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.

compiler/rustc_next_trait_solver/src/solve/inspect/build.rs

@@ -5,11 +5,10 @@
 //! see the comment on [ProofTreeBuilder].
 
 use std::marker::PhantomData;
-use std::mem;
 
 use derive_where::derive_where;
 use rustc_type_ir::inherent::*;
-use rustc_type_ir::{self as ty, search_graph, Interner};
+use rustc_type_ir::{self as ty, Interner};
 
 use crate::delegate::SolverDelegate;
 use crate::solve::eval_ctxt::canonical;
@@ -94,31 +93,10 @@ impl<I: Interner> WipGoalEvaluation<I> {
     }
 }
 
-#[derive_where(PartialEq, Eq; I: Interner)]
-pub(in crate::solve) enum WipCanonicalGoalEvaluationKind<I: Interner> {
-    Overflow,
-    CycleInStack,
-    ProvisionalCacheHit,
-    Interned { final_revision: I::CanonicalGoalEvaluationStepRef },
-}
-
-impl<I: Interner> std::fmt::Debug for WipCanonicalGoalEvaluationKind<I> {
-    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
-        match self {
-            Self::Overflow => write!(f, "Overflow"),
-            Self::CycleInStack => write!(f, "CycleInStack"),
-            Self::ProvisionalCacheHit => write!(f, "ProvisionalCacheHit"),
-            Self::Interned { final_revision: _ } => {
-                f.debug_struct("Interned").finish_non_exhaustive()
-            }
-        }
-    }
-}
-
 #[derive_where(PartialEq, Eq, Debug; I: Interner)]
 struct WipCanonicalGoalEvaluation<I: Interner> {
     goal: CanonicalInput<I>,
-    kind: Option<WipCanonicalGoalEvaluationKind<I>>,
+    encountered_overflow: bool,
     /// Only used for uncached goals. After we finished evaluating
     /// the goal, this is interned and moved into `kind`.
     final_revision: Option<WipCanonicalGoalEvaluationStep<I>>,
@@ -127,25 +105,17 @@ struct WipCanonicalGoalEvaluation<I: Interner> {
 
 impl<I: Interner> WipCanonicalGoalEvaluation<I> {
     fn finalize(self) -> inspect::CanonicalGoalEvaluation<I> {
-        // We've already interned the final revision in
-        // `fn finalize_canonical_goal_evaluation`.
-        assert!(self.final_revision.is_none());
-        let kind = match self.kind.unwrap() {
-            WipCanonicalGoalEvaluationKind::Overflow => {
+        inspect::CanonicalGoalEvaluation {
+            goal: self.goal,
+            kind: if self.encountered_overflow {
+                assert!(self.final_revision.is_none());
                 inspect::CanonicalGoalEvaluationKind::Overflow
-            }
-            WipCanonicalGoalEvaluationKind::CycleInStack => {
-                inspect::CanonicalGoalEvaluationKind::CycleInStack
-            }
-            WipCanonicalGoalEvaluationKind::ProvisionalCacheHit => {
-                inspect::CanonicalGoalEvaluationKind::ProvisionalCacheHit
-            }
-            WipCanonicalGoalEvaluationKind::Interned { final_revision } => {
+            } else {
+                let final_revision = self.final_revision.unwrap().finalize();
                 inspect::CanonicalGoalEvaluationKind::Evaluation { final_revision }
-            }
-        };
-
-        inspect::CanonicalGoalEvaluation { goal: self.goal, kind, result: self.result.unwrap() }
+            },
+            result: self.result.unwrap(),
+        }
     }
 }
 
@@ -308,7 +278,7 @@ impl<D: SolverDelegate<Interner = I>, I: Interner> ProofTreeBuilder<D> {
     ) -> ProofTreeBuilder<D> {
         self.nested(|| WipCanonicalGoalEvaluation {
             goal,
-            kind: None,
+            encountered_overflow: false,
             final_revision: None,
             result: None,
         })
@@ -329,11 +299,11 @@ impl<D: SolverDelegate<Interner = I>, I: Interner> ProofTreeBuilder<D> {
         }
     }
 
-    pub fn canonical_goal_evaluation_kind(&mut self, kind: WipCanonicalGoalEvaluationKind<I>) {
+    pub fn canonical_goal_evaluation_overflow(&mut self) {
         if let Some(this) = self.as_mut() {
             match this {
                 DebugSolver::CanonicalGoalEvaluation(canonical_goal_evaluation) => {
-                    assert_eq!(canonical_goal_evaluation.kind.replace(kind), None);
+                    canonical_goal_evaluation.encountered_overflow = true;
                 }
                 _ => unreachable!(),
             };
@@ -547,51 +517,3 @@ impl<D: SolverDelegate<Interner = I>, I: Interner> ProofTreeBuilder<D> {
         }
     }
 }
-
-impl<D, I> search_graph::ProofTreeBuilder<I> for ProofTreeBuilder<D>
-where
-    D: SolverDelegate<Interner = I>,
-    I: Interner,
-{
-    fn try_apply_proof_tree(
-        &mut self,
-        proof_tree: Option<I::CanonicalGoalEvaluationStepRef>,
-    ) -> bool {
-        if !self.is_noop() {
-            if let Some(final_revision) = proof_tree {
-                let kind = WipCanonicalGoalEvaluationKind::Interned { final_revision };
-                self.canonical_goal_evaluation_kind(kind);
-                true
-            } else {
-                false
-            }
-        } else {
-            true
-        }
-    }
-
-    fn on_provisional_cache_hit(&mut self) {
-        self.canonical_goal_evaluation_kind(WipCanonicalGoalEvaluationKind::ProvisionalCacheHit);
-    }
-
-    fn on_cycle_in_stack(&mut self) {
-        self.canonical_goal_evaluation_kind(WipCanonicalGoalEvaluationKind::CycleInStack);
-    }
-
-    fn finalize_canonical_goal_evaluation(
-        &mut self,
-        tcx: I,
-    ) -> Option<I::CanonicalGoalEvaluationStepRef> {
-        self.as_mut().map(|this| match this {
-            DebugSolver::CanonicalGoalEvaluation(evaluation) => {
-                let final_revision = mem::take(&mut evaluation.final_revision).unwrap();
-                let final_revision =
-                    tcx.intern_canonical_goal_evaluation_step(final_revision.finalize());
-                let kind = WipCanonicalGoalEvaluationKind::Interned { final_revision };
-                assert_eq!(evaluation.kind.replace(kind), None);
-                final_revision
-            }
-            _ => unreachable!(),
-        })
-    }
-}

compiler/rustc_next_trait_solver/src/solve/search_graph.rs

@@ -5,7 +5,7 @@ use rustc_type_ir::search_graph::{self, CycleKind, UsageKind};
 use rustc_type_ir::solve::{CanonicalInput, Certainty, QueryResult};
 use rustc_type_ir::Interner;
 
-use super::inspect::{self, ProofTreeBuilder};
+use super::inspect::ProofTreeBuilder;
 use super::FIXPOINT_STEP_LIMIT;
 use crate::delegate::SolverDelegate;
 
@@ -25,6 +25,9 @@ where
     const FIXPOINT_STEP_LIMIT: usize = FIXPOINT_STEP_LIMIT;
 
     type ProofTreeBuilder = ProofTreeBuilder<D>;
+    fn inspect_is_noop(inspect: &mut Self::ProofTreeBuilder) -> bool {
+        inspect.is_noop()
+    }
 
     fn recursion_limit(cx: I) -> usize {
         cx.recursion_limit()
@@ -68,7 +71,7 @@ where
         inspect: &mut ProofTreeBuilder<D>,
         input: CanonicalInput<I>,
     ) -> QueryResult<I> {
-        inspect.canonical_goal_evaluation_kind(inspect::WipCanonicalGoalEvaluationKind::Overflow);
+        inspect.canonical_goal_evaluation_overflow();
         response_no_constraints(cx, input, Certainty::overflow(true))
     }