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, WithConstness,
37 COMMON_VTABLE_ENTRIES,
39 use rustc_span::{sym, Span};
40 use smallvec::SmallVec;
43 use std::ops::ControlFlow;
45 pub use self::FulfillmentErrorCode::*;
46 pub use self::ImplSource::*;
47 pub use self::ObligationCauseCode::*;
48 pub use self::SelectionError::*;
50 pub use self::coherence::{add_placeholder_note, orphan_check, overlapping_impls};
51 pub use self::coherence::{OrphanCheckErr, OverlapResult};
52 pub use self::engine::TraitEngineExt;
53 pub use self::fulfill::{FulfillmentContext, PendingPredicateObligation};
54 pub use self::object_safety::astconv_object_safety_violations;
55 pub use self::object_safety::is_vtable_safe_method;
56 pub use self::object_safety::MethodViolationCode;
57 pub use self::object_safety::ObjectSafetyViolation;
58 pub use self::on_unimplemented::{OnUnimplementedDirective, OnUnimplementedNote};
59 pub use self::project::{normalize, normalize_projection_type, normalize_to};
60 pub use self::select::{EvaluationCache, SelectionCache, SelectionContext};
61 pub use self::select::{EvaluationResult, IntercrateAmbiguityCause, OverflowError};
62 pub use self::specialize::specialization_graph::FutureCompatOverlapError;
63 pub use self::specialize::specialization_graph::FutureCompatOverlapErrorKind;
64 pub use self::specialize::{specialization_graph, translate_substs, OverlapError};
65 pub use self::structural_match::search_for_structural_match_violation;
66 pub use self::structural_match::NonStructuralMatchTy;
68 elaborate_obligations, elaborate_predicates, elaborate_predicates_with_span,
69 elaborate_trait_ref, elaborate_trait_refs,
71 pub use self::util::{expand_trait_aliases, TraitAliasExpander};
73 get_vtable_index_of_object_method, impl_item_is_final, predicate_for_trait_def, upcast_choices,
76 supertrait_def_ids, supertraits, transitive_bounds, transitive_bounds_that_define_assoc_type,
77 SupertraitDefIds, Supertraits,
80 pub use self::chalk_fulfill::FulfillmentContext as ChalkFulfillmentContext;
82 pub use rustc_infer::traits::*;
84 /// Whether to skip the leak check, as part of a future compatibility warning step.
85 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
86 pub enum SkipLeakCheck {
92 fn is_yes(self) -> bool {
93 self == SkipLeakCheck::Yes
97 /// The "default" for skip-leak-check corresponds to the current
98 /// behavior (do not skip the leak check) -- not the behavior we are
99 /// transitioning into.
100 impl Default for SkipLeakCheck {
101 fn default() -> Self {
106 /// The mode that trait queries run in.
107 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
108 pub enum TraitQueryMode {
109 /// Standard/un-canonicalized queries get accurate
110 /// spans etc. passed in and hence can do reasonable
111 /// error reporting on their own.
113 /// Canonicalized queries get dummy spans and hence
114 /// must generally propagate errors to
115 /// pre-canonicalization callsites.
119 /// Creates predicate obligations from the generic bounds.
120 pub fn predicates_for_generics<'tcx>(
121 cause: ObligationCause<'tcx>,
122 param_env: ty::ParamEnv<'tcx>,
123 generic_bounds: ty::InstantiatedPredicates<'tcx>,
124 ) -> impl Iterator<Item = PredicateObligation<'tcx>> {
125 util::predicates_for_generics(cause, 0, param_env, generic_bounds)
128 /// Determines whether the type `ty` is known to meet `bound` and
129 /// returns true if so. Returns false if `ty` either does not meet
130 /// `bound` or is not known to meet bound (note that this is
131 /// conservative towards *no impl*, which is the opposite of the
132 /// `evaluate` methods).
133 pub fn type_known_to_meet_bound_modulo_regions<'a, 'tcx>(
134 infcx: &InferCtxt<'a, 'tcx>,
135 param_env: ty::ParamEnv<'tcx>,
141 "type_known_to_meet_bound_modulo_regions(ty={:?}, bound={:?})",
143 infcx.tcx.def_path_str(def_id)
147 ty::Binder::dummy(ty::TraitRef { def_id, substs: infcx.tcx.mk_substs_trait(ty, &[]) });
148 let obligation = Obligation {
150 cause: ObligationCause::misc(span, hir::CRATE_HIR_ID),
152 predicate: trait_ref.without_const().to_predicate(infcx.tcx),
155 let result = infcx.predicate_must_hold_modulo_regions(&obligation);
157 "type_known_to_meet_ty={:?} bound={} => {:?}",
159 infcx.tcx.def_path_str(def_id),
163 if result && ty.has_infer_types_or_consts() {
164 // Because of inference "guessing", selection can sometimes claim
165 // to succeed while the success requires a guess. To ensure
166 // this function's result remains infallible, we must confirm
167 // that guess. While imperfect, I believe this is sound.
169 // The handling of regions in this area of the code is terrible,
170 // see issue #29149. We should be able to improve on this with
172 let mut fulfill_cx = FulfillmentContext::new_ignoring_regions();
174 // We can use a dummy node-id here because we won't pay any mind
175 // to region obligations that arise (there shouldn't really be any
177 let cause = ObligationCause::misc(span, hir::CRATE_HIR_ID);
179 fulfill_cx.register_bound(infcx, param_env, ty, def_id, cause);
181 // Note: we only assume something is `Copy` if we can
182 // *definitively* show that it implements `Copy`. Otherwise,
183 // assume it is move; linear is always ok.
184 match fulfill_cx.select_all_or_error(infcx).as_slice() {
187 "type_known_to_meet_bound_modulo_regions: ty={:?} bound={} success",
189 infcx.tcx.def_path_str(def_id)
196 bound = %infcx.tcx.def_path_str(def_id),
198 "type_known_to_meet_bound_modulo_regions"
208 fn do_normalize_predicates<'tcx>(
210 region_context: DefId,
211 cause: ObligationCause<'tcx>,
212 elaborated_env: ty::ParamEnv<'tcx>,
213 predicates: Vec<ty::Predicate<'tcx>>,
214 ) -> Result<Vec<ty::Predicate<'tcx>>, ErrorReported> {
216 "do_normalize_predicates(predicates={:?}, region_context={:?}, cause={:?})",
217 predicates, region_context, cause,
219 let span = cause.span;
220 tcx.infer_ctxt().enter(|infcx| {
221 // FIXME. We should really... do something with these region
222 // obligations. But this call just continues the older
223 // behavior (i.e., doesn't cause any new bugs), and it would
224 // take some further refactoring to actually solve them. In
225 // particular, we would have to handle implied bounds
226 // properly, and that code is currently largely confined to
227 // regionck (though I made some efforts to extract it
230 // @arielby: In any case, these obligations are checked
231 // by wfcheck anyway, so I'm not sure we have to check
232 // them here too, and we will remove this function when
233 // we move over to lazy normalization *anyway*.
234 let fulfill_cx = FulfillmentContext::new_ignoring_regions();
236 match fully_normalize(&infcx, fulfill_cx, cause, elaborated_env, predicates) {
237 Ok(predicates) => predicates,
239 infcx.report_fulfillment_errors(&errors, None, false);
240 return Err(ErrorReported);
244 debug!("do_normalize_predictes: normalized predicates = {:?}", predicates);
246 // We can use the `elaborated_env` here; the region code only
247 // cares about declarations like `'a: 'b`.
248 let outlives_env = OutlivesEnvironment::new(elaborated_env);
250 infcx.resolve_regions_and_report_errors(
253 RegionckMode::default(),
256 let predicates = match infcx.fully_resolve(predicates) {
257 Ok(predicates) => predicates,
259 // If we encounter a fixup error, it means that some type
260 // variable wound up unconstrained. I actually don't know
261 // if this can happen, and I certainly don't expect it to
262 // happen often, but if it did happen it probably
263 // represents a legitimate failure due to some kind of
264 // unconstrained variable, and it seems better not to ICE,
265 // all things considered.
266 tcx.sess.span_err(span, &fixup_err.to_string());
267 return Err(ErrorReported);
270 if predicates.needs_infer() {
271 tcx.sess.delay_span_bug(span, "encountered inference variables after `fully_resolve`");
279 // FIXME: this is gonna need to be removed ...
280 /// Normalizes the parameter environment, reporting errors if they occur.
281 pub fn normalize_param_env_or_error<'tcx>(
283 region_context: DefId,
284 unnormalized_env: ty::ParamEnv<'tcx>,
285 cause: ObligationCause<'tcx>,
286 ) -> ty::ParamEnv<'tcx> {
287 // I'm not wild about reporting errors here; I'd prefer to
288 // have the errors get reported at a defined place (e.g.,
289 // during typeck). Instead I have all parameter
290 // environments, in effect, going through this function
291 // and hence potentially reporting errors. This ensures of
292 // course that we never forget to normalize (the
293 // alternative seemed like it would involve a lot of
294 // manual invocations of this fn -- and then we'd have to
295 // deal with the errors at each of those sites).
297 // In any case, in practice, typeck constructs all the
298 // parameter environments once for every fn as it goes,
299 // and errors will get reported then; so after typeck we
300 // can be sure that no errors should occur.
303 "normalize_param_env_or_error(region_context={:?}, unnormalized_env={:?}, cause={:?})",
304 region_context, unnormalized_env, cause
307 let mut predicates: Vec<_> =
308 util::elaborate_predicates(tcx, unnormalized_env.caller_bounds().into_iter())
309 .map(|obligation| obligation.predicate)
312 debug!("normalize_param_env_or_error: elaborated-predicates={:?}", predicates);
315 ty::ParamEnv::new(tcx.intern_predicates(&predicates), unnormalized_env.reveal());
317 // HACK: we are trying to normalize the param-env inside *itself*. The problem is that
318 // normalization expects its param-env to be already normalized, which means we have
321 // The way we handle this is by normalizing the param-env inside an unnormalized version
322 // of the param-env, which means that if the param-env contains unnormalized projections,
323 // we'll have some normalization failures. This is unfortunate.
325 // Lazy normalization would basically handle this by treating just the
326 // normalizing-a-trait-ref-requires-itself cycles as evaluation failures.
328 // Inferred outlives bounds can create a lot of `TypeOutlives` predicates for associated
329 // types, so to make the situation less bad, we normalize all the predicates *but*
330 // the `TypeOutlives` predicates first inside the unnormalized parameter environment, and
331 // then we normalize the `TypeOutlives` bounds inside the normalized parameter environment.
333 // This works fairly well because trait matching does not actually care about param-env
334 // TypeOutlives predicates - these are normally used by regionck.
335 let outlives_predicates: Vec<_> = predicates
336 .drain_filter(|predicate| {
337 matches!(predicate.kind().skip_binder(), ty::PredicateKind::TypeOutlives(..))
342 "normalize_param_env_or_error: predicates=(non-outlives={:?}, outlives={:?})",
343 predicates, outlives_predicates
345 let non_outlives_predicates = match do_normalize_predicates(
352 Ok(predicates) => predicates,
353 // An unnormalized env is better than nothing.
354 Err(ErrorReported) => {
355 debug!("normalize_param_env_or_error: errored resolving non-outlives predicates");
356 return elaborated_env;
360 debug!("normalize_param_env_or_error: non-outlives predicates={:?}", non_outlives_predicates);
362 // Not sure whether it is better to include the unnormalized TypeOutlives predicates
363 // here. I believe they should not matter, because we are ignoring TypeOutlives param-env
364 // predicates here anyway. Keeping them here anyway because it seems safer.
365 let outlives_env: Vec<_> =
366 non_outlives_predicates.iter().chain(&outlives_predicates).cloned().collect();
368 ty::ParamEnv::new(tcx.intern_predicates(&outlives_env), unnormalized_env.reveal());
369 let outlives_predicates = match do_normalize_predicates(
376 Ok(predicates) => predicates,
377 // An unnormalized env is better than nothing.
378 Err(ErrorReported) => {
379 debug!("normalize_param_env_or_error: errored resolving outlives predicates");
380 return elaborated_env;
383 debug!("normalize_param_env_or_error: outlives predicates={:?}", outlives_predicates);
385 let mut predicates = non_outlives_predicates;
386 predicates.extend(outlives_predicates);
387 debug!("normalize_param_env_or_error: final predicates={:?}", predicates);
388 ty::ParamEnv::new(tcx.intern_predicates(&predicates), unnormalized_env.reveal())
391 pub fn fully_normalize<'a, 'tcx, T>(
392 infcx: &InferCtxt<'a, 'tcx>,
393 mut fulfill_cx: FulfillmentContext<'tcx>,
394 cause: ObligationCause<'tcx>,
395 param_env: ty::ParamEnv<'tcx>,
397 ) -> Result<T, Vec<FulfillmentError<'tcx>>>
399 T: TypeFoldable<'tcx>,
401 debug!("fully_normalize_with_fulfillcx(value={:?})", value);
402 let selcx = &mut SelectionContext::new(infcx);
403 let Normalized { value: normalized_value, obligations } =
404 project::normalize(selcx, param_env, cause, value);
406 "fully_normalize: normalized_value={:?} obligations={:?}",
407 normalized_value, obligations
409 for obligation in obligations {
410 fulfill_cx.register_predicate_obligation(selcx.infcx(), obligation);
413 debug!("fully_normalize: select_all_or_error start");
414 let errors = fulfill_cx.select_all_or_error(infcx);
415 if !errors.is_empty() {
418 debug!("fully_normalize: select_all_or_error complete");
419 let resolved_value = infcx.resolve_vars_if_possible(normalized_value);
420 debug!("fully_normalize: resolved_value={:?}", resolved_value);
424 /// Normalizes the predicates and checks whether they hold in an empty environment. If this
425 /// returns true, then either normalize encountered an error or one of the predicates did not
426 /// hold. Used when creating vtables to check for unsatisfiable methods.
427 pub fn impossible_predicates<'tcx>(
429 predicates: Vec<ty::Predicate<'tcx>>,
431 debug!("impossible_predicates(predicates={:?})", predicates);
433 let result = tcx.infer_ctxt().enter(|infcx| {
434 let param_env = ty::ParamEnv::reveal_all();
435 let mut selcx = SelectionContext::new(&infcx);
436 let mut fulfill_cx = FulfillmentContext::new();
437 let cause = ObligationCause::dummy();
438 let Normalized { value: predicates, obligations } =
439 normalize(&mut selcx, param_env, cause.clone(), predicates);
440 for obligation in obligations {
441 fulfill_cx.register_predicate_obligation(&infcx, obligation);
443 for predicate in predicates {
444 let obligation = Obligation::new(cause.clone(), param_env, predicate);
445 fulfill_cx.register_predicate_obligation(&infcx, obligation);
448 let errors = fulfill_cx.select_all_or_error(&infcx);
452 debug!("impossible_predicates = {:?}", result);
456 fn subst_and_check_impossible_predicates<'tcx>(
458 key: (DefId, SubstsRef<'tcx>),
460 debug!("subst_and_check_impossible_predicates(key={:?})", key);
462 let mut predicates = tcx.predicates_of(key.0).instantiate(tcx, key.1).predicates;
463 predicates.retain(|predicate| !predicate.definitely_needs_subst(tcx));
464 let result = impossible_predicates(tcx, predicates);
466 debug!("subst_and_check_impossible_predicates(key={:?}) = {:?}", key, result);
470 #[derive(Clone, Debug)]
471 enum VtblSegment<'tcx> {
473 TraitOwnEntries { trait_ref: ty::PolyTraitRef<'tcx>, emit_vptr: bool },
476 /// Prepare the segments for a vtable
477 fn prepare_vtable_segments<'tcx, T>(
479 trait_ref: ty::PolyTraitRef<'tcx>,
480 mut segment_visitor: impl FnMut(VtblSegment<'tcx>) -> ControlFlow<T>,
482 // The following constraints holds for the final arrangement.
483 // 1. The whole virtual table of the first direct super trait is included as the
484 // the prefix. If this trait doesn't have any super traits, then this step
485 // consists of the dsa metadata.
486 // 2. Then comes the proper pointer metadata(vptr) and all own methods for all
487 // other super traits except those already included as part of the first
488 // direct super trait virtual table.
489 // 3. finally, the own methods of this trait.
491 // This has the advantage that trait upcasting to the first direct super trait on each level
492 // is zero cost, and to another trait includes only replacing the pointer with one level indirection,
493 // while not using too much extra memory.
495 // For a single inheritance relationship like this,
496 // D --> C --> B --> A
497 // The resulting vtable will consists of these segments:
500 // For a multiple inheritance relationship like this,
503 // The resulting vtable will consists of these segments:
504 // DSA, A, B, B-vptr, C, D
506 // For a diamond inheritance relationship like this,
509 // The resulting vtable will consists of these segments:
510 // DSA, A, B, C, C-vptr, D
512 // For a more complex inheritance relationship like this:
513 // O --> G --> C --> A
521 // The resulting vtable will consists of these segments:
522 // DSA, A, B, B-vptr, C, D, D-vptr, E, E-vptr, F, F-vptr, G,
523 // H, H-vptr, I, I-vptr, J, J-vptr, K, K-vptr, L, L-vptr, M, M-vptr,
526 // emit dsa segment first.
527 if let ControlFlow::Break(v) = (segment_visitor)(VtblSegment::MetadataDSA) {
531 let mut emit_vptr_on_new_entry = false;
532 let mut visited = util::PredicateSet::new(tcx);
533 let predicate = trait_ref.without_const().to_predicate(tcx);
534 let mut stack: SmallVec<[(ty::PolyTraitRef<'tcx>, _, _); 5]> =
535 smallvec![(trait_ref, emit_vptr_on_new_entry, None)];
536 visited.insert(predicate);
538 // the main traversal loop:
539 // basically we want to cut the inheritance directed graph into a few non-overlapping slices of nodes
540 // that each node is emited after all its descendents have been emitted.
541 // so we convert the directed graph into a tree by skipping all previously visted nodes using a visited set.
542 // this is done on the fly.
543 // Each loop run emits a slice - it starts by find a "childless" unvisited node, backtracking upwards, and it
544 // stops after it finds a node that has a next-sibling node.
545 // This next-sibling node will used as the starting point of next slice.
548 // For a diamond inheritance relationship like this,
549 // D#1 --> B#0 --> A#0
552 // Starting point 0 stack [D]
553 // Loop run #0: Stack after diving in is [D B A], A is "childless"
554 // after this point, all newly visited nodes won't have a vtable that equals to a prefix of this one.
555 // Loop run #0: Emiting the slice [B A] (in reverse order), B has a next-sibling node, so this slice stops here.
556 // Loop run #0: Stack after exiting out is [D C], C is the next starting point.
557 // Loop run #1: Stack after diving in is [D C], C is "childless", since its child A is skipped(already emitted).
558 // Loop run #1: Emiting the slice [D C] (in reverse order). No one has a next-sibling node.
559 // Loop run #1: Stack after exiting out is []. Now the function exits.
562 // dive deeper into the stack, recording the path
564 if let Some((inner_most_trait_ref, _, _)) = stack.last() {
565 let inner_most_trait_ref = *inner_most_trait_ref;
566 let mut direct_super_traits_iter = tcx
567 .super_predicates_of(inner_most_trait_ref.def_id())
570 .filter_map(move |(pred, _)| {
571 pred.subst_supertrait(tcx, &inner_most_trait_ref).to_opt_poly_trait_ref()
574 'diving_in_skip_visited_traits: loop {
575 if let Some(next_super_trait) = direct_super_traits_iter.next() {
576 if visited.insert(next_super_trait.to_predicate(tcx)) {
578 next_super_trait.value,
579 emit_vptr_on_new_entry,
580 Some(direct_super_traits_iter),
582 break 'diving_in_skip_visited_traits;
584 continue 'diving_in_skip_visited_traits;
593 // Other than the left-most path, vptr should be emitted for each trait.
594 emit_vptr_on_new_entry = true;
596 // emit innermost item, move to next sibling and stop there if possible, otherwise jump to outer level.
598 if let Some((inner_most_trait_ref, emit_vptr, siblings_opt)) = stack.last_mut() {
599 if let ControlFlow::Break(v) = (segment_visitor)(VtblSegment::TraitOwnEntries {
600 trait_ref: *inner_most_trait_ref,
601 emit_vptr: *emit_vptr,
606 'exiting_out_skip_visited_traits: loop {
607 if let Some(siblings) = siblings_opt {
608 if let Some(next_inner_most_trait_ref) = siblings.next() {
609 if visited.insert(next_inner_most_trait_ref.to_predicate(tcx)) {
610 *inner_most_trait_ref = next_inner_most_trait_ref.value;
611 *emit_vptr = emit_vptr_on_new_entry;
614 continue 'exiting_out_skip_visited_traits;
619 continue 'exiting_out;
628 fn dump_vtable_entries<'tcx>(
631 trait_ref: ty::PolyTraitRef<'tcx>,
632 entries: &[VtblEntry<'tcx>],
634 let msg = format!("vtable entries for `{}`: {:#?}", trait_ref, entries);
635 tcx.sess.struct_span_err(sp, &msg).emit();
638 fn own_existential_vtable_entries<'tcx>(
640 trait_ref: ty::PolyExistentialTraitRef<'tcx>,
642 let trait_methods = tcx
643 .associated_items(trait_ref.def_id())
644 .in_definition_order()
645 .filter(|item| item.kind == ty::AssocKind::Fn);
646 // Now list each method's DefId (for within its trait).
647 let own_entries = trait_methods.filter_map(move |trait_method| {
648 debug!("own_existential_vtable_entry: trait_method={:?}", trait_method);
649 let def_id = trait_method.def_id;
651 // Some methods cannot be called on an object; skip those.
652 if !is_vtable_safe_method(tcx, trait_ref.def_id(), &trait_method) {
653 debug!("own_existential_vtable_entry: not vtable safe");
660 tcx.arena.alloc_from_iter(own_entries.into_iter())
663 /// Given a trait `trait_ref`, iterates the vtable entries
664 /// that come from `trait_ref`, including its supertraits.
665 fn vtable_entries<'tcx>(
667 trait_ref: ty::PolyTraitRef<'tcx>,
668 ) -> &'tcx [VtblEntry<'tcx>] {
669 debug!("vtable_entries({:?})", trait_ref);
671 let mut entries = vec![];
673 let vtable_segment_callback = |segment| -> ControlFlow<()> {
675 VtblSegment::MetadataDSA => {
676 entries.extend(COMMON_VTABLE_ENTRIES);
678 VtblSegment::TraitOwnEntries { trait_ref, emit_vptr } => {
679 let existential_trait_ref = trait_ref
680 .map_bound(|trait_ref| ty::ExistentialTraitRef::erase_self_ty(tcx, trait_ref));
682 // Lookup the shape of vtable for the trait.
683 let own_existential_entries =
684 tcx.own_existential_vtable_entries(existential_trait_ref);
686 let own_entries = own_existential_entries.iter().copied().map(|def_id| {
687 debug!("vtable_entries: trait_method={:?}", def_id);
689 // The method may have some early-bound lifetimes; add regions for those.
690 let substs = trait_ref.map_bound(|trait_ref| {
691 InternalSubsts::for_item(tcx, def_id, |param, _| match param.kind {
692 GenericParamDefKind::Lifetime => tcx.lifetimes.re_erased.into(),
693 GenericParamDefKind::Type { .. }
694 | GenericParamDefKind::Const { .. } => {
695 trait_ref.substs[param.index as usize]
700 // The trait type may have higher-ranked lifetimes in it;
701 // erase them if they appear, so that we get the type
702 // at some particular call site.
704 .normalize_erasing_late_bound_regions(ty::ParamEnv::reveal_all(), substs);
706 // It's possible that the method relies on where-clauses that
707 // do not hold for this particular set of type parameters.
708 // Note that this method could then never be called, so we
709 // do not want to try and codegen it, in that case (see #23435).
710 let predicates = tcx.predicates_of(def_id).instantiate_own(tcx, substs);
711 if impossible_predicates(tcx, predicates.predicates) {
712 debug!("vtable_entries: predicates do not hold");
713 return VtblEntry::Vacant;
716 let instance = ty::Instance::resolve_for_vtable(
718 ty::ParamEnv::reveal_all(),
722 .expect("resolution failed during building vtable representation");
723 VtblEntry::Method(instance)
726 entries.extend(own_entries);
729 entries.push(VtblEntry::TraitVPtr(trait_ref));
734 ControlFlow::Continue(())
737 let _ = prepare_vtable_segments(tcx, trait_ref, vtable_segment_callback);
739 if tcx.has_attr(trait_ref.def_id(), sym::rustc_dump_vtable) {
740 let sp = tcx.def_span(trait_ref.def_id());
741 dump_vtable_entries(tcx, sp, trait_ref, &entries);
744 tcx.arena.alloc_from_iter(entries.into_iter())
747 /// Find slot base for trait methods within vtable entries of another trait
748 fn vtable_trait_first_method_offset<'tcx>(
751 ty::PolyTraitRef<'tcx>, // trait_to_be_found
752 ty::PolyTraitRef<'tcx>, // trait_owning_vtable
755 let (trait_to_be_found, trait_owning_vtable) = key;
758 let trait_to_be_found_erased = tcx.erase_regions(trait_to_be_found);
760 let vtable_segment_callback = {
761 let mut vtable_base = 0;
765 VtblSegment::MetadataDSA => {
766 vtable_base += COMMON_VTABLE_ENTRIES.len();
768 VtblSegment::TraitOwnEntries { trait_ref, emit_vptr } => {
769 if tcx.erase_regions(trait_ref) == trait_to_be_found_erased {
770 return ControlFlow::Break(vtable_base);
772 vtable_base += util::count_own_vtable_entries(tcx, trait_ref);
778 ControlFlow::Continue(())
782 if let Some(vtable_base) =
783 prepare_vtable_segments(tcx, trait_owning_vtable, vtable_segment_callback)
787 bug!("Failed to find info for expected trait in vtable");
791 /// Find slot offset for trait vptr within vtable entries of another trait
792 pub fn vtable_trait_upcasting_coercion_new_vptr_slot(
795 Ty<'tcx>, // trait object type whose trait owning vtable
796 Ty<'tcx>, // trait object for supertrait
799 let (source, target) = key;
800 assert!(matches!(&source.kind(), &ty::Dynamic(..)) && !source.needs_infer());
801 assert!(matches!(&target.kind(), &ty::Dynamic(..)) && !target.needs_infer());
803 // this has been typecked-before, so diagnostics is not really needed.
804 let unsize_trait_did = tcx.require_lang_item(LangItem::Unsize, None);
806 let trait_ref = ty::TraitRef {
807 def_id: unsize_trait_did,
808 substs: tcx.mk_substs_trait(source, &[target.into()]),
810 let obligation = Obligation::new(
811 ObligationCause::dummy(),
812 ty::ParamEnv::reveal_all(),
813 ty::Binder::dummy(ty::TraitPredicate {
815 constness: ty::BoundConstness::NotConst,
816 polarity: ty::ImplPolarity::Positive,
820 let implsrc = tcx.infer_ctxt().enter(|infcx| {
821 let mut selcx = SelectionContext::new(&infcx);
822 selcx.select(&obligation).unwrap()
825 let implsrc_traitcasting = match implsrc {
826 Some(ImplSource::TraitUpcasting(data)) => data,
830 implsrc_traitcasting.vtable_vptr_slot
833 pub fn provide(providers: &mut ty::query::Providers) {
834 object_safety::provide(providers);
835 structural_match::provide(providers);
836 *providers = ty::query::Providers {
837 specialization_graph_of: specialize::specialization_graph_provider,
838 specializes: specialize::specializes,
839 codegen_fulfill_obligation: codegen::codegen_fulfill_obligation,
840 own_existential_vtable_entries,
842 vtable_trait_upcasting_coercion_new_vptr_slot,
843 subst_and_check_impossible_predicates,
844 thir_abstract_const: |tcx, def_id| {
845 let def_id = def_id.expect_local();
846 if let Some(def) = ty::WithOptConstParam::try_lookup(def_id, tcx) {
847 tcx.thir_abstract_const_of_const_arg(def)
849 const_evaluatable::thir_abstract_const(tcx, ty::WithOptConstParam::unknown(def_id))
852 thir_abstract_const_of_const_arg: |tcx, (did, param_did)| {
853 const_evaluatable::thir_abstract_const(
855 ty::WithOptConstParam { did, const_param_did: Some(param_did) },
858 try_unify_abstract_consts: const_evaluatable::try_unify_abstract_consts,