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Diffstat (limited to 'src/librustc_trait_selection/traits/mod.rs')
| -rw-r--r-- | src/librustc_trait_selection/traits/mod.rs | 531 |
1 files changed, 531 insertions, 0 deletions
diff --git a/src/librustc_trait_selection/traits/mod.rs b/src/librustc_trait_selection/traits/mod.rs new file mode 100644 index 00000000000..9a853c32eaa --- /dev/null +++ b/src/librustc_trait_selection/traits/mod.rs @@ -0,0 +1,531 @@ +//! Trait Resolution. See the [rustc dev guide] for more information on how this works. +//! +//! [rustc dev guide]: https://rustc-dev-guide.rust-lang.org/traits/resolution.html + +#[allow(dead_code)] +pub mod auto_trait; +pub mod codegen; +mod coherence; +mod engine; +pub mod error_reporting; +mod fulfill; +pub mod misc; +mod object_safety; +mod on_unimplemented; +mod project; +pub mod query; +mod select; +mod specialize; +mod structural_match; +mod util; +pub mod wf; + +use crate::infer::outlives::env::OutlivesEnvironment; +use crate::infer::{InferCtxt, RegionckMode, TyCtxtInferExt}; +use crate::traits::error_reporting::InferCtxtExt as _; +use crate::traits::query::evaluate_obligation::InferCtxtExt as _; +use rustc_errors::ErrorReported; +use rustc_hir as hir; +use rustc_hir::def_id::DefId; +use rustc_middle::middle::region; +use rustc_middle::ty::fold::TypeFoldable; +use rustc_middle::ty::subst::{InternalSubsts, SubstsRef}; +use rustc_middle::ty::{self, GenericParamDefKind, ToPredicate, Ty, TyCtxt, WithConstness}; +use rustc_span::{Span, DUMMY_SP}; + +use std::fmt::Debug; + +pub use self::FulfillmentErrorCode::*; +pub use self::ObligationCauseCode::*; +pub use self::SelectionError::*; +pub use self::Vtable::*; + +pub use self::coherence::{add_placeholder_note, orphan_check, overlapping_impls}; +pub use self::coherence::{OrphanCheckErr, OverlapResult}; +pub use self::engine::TraitEngineExt; +pub use self::fulfill::{FulfillmentContext, PendingPredicateObligation}; +pub use self::object_safety::astconv_object_safety_violations; +pub use self::object_safety::is_vtable_safe_method; +pub use self::object_safety::MethodViolationCode; +pub use self::object_safety::ObjectSafetyViolation; +pub use self::on_unimplemented::{OnUnimplementedDirective, OnUnimplementedNote}; +pub use self::project::{ + normalize, normalize_projection_type, normalize_to, poly_project_and_unify_type, +}; +pub use self::select::{EvaluationCache, SelectionCache, SelectionContext}; +pub use self::select::{EvaluationResult, IntercrateAmbiguityCause, OverflowError}; +pub use self::specialize::specialization_graph::FutureCompatOverlapError; +pub use self::specialize::specialization_graph::FutureCompatOverlapErrorKind; +pub use self::specialize::{specialization_graph, translate_substs, OverlapError}; +pub use self::structural_match::search_for_structural_match_violation; +pub use self::structural_match::type_marked_structural; +pub use self::structural_match::NonStructuralMatchTy; +pub use self::util::{elaborate_predicates, elaborate_trait_ref, elaborate_trait_refs}; +pub use self::util::{expand_trait_aliases, TraitAliasExpander}; +pub use self::util::{ + get_vtable_index_of_object_method, impl_item_is_final, predicate_for_trait_def, upcast_choices, +}; +pub use self::util::{ + supertrait_def_ids, supertraits, transitive_bounds, SupertraitDefIds, Supertraits, +}; + +pub use rustc_infer::traits::*; + +/// Whether to skip the leak check, as part of a future compatibility warning step. +#[derive(Copy, Clone, PartialEq, Eq, Debug)] +pub enum SkipLeakCheck { + Yes, + No, +} + +impl SkipLeakCheck { + fn is_yes(self) -> bool { + self == SkipLeakCheck::Yes + } +} + +/// The "default" for skip-leak-check corresponds to the current +/// behavior (do not skip the leak check) -- not the behavior we are +/// transitioning into. +impl Default for SkipLeakCheck { + fn default() -> Self { + SkipLeakCheck::No + } +} + +/// The mode that trait queries run in. +#[derive(Copy, Clone, PartialEq, Eq, Debug)] +pub enum TraitQueryMode { + // Standard/un-canonicalized queries get accurate + // spans etc. passed in and hence can do reasonable + // error reporting on their own. + Standard, + // Canonicalized queries get dummy spans and hence + // must generally propagate errors to + // pre-canonicalization callsites. + Canonical, +} + +/// Creates predicate obligations from the generic bounds. +pub fn predicates_for_generics<'tcx>( + cause: ObligationCause<'tcx>, + param_env: ty::ParamEnv<'tcx>, + generic_bounds: &ty::InstantiatedPredicates<'tcx>, +) -> PredicateObligations<'tcx> { + util::predicates_for_generics(cause, 0, param_env, generic_bounds) +} + +/// Determines whether the type `ty` is known to meet `bound` and +/// returns true if so. Returns false if `ty` either does not meet +/// `bound` or is not known to meet bound (note that this is +/// conservative towards *no impl*, which is the opposite of the +/// `evaluate` methods). +pub fn type_known_to_meet_bound_modulo_regions<'a, 'tcx>( + infcx: &InferCtxt<'a, 'tcx>, + param_env: ty::ParamEnv<'tcx>, + ty: Ty<'tcx>, + def_id: DefId, + span: Span, +) -> bool { + debug!( + "type_known_to_meet_bound_modulo_regions(ty={:?}, bound={:?})", + ty, + infcx.tcx.def_path_str(def_id) + ); + + let trait_ref = ty::TraitRef { def_id, substs: infcx.tcx.mk_substs_trait(ty, &[]) }; + let obligation = Obligation { + param_env, + cause: ObligationCause::misc(span, hir::DUMMY_HIR_ID), + recursion_depth: 0, + predicate: trait_ref.without_const().to_predicate(), + }; + + let result = infcx.predicate_must_hold_modulo_regions(&obligation); + debug!( + "type_known_to_meet_ty={:?} bound={} => {:?}", + ty, + infcx.tcx.def_path_str(def_id), + result + ); + + if result && ty.has_infer_types_or_consts() { + // Because of inference "guessing", selection can sometimes claim + // to succeed while the success requires a guess. To ensure + // this function's result remains infallible, we must confirm + // that guess. While imperfect, I believe this is sound. + + // The handling of regions in this area of the code is terrible, + // see issue #29149. We should be able to improve on this with + // NLL. + let mut fulfill_cx = FulfillmentContext::new_ignoring_regions(); + + // We can use a dummy node-id here because we won't pay any mind + // to region obligations that arise (there shouldn't really be any + // anyhow). + let cause = ObligationCause::misc(span, hir::DUMMY_HIR_ID); + + fulfill_cx.register_bound(infcx, param_env, ty, def_id, cause); + + // Note: we only assume something is `Copy` if we can + // *definitively* show that it implements `Copy`. Otherwise, + // assume it is move; linear is always ok. + match fulfill_cx.select_all_or_error(infcx) { + Ok(()) => { + debug!( + "type_known_to_meet_bound_modulo_regions: ty={:?} bound={} success", + ty, + infcx.tcx.def_path_str(def_id) + ); + true + } + Err(e) => { + debug!( + "type_known_to_meet_bound_modulo_regions: ty={:?} bound={} errors={:?}", + ty, + infcx.tcx.def_path_str(def_id), + e + ); + false + } + } + } else { + result + } +} + +fn do_normalize_predicates<'tcx>( + tcx: TyCtxt<'tcx>, + region_context: DefId, + cause: ObligationCause<'tcx>, + elaborated_env: ty::ParamEnv<'tcx>, + predicates: Vec<ty::Predicate<'tcx>>, +) -> Result<Vec<ty::Predicate<'tcx>>, ErrorReported> { + debug!( + "do_normalize_predicates(predicates={:?}, region_context={:?}, cause={:?})", + predicates, region_context, cause, + ); + let span = cause.span; + tcx.infer_ctxt().enter(|infcx| { + // FIXME. We should really... do something with these region + // obligations. But this call just continues the older + // behavior (i.e., doesn't cause any new bugs), and it would + // take some further refactoring to actually solve them. In + // particular, we would have to handle implied bounds + // properly, and that code is currently largely confined to + // regionck (though I made some efforts to extract it + // out). -nmatsakis + // + // @arielby: In any case, these obligations are checked + // by wfcheck anyway, so I'm not sure we have to check + // them here too, and we will remove this function when + // we move over to lazy normalization *anyway*. + let fulfill_cx = FulfillmentContext::new_ignoring_regions(); + let predicates = + match fully_normalize(&infcx, fulfill_cx, cause, elaborated_env, &predicates) { + Ok(predicates) => predicates, + Err(errors) => { + infcx.report_fulfillment_errors(&errors, None, false); + return Err(ErrorReported); + } + }; + + debug!("do_normalize_predictes: normalized predicates = {:?}", predicates); + + let region_scope_tree = region::ScopeTree::default(); + + // We can use the `elaborated_env` here; the region code only + // cares about declarations like `'a: 'b`. + let outlives_env = OutlivesEnvironment::new(elaborated_env); + + infcx.resolve_regions_and_report_errors( + region_context, + ®ion_scope_tree, + &outlives_env, + RegionckMode::default(), + ); + + let predicates = match infcx.fully_resolve(&predicates) { + Ok(predicates) => predicates, + Err(fixup_err) => { + // If we encounter a fixup error, it means that some type + // variable wound up unconstrained. I actually don't know + // if this can happen, and I certainly don't expect it to + // happen often, but if it did happen it probably + // represents a legitimate failure due to some kind of + // unconstrained variable, and it seems better not to ICE, + // all things considered. + tcx.sess.span_err(span, &fixup_err.to_string()); + return Err(ErrorReported); + } + }; + if predicates.has_local_value() { + // FIXME: shouldn't we, you know, actually report an error here? or an ICE? + Err(ErrorReported) + } else { + Ok(predicates) + } + }) +} + +// FIXME: this is gonna need to be removed ... +/// Normalizes the parameter environment, reporting errors if they occur. +pub fn normalize_param_env_or_error<'tcx>( + tcx: TyCtxt<'tcx>, + region_context: DefId, + unnormalized_env: ty::ParamEnv<'tcx>, + cause: ObligationCause<'tcx>, +) -> ty::ParamEnv<'tcx> { + // I'm not wild about reporting errors here; I'd prefer to + // have the errors get reported at a defined place (e.g., + // during typeck). Instead I have all parameter + // environments, in effect, going through this function + // and hence potentially reporting errors. This ensures of + // course that we never forget to normalize (the + // alternative seemed like it would involve a lot of + // manual invocations of this fn -- and then we'd have to + // deal with the errors at each of those sites). + // + // In any case, in practice, typeck constructs all the + // parameter environments once for every fn as it goes, + // and errors will get reported then; so after typeck we + // can be sure that no errors should occur. + + debug!( + "normalize_param_env_or_error(region_context={:?}, unnormalized_env={:?}, cause={:?})", + region_context, unnormalized_env, cause + ); + + let mut predicates: Vec<_> = + util::elaborate_predicates(tcx, unnormalized_env.caller_bounds.to_vec()).collect(); + + debug!("normalize_param_env_or_error: elaborated-predicates={:?}", predicates); + + let elaborated_env = ty::ParamEnv::new( + tcx.intern_predicates(&predicates), + unnormalized_env.reveal, + unnormalized_env.def_id, + ); + + // HACK: we are trying to normalize the param-env inside *itself*. The problem is that + // normalization expects its param-env to be already normalized, which means we have + // a circularity. + // + // The way we handle this is by normalizing the param-env inside an unnormalized version + // of the param-env, which means that if the param-env contains unnormalized projections, + // we'll have some normalization failures. This is unfortunate. + // + // Lazy normalization would basically handle this by treating just the + // normalizing-a-trait-ref-requires-itself cycles as evaluation failures. + // + // Inferred outlives bounds can create a lot of `TypeOutlives` predicates for associated + // types, so to make the situation less bad, we normalize all the predicates *but* + // the `TypeOutlives` predicates first inside the unnormalized parameter environment, and + // then we normalize the `TypeOutlives` bounds inside the normalized parameter environment. + // + // This works fairly well because trait matching does not actually care about param-env + // TypeOutlives predicates - these are normally used by regionck. + let outlives_predicates: Vec<_> = predicates + .drain_filter(|predicate| match predicate { + ty::Predicate::TypeOutlives(..) => true, + _ => false, + }) + .collect(); + + debug!( + "normalize_param_env_or_error: predicates=(non-outlives={:?}, outlives={:?})", + predicates, outlives_predicates + ); + let non_outlives_predicates = match do_normalize_predicates( + tcx, + region_context, + cause.clone(), + elaborated_env, + predicates, + ) { + Ok(predicates) => predicates, + // An unnormalized env is better than nothing. + Err(ErrorReported) => { + debug!("normalize_param_env_or_error: errored resolving non-outlives predicates"); + return elaborated_env; + } + }; + + debug!("normalize_param_env_or_error: non-outlives predicates={:?}", non_outlives_predicates); + + // Not sure whether it is better to include the unnormalized TypeOutlives predicates + // here. I believe they should not matter, because we are ignoring TypeOutlives param-env + // predicates here anyway. Keeping them here anyway because it seems safer. + let outlives_env: Vec<_> = + non_outlives_predicates.iter().chain(&outlives_predicates).cloned().collect(); + let outlives_env = + ty::ParamEnv::new(tcx.intern_predicates(&outlives_env), unnormalized_env.reveal, None); + let outlives_predicates = match do_normalize_predicates( + tcx, + region_context, + cause, + outlives_env, + outlives_predicates, + ) { + Ok(predicates) => predicates, + // An unnormalized env is better than nothing. + Err(ErrorReported) => { + debug!("normalize_param_env_or_error: errored resolving outlives predicates"); + return elaborated_env; + } + }; + debug!("normalize_param_env_or_error: outlives predicates={:?}", outlives_predicates); + + let mut predicates = non_outlives_predicates; + predicates.extend(outlives_predicates); + debug!("normalize_param_env_or_error: final predicates={:?}", predicates); + ty::ParamEnv::new( + tcx.intern_predicates(&predicates), + unnormalized_env.reveal, + unnormalized_env.def_id, + ) +} + +pub fn fully_normalize<'a, 'tcx, T>( + infcx: &InferCtxt<'a, 'tcx>, + mut fulfill_cx: FulfillmentContext<'tcx>, + cause: ObligationCause<'tcx>, + param_env: ty::ParamEnv<'tcx>, + value: &T, +) -> Result<T, Vec<FulfillmentError<'tcx>>> +where + T: TypeFoldable<'tcx>, +{ + debug!("fully_normalize_with_fulfillcx(value={:?})", value); + let selcx = &mut SelectionContext::new(infcx); + let Normalized { value: normalized_value, obligations } = + project::normalize(selcx, param_env, cause, value); + debug!( + "fully_normalize: normalized_value={:?} obligations={:?}", + normalized_value, obligations + ); + for obligation in obligations { + fulfill_cx.register_predicate_obligation(selcx.infcx(), obligation); + } + + debug!("fully_normalize: select_all_or_error start"); + fulfill_cx.select_all_or_error(infcx)?; + debug!("fully_normalize: select_all_or_error complete"); + let resolved_value = infcx.resolve_vars_if_possible(&normalized_value); + debug!("fully_normalize: resolved_value={:?}", resolved_value); + Ok(resolved_value) +} + +/// Normalizes the predicates and checks whether they hold in an empty +/// environment. If this returns false, then either normalize +/// encountered an error or one of the predicates did not hold. Used +/// when creating vtables to check for unsatisfiable methods. +pub fn normalize_and_test_predicates<'tcx>( + tcx: TyCtxt<'tcx>, + predicates: Vec<ty::Predicate<'tcx>>, +) -> bool { + debug!("normalize_and_test_predicates(predicates={:?})", predicates); + + let result = tcx.infer_ctxt().enter(|infcx| { + let param_env = ty::ParamEnv::reveal_all(); + let mut selcx = SelectionContext::new(&infcx); + let mut fulfill_cx = FulfillmentContext::new(); + let cause = ObligationCause::dummy(); + let Normalized { value: predicates, obligations } = + normalize(&mut selcx, param_env, cause.clone(), &predicates); + for obligation in obligations { + fulfill_cx.register_predicate_obligation(&infcx, obligation); + } + for predicate in predicates { + let obligation = Obligation::new(cause.clone(), param_env, predicate); + fulfill_cx.register_predicate_obligation(&infcx, obligation); + } + + fulfill_cx.select_all_or_error(&infcx).is_ok() + }); + debug!("normalize_and_test_predicates(predicates={:?}) = {:?}", predicates, result); + result +} + +fn substitute_normalize_and_test_predicates<'tcx>( + tcx: TyCtxt<'tcx>, + key: (DefId, SubstsRef<'tcx>), +) -> bool { + debug!("substitute_normalize_and_test_predicates(key={:?})", key); + + let predicates = tcx.predicates_of(key.0).instantiate(tcx, key.1).predicates; + let result = normalize_and_test_predicates(tcx, predicates); + + debug!("substitute_normalize_and_test_predicates(key={:?}) = {:?}", key, result); + result +} + +/// Given a trait `trait_ref`, iterates the vtable entries +/// that come from `trait_ref`, including its supertraits. +#[inline] // FIXME(#35870): avoid closures being unexported due to `impl Trait`. +fn vtable_methods<'tcx>( + tcx: TyCtxt<'tcx>, + trait_ref: ty::PolyTraitRef<'tcx>, +) -> &'tcx [Option<(DefId, SubstsRef<'tcx>)>] { + debug!("vtable_methods({:?})", trait_ref); + + tcx.arena.alloc_from_iter(supertraits(tcx, trait_ref).flat_map(move |trait_ref| { + let trait_methods = tcx + .associated_items(trait_ref.def_id()) + .in_definition_order() + .filter(|item| item.kind == ty::AssocKind::Method); + + // Now list each method's DefId and InternalSubsts (for within its trait). + // If the method can never be called from this object, produce None. + trait_methods.map(move |trait_method| { + debug!("vtable_methods: trait_method={:?}", trait_method); + let def_id = trait_method.def_id; + + // Some methods cannot be called on an object; skip those. + if !is_vtable_safe_method(tcx, trait_ref.def_id(), &trait_method) { + debug!("vtable_methods: not vtable safe"); + return None; + } + + // The method may have some early-bound lifetimes; add regions for those. + let substs = trait_ref.map_bound(|trait_ref| { + InternalSubsts::for_item(tcx, def_id, |param, _| match param.kind { + GenericParamDefKind::Lifetime => tcx.lifetimes.re_erased.into(), + GenericParamDefKind::Type { .. } | GenericParamDefKind::Const => { + trait_ref.substs[param.index as usize] + } + }) + }); + + // The trait type may have higher-ranked lifetimes in it; + // erase them if they appear, so that we get the type + // at some particular call site. + let substs = + tcx.normalize_erasing_late_bound_regions(ty::ParamEnv::reveal_all(), &substs); + + // It's possible that the method relies on where-clauses that + // do not hold for this particular set of type parameters. + // Note that this method could then never be called, so we + // do not want to try and codegen it, in that case (see #23435). + let predicates = tcx.predicates_of(def_id).instantiate_own(tcx, substs); + if !normalize_and_test_predicates(tcx, predicates.predicates) { + debug!("vtable_methods: predicates do not hold"); + return None; + } + + Some((def_id, substs)) + }) + })) +} + +pub fn provide(providers: &mut ty::query::Providers<'_>) { + object_safety::provide(providers); + *providers = ty::query::Providers { + specialization_graph_of: specialize::specialization_graph_provider, + specializes: specialize::specializes, + codegen_fulfill_obligation: codegen::codegen_fulfill_obligation, + vtable_methods, + substitute_normalize_and_test_predicates, + ..*providers + }; +} |