1 //! Trait Resolution. See the [rustc dev guide] for more information on how this works.
3 //! [rustc dev guide]: https://rustc-dev-guide.rust-lang.org/traits/resolution.html
9 pub mod const_evaluatable;
11 pub mod error_reporting;
18 pub(crate) mod relationships;
25 use crate::infer::outlives::env::OutlivesEnvironment;
26 use crate::infer::{InferCtxt, RegionckMode, TyCtxtInferExt};
27 use crate::traits::error_reporting::InferCtxtExt as _;
28 use crate::traits::query::evaluate_obligation::InferCtxtExt as _;
29 use rustc_errors::ErrorReported;
31 use rustc_hir::def_id::DefId;
32 use rustc_hir::lang_items::LangItem;
33 use rustc_middle::ty::fold::TypeFoldable;
34 use rustc_middle::ty::subst::{InternalSubsts, SubstsRef};
35 use rustc_middle::ty::{
36 self, GenericParamDefKind, ToPredicate, Ty, TyCtxt, VtblEntry, COMMON_VTABLE_ENTRIES,
38 use rustc_span::{sym, Span};
39 use smallvec::SmallVec;
42 use std::ops::ControlFlow;
44 pub use self::FulfillmentErrorCode::*;
45 pub use self::ImplSource::*;
46 pub use self::ObligationCauseCode::*;
47 pub use self::SelectionError::*;
49 pub use self::coherence::{add_placeholder_note, orphan_check, overlapping_impls};
50 pub use self::coherence::{OrphanCheckErr, OverlapResult};
51 pub use self::engine::TraitEngineExt;
52 pub use self::fulfill::{FulfillmentContext, PendingPredicateObligation};
53 pub use self::object_safety::astconv_object_safety_violations;
54 pub use self::object_safety::is_vtable_safe_method;
55 pub use self::object_safety::MethodViolationCode;
56 pub use self::object_safety::ObjectSafetyViolation;
57 pub use self::on_unimplemented::{OnUnimplementedDirective, OnUnimplementedNote};
58 pub use self::project::{normalize, normalize_projection_type, normalize_to};
59 pub use self::select::{EvaluationCache, SelectionCache, SelectionContext};
60 pub use self::select::{EvaluationResult, IntercrateAmbiguityCause, OverflowError};
61 pub use self::specialize::specialization_graph::FutureCompatOverlapError;
62 pub use self::specialize::specialization_graph::FutureCompatOverlapErrorKind;
63 pub use self::specialize::{specialization_graph, translate_substs, OverlapError};
64 pub use self::structural_match::search_for_structural_match_violation;
65 pub use self::structural_match::NonStructuralMatchTy;
67 elaborate_obligations, elaborate_predicates, elaborate_predicates_with_span,
68 elaborate_trait_ref, elaborate_trait_refs,
70 pub use self::util::{expand_trait_aliases, TraitAliasExpander};
72 get_vtable_index_of_object_method, impl_item_is_final, predicate_for_trait_def, upcast_choices,
75 supertrait_def_ids, supertraits, transitive_bounds, transitive_bounds_that_define_assoc_type,
76 SupertraitDefIds, Supertraits,
79 pub use self::chalk_fulfill::FulfillmentContext as ChalkFulfillmentContext;
81 pub use rustc_infer::traits::*;
83 /// Whether to skip the leak check, as part of a future compatibility warning step.
85 /// The "default" for skip-leak-check corresponds to the current
86 /// behavior (do not skip the leak check) -- not the behavior we are
87 /// transitioning into.
88 #[derive(Copy, Clone, PartialEq, Eq, Debug, Default)]
89 pub enum SkipLeakCheck {
96 fn is_yes(self) -> bool {
97 self == SkipLeakCheck::Yes
101 /// The mode that trait queries run in.
102 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
103 pub enum TraitQueryMode {
104 /// Standard/un-canonicalized queries get accurate
105 /// spans etc. passed in and hence can do reasonable
106 /// error reporting on their own.
108 /// Canonicalized queries get dummy spans and hence
109 /// must generally propagate errors to
110 /// pre-canonicalization callsites.
114 /// Creates predicate obligations from the generic bounds.
115 pub fn predicates_for_generics<'tcx>(
116 cause: ObligationCause<'tcx>,
117 param_env: ty::ParamEnv<'tcx>,
118 generic_bounds: ty::InstantiatedPredicates<'tcx>,
119 ) -> impl Iterator<Item = PredicateObligation<'tcx>> {
120 util::predicates_for_generics(cause, 0, param_env, generic_bounds)
123 /// Determines whether the type `ty` is known to meet `bound` and
124 /// returns true if so. Returns false if `ty` either does not meet
125 /// `bound` or is not known to meet bound (note that this is
126 /// conservative towards *no impl*, which is the opposite of the
127 /// `evaluate` methods).
128 pub fn type_known_to_meet_bound_modulo_regions<'a, 'tcx>(
129 infcx: &InferCtxt<'a, 'tcx>,
130 param_env: ty::ParamEnv<'tcx>,
136 "type_known_to_meet_bound_modulo_regions(ty={:?}, bound={:?})",
138 infcx.tcx.def_path_str(def_id)
142 ty::Binder::dummy(ty::TraitRef { def_id, substs: infcx.tcx.mk_substs_trait(ty, &[]) });
143 let obligation = Obligation {
145 cause: ObligationCause::misc(span, hir::CRATE_HIR_ID),
147 predicate: trait_ref.without_const().to_predicate(infcx.tcx),
150 let result = infcx.predicate_must_hold_modulo_regions(&obligation);
152 "type_known_to_meet_ty={:?} bound={} => {:?}",
154 infcx.tcx.def_path_str(def_id),
158 if result && ty.has_infer_types_or_consts() {
159 // Because of inference "guessing", selection can sometimes claim
160 // to succeed while the success requires a guess. To ensure
161 // this function's result remains infallible, we must confirm
162 // that guess. While imperfect, I believe this is sound.
164 // The handling of regions in this area of the code is terrible,
165 // see issue #29149. We should be able to improve on this with
167 let mut fulfill_cx = FulfillmentContext::new_ignoring_regions();
169 // We can use a dummy node-id here because we won't pay any mind
170 // to region obligations that arise (there shouldn't really be any
172 let cause = ObligationCause::misc(span, hir::CRATE_HIR_ID);
174 fulfill_cx.register_bound(infcx, param_env, ty, def_id, cause);
176 // Note: we only assume something is `Copy` if we can
177 // *definitively* show that it implements `Copy`. Otherwise,
178 // assume it is move; linear is always ok.
179 match fulfill_cx.select_all_or_error(infcx).as_slice() {
182 "type_known_to_meet_bound_modulo_regions: ty={:?} bound={} success",
184 infcx.tcx.def_path_str(def_id)
191 bound = %infcx.tcx.def_path_str(def_id),
193 "type_known_to_meet_bound_modulo_regions"
203 fn do_normalize_predicates<'tcx>(
205 region_context: DefId,
206 cause: ObligationCause<'tcx>,
207 elaborated_env: ty::ParamEnv<'tcx>,
208 predicates: Vec<ty::Predicate<'tcx>>,
209 ) -> Result<Vec<ty::Predicate<'tcx>>, ErrorReported> {
211 "do_normalize_predicates(predicates={:?}, region_context={:?}, cause={:?})",
212 predicates, region_context, cause,
214 let span = cause.span;
215 tcx.infer_ctxt().enter(|infcx| {
216 // FIXME. We should really... do something with these region
217 // obligations. But this call just continues the older
218 // behavior (i.e., doesn't cause any new bugs), and it would
219 // take some further refactoring to actually solve them. In
220 // particular, we would have to handle implied bounds
221 // properly, and that code is currently largely confined to
222 // regionck (though I made some efforts to extract it
225 // @arielby: In any case, these obligations are checked
226 // by wfcheck anyway, so I'm not sure we have to check
227 // them here too, and we will remove this function when
228 // we move over to lazy normalization *anyway*.
229 let fulfill_cx = FulfillmentContext::new_ignoring_regions();
231 match fully_normalize(&infcx, fulfill_cx, cause, elaborated_env, predicates) {
232 Ok(predicates) => predicates,
234 infcx.report_fulfillment_errors(&errors, None, false);
235 return Err(ErrorReported);
239 debug!("do_normalize_predictes: normalized predicates = {:?}", predicates);
241 // We can use the `elaborated_env` here; the region code only
242 // cares about declarations like `'a: 'b`.
243 let outlives_env = OutlivesEnvironment::new(elaborated_env);
245 infcx.resolve_regions_and_report_errors(
248 RegionckMode::default(),
251 let predicates = match infcx.fully_resolve(predicates) {
252 Ok(predicates) => predicates,
254 // If we encounter a fixup error, it means that some type
255 // variable wound up unconstrained. I actually don't know
256 // if this can happen, and I certainly don't expect it to
257 // happen often, but if it did happen it probably
258 // represents a legitimate failure due to some kind of
259 // unconstrained variable, and it seems better not to ICE,
260 // all things considered.
261 tcx.sess.span_err(span, &fixup_err.to_string());
262 return Err(ErrorReported);
265 if predicates.needs_infer() {
266 tcx.sess.delay_span_bug(span, "encountered inference variables after `fully_resolve`");
274 // FIXME: this is gonna need to be removed ...
275 /// Normalizes the parameter environment, reporting errors if they occur.
276 pub fn normalize_param_env_or_error<'tcx>(
278 region_context: DefId,
279 unnormalized_env: ty::ParamEnv<'tcx>,
280 cause: ObligationCause<'tcx>,
281 ) -> ty::ParamEnv<'tcx> {
282 // I'm not wild about reporting errors here; I'd prefer to
283 // have the errors get reported at a defined place (e.g.,
284 // during typeck). Instead I have all parameter
285 // environments, in effect, going through this function
286 // and hence potentially reporting errors. This ensures of
287 // course that we never forget to normalize (the
288 // alternative seemed like it would involve a lot of
289 // manual invocations of this fn -- and then we'd have to
290 // deal with the errors at each of those sites).
292 // In any case, in practice, typeck constructs all the
293 // parameter environments once for every fn as it goes,
294 // and errors will get reported then; so outside of type inference we
295 // can be sure that no errors should occur.
298 "normalize_param_env_or_error(region_context={:?}, unnormalized_env={:?}, cause={:?})",
299 region_context, unnormalized_env, cause
302 let mut predicates: Vec<_> =
303 util::elaborate_predicates(tcx, unnormalized_env.caller_bounds().into_iter())
304 .map(|obligation| obligation.predicate)
307 debug!("normalize_param_env_or_error: elaborated-predicates={:?}", predicates);
309 let elaborated_env = ty::ParamEnv::new(
310 tcx.intern_predicates(&predicates),
311 unnormalized_env.reveal(),
312 unnormalized_env.constness(),
315 // HACK: we are trying to normalize the param-env inside *itself*. The problem is that
316 // normalization expects its param-env to be already normalized, which means we have
319 // The way we handle this is by normalizing the param-env inside an unnormalized version
320 // of the param-env, which means that if the param-env contains unnormalized projections,
321 // we'll have some normalization failures. This is unfortunate.
323 // Lazy normalization would basically handle this by treating just the
324 // normalizing-a-trait-ref-requires-itself cycles as evaluation failures.
326 // Inferred outlives bounds can create a lot of `TypeOutlives` predicates for associated
327 // types, so to make the situation less bad, we normalize all the predicates *but*
328 // the `TypeOutlives` predicates first inside the unnormalized parameter environment, and
329 // then we normalize the `TypeOutlives` bounds inside the normalized parameter environment.
331 // This works fairly well because trait matching does not actually care about param-env
332 // TypeOutlives predicates - these are normally used by regionck.
333 let outlives_predicates: Vec<_> = predicates
334 .drain_filter(|predicate| {
335 matches!(predicate.kind().skip_binder(), ty::PredicateKind::TypeOutlives(..))
340 "normalize_param_env_or_error: predicates=(non-outlives={:?}, outlives={:?})",
341 predicates, outlives_predicates
343 let non_outlives_predicates = match do_normalize_predicates(
350 Ok(predicates) => predicates,
351 // An unnormalized env is better than nothing.
352 Err(ErrorReported) => {
353 debug!("normalize_param_env_or_error: errored resolving non-outlives predicates");
354 return elaborated_env;
358 debug!("normalize_param_env_or_error: non-outlives predicates={:?}", non_outlives_predicates);
360 // Not sure whether it is better to include the unnormalized TypeOutlives predicates
361 // here. I believe they should not matter, because we are ignoring TypeOutlives param-env
362 // predicates here anyway. Keeping them here anyway because it seems safer.
363 let outlives_env: Vec<_> =
364 non_outlives_predicates.iter().chain(&outlives_predicates).cloned().collect();
365 let outlives_env = ty::ParamEnv::new(
366 tcx.intern_predicates(&outlives_env),
367 unnormalized_env.reveal(),
368 unnormalized_env.constness(),
370 let outlives_predicates = match do_normalize_predicates(
377 Ok(predicates) => predicates,
378 // An unnormalized env is better than nothing.
379 Err(ErrorReported) => {
380 debug!("normalize_param_env_or_error: errored resolving outlives predicates");
381 return elaborated_env;
384 debug!("normalize_param_env_or_error: outlives predicates={:?}", outlives_predicates);
386 let mut predicates = non_outlives_predicates;
387 predicates.extend(outlives_predicates);
388 debug!("normalize_param_env_or_error: final predicates={:?}", predicates);
390 tcx.intern_predicates(&predicates),
391 unnormalized_env.reveal(),
392 unnormalized_env.constness(),
396 pub fn fully_normalize<'a, 'tcx, T>(
397 infcx: &InferCtxt<'a, 'tcx>,
398 mut fulfill_cx: FulfillmentContext<'tcx>,
399 cause: ObligationCause<'tcx>,
400 param_env: ty::ParamEnv<'tcx>,
402 ) -> Result<T, Vec<FulfillmentError<'tcx>>>
404 T: TypeFoldable<'tcx>,
406 debug!("fully_normalize_with_fulfillcx(value={:?})", value);
407 let selcx = &mut SelectionContext::new(infcx);
408 let Normalized { value: normalized_value, obligations } =
409 project::normalize(selcx, param_env, cause, value);
411 "fully_normalize: normalized_value={:?} obligations={:?}",
412 normalized_value, obligations
414 for obligation in obligations {
415 fulfill_cx.register_predicate_obligation(selcx.infcx(), obligation);
418 debug!("fully_normalize: select_all_or_error start");
419 let errors = fulfill_cx.select_all_or_error(infcx);
420 if !errors.is_empty() {
423 debug!("fully_normalize: select_all_or_error complete");
424 let resolved_value = infcx.resolve_vars_if_possible(normalized_value);
425 debug!("fully_normalize: resolved_value={:?}", resolved_value);
429 /// Normalizes the predicates and checks whether they hold in an empty environment. If this
430 /// returns true, then either normalize encountered an error or one of the predicates did not
431 /// hold. Used when creating vtables to check for unsatisfiable methods.
432 pub fn impossible_predicates<'tcx>(
434 predicates: Vec<ty::Predicate<'tcx>>,
436 debug!("impossible_predicates(predicates={:?})", predicates);
438 let result = tcx.infer_ctxt().enter(|infcx| {
439 let param_env = ty::ParamEnv::reveal_all();
440 let mut selcx = SelectionContext::new(&infcx);
441 let mut fulfill_cx = FulfillmentContext::new();
442 let cause = ObligationCause::dummy();
443 let Normalized { value: predicates, obligations } =
444 normalize(&mut selcx, param_env, cause.clone(), predicates);
445 for obligation in obligations {
446 fulfill_cx.register_predicate_obligation(&infcx, obligation);
448 for predicate in predicates {
449 let obligation = Obligation::new(cause.clone(), param_env, predicate);
450 fulfill_cx.register_predicate_obligation(&infcx, obligation);
453 let errors = fulfill_cx.select_all_or_error(&infcx);
457 debug!("impossible_predicates = {:?}", result);
461 fn subst_and_check_impossible_predicates<'tcx>(
463 key: (DefId, SubstsRef<'tcx>),
465 debug!("subst_and_check_impossible_predicates(key={:?})", key);
467 let mut predicates = tcx.predicates_of(key.0).instantiate(tcx, key.1).predicates;
468 predicates.retain(|predicate| !predicate.needs_subst());
469 let result = impossible_predicates(tcx, predicates);
471 debug!("subst_and_check_impossible_predicates(key={:?}) = {:?}", key, result);
475 #[derive(Clone, Debug)]
476 enum VtblSegment<'tcx> {
478 TraitOwnEntries { trait_ref: ty::PolyTraitRef<'tcx>, emit_vptr: bool },
481 /// Prepare the segments for a vtable
482 fn prepare_vtable_segments<'tcx, T>(
484 trait_ref: ty::PolyTraitRef<'tcx>,
485 mut segment_visitor: impl FnMut(VtblSegment<'tcx>) -> ControlFlow<T>,
487 // The following constraints holds for the final arrangement.
488 // 1. The whole virtual table of the first direct super trait is included as the
489 // the prefix. If this trait doesn't have any super traits, then this step
490 // consists of the dsa metadata.
491 // 2. Then comes the proper pointer metadata(vptr) and all own methods for all
492 // other super traits except those already included as part of the first
493 // direct super trait virtual table.
494 // 3. finally, the own methods of this trait.
496 // This has the advantage that trait upcasting to the first direct super trait on each level
497 // is zero cost, and to another trait includes only replacing the pointer with one level indirection,
498 // while not using too much extra memory.
500 // For a single inheritance relationship like this,
501 // D --> C --> B --> A
502 // The resulting vtable will consists of these segments:
505 // For a multiple inheritance relationship like this,
508 // The resulting vtable will consists of these segments:
509 // DSA, A, B, B-vptr, C, D
511 // For a diamond inheritance relationship like this,
514 // The resulting vtable will consists of these segments:
515 // DSA, A, B, C, C-vptr, D
517 // For a more complex inheritance relationship like this:
518 // O --> G --> C --> A
526 // The resulting vtable will consists of these segments:
527 // DSA, A, B, B-vptr, C, D, D-vptr, E, E-vptr, F, F-vptr, G,
528 // H, H-vptr, I, I-vptr, J, J-vptr, K, K-vptr, L, L-vptr, M, M-vptr,
531 // emit dsa segment first.
532 if let ControlFlow::Break(v) = (segment_visitor)(VtblSegment::MetadataDSA) {
536 let mut emit_vptr_on_new_entry = false;
537 let mut visited = util::PredicateSet::new(tcx);
538 let predicate = trait_ref.without_const().to_predicate(tcx);
539 let mut stack: SmallVec<[(ty::PolyTraitRef<'tcx>, _, _); 5]> =
540 smallvec![(trait_ref, emit_vptr_on_new_entry, None)];
541 visited.insert(predicate);
543 // the main traversal loop:
544 // basically we want to cut the inheritance directed graph into a few non-overlapping slices of nodes
545 // that each node is emited after all its descendents have been emitted.
546 // so we convert the directed graph into a tree by skipping all previously visted nodes using a visited set.
547 // this is done on the fly.
548 // Each loop run emits a slice - it starts by find a "childless" unvisited node, backtracking upwards, and it
549 // stops after it finds a node that has a next-sibling node.
550 // This next-sibling node will used as the starting point of next slice.
553 // For a diamond inheritance relationship like this,
554 // D#1 --> B#0 --> A#0
557 // Starting point 0 stack [D]
558 // Loop run #0: Stack after diving in is [D B A], A is "childless"
559 // after this point, all newly visited nodes won't have a vtable that equals to a prefix of this one.
560 // Loop run #0: Emiting the slice [B A] (in reverse order), B has a next-sibling node, so this slice stops here.
561 // Loop run #0: Stack after exiting out is [D C], C is the next starting point.
562 // Loop run #1: Stack after diving in is [D C], C is "childless", since its child A is skipped(already emitted).
563 // Loop run #1: Emiting the slice [D C] (in reverse order). No one has a next-sibling node.
564 // Loop run #1: Stack after exiting out is []. Now the function exits.
567 // dive deeper into the stack, recording the path
569 if let Some((inner_most_trait_ref, _, _)) = stack.last() {
570 let inner_most_trait_ref = *inner_most_trait_ref;
571 let mut direct_super_traits_iter = tcx
572 .super_predicates_of(inner_most_trait_ref.def_id())
575 .filter_map(move |(pred, _)| {
576 pred.subst_supertrait(tcx, &inner_most_trait_ref).to_opt_poly_trait_pred()
579 'diving_in_skip_visited_traits: loop {
580 if let Some(next_super_trait) = direct_super_traits_iter.next() {
581 if visited.insert(next_super_trait.to_predicate(tcx)) {
582 // We're throwing away potential constness of super traits here.
583 // FIXME: handle ~const super traits
584 let next_super_trait = next_super_trait.map_bound(|t| t.trait_ref);
587 emit_vptr_on_new_entry,
588 Some(direct_super_traits_iter),
590 break 'diving_in_skip_visited_traits;
592 continue 'diving_in_skip_visited_traits;
601 // Other than the left-most path, vptr should be emitted for each trait.
602 emit_vptr_on_new_entry = true;
604 // emit innermost item, move to next sibling and stop there if possible, otherwise jump to outer level.
606 if let Some((inner_most_trait_ref, emit_vptr, siblings_opt)) = stack.last_mut() {
607 if let ControlFlow::Break(v) = (segment_visitor)(VtblSegment::TraitOwnEntries {
608 trait_ref: *inner_most_trait_ref,
609 emit_vptr: *emit_vptr,
614 'exiting_out_skip_visited_traits: loop {
615 if let Some(siblings) = siblings_opt {
616 if let Some(next_inner_most_trait_ref) = siblings.next() {
617 if visited.insert(next_inner_most_trait_ref.to_predicate(tcx)) {
618 // We're throwing away potential constness of super traits here.
619 // FIXME: handle ~const super traits
620 let next_inner_most_trait_ref =
621 next_inner_most_trait_ref.map_bound(|t| t.trait_ref);
622 *inner_most_trait_ref = next_inner_most_trait_ref;
623 *emit_vptr = emit_vptr_on_new_entry;
626 continue 'exiting_out_skip_visited_traits;
631 continue 'exiting_out;
640 fn dump_vtable_entries<'tcx>(
643 trait_ref: ty::PolyTraitRef<'tcx>,
644 entries: &[VtblEntry<'tcx>],
646 let msg = format!("vtable entries for `{}`: {:#?}", trait_ref, entries);
647 tcx.sess.struct_span_err(sp, &msg).emit();
650 fn own_existential_vtable_entries<'tcx>(
652 trait_ref: ty::PolyExistentialTraitRef<'tcx>,
654 let trait_methods = tcx
655 .associated_items(trait_ref.def_id())
656 .in_definition_order()
657 .filter(|item| item.kind == ty::AssocKind::Fn);
658 // Now list each method's DefId (for within its trait).
659 let own_entries = trait_methods.filter_map(move |trait_method| {
660 debug!("own_existential_vtable_entry: trait_method={:?}", trait_method);
661 let def_id = trait_method.def_id;
663 // Some methods cannot be called on an object; skip those.
664 if !is_vtable_safe_method(tcx, trait_ref.def_id(), &trait_method) {
665 debug!("own_existential_vtable_entry: not vtable safe");
672 tcx.arena.alloc_from_iter(own_entries.into_iter())
675 /// Given a trait `trait_ref`, iterates the vtable entries
676 /// that come from `trait_ref`, including its supertraits.
677 fn vtable_entries<'tcx>(
679 trait_ref: ty::PolyTraitRef<'tcx>,
680 ) -> &'tcx [VtblEntry<'tcx>] {
681 debug!("vtable_entries({:?})", trait_ref);
683 let mut entries = vec![];
685 let vtable_segment_callback = |segment| -> ControlFlow<()> {
687 VtblSegment::MetadataDSA => {
688 entries.extend(COMMON_VTABLE_ENTRIES);
690 VtblSegment::TraitOwnEntries { trait_ref, emit_vptr } => {
691 let existential_trait_ref = trait_ref
692 .map_bound(|trait_ref| ty::ExistentialTraitRef::erase_self_ty(tcx, trait_ref));
694 // Lookup the shape of vtable for the trait.
695 let own_existential_entries =
696 tcx.own_existential_vtable_entries(existential_trait_ref);
698 let own_entries = own_existential_entries.iter().copied().map(|def_id| {
699 debug!("vtable_entries: trait_method={:?}", def_id);
701 // The method may have some early-bound lifetimes; add regions for those.
702 let substs = trait_ref.map_bound(|trait_ref| {
703 InternalSubsts::for_item(tcx, def_id, |param, _| match param.kind {
704 GenericParamDefKind::Lifetime => tcx.lifetimes.re_erased.into(),
705 GenericParamDefKind::Type { .. }
706 | GenericParamDefKind::Const { .. } => {
707 trait_ref.substs[param.index as usize]
712 // The trait type may have higher-ranked lifetimes in it;
713 // erase them if they appear, so that we get the type
714 // at some particular call site.
716 .normalize_erasing_late_bound_regions(ty::ParamEnv::reveal_all(), substs);
718 // It's possible that the method relies on where-clauses that
719 // do not hold for this particular set of type parameters.
720 // Note that this method could then never be called, so we
721 // do not want to try and codegen it, in that case (see #23435).
722 let predicates = tcx.predicates_of(def_id).instantiate_own(tcx, substs);
723 if impossible_predicates(tcx, predicates.predicates) {
724 debug!("vtable_entries: predicates do not hold");
725 return VtblEntry::Vacant;
728 let instance = ty::Instance::resolve_for_vtable(
730 ty::ParamEnv::reveal_all(),
734 .expect("resolution failed during building vtable representation");
735 VtblEntry::Method(instance)
738 entries.extend(own_entries);
741 entries.push(VtblEntry::TraitVPtr(trait_ref));
746 ControlFlow::Continue(())
749 let _ = prepare_vtable_segments(tcx, trait_ref, vtable_segment_callback);
751 if tcx.has_attr(trait_ref.def_id(), sym::rustc_dump_vtable) {
752 let sp = tcx.def_span(trait_ref.def_id());
753 dump_vtable_entries(tcx, sp, trait_ref, &entries);
756 tcx.arena.alloc_from_iter(entries.into_iter())
759 /// Find slot base for trait methods within vtable entries of another trait
760 fn vtable_trait_first_method_offset<'tcx>(
763 ty::PolyTraitRef<'tcx>, // trait_to_be_found
764 ty::PolyTraitRef<'tcx>, // trait_owning_vtable
767 let (trait_to_be_found, trait_owning_vtable) = key;
770 let trait_to_be_found_erased = tcx.erase_regions(trait_to_be_found);
772 let vtable_segment_callback = {
773 let mut vtable_base = 0;
777 VtblSegment::MetadataDSA => {
778 vtable_base += COMMON_VTABLE_ENTRIES.len();
780 VtblSegment::TraitOwnEntries { trait_ref, emit_vptr } => {
781 if tcx.erase_regions(trait_ref) == trait_to_be_found_erased {
782 return ControlFlow::Break(vtable_base);
784 vtable_base += util::count_own_vtable_entries(tcx, trait_ref);
790 ControlFlow::Continue(())
794 if let Some(vtable_base) =
795 prepare_vtable_segments(tcx, trait_owning_vtable, vtable_segment_callback)
799 bug!("Failed to find info for expected trait in vtable");
803 /// Find slot offset for trait vptr within vtable entries of another trait
804 pub fn vtable_trait_upcasting_coercion_new_vptr_slot<'tcx>(
807 Ty<'tcx>, // trait object type whose trait owning vtable
808 Ty<'tcx>, // trait object for supertrait
811 let (source, target) = key;
812 assert!(matches!(&source.kind(), &ty::Dynamic(..)) && !source.needs_infer());
813 assert!(matches!(&target.kind(), &ty::Dynamic(..)) && !target.needs_infer());
815 // this has been typecked-before, so diagnostics is not really needed.
816 let unsize_trait_did = tcx.require_lang_item(LangItem::Unsize, None);
818 let trait_ref = ty::TraitRef {
819 def_id: unsize_trait_did,
820 substs: tcx.mk_substs_trait(source, &[target.into()]),
822 let obligation = Obligation::new(
823 ObligationCause::dummy(),
824 ty::ParamEnv::reveal_all(),
825 ty::Binder::dummy(ty::TraitPredicate {
827 constness: ty::BoundConstness::NotConst,
828 polarity: ty::ImplPolarity::Positive,
832 let implsrc = tcx.infer_ctxt().enter(|infcx| {
833 let mut selcx = SelectionContext::new(&infcx);
834 selcx.select(&obligation).unwrap()
837 let implsrc_traitcasting = match implsrc {
838 Some(ImplSource::TraitUpcasting(data)) => data,
842 implsrc_traitcasting.vtable_vptr_slot
845 pub fn provide(providers: &mut ty::query::Providers) {
846 object_safety::provide(providers);
847 structural_match::provide(providers);
848 *providers = ty::query::Providers {
849 specialization_graph_of: specialize::specialization_graph_provider,
850 specializes: specialize::specializes,
851 codegen_fulfill_obligation: codegen::codegen_fulfill_obligation,
852 own_existential_vtable_entries,
854 vtable_trait_upcasting_coercion_new_vptr_slot,
855 subst_and_check_impossible_predicates,
856 thir_abstract_const: |tcx, def_id| {
857 let def_id = def_id.expect_local();
858 if let Some(def) = ty::WithOptConstParam::try_lookup(def_id, tcx) {
859 tcx.thir_abstract_const_of_const_arg(def)
861 const_evaluatable::thir_abstract_const(tcx, ty::WithOptConstParam::unknown(def_id))
864 thir_abstract_const_of_const_arg: |tcx, (did, param_did)| {
865 const_evaluatable::thir_abstract_const(
867 ty::WithOptConstParam { did, const_param_did: Some(param_did) },
870 try_unify_abstract_consts: const_evaluatable::try_unify_abstract_consts,