| //! 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; |
| mod chalk_fulfill; |
| 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::ty::fold::TypeFoldable; |
| use rustc_middle::ty::subst::{InternalSubsts, SubstsRef}; |
| use rustc_middle::ty::{ |
| self, GenericParamDefKind, ParamEnv, ToPredicate, Ty, TyCtxt, WithConstness, |
| }; |
| use rustc_span::Span; |
| |
| use std::fmt::Debug; |
| |
| pub use self::FulfillmentErrorCode::*; |
| pub use self::ImplSource::*; |
| pub use self::ObligationCauseCode::*; |
| pub use self::SelectionError::*; |
| |
| 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::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 self::chalk_fulfill::FulfillmentContext as ChalkFulfillmentContext; |
| |
| 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>, |
| ) -> impl Iterator<Item = PredicateObligation<'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::CRATE_HIR_ID), |
| recursion_depth: 0, |
| predicate: trait_ref.without_const().to_predicate(infcx.tcx), |
| }; |
| |
| 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::CRATE_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); |
| |
| // 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, |
| &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.needs_infer() { |
| tcx.sess.delay_span_bug(span, "encountered inference variables after `fully_resolve`"); |
| 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().into_iter()) |
| .map(|obligation| obligation.predicate) |
| .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.kind() { |
| ty::PredicateKind::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::Fn); |
| |
| // 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)) |
| }) |
| })) |
| } |
| |
| /// Check whether a `ty` implements given trait(trait_def_id). |
| /// |
| /// NOTE: Always return `false` for a type which needs inference. |
| fn type_implements_trait<'tcx>( |
| tcx: TyCtxt<'tcx>, |
| key: ( |
| DefId, // trait_def_id, |
| Ty<'tcx>, // type |
| SubstsRef<'tcx>, |
| ParamEnv<'tcx>, |
| ), |
| ) -> bool { |
| let (trait_def_id, ty, params, param_env) = key; |
| |
| debug!( |
| "type_implements_trait: trait_def_id={:?}, type={:?}, params={:?}, param_env={:?}", |
| trait_def_id, ty, params, param_env |
| ); |
| |
| let trait_ref = ty::TraitRef { def_id: trait_def_id, substs: tcx.mk_substs_trait(ty, params) }; |
| |
| let obligation = Obligation { |
| cause: ObligationCause::dummy(), |
| param_env, |
| recursion_depth: 0, |
| predicate: trait_ref.without_const().to_predicate(tcx), |
| }; |
| tcx.infer_ctxt().enter(|infcx| infcx.predicate_must_hold_modulo_regions(&obligation)) |
| } |
| |
| pub fn provide(providers: &mut ty::query::Providers) { |
| object_safety::provide(providers); |
| structural_match::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, |
| type_implements_trait, |
| ..*providers |
| }; |
| } |