            // An annoying edge case in case the recursion limit is 0.
+            inspect::CanonicalGoalEvaluationKind::Overflow => return vec![],
             inspect::CanonicalGoalEvaluationKind::Evaluation { final_revision } => final_revision,
         };