Auto merge of rust-lang#124203 - lukas-code:delete-deleting-caches, r=<try>

fix normalizing in different `ParamEnv`s with the same `InferCtxt`

This PR changes the key of the projection cache from just `AliasTy` to `(AliasTy, ParamEnv)` to allow normalizing in different `ParamEnv`s without resetting caches. Previously, normalizing the same alias in different param envs would always reuse the cached result from the first normalization, which is incorrect if the projection clauses in the param env have changed.

Fixing this bug allows us to get rid of `InferCtxt::clear_caches`, which was only used by the `AutoTraitFinder`, because it requires normalizing in different param envs.

r? `@fmease`

Author: bors

compiler/rustc_infer/src/infer/mod.rs

@@ -1521,15 +1521,6 @@ impl<'tcx> InferCtxt<'tcx> {
         closure_kind_ty.to_opt_closure_kind()
     }
 
-    /// Clears the selection, evaluation, and projection caches. This is useful when
-    /// repeatedly attempting to select an `Obligation` while changing only
-    /// its `ParamEnv`, since `FulfillmentContext` doesn't use probing.
-    pub fn clear_caches(&self) {
-        self.selection_cache.clear();
-        self.evaluation_cache.clear();
-        self.inner.borrow_mut().projection_cache().clear();
-    }
-
     pub fn universe(&self) -> ty::UniverseIndex {
         self.universe.get()
     }

compiler/rustc_infer/src/traits/project.rs

@@ -78,11 +78,12 @@ pub struct ProjectionCacheStorage<'tcx> {
 #[derive(Copy, Clone, Debug, Hash, PartialEq, Eq)]
 pub struct ProjectionCacheKey<'tcx> {
     ty: ty::AliasTy<'tcx>,
+    param_env: ty::ParamEnv<'tcx>,
 }
 
 impl<'tcx> ProjectionCacheKey<'tcx> {
-    pub fn new(ty: ty::AliasTy<'tcx>) -> Self {
-        Self { ty }
+    pub fn new(ty: ty::AliasTy<'tcx>, param_env: ty::ParamEnv<'tcx>) -> Self {
+        Self { ty, param_env }
     }
 }
 

compiler/rustc_trait_selection/src/traits/auto_trait.rs

@@ -152,7 +152,6 @@ impl<'tcx> AutoTraitFinder<'tcx> {
              with {:?}",
             trait_ref, full_env
         );
-        infcx.clear_caches();
 
         // At this point, we already have all of the bounds we need. FulfillmentContext is used
         // to store all of the necessary region/lifetime bounds in the InferContext, as well as
@@ -176,9 +175,7 @@ impl<'tcx> AutoTraitFinder<'tcx> {
 
         AutoTraitResult::PositiveImpl(auto_trait_callback(info))
     }
-}
 
-impl<'tcx> AutoTraitFinder<'tcx> {
     /// The core logic responsible for computing the bounds for our synthesized impl.
     ///
     /// To calculate the bounds, we call `SelectionContext.select` in a loop. Like
@@ -255,8 +252,6 @@ impl<'tcx> AutoTraitFinder<'tcx> {
         let dummy_cause = ObligationCause::dummy();
 
         while let Some(pred) = predicates.pop_front() {
-            infcx.clear_caches();
-
             if !already_visited.insert(pred) {
                 continue;
             }

compiler/rustc_trait_selection/src/traits/fulfill.rs

@@ -758,9 +758,9 @@ impl<'a, 'tcx> FulfillProcessor<'a, 'tcx> {
             // no type variables present, can use evaluation for better caching.
             // FIXME: consider caching errors too.
             if self.selcx.infcx.predicate_must_hold_considering_regions(obligation) {
-                if let Some(key) = ProjectionCacheKey::from_poly_projection_predicate(
+                if let Some(key) = ProjectionCacheKey::from_poly_projection_obligation(
                     &mut self.selcx,
-                    project_obligation.predicate,
+                    &project_obligation,
                 ) {
                     // If `predicate_must_hold_considering_regions` succeeds, then we've
                     // evaluated all sub-obligations. We can therefore mark the 'root'

compiler/rustc_trait_selection/src/traits/project.rs

@@ -344,7 +344,7 @@ pub(super) fn opt_normalize_projection_type<'a, 'b, 'tcx>(
     let use_cache = !selcx.is_intercrate();
 
     let projection_ty = infcx.resolve_vars_if_possible(projection_ty);
-    let cache_key = ProjectionCacheKey::new(projection_ty);
+    let cache_key = ProjectionCacheKey::new(projection_ty, param_env);
 
     // FIXME(#20304) For now, I am caching here, which is good, but it
     // means we don't capture the type variables that are created in
@@ -2105,27 +2105,28 @@ fn assoc_ty_own_obligations<'cx, 'tcx>(
 }
 
 pub(crate) trait ProjectionCacheKeyExt<'cx, 'tcx>: Sized {
-    fn from_poly_projection_predicate(
+    fn from_poly_projection_obligation(
         selcx: &mut SelectionContext<'cx, 'tcx>,
-        predicate: ty::PolyProjectionPredicate<'tcx>,
+        obligation: &PolyProjectionObligation<'tcx>,
     ) -> Option<Self>;
 }
 
 impl<'cx, 'tcx> ProjectionCacheKeyExt<'cx, 'tcx> for ProjectionCacheKey<'tcx> {
-    fn from_poly_projection_predicate(
+    fn from_poly_projection_obligation(
         selcx: &mut SelectionContext<'cx, 'tcx>,
-        predicate: ty::PolyProjectionPredicate<'tcx>,
+        obligation: &PolyProjectionObligation<'tcx>,
     ) -> Option<Self> {
         let infcx = selcx.infcx;
         // We don't do cross-snapshot caching of obligations with escaping regions,
         // so there's no cache key to use
-        predicate.no_bound_vars().map(|predicate| {
+        obligation.predicate.no_bound_vars().map(|predicate| {
             ProjectionCacheKey::new(
                 // We don't attempt to match up with a specific type-variable state
                 // from a specific call to `opt_normalize_projection_type` - if
                 // there's no precise match, the original cache entry is "stranded"
                 // anyway.
                 infcx.resolve_vars_if_possible(predicate.projection_ty),
+                obligation.param_env,
             )
         })
     }

compiler/rustc_trait_selection/src/traits/select/mod.rs

@@ -815,7 +815,10 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                                 // `EvaluatedToOkModuloRegions`), and skip re-evaluating the
                                 // sub-obligations.
                                 if let Some(key) =
-                                    ProjectionCacheKey::from_poly_projection_predicate(self, data)
+                                    ProjectionCacheKey::from_poly_projection_obligation(
+                                        self,
+                                        &project_obligation,
+                                    )
                                 {
                                     if let Some(cached_res) = self
                                         .infcx
@@ -844,8 +847,9 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                                     && (eval_rslt == EvaluatedToOk
                                         || eval_rslt == EvaluatedToOkModuloRegions)
                                     && let Some(key) =
-                                        ProjectionCacheKey::from_poly_projection_predicate(
-                                            self, data,
+                                        ProjectionCacheKey::from_poly_projection_obligation(
+                                            self,
+                                            &project_obligation,
                                         )
                                 {
                                     // If the result is something that we can cache, then mark this