diff --git a/compiler/rustc_trait_selection/src/solve/eval_ctxt/select.rs b/compiler/rustc_trait_selection/src/solve/eval_ctxt/select.rs index 6de19df1067..16fe045b82d 100644 --- a/compiler/rustc_trait_selection/src/solve/eval_ctxt/select.rs +++ b/compiler/rustc_trait_selection/src/solve/eval_ctxt/select.rs @@ -1,22 +1,17 @@ -use rustc_hir as hir; +use std::ops::ControlFlow; + use rustc_hir::def_id::DefId; -use rustc_infer::infer::{DefineOpaqueTypes, InferCtxt}; +use rustc_infer::infer::{DefineOpaqueTypes, InferCtxt, InferOk}; +use rustc_infer::traits::solve::inspect::ProbeKind; +use rustc_infer::traits::solve::{CandidateSource, Certainty, Goal}; use rustc_infer::traits::{ - Obligation, PolyTraitObligation, PredicateObligation, Selection, SelectionResult, TraitEngine, + BuiltinImplSource, ImplSource, ImplSourceUserDefinedData, Obligation, ObligationCause, + PolyTraitObligation, PredicateObligation, Selection, SelectionError, SelectionResult, }; use rustc_macros::extension; -use rustc_middle::traits::solve::{CandidateSource, CanonicalInput, Certainty, Goal}; -use rustc_middle::traits::{ - BuiltinImplSource, ImplSource, ImplSourceUserDefinedData, ObligationCause, SelectionError, -}; -use rustc_middle::ty::{self, Ty, TyCtxt}; -use rustc_span::DUMMY_SP; +use rustc_span::Span; -use crate::solve::assembly::Candidate; -use crate::solve::eval_ctxt::{EvalCtxt, GenerateProofTree}; -use crate::solve::inspect::ProofTreeBuilder; -use crate::traits::StructurallyNormalizeExt; -use crate::traits::TraitEngineExt; +use crate::solve::inspect::{self, ProofTreeInferCtxtExt}; #[extension(pub trait InferCtxtSelectExt<'tcx>)] impl<'tcx> InferCtxt<'tcx> { @@ -26,359 +21,192 @@ fn select_in_new_trait_solver( ) -> SelectionResult<'tcx, Selection<'tcx>> { assert!(self.next_trait_solver()); - self.enter_forall(obligation.predicate, |pred| { - let trait_goal = Goal::new(self.tcx, obligation.param_env, pred); - - let (result, _) = EvalCtxt::enter_root(self, GenerateProofTree::Never, |ecx| { - let goal = Goal::new(ecx.tcx(), trait_goal.param_env, trait_goal.predicate); - let (orig_values, canonical_goal) = ecx.canonicalize_goal(goal); - let mut candidates = ecx.compute_canonical_trait_candidates(canonical_goal); - - // pseudo-winnow - if candidates.len() == 0 { - return Err(SelectionError::Unimplemented); - } else if candidates.len() > 1 { - let mut i = 0; - while i < candidates.len() { - let should_drop_i = (0..candidates.len()).filter(|&j| i != j).any(|j| { - candidate_should_be_dropped_in_favor_of( - ecx.tcx(), - &candidates[i], - &candidates[j], - ) - }); - if should_drop_i { - candidates.swap_remove(i); - } else { - i += 1; - if i > 1 { - return Ok(None); - } - } - } - } - - let candidate = candidates.pop().unwrap(); - let (normalization_nested_goals, certainty) = ecx - .instantiate_and_apply_query_response( - trait_goal.param_env, - orig_values, - candidate.result, - ); - assert!(normalization_nested_goals.is_empty()); - Ok(Some((candidate, certainty))) - }); - - let (candidate, certainty) = match result { - Ok(Some(result)) => result, - Ok(None) => return Ok(None), - Err(e) => return Err(e), - }; - - let goal = self.resolve_vars_if_possible(trait_goal); - match (certainty, candidate.source) { - // Rematching the implementation will instantiate the same nested goals that - // would have caused the ambiguity, so we can still make progress here regardless. - (_, CandidateSource::Impl(def_id)) => rematch_impl(self, goal, def_id), - - // If an unsize goal is ambiguous, then we can manually rematch it to make - // selection progress for coercion during HIR typeck. If it is *not* ambiguous, - // but is `BuiltinImplSource::Misc`, it may have nested `Unsize` goals, - // and we need to rematch those to detect tuple unsizing and trait upcasting. - // FIXME: This will be wrong if we have param-env or where-clause bounds - // with the unsize goal -- we may need to mark those with different impl - // sources. - (Certainty::Maybe(_), CandidateSource::BuiltinImpl(src)) - | (Certainty::Yes, CandidateSource::BuiltinImpl(src @ BuiltinImplSource::Misc)) - if self.tcx.lang_items().unsize_trait() == Some(goal.predicate.def_id()) => - { - rematch_unsize(self, goal, src, certainty) - } - - // Technically some builtin impls have nested obligations, but if - // `Certainty::Yes`, then they should've all been verified and don't - // need re-checking. - (Certainty::Yes, CandidateSource::BuiltinImpl(src)) => { - Ok(Some(ImplSource::Builtin(src, vec![]))) - } - - // It's fine not to do anything to rematch these, since there are no - // nested obligations. - (Certainty::Yes, CandidateSource::ParamEnv(_) | CandidateSource::AliasBound) => { - Ok(Some(ImplSource::Param(vec![]))) - } - - (_, CandidateSource::CoherenceUnknowable) => bug!(), - - (Certainty::Maybe(_), _) => Ok(None), - } - }) - } -} - -impl<'tcx> EvalCtxt<'_, 'tcx> { - fn compute_canonical_trait_candidates( - &mut self, - canonical_input: CanonicalInput<'tcx>, - ) -> Vec> { - // This doesn't record the canonical goal on the stack during the - // candidate assembly step, but that's fine. Selection is conceptually - // outside of the solver, and if there were any cycles, we'd encounter - // the cycle anyways one step later. - EvalCtxt::enter_canonical( - self.tcx(), - self.search_graph, - canonical_input, - // FIXME: This is wrong, idk if we even want to track stuff here. - &mut ProofTreeBuilder::new_noop(), - |ecx, goal| { - let trait_goal = Goal { - param_env: goal.param_env, - predicate: goal - .predicate - .to_opt_poly_trait_pred() - .expect("we canonicalized a trait goal") - .no_bound_vars() - .expect("we instantiated all bound vars"), - }; - ecx.assemble_and_evaluate_candidates(trait_goal) - }, + self.visit_proof_tree( + Goal::new(self.tcx, obligation.param_env, obligation.predicate), + &mut Select { span: obligation.cause.span }, ) + .break_value() + .unwrap() } } -fn candidate_should_be_dropped_in_favor_of<'tcx>( - tcx: TyCtxt<'tcx>, - victim: &Candidate<'tcx>, - other: &Candidate<'tcx>, -) -> bool { - match (victim.source, other.source) { - (CandidateSource::ParamEnv(victim_idx), CandidateSource::ParamEnv(other_idx)) => { - victim_idx >= other_idx - } - (_, CandidateSource::ParamEnv(_)) => true, +struct Select { + span: Span, +} - // FIXME: we could prefer earlier vtable bases perhaps... +impl<'tcx> inspect::ProofTreeVisitor<'tcx> for Select { + type Result = ControlFlow>>; + + fn span(&self) -> Span { + self.span + } + + fn visit_goal(&mut self, goal: &inspect::InspectGoal<'_, 'tcx>) -> Self::Result { + let mut candidates = goal.candidates(); + candidates.retain(|cand| cand.result().is_ok()); + + // No candidates -- not implemented. + if candidates.is_empty() { + return ControlFlow::Break(Err(SelectionError::Unimplemented)); + } + + // One candidate, no need to winnow. + if candidates.len() == 1 { + return ControlFlow::Break(Ok(to_selection( + self.span, + candidates.into_iter().next().unwrap(), + ))); + } + + // We need to winnow. See comments on `candidate_should_be_dropped_in_favor_of`. + let mut i = 0; + while i < candidates.len() { + let should_drop_i = (0..candidates.len()) + .filter(|&j| i != j) + .any(|j| candidate_should_be_dropped_in_favor_of(&candidates[i], &candidates[j])); + if should_drop_i { + candidates.swap_remove(i); + } else { + i += 1; + if i > 1 { + return ControlFlow::Break(Ok(None)); + } + } + } + + ControlFlow::Break(Ok(to_selection(self.span, candidates.into_iter().next().unwrap()))) + } +} + +/// This is a lot more limited than the old solver's equivalent method. This may lead to more `Ok(None)` +/// results when selecting traits in polymorphic contexts, but we should never rely on the lack of ambiguity, +/// and should always just gracefully fail here. We shouldn't rely on this incompleteness. +fn candidate_should_be_dropped_in_favor_of<'tcx>( + victim: &inspect::InspectCandidate<'_, 'tcx>, + other: &inspect::InspectCandidate<'_, 'tcx>, +) -> bool { + // Don't winnow until `Certainty::Yes` -- we don't need to winnow until + // codegen, technically. + if matches!(other.result().unwrap(), Certainty::Maybe(..)) { + return false; + } + + let inspect::ProbeKind::TraitCandidate { source: victim_source, result: _ } = victim.kind() + else { + return false; + }; + let inspect::ProbeKind::TraitCandidate { source: other_source, result: _ } = other.kind() + else { + return false; + }; + + match (victim_source, other_source) { + (_, CandidateSource::CoherenceUnknowable) | (CandidateSource::CoherenceUnknowable, _) => { + bug!("should not have assembled a CoherenceUnknowable candidate") + } + + // Prefer dyn candidates over non-dyn candidates. This is necessary to + // handle the unsoundness between `impl Any for T` and `dyn Any: Any`. ( CandidateSource::BuiltinImpl(BuiltinImplSource::Object { .. }), CandidateSource::BuiltinImpl(BuiltinImplSource::Object { .. }), ) => false, - (_, CandidateSource::BuiltinImpl(BuiltinImplSource::Object { .. })) => true, + ( + CandidateSource::Impl(_) | CandidateSource::ParamEnv(_) | CandidateSource::AliasBound, + CandidateSource::BuiltinImpl(BuiltinImplSource::Object { .. }), + ) => true, + // Prefer specializing candidates over specialized candidates. (CandidateSource::Impl(victim_def_id), CandidateSource::Impl(other_def_id)) => { - tcx.specializes((other_def_id, victim_def_id)) - && other.result.value.certainty == Certainty::Yes + victim.goal().infcx().tcx.specializes((other_def_id, victim_def_id)) } _ => false, } } +fn to_selection<'tcx>( + span: Span, + cand: inspect::InspectCandidate<'_, 'tcx>, +) -> Option> { + if let Certainty::Maybe(..) = cand.shallow_certainty() { + return None; + } + + let make_nested = || { + cand.instantiate_nested_goals(span) + .into_iter() + .map(|nested| { + Obligation::new( + nested.infcx().tcx, + ObligationCause::dummy_with_span(span), + nested.goal().param_env, + nested.goal().predicate, + ) + }) + .collect() + }; + + Some(match cand.kind() { + ProbeKind::TraitCandidate { source, result: _ } => match source { + CandidateSource::Impl(impl_def_id) => { + // FIXME: Remove this in favor of storing this in the tree + // For impl candidates, we do the rematch manually to compute the args. + ImplSource::UserDefined(rematch_impl(cand.goal(), impl_def_id, span)) + } + CandidateSource::BuiltinImpl(builtin) => ImplSource::Builtin(builtin, make_nested()), + CandidateSource::ParamEnv(_) => ImplSource::Param(make_nested()), + CandidateSource::AliasBound => { + ImplSource::Builtin(BuiltinImplSource::Misc, make_nested()) + } + CandidateSource::CoherenceUnknowable => { + span_bug!(span, "didn't expect to select an unknowable candidate") + } + }, + ProbeKind::TryNormalizeNonRigid { result: _ } + | ProbeKind::NormalizedSelfTyAssembly + | ProbeKind::UnsizeAssembly + | ProbeKind::UpcastProjectionCompatibility + | ProbeKind::OpaqueTypeStorageLookup { result: _ } + | ProbeKind::Root { result: _ } => { + span_bug!(span, "didn't expect to assemble trait candidate from {:#?}", cand.kind()) + } + }) +} + fn rematch_impl<'tcx>( - infcx: &InferCtxt<'tcx>, - goal: Goal<'tcx, ty::TraitPredicate<'tcx>>, + goal: &inspect::InspectGoal<'_, 'tcx>, impl_def_id: DefId, -) -> SelectionResult<'tcx, Selection<'tcx>> { - let args = infcx.fresh_args_for_item(DUMMY_SP, impl_def_id); + span: Span, +) -> ImplSourceUserDefinedData<'tcx, PredicateObligation<'tcx>> { + let infcx = goal.infcx(); + let goal_trait_ref = infcx + .enter_forall_and_leak_universe(goal.goal().predicate.to_opt_poly_trait_pred().unwrap()) + .trait_ref; + + let args = infcx.fresh_args_for_item(span, impl_def_id); let impl_trait_ref = infcx.tcx.impl_trait_ref(impl_def_id).unwrap().instantiate(infcx.tcx, args); - let mut nested = infcx - .at(&ObligationCause::dummy(), goal.param_env) - // New solver ignores DefineOpaqueTypes, so choose Yes for consistency - .eq(DefineOpaqueTypes::Yes, goal.predicate.trait_ref, impl_trait_ref) - .map_err(|_| SelectionError::Unimplemented)? - .into_obligations(); + let InferOk { value: (), obligations: mut nested } = infcx + .at(&ObligationCause::dummy_with_span(span), goal.goal().param_env) + .eq(DefineOpaqueTypes::Yes, goal_trait_ref, impl_trait_ref) + .expect("rematching impl failed"); + + // FIXME(-Znext-solver=coinductive): We need to add supertraits here eventually. nested.extend( infcx.tcx.predicates_of(impl_def_id).instantiate(infcx.tcx, args).into_iter().map( - |(pred, _)| Obligation::new(infcx.tcx, ObligationCause::dummy(), goal.param_env, pred), + |(clause, _)| { + Obligation::new( + infcx.tcx, + ObligationCause::dummy_with_span(span), + goal.goal().param_env, + clause, + ) + }, ), ); - Ok(Some(ImplSource::UserDefined(ImplSourceUserDefinedData { impl_def_id, args, nested }))) -} - -/// The `Unsize` trait is particularly important to coercion, so we try rematch it. -/// NOTE: This must stay in sync with `consider_builtin_unsize_candidate` in trait -/// goal assembly in the solver, both for soundness and in order to avoid ICEs. -fn rematch_unsize<'tcx>( - infcx: &InferCtxt<'tcx>, - goal: Goal<'tcx, ty::TraitPredicate<'tcx>>, - source: BuiltinImplSource, - certainty: Certainty, -) -> SelectionResult<'tcx, Selection<'tcx>> { - let tcx = infcx.tcx; - let mut nested = vec![]; - let a_ty = structurally_normalize(goal.predicate.self_ty(), infcx, goal.param_env, &mut nested); - let b_ty = structurally_normalize( - goal.predicate.trait_ref.args.type_at(1), - infcx, - goal.param_env, - &mut nested, - ); - - match (a_ty.kind(), b_ty.kind()) { - // Don't try to coerce `?0` to `dyn Trait` - (ty::Infer(ty::TyVar(_)), _) | (_, ty::Infer(ty::TyVar(_))) => Ok(None), - // Stall any ambiguous upcasting goals, since we can't rematch those - (ty::Dynamic(_, _, ty::Dyn), ty::Dynamic(_, _, ty::Dyn)) => match certainty { - Certainty::Yes => Ok(Some(ImplSource::Builtin(source, nested))), - _ => Ok(None), - }, - // `T` -> `dyn Trait` upcasting - (_, &ty::Dynamic(data, region, ty::Dyn)) => { - // Check that the type implements all of the predicates of the def-id. - // (i.e. the principal, all of the associated types match, and any auto traits) - nested.extend(data.iter().map(|pred| { - Obligation::new( - infcx.tcx, - ObligationCause::dummy(), - goal.param_env, - pred.with_self_ty(tcx, a_ty), - ) - })); - // The type must be Sized to be unsized. - let sized_def_id = tcx.require_lang_item(hir::LangItem::Sized, None); - nested.push(Obligation::new( - infcx.tcx, - ObligationCause::dummy(), - goal.param_env, - ty::TraitRef::new(tcx, sized_def_id, [a_ty]), - )); - // The type must outlive the lifetime of the `dyn` we're unsizing into. - nested.push(Obligation::new( - infcx.tcx, - ObligationCause::dummy(), - goal.param_env, - ty::OutlivesPredicate(a_ty, region), - )); - - Ok(Some(ImplSource::Builtin(source, nested))) - } - // `[T; n]` -> `[T]` unsizing - (&ty::Array(a_elem_ty, ..), &ty::Slice(b_elem_ty)) => { - nested.extend( - infcx - .at(&ObligationCause::dummy(), goal.param_env) - // New solver ignores DefineOpaqueTypes, so choose Yes for consistency - .eq(DefineOpaqueTypes::Yes, a_elem_ty, b_elem_ty) - .expect("expected rematch to succeed") - .into_obligations(), - ); - - Ok(Some(ImplSource::Builtin(source, nested))) - } - // Struct unsizing `Struct` -> `Struct` where `T: Unsize` - (&ty::Adt(a_def, a_args), &ty::Adt(b_def, b_args)) - if a_def.is_struct() && a_def.did() == b_def.did() => - { - let unsizing_params = tcx.unsizing_params_for_adt(a_def.did()); - // We must be unsizing some type parameters. This also implies - // that the struct has a tail field. - if unsizing_params.is_empty() { - bug!("expected rematch to succeed") - } - - let tail_field = a_def - .non_enum_variant() - .fields - .raw - .last() - .expect("expected unsized ADT to have a tail field"); - let tail_field_ty = tcx.type_of(tail_field.did); - - let a_tail_ty = tail_field_ty.instantiate(tcx, a_args); - let b_tail_ty = tail_field_ty.instantiate(tcx, b_args); - - // Instantiate just the unsizing params from B into A. The type after - // this instantiation must be equal to B. This is so we don't unsize - // unrelated type parameters. - let new_a_args = tcx.mk_args_from_iter( - a_args - .iter() - .enumerate() - .map(|(i, a)| if unsizing_params.contains(i as u32) { b_args[i] } else { a }), - ); - let unsized_a_ty = Ty::new_adt(tcx, a_def, new_a_args); - - nested.extend( - infcx - .at(&ObligationCause::dummy(), goal.param_env) - // New solver ignores DefineOpaqueTypes, so choose Yes for consistency - .eq(DefineOpaqueTypes::Yes, unsized_a_ty, b_ty) - .expect("expected rematch to succeed") - .into_obligations(), - ); - - // Finally, we require that `TailA: Unsize` for the tail field - // types. - nested.push(Obligation::new( - tcx, - ObligationCause::dummy(), - goal.param_env, - ty::TraitRef::new(tcx, goal.predicate.def_id(), [a_tail_ty, b_tail_ty]), - )); - - Ok(Some(ImplSource::Builtin(source, nested))) - } - // Tuple unsizing `(.., T)` -> `(.., U)` where `T: Unsize` - (&ty::Tuple(a_tys), &ty::Tuple(b_tys)) - if a_tys.len() == b_tys.len() && !a_tys.is_empty() => - { - let (a_last_ty, a_rest_tys) = a_tys.split_last().unwrap(); - let b_last_ty = b_tys.last().unwrap(); - - // Instantiate just the tail field of B., and require that they're equal. - let unsized_a_ty = - Ty::new_tup_from_iter(tcx, a_rest_tys.iter().chain([b_last_ty]).copied()); - nested.extend( - infcx - .at(&ObligationCause::dummy(), goal.param_env) - // New solver ignores DefineOpaqueTypes, so choose Yes for consistency - .eq(DefineOpaqueTypes::Yes, unsized_a_ty, b_ty) - .expect("expected rematch to succeed") - .into_obligations(), - ); - - // Similar to ADTs, require that we can unsize the tail. - nested.push(Obligation::new( - tcx, - ObligationCause::dummy(), - goal.param_env, - ty::TraitRef::new(tcx, goal.predicate.def_id(), [*a_last_ty, *b_last_ty]), - )); - - // We need to be able to detect tuple unsizing to require its feature gate. - assert_eq!( - source, - BuiltinImplSource::TupleUnsizing, - "compiler-errors wants to know if this can ever be triggered..." - ); - Ok(Some(ImplSource::Builtin(source, nested))) - } - _ => { - assert_ne!(certainty, Certainty::Yes); - Ok(None) - } - } -} - -fn structurally_normalize<'tcx>( - ty: Ty<'tcx>, - infcx: &InferCtxt<'tcx>, - param_env: ty::ParamEnv<'tcx>, - nested: &mut Vec>, -) -> Ty<'tcx> { - if matches!(ty.kind(), ty::Alias(..)) { - let mut engine = >::new(infcx); - let normalized_ty = infcx - .at(&ObligationCause::dummy(), param_env) - .structurally_normalize(ty, &mut *engine) - .expect("normalization shouldn't fail if we got to here"); - nested.extend(engine.pending_obligations()); - normalized_ty - } else { - ty - } + ImplSourceUserDefinedData { impl_def_id, nested, args } } diff --git a/tests/ui/traits/dyn-any-prefer-vtable.rs b/tests/ui/traits/dyn-any-prefer-vtable.rs new file mode 100644 index 00000000000..ca9d655239d --- /dev/null +++ b/tests/ui/traits/dyn-any-prefer-vtable.rs @@ -0,0 +1,9 @@ +//@ run-pass +//@ revisions: current next +//@ ignore-compare-mode-next-solver (explicit revisions) +//@[next] compile-flags: -Znext-solver + +fn main() { + let x: &dyn std::any::Any = &1i32; + assert_eq!(x.type_id(), std::any::TypeId::of::()); +}