Auto merge of rust-lang#85868 - Aaron1011:projection-cache, r=jackh726

Preserve most sub-obligations in the projection cache

Fixes rust-lang#85360

When we evaluate a projection predicate, we may produce sub-obligations. During trait evaluation, evaluating these sub-obligations might cause us to produce `EvaluatedToOkModuloRegions`.

When we cache the result of projection in our projection cache, we try to throw away some of the sub-obligations, so that we don't need to re-evaluate/process them the next time we need to perform this particular projection. However, we may end up throwing away predicates that will (recursively) evaluate to `EvaluatedToOkModuloRegions`. If we do, then the result of evaluating a predicate will depend on the state of the predicate cache - this is global untracked state, which interacts badly with incremental compilation.

To fix this, we now only discard global predicates that evaluate to `EvaluatedToOk`. This ensures that any predicates that (may) evaluate to `EvaluatedToOkModuloRegions` are kept in the cache, and influence the results of any queries which perform this projection.

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

@@ -224,7 +224,9 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
 
  debug!("report_overflow_error_cycle: cycle={:?}", cycle);
 
- self.report_overflow_error(&cycle[0], false);
+ // The 'deepest' obligation is most likely to have a useful
+ // cause 'backtrace'
+ self.report_overflow_error(cycle.iter().max_by_key(|p| p.recursion_depth).unwrap(), false);
  }
 
  fn report_selection_error(

compiler/rustc_trait_selection/src/traits/project.rs

@@ -10,6 +10,7 @@ use super::PredicateObligation;
 use super::Selection;
 use super::SelectionContext;
 use super::SelectionError;
+use super::TraitQueryMode;
 use super::{
  ImplSourceClosureData, ImplSourceDiscriminantKindData, ImplSourceFnPointerData,
  ImplSourceGeneratorData, ImplSourcePointeeData, ImplSourceUserDefinedData,
@@ -18,7 +19,7 @@ use super::{Normalized, NormalizedTy, ProjectionCacheEntry, ProjectionCacheKey};
 
 use crate::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
 use crate::infer::{InferCtxt, InferOk, LateBoundRegionConversionTime};
-use crate::traits::error_reporting::InferCtxtExt;
+use crate::traits::error_reporting::InferCtxtExt as _;
 use rustc_data_structures::stack::ensure_sufficient_stack;
 use rustc_errors::ErrorReported;
 use rustc_hir::def_id::DefId;
@@ -912,6 +913,7 @@ fn opt_normalize_projection_type<'a, 'b, 'tcx>(
  }
 
  let obligation = Obligation::with_depth(cause.clone(), depth, param_env, projection_ty);
+
  match project_type(selcx, &obligation) {
  Ok(ProjectedTy::Progress(Progress {
  ty: projected_ty,
@@ -925,7 +927,7 @@ fn opt_normalize_projection_type<'a, 'b, 'tcx>(
  let projected_ty = selcx.infcx().resolve_vars_if_possible(projected_ty);
  debug!(?projected_ty, ?depth, ?projected_obligations);
 
- let result = if projected_ty.has_projections() {
+ let mut result = if projected_ty.has_projections() {
  let mut normalizer = AssocTypeNormalizer::new(
  selcx,
  param_env,
@@ -942,8 +944,26 @@ fn opt_normalize_projection_type<'a, 'b, 'tcx>(
  Normalized { value: projected_ty, obligations: projected_obligations }
  };
 
- let cache_value = prune_cache_value_obligations(infcx, &result);
- infcx.inner.borrow_mut().projection_cache().insert_ty(cache_key, cache_value);
+ let mut canonical =
+ SelectionContext::with_query_mode(selcx.infcx(), TraitQueryMode::Canonical);
+ result.obligations.drain_filter(|projected_obligation| {
+ // If any global obligations always apply, considering regions, then we don't
+ // need to include them. The `is_global` check rules out inference variables,
+ // so there's no need for the caller of `opt_normalize_projection_type`
+ // to evaluate them.
+ // Note that we do *not* discard obligations that evaluate to
+ // `EvaluatedtoOkModuloRegions`. Evaluating these obligations
+ // inside of a query (e.g. `evaluate_obligation`) can change
+ // the result to `EvaluatedToOkModuloRegions`, while an
+ // `EvaluatedToOk` obligation will never change the result.
+ // See #85360 for more details
+ projected_obligation.is_global(canonical.tcx())
+ && canonical
+ .evaluate_root_obligation(projected_obligation)
+ .map_or(false, |res| res.must_apply_considering_regions())
+ });
+
+ infcx.inner.borrow_mut().projection_cache().insert_ty(cache_key, result.clone());
  obligations.extend(result.obligations);
  Ok(Some(result.value))
  }
@@ -974,49 +994,6 @@ fn opt_normalize_projection_type<'a, 'b, 'tcx>(
  }
 }
 
-/// If there are unresolved type variables, then we need to include
-/// any subobligations that bind them, at least until those type
-/// variables are fully resolved.
-fn prune_cache_value_obligations<'a, 'tcx>(
- infcx: &'a InferCtxt<'a, 'tcx>,
- result: &NormalizedTy<'tcx>,
-) -> NormalizedTy<'tcx> {
- if infcx.unresolved_type_vars(&result.value).is_none() {
- return NormalizedTy { value: result.value, obligations: vec![] };
- }
-
- let mut obligations: Vec<_> = result
- .obligations
- .iter()
- .filter(|obligation| {
- let bound_predicate = obligation.predicate.kind();
- match bound_predicate.skip_binder() {
- // We found a `T: Foo<X = U>` predicate, let's check
- // if `U` references any unresolved type
- // variables. In principle, we only care if this
- // projection can help resolve any of the type
- // variables found in `result.value` -- but we just
- // check for any type variables here, for fear of
- // indirect obligations (e.g., we project to `?0`,
- // but we have `T: Foo<X = ?1>` and `?1: Bar<X =
- // ?0>`).
- ty::PredicateKind::Projection(data) => {
- infcx.unresolved_type_vars(&bound_predicate.rebind(data.ty)).is_some()
- }
-
- // We are only interested in `T: Foo<X = U>` predicates, whre
- // `U` references one of `unresolved_type_vars`. =)
- _ => false,
- }
- })
- .cloned()
- .collect();
-
- obligations.shrink_to_fit();
-
- NormalizedTy { value: result.value, obligations }
-}
-
 /// If we are projecting `<T as Trait>::Item`, but `T: Trait` does not
 /// hold. In various error cases, we cannot generate a valid
 /// normalized projection. Therefore, we create an inference variable

compiler/rustc_trait_selection/src/traits/query/evaluate_obligation.rs

@@ -71,7 +71,7 @@ impl<'cx, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'cx, 'tcx> {
  // Run canonical query. If overflow occurs, rerun from scratch but this time
  // in standard trait query mode so that overflow is handled appropriately
  // within `SelectionContext`.
- self.tcx.evaluate_obligation(c_pred)
+ self.tcx.at(obligation.cause.span(self.tcx)).evaluate_obligation(c_pred)
  }
 
  // Helper function that canonicalizes and runs the query. If an

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

@@ -682,7 +682,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
  }
  });
 
- debug!(?result);
+ debug!("finished: {:?} from {:?}", result, obligation);
 
  result
  }

src/test/incremental/const-generics/hash-tyvid-regression-1.rs

@@ -9,7 +9,8 @@ where
  use std::convert::TryFrom;
  <[T; N.get()]>::try_from(())
  //~^ error: the trait bound
- //~^^ error: mismatched types
+ //~| error: the trait bound
+ //~| error: mismatched types
 }
 
 fn main() {}

src/test/ui/impl-trait/auto-trait-leak.stderr

@@ -30,10 +30,10 @@ note: ...which requires building MIR for `cycle1`...
 LL | fn cycle1() -> impl Clone {
  | ^^^^^^^^^^^^^^^^^^^^^^^^^
 note: ...which requires type-checking `cycle1`...
- --> $DIR/auto-trait-leak.rs:12:1
+ --> $DIR/auto-trait-leak.rs:14:5
  |
-LL | fn cycle1() -> impl Clone {
- | ^^^^^^^^^^^^^^^^^^^^^^^^^
+LL |  send(cycle2().clone());
+ |  ^^^^
  = note: ...which requires evaluating trait selection obligation `impl std::clone::Clone: std::marker::Send`...
 note: ...which requires computing type of `cycle2::{opaque#0}`...
  --> $DIR/auto-trait-leak.rs:19:16
@@ -66,10 +66,10 @@ note: ...which requires building MIR for `cycle2`...
 LL | fn cycle2() -> impl Clone {
  | ^^^^^^^^^^^^^^^^^^^^^^^^^
 note: ...which requires type-checking `cycle2`...
- --> $DIR/auto-trait-leak.rs:19:1
+ --> $DIR/auto-trait-leak.rs:20:5
  |
-LL | fn cycle2() -> impl Clone {
- | ^^^^^^^^^^^^^^^^^^^^^^^^^
+LL |  send(cycle1().clone());
+ |  ^^^^
  = note: ...which requires evaluating trait selection obligation `impl std::clone::Clone: std::marker::Send`...
  = note: ...which again requires computing type of `cycle1::{opaque#0}`, completing the cycle
 note: cycle used when checking item types in top-level module

src/test/ui/traits/cycle-cache-err-60010.rs

@@ -25,6 +25,7 @@ struct Runtime<DB: Database> {
 }
 struct SalsaStorage {
  _parse: <ParseQuery as Query<RootDatabase>>::Data,
+ //~^ ERROR overflow
 }
 
 impl Database for RootDatabase {
@@ -67,7 +68,6 @@ pub(crate) fn goto_implementation(db: &RootDatabase) -> u32 {
  // we used to fail to report an error here because we got the
  // caching wrong.
  SourceDatabase::parse(db);
- //~^ ERROR overflow
  22
 }
 

src/test/ui/traits/cycle-cache-err-60010.stderr

@@ -1,8 +1,8 @@
 error[E0275]: overflow evaluating the requirement `SalsaStorage: RefUnwindSafe`
- --> $DIR/cycle-cache-err-60010.rs:69:5
+ --> $DIR/cycle-cache-err-60010.rs:27:13
  |
-LL | SourceDatabase::parse(db);
- | ^^^^^^^^^^^^^^^^^^^^^
+LL | _parse: <ParseQuery as Query<RootDatabase>>::Data,
+ |  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  |
  = note: required because it appears within the type `*const SalsaStorage`
  = note: required because it appears within the type `Unique<SalsaStorage>`
@@ -18,15 +18,15 @@ note: required because it appears within the type `RootDatabase`
 LL | struct RootDatabase {
  | ^^^^^^^^^^^^
 note: required because of the requirements on the impl of `SourceDatabase` for `RootDatabase`
- --> $DIR/cycle-cache-err-60010.rs:43:9
+ --> $DIR/cycle-cache-err-60010.rs:44:9
  |
 LL | impl<T> SourceDatabase for T
  | ^^^^^^^^^^^^^^ ^
-note: required by `SourceDatabase::parse`
- --> $DIR/cycle-cache-err-60010.rs:14:5
+note: required because of the requirements on the impl of `Query<RootDatabase>` for `ParseQuery`
+ --> $DIR/cycle-cache-err-60010.rs:37:10
  |
-LL |  fn parse(&self) {
- | ^^^^^^^^^^^^^^^
+LL | impl<DB> Query<DB> for ParseQuery
+ |  ^^^^^^^^^ ^^^^^^^^^^
 
 error: aborting due to previous error
 

src/test/ui/traits/inductive-overflow/lifetime.rs

@@ -15,8 +15,8 @@ impl<'a> Y for C<'a> {
 struct C<'a>(&'a ());
 struct X<T: Y>(T::P);
 
-impl<T: NotAuto> NotAuto for Box<T> {}
-impl<T: Y> NotAuto for X<T> where T::P: NotAuto {} //~ NOTE: required
+impl<T: NotAuto> NotAuto for Box<T> {} //~ NOTE: required
+impl<T: Y> NotAuto for X<T> where T::P: NotAuto {}
 impl<'a> NotAuto for C<'a> {}
 
 fn is_send<S: NotAuto>() {}
@@ -26,6 +26,6 @@ fn main() {
  // Should only be a few notes.
  is_send::<X<C<'static>>>();
  //~^ ERROR overflow evaluating
- //~| 2 redundant requirements hidden
+ //~| 3 redundant requirements hidden
  //~| required because of
 }

src/test/ui/traits/inductive-overflow/lifetime.stderr

@@ -1,15 +1,15 @@
-error[E0275]: overflow evaluating the requirement `Box<X<C<'_>>>: NotAuto`
+error[E0275]: overflow evaluating the requirement `X<C<'_>>: NotAuto`
  --> $DIR/lifetime.rs:27:5
  |
 LL | is_send::<X<C<'static>>>();
  | ^^^^^^^^^^^^^^^^^^^^^^^^
  |
-note: required because of the requirements on the impl of `NotAuto` for `X<C<'_>>`
- --> $DIR/lifetime.rs:19:12
+note: required because of the requirements on the impl of `NotAuto` for `Box<X<C<'_>>>`
+ --> $DIR/lifetime.rs:18:18
  |
-LL | impl<T: Y> NotAuto for X<T> where T::P: NotAuto {}
- | ^^^^^^^ ^^^^
- = note: 2 redundant requirements hidden
+LL | impl<T: NotAuto> NotAuto for Box<T> {}
+ |  ^^^^^^^ ^^^^^^
+ = note: 3 redundant requirements hidden
  = note: required because of the requirements on the impl of `NotAuto` for `X<C<'static>>`
 note: required by a bound in `is_send`
  --> $DIR/lifetime.rs:22:15

src/test/ui/traits/inductive-overflow/simultaneous.stderr

@@ -1,4 +1,4 @@
-error[E0275]: overflow evaluating the requirement `{integer}: Tweedledee`
+error[E0275]: overflow evaluating the requirement `{integer}: Tweedledum`
  --> $DIR/simultaneous.rs:18:5
  |
 LL | is_ee(4);

src/test/ui/type-alias-impl-trait/auto-trait-leakage3.stderr

@@ -5,10 +5,10 @@ LL | type Foo = impl std::fmt::Debug;
  | ^^^^^^^^^^^^^^^^^^^^
  |
 note: ...which requires type-checking `m::bar`...
- --> $DIR/auto-trait-leakage3.rs:14:5
+ --> $DIR/auto-trait-leakage3.rs:15:9
  |
-LL | pub fn bar() {
- | ^^^^^^^^^^^^
+LL |  is_send(foo());
+ |  ^^^^^^^
  = note: ...which requires evaluating trait selection obligation `impl std::fmt::Debug: std::marker::Send`...
  = note: ...which again requires computing type of `m::Foo::{opaque#0}`, completing the cycle
 note: cycle used when checking item types in module `m`

src/test/ui/type-alias-impl-trait/inference-cycle.stderr

@@ -5,10 +5,10 @@ LL | type Foo = impl std::fmt::Debug;
  | ^^^^^^^^^^^^^^^^^^^^
  |
 note: ...which requires type-checking `m::bar`...
- --> $DIR/inference-cycle.rs:14:5
+ --> $DIR/inference-cycle.rs:15:9
  |
-LL | pub fn bar() {
- | ^^^^^^^^^^^^
+LL |  is_send(foo()); // Today: error
+ |  ^^^^^^^
  = note: ...which requires evaluating trait selection obligation `impl std::fmt::Debug: std::marker::Send`...
  = note: ...which again requires computing type of `m::Foo::{opaque#0}`, completing the cycle
 note: cycle used when checking item types in module `m`