diff options
7 files changed, 128 insertions, 19 deletions
diff --git a/compiler/rustc_hir_typeck/src/lib.rs b/compiler/rustc_hir_typeck/src/lib.rs index 9e324286fa1..b395aa8162c 100644 --- a/compiler/rustc_hir_typeck/src/lib.rs +++ b/compiler/rustc_hir_typeck/src/lib.rs @@ -53,7 +53,7 @@ use rustc_hir_analysis::check::{check_abi, check_custom_abi}; use rustc_hir_analysis::hir_ty_lowering::HirTyLowerer; use rustc_infer::traits::{ObligationCauseCode, ObligationInspector, WellFormedLoc}; use rustc_middle::query::Providers; -use rustc_middle::ty::{self, Ty, TyCtxt}; +use rustc_middle::ty::{self, Ty, TyCtxt, TypeVisitableExt}; use rustc_middle::{bug, span_bug}; use rustc_session::config; use rustc_span::Span; @@ -259,6 +259,21 @@ fn typeck_with_inspect<'tcx>( let typeck_results = fcx.resolve_type_vars_in_body(body); + // Handle potentially region dependent goals, see `InferCtxt::in_hir_typeck`. + if let None = fcx.infcx.tainted_by_errors() { + for obligation in fcx.take_hir_typeck_potentially_region_dependent_goals() { + let obligation = fcx.resolve_vars_if_possible(obligation); + if obligation.has_non_region_infer() { + bug!("unexpected inference variable after writeback: {obligation:?}"); + } + fcx.register_predicate(obligation); + } + fcx.select_obligations_where_possible(|_| {}); + if let None = fcx.infcx.tainted_by_errors() { + fcx.report_ambiguity_errors(); + } + } + fcx.detect_opaque_types_added_during_writeback(); // Consistency check our TypeckResults instance can hold all ItemLocalIds diff --git a/compiler/rustc_infer/src/infer/mod.rs b/compiler/rustc_infer/src/infer/mod.rs index 17c587c5e7f..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(), } } @@ -247,24 +255,25 @@ pub struct InferCtxt<'tcx> { /// the root universe. Most notably, this is used during HIR typeck as region /// solving is left to borrowck instead. pub considering_regions: bool, - /// Whether this inference context is used by HIR typeck. If so, we uniquify regions - /// with `-Znext-solver`. This is necessary as borrowck will start by replacing each - /// occurance of a free region with a unique inference variable so 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. + /// `-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, but if we replace - /// each occurance of `'a` with a unique region the goal now equates these regions. - /// - /// See the tests in trait-system-refactor-initiative#27 for concrete examples. + /// 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. /// - /// FIXME(-Znext-solver): This is insufficient in theory as a goal `T: Trait<?x, ?x>` - /// may rely on the two occurances of `?x` being identical. If `?x` gets inferred to a - /// type containing regions, this will no longer be the case. We can handle this case - /// by storing goals which hold while still depending on inference vars and then - /// reproving them before writeback. + /// 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 @@ -1010,6 +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() } diff --git a/compiler/rustc_infer/src/infer/outlives/obligations.rs b/compiler/rustc_infer/src/infer/outlives/obligations.rs index a8520c0e71d..bb3b51c0ab2 100644 --- a/compiler/rustc_infer/src/infer/outlives/obligations.rs +++ b/compiler/rustc_infer/src/infer/outlives/obligations.rs @@ -177,6 +177,7 @@ impl<'tcx> InferCtxt<'tcx> { } pub fn take_registered_region_assumptions(&self) -> Vec<ty::ArgOutlivesPredicate<'tcx>> { + assert!(!self.in_snapshot(), "cannot take registered region assumptions in a snapshot"); std::mem::take(&mut self.inner.borrow_mut().region_assumptions) } diff --git a/compiler/rustc_infer/src/infer/snapshot/undo_log.rs b/compiler/rustc_infer/src/infer/snapshot/undo_log.rs index 40e4c329446..fcc0ab3af41 100644 --- a/compiler/rustc_infer/src/infer/snapshot/undo_log.rs +++ b/compiler/rustc_infer/src/infer/snapshot/undo_log.rs @@ -29,6 +29,7 @@ pub(crate) enum UndoLog<'tcx> { ProjectionCache(traits::UndoLog<'tcx>), PushTypeOutlivesConstraint, PushRegionAssumption, + PushHirTypeckPotentiallyRegionDependentGoal, } macro_rules! impl_from { @@ -79,7 +80,12 @@ impl<'tcx> Rollback<UndoLog<'tcx>> for InferCtxtInner<'tcx> { assert_matches!(popped, Some(_), "pushed region constraint but could not pop it"); } UndoLog::PushRegionAssumption => { - self.region_assumptions.pop(); + let popped = self.region_assumptions.pop(); + assert_matches!(popped, Some(_), "pushed region assumption but could not pop it"); + } + UndoLog::PushHirTypeckPotentiallyRegionDependentGoal => { + let popped = self.hir_typeck_potentially_region_dependent_goals.pop(); + assert_matches!(popped, Some(_), "pushed goal but could not pop it"); } } } diff --git a/compiler/rustc_trait_selection/src/solve/fulfill.rs b/compiler/rustc_trait_selection/src/solve/fulfill.rs index 70452947a8b..e0b9380eca3 100644 --- a/compiler/rustc_trait_selection/src/solve/fulfill.rs +++ b/compiler/rustc_trait_selection/src/solve/fulfill.rs @@ -197,6 +197,12 @@ where delegate.compute_goal_fast_path(goal, obligation.cause.span) { match certainty { + // This fast path doesn't depend on region identity so it doesn't + // matter if the goal contains inference variables or not, so we + // don't need to call `push_hir_typeck_potentially_region_dependent_goal` + // here. + // + // Only goals proven via the trait solver should be region dependent. Certainty::Yes => {} Certainty::Maybe(_) => { self.obligations.register(obligation, None); @@ -234,7 +240,11 @@ where } match certainty { - Certainty::Yes => {} + Certainty::Yes => { + if infcx.in_hir_typeck && obligation.has_non_region_infer() { + infcx.push_hir_typeck_potentially_region_dependent_goal(obligation); + } + } Certainty::Maybe(_) => self.obligations.register(obligation, stalled_on), } } diff --git a/tests/ui/traits/next-solver/assembly/ambiguity-due-to-uniquification-3.next.stderr b/tests/ui/traits/next-solver/assembly/ambiguity-due-to-uniquification-3.next.stderr new file mode 100644 index 00000000000..e25f892b365 --- /dev/null +++ b/tests/ui/traits/next-solver/assembly/ambiguity-due-to-uniquification-3.next.stderr @@ -0,0 +1,19 @@ +error[E0283]: type annotations needed: cannot satisfy `(dyn Object<&(), &()> + 'static): Trait<&()>` + --> $DIR/ambiguity-due-to-uniquification-3.rs:28:17 + | +LL | impls_trait(obj, t); + | ----------- ^^^ + | | + | required by a bound introduced by this call + | + = note: cannot satisfy `(dyn Object<&(), &()> + 'static): Trait<&()>` + = help: the trait `Trait<T>` is implemented for `()` +note: required by a bound in `impls_trait` + --> $DIR/ambiguity-due-to-uniquification-3.rs:24:19 + | +LL | fn impls_trait<T: Trait<U>, U>(_: Inv<T>, _: Inv<U>) {} + | ^^^^^^^^ required by this bound in `impls_trait` + +error: aborting due to 1 previous error + +For more information about this error, try `rustc --explain E0283`. diff --git a/tests/ui/traits/next-solver/assembly/ambiguity-due-to-uniquification-3.rs b/tests/ui/traits/next-solver/assembly/ambiguity-due-to-uniquification-3.rs new file mode 100644 index 00000000000..6dcd9d5bdf4 --- /dev/null +++ b/tests/ui/traits/next-solver/assembly/ambiguity-due-to-uniquification-3.rs @@ -0,0 +1,33 @@ +//@ revisions: current next +//@[next] compile-flags: -Znext-solver +//@ ignore-compare-mode-next-solver (explicit revisions) +//@[current] check-pass + +// Regression test from trait-system-refactor-initiative#27. +// +// Unlike in the previous two tests, `dyn Object<?x, ?y>: Trait<?x>` relies +// on structural identity of type inference variables. This inference variable +// gets constrained to a type containing a region later on. To prevent this +// from causing an ICE during MIR borrowck, we stash goals which depend on +// inference variables and then reprove them at the end of HIR typeck. + +#![feature(rustc_attrs)] +#![rustc_no_implicit_bounds] +trait Trait<T> {} +impl<T> Trait<T> for () {} + +trait Object<T, U>: Trait<T> + Trait<U> {} + +#[derive(Clone, Copy)] +struct Inv<T>(*mut T); +fn foo<T: Sized, U: Sized>() -> (Inv<dyn Object<T, U>>, Inv<T>) { todo!() } +fn impls_trait<T: Trait<U>, U>(_: Inv<T>, _: Inv<U>) {} + +fn bar() { + let (obj, t) = foo(); + impls_trait(obj, t); + //[next]~^ ERROR type annotations needed + let _: Inv<dyn Object<&(), &()>> = obj; +} + +fn main() {} |