diff options
Diffstat (limited to 'compiler/rustc_infer/src/infer/mod.rs')
| -rw-r--r-- | compiler/rustc_infer/src/infer/mod.rs | 67 |
1 files changed, 62 insertions, 5 deletions
diff --git a/compiler/rustc_infer/src/infer/mod.rs b/compiler/rustc_infer/src/infer/mod.rs index 2d269e320b6..5bbd8a84b7f 100644 --- a/compiler/rustc_infer/src/infer/mod.rs +++ b/compiler/rustc_infer/src/infer/mod.rs @@ -37,10 +37,11 @@ use snapshot::undo_log::InferCtxtUndoLogs; use tracing::{debug, instrument}; use type_variable::TypeVariableOrigin; -use crate::infer::region_constraints::UndoLog; +use crate::infer::snapshot::undo_log::UndoLog; use crate::infer::unify_key::{ConstVariableOrigin, ConstVariableValue, ConstVidKey}; use crate::traits::{ - self, ObligationCause, ObligationInspector, PredicateObligations, TraitEngine, + self, ObligationCause, ObligationInspector, PredicateObligation, PredicateObligations, + TraitEngine, }; pub mod at; @@ -156,6 +157,12 @@ pub struct InferCtxtInner<'tcx> { /// which may cause types to no longer be considered well-formed. region_assumptions: Vec<ty::ArgOutlivesPredicate<'tcx>>, + /// `-Znext-solver`: Successfully proven goals during HIR typeck which + /// reference inference variables and get reproven after writeback. + /// + /// See the documentation of `InferCtxt::in_hir_typeck` for more details. + hir_typeck_potentially_region_dependent_goals: Vec<PredicateObligation<'tcx>>, + /// Caches for opaque type inference. opaque_type_storage: OpaqueTypeStorage<'tcx>, } @@ -173,6 +180,7 @@ impl<'tcx> InferCtxtInner<'tcx> { region_constraint_storage: Some(Default::default()), region_obligations: Default::default(), region_assumptions: Default::default(), + hir_typeck_potentially_region_dependent_goals: Default::default(), opaque_type_storage: Default::default(), } } @@ -244,9 +252,29 @@ pub struct InferCtxt<'tcx> { typing_mode: TypingMode<'tcx>, /// Whether this inference context should care about region obligations in - /// the root universe. Most notably, this is used during hir typeck as region + /// the root universe. Most notably, this is used during HIR typeck as region /// solving is left to borrowck instead. pub considering_regions: bool, + /// `-Znext-solver`: Whether this inference context is used by HIR typeck. If so, we + /// need to make sure we don't rely on region identity in the trait solver or when + /// relating types. This is necessary as borrowck starts by replacing each occurrence of a + /// free region with a unique inference variable. If HIR typeck ends up depending on two + /// regions being equal we'd get unexpected mismatches between HIR typeck and MIR typeck, + /// resulting in an ICE. + /// + /// The trait solver sometimes depends on regions being identical. As a concrete example + /// the trait solver ignores other candidates if one candidate exists without any constraints. + /// The goal `&'a u32: Equals<&'a u32>` has no constraints right now. If we replace each + /// occurrence of `'a` with a unique region the goal now equates these regions. See + /// the tests in trait-system-refactor-initiative#27 for concrete examples. + /// + /// We handle this by *uniquifying* region when canonicalizing root goals during HIR typeck. + /// This is still insufficient as inference variables may *hide* region variables, so e.g. + /// `dyn TwoSuper<?x, ?x>: Super<?x>` may hold but MIR typeck could end up having to prove + /// `dyn TwoSuper<&'0 (), &'1 ()>: Super<&'2 ()>` which is now ambiguous. Because of this we + /// stash all successfully proven goals which reference inference variables and then reprove + /// them after writeback. + pub in_hir_typeck: bool, /// If set, this flag causes us to skip the 'leak check' during /// higher-ranked subtyping operations. This flag is a temporary one used @@ -506,6 +534,7 @@ pub struct TypeOutlivesConstraint<'tcx> { pub struct InferCtxtBuilder<'tcx> { tcx: TyCtxt<'tcx>, considering_regions: bool, + in_hir_typeck: bool, skip_leak_check: bool, /// Whether we should use the new trait solver in the local inference context, /// which affects things like which solver is used in `predicate_may_hold`. @@ -518,6 +547,7 @@ impl<'tcx> TyCtxt<'tcx> { InferCtxtBuilder { tcx: self, considering_regions: true, + in_hir_typeck: false, skip_leak_check: false, next_trait_solver: self.next_trait_solver_globally(), } @@ -535,6 +565,11 @@ impl<'tcx> InferCtxtBuilder<'tcx> { self } + pub fn in_hir_typeck(mut self) -> Self { + self.in_hir_typeck = true; + self + } + pub fn skip_leak_check(mut self, skip_leak_check: bool) -> Self { self.skip_leak_check = skip_leak_check; self @@ -568,12 +603,18 @@ impl<'tcx> InferCtxtBuilder<'tcx> { } pub fn build(&mut self, typing_mode: TypingMode<'tcx>) -> InferCtxt<'tcx> { - let InferCtxtBuilder { tcx, considering_regions, skip_leak_check, next_trait_solver } = - *self; + let InferCtxtBuilder { + tcx, + considering_regions, + in_hir_typeck, + skip_leak_check, + next_trait_solver, + } = *self; InferCtxt { tcx, typing_mode, considering_regions, + in_hir_typeck, skip_leak_check, inner: RefCell::new(InferCtxtInner::new()), lexical_region_resolutions: RefCell::new(None), @@ -978,6 +1019,22 @@ impl<'tcx> InferCtxt<'tcx> { } } + pub fn push_hir_typeck_potentially_region_dependent_goal( + &self, + goal: PredicateObligation<'tcx>, + ) { + let mut inner = self.inner.borrow_mut(); + inner.undo_log.push(UndoLog::PushHirTypeckPotentiallyRegionDependentGoal); + inner.hir_typeck_potentially_region_dependent_goals.push(goal); + } + + pub fn take_hir_typeck_potentially_region_dependent_goals( + &self, + ) -> Vec<PredicateObligation<'tcx>> { + assert!(!self.in_snapshot(), "cannot take goals in a snapshot"); + std::mem::take(&mut self.inner.borrow_mut().hir_typeck_potentially_region_dependent_goals) + } + pub fn ty_to_string(&self, t: Ty<'tcx>) -> String { self.resolve_vars_if_possible(t).to_string() } |