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, TyCtxtInferExt};
27 use crate::traits::error_reporting::InferCtxtExt as _;
28 use crate::traits::query::evaluate_obligation::InferCtxtExt as _;
29 use rustc_errors::ErrorGuaranteed;
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::{self, GenericParamDefKind, ToPredicate, Ty, TyCtxt, VtblEntry};
36 use rustc_span::{sym, Span};
37 use smallvec::SmallVec;
40 use std::ops::ControlFlow;
42 pub use self::FulfillmentErrorCode::*;
43 pub use self::ImplSource::*;
44 pub use self::ObligationCauseCode::*;
45 pub use self::SelectionError::*;
47 pub use self::coherence::{add_placeholder_note, orphan_check, overlapping_impls};
48 pub use self::coherence::{OrphanCheckErr, OverlapResult};
49 pub use self::engine::TraitEngineExt;
50 pub use self::fulfill::{FulfillmentContext, PendingPredicateObligation};
51 pub use self::object_safety::astconv_object_safety_violations;
52 pub use self::object_safety::is_vtable_safe_method;
53 pub use self::object_safety::MethodViolationCode;
54 pub use self::object_safety::ObjectSafetyViolation;
55 pub use self::on_unimplemented::{OnUnimplementedDirective, OnUnimplementedNote};
56 pub use self::project::{normalize, normalize_projection_type, normalize_to};
57 pub use self::select::{EvaluationCache, SelectionCache, SelectionContext};
58 pub use self::select::{EvaluationResult, IntercrateAmbiguityCause, OverflowError};
59 pub use self::specialize::specialization_graph::FutureCompatOverlapError;
60 pub use self::specialize::specialization_graph::FutureCompatOverlapErrorKind;
61 pub use self::specialize::{specialization_graph, translate_substs, OverlapError};
62 pub use self::structural_match::search_for_structural_match_violation;
63 pub use self::structural_match::{NonStructuralMatchTy, NonStructuralMatchTyKind};
65 elaborate_obligations, elaborate_predicates, elaborate_predicates_with_span,
66 elaborate_trait_ref, elaborate_trait_refs,
68 pub use self::util::{expand_trait_aliases, TraitAliasExpander};
70 get_vtable_index_of_object_method, impl_item_is_final, predicate_for_trait_def, upcast_choices,
73 supertrait_def_ids, supertraits, transitive_bounds, transitive_bounds_that_define_assoc_type,
74 SupertraitDefIds, Supertraits,
77 pub use self::chalk_fulfill::FulfillmentContext as ChalkFulfillmentContext;
79 pub use rustc_infer::traits::*;
81 /// Whether to skip the leak check, as part of a future compatibility warning step.
83 /// The "default" for skip-leak-check corresponds to the current
84 /// behavior (do not skip the leak check) -- not the behavior we are
85 /// transitioning into.
86 #[derive(Copy, Clone, PartialEq, Eq, Debug, Default)]
87 pub enum SkipLeakCheck {
94 fn is_yes(self) -> bool {
95 self == SkipLeakCheck::Yes
99 /// The mode that trait queries run in.
100 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
101 pub enum TraitQueryMode {
102 /// Standard/un-canonicalized queries get accurate
103 /// spans etc. passed in and hence can do reasonable
104 /// error reporting on their own.
106 /// Canonicalized queries get dummy spans and hence
107 /// must generally propagate errors to
108 /// pre-canonicalization callsites.
112 /// Creates predicate obligations from the generic bounds.
113 pub fn predicates_for_generics<'tcx>(
114 cause: ObligationCause<'tcx>,
115 param_env: ty::ParamEnv<'tcx>,
116 generic_bounds: ty::InstantiatedPredicates<'tcx>,
117 ) -> impl Iterator<Item = PredicateObligation<'tcx>> {
118 util::predicates_for_generics(cause, 0, param_env, generic_bounds)
121 /// Determines whether the type `ty` is known to meet `bound` and
122 /// returns true if so. Returns false if `ty` either does not meet
123 /// `bound` or is not known to meet bound (note that this is
124 /// conservative towards *no impl*, which is the opposite of the
125 /// `evaluate` methods).
126 pub fn type_known_to_meet_bound_modulo_regions<'a, 'tcx>(
127 infcx: &InferCtxt<'a, 'tcx>,
128 param_env: ty::ParamEnv<'tcx>,
134 "type_known_to_meet_bound_modulo_regions(ty={:?}, bound={:?})",
136 infcx.tcx.def_path_str(def_id)
140 ty::Binder::dummy(ty::TraitRef { def_id, substs: infcx.tcx.mk_substs_trait(ty, &[]) });
141 let obligation = Obligation {
143 cause: ObligationCause::misc(span, hir::CRATE_HIR_ID),
145 predicate: trait_ref.without_const().to_predicate(infcx.tcx),
148 let result = infcx.predicate_must_hold_modulo_regions(&obligation);
150 "type_known_to_meet_ty={:?} bound={} => {:?}",
152 infcx.tcx.def_path_str(def_id),
156 if result && ty.has_infer_types_or_consts() {
157 // Because of inference "guessing", selection can sometimes claim
158 // to succeed while the success requires a guess. To ensure
159 // this function's result remains infallible, we must confirm
160 // that guess. While imperfect, I believe this is sound.
162 // The handling of regions in this area of the code is terrible,
163 // see issue #29149. We should be able to improve on this with
165 let mut fulfill_cx = FulfillmentContext::new_ignoring_regions();
167 // We can use a dummy node-id here because we won't pay any mind
168 // to region obligations that arise (there shouldn't really be any
170 let cause = ObligationCause::misc(span, hir::CRATE_HIR_ID);
172 fulfill_cx.register_bound(infcx, param_env, ty, def_id, cause);
174 // Note: we only assume something is `Copy` if we can
175 // *definitively* show that it implements `Copy`. Otherwise,
176 // assume it is move; linear is always ok.
177 match fulfill_cx.select_all_or_error(infcx).as_slice() {
180 "type_known_to_meet_bound_modulo_regions: ty={:?} bound={} success",
182 infcx.tcx.def_path_str(def_id)
189 bound = %infcx.tcx.def_path_str(def_id),
191 "type_known_to_meet_bound_modulo_regions"
201 fn do_normalize_predicates<'tcx>(
203 region_context: DefId,
204 cause: ObligationCause<'tcx>,
205 elaborated_env: ty::ParamEnv<'tcx>,
206 predicates: Vec<ty::Predicate<'tcx>>,
207 ) -> Result<Vec<ty::Predicate<'tcx>>, ErrorGuaranteed> {
209 "do_normalize_predicates(predicates={:?}, region_context={:?}, cause={:?})",
210 predicates, region_context, cause,
212 let span = cause.span;
213 tcx.infer_ctxt().enter(|infcx| {
214 // FIXME. We should really... do something with these region
215 // obligations. But this call just continues the older
216 // behavior (i.e., doesn't cause any new bugs), and it would
217 // take some further refactoring to actually solve them. In
218 // particular, we would have to handle implied bounds
219 // properly, and that code is currently largely confined to
220 // regionck (though I made some efforts to extract it
223 // @arielby: In any case, these obligations are checked
224 // by wfcheck anyway, so I'm not sure we have to check
225 // them here too, and we will remove this function when
226 // we move over to lazy normalization *anyway*.
227 let fulfill_cx = FulfillmentContext::new_ignoring_regions();
229 match fully_normalize(&infcx, fulfill_cx, cause, elaborated_env, predicates) {
230 Ok(predicates) => predicates,
232 let reported = infcx.report_fulfillment_errors(&errors, None, false);
233 return Err(reported);
237 debug!("do_normalize_predictes: normalized predicates = {:?}", predicates);
239 // We can use the `elaborated_env` here; the region code only
240 // cares about declarations like `'a: 'b`.
241 let outlives_env = OutlivesEnvironment::new(elaborated_env);
243 infcx.resolve_regions_and_report_errors(region_context, &outlives_env);
245 let predicates = match infcx.fully_resolve(predicates) {
246 Ok(predicates) => predicates,
248 // If we encounter a fixup error, it means that some type
249 // variable wound up unconstrained. I actually don't know
250 // if this can happen, and I certainly don't expect it to
251 // happen often, but if it did happen it probably
252 // represents a legitimate failure due to some kind of
253 // unconstrained variable, and it seems better not to ICE,
254 // all things considered.
255 let reported = tcx.sess.span_err(span, &fixup_err.to_string());
256 return Err(reported);
259 if predicates.needs_infer() {
262 .delay_span_bug(span, "encountered inference variables after `fully_resolve`");
270 // FIXME: this is gonna need to be removed ...
271 /// Normalizes the parameter environment, reporting errors if they occur.
272 pub fn normalize_param_env_or_error<'tcx>(
274 region_context: DefId,
275 unnormalized_env: ty::ParamEnv<'tcx>,
276 cause: ObligationCause<'tcx>,
277 ) -> ty::ParamEnv<'tcx> {
278 // I'm not wild about reporting errors here; I'd prefer to
279 // have the errors get reported at a defined place (e.g.,
280 // during typeck). Instead I have all parameter
281 // environments, in effect, going through this function
282 // and hence potentially reporting errors. This ensures of
283 // course that we never forget to normalize (the
284 // alternative seemed like it would involve a lot of
285 // manual invocations of this fn -- and then we'd have to
286 // deal with the errors at each of those sites).
288 // In any case, in practice, typeck constructs all the
289 // parameter environments once for every fn as it goes,
290 // and errors will get reported then; so outside of type inference we
291 // can be sure that no errors should occur.
294 "normalize_param_env_or_error(region_context={:?}, unnormalized_env={:?}, cause={:?})",
295 region_context, unnormalized_env, cause
298 let mut predicates: Vec<_> =
299 util::elaborate_predicates(tcx, unnormalized_env.caller_bounds().into_iter())
300 .map(|obligation| obligation.predicate)
303 debug!("normalize_param_env_or_error: elaborated-predicates={:?}", predicates);
305 let elaborated_env = ty::ParamEnv::new(
306 tcx.intern_predicates(&predicates),
307 unnormalized_env.reveal(),
308 unnormalized_env.constness(),
311 // HACK: we are trying to normalize the param-env inside *itself*. The problem is that
312 // normalization expects its param-env to be already normalized, which means we have
315 // The way we handle this is by normalizing the param-env inside an unnormalized version
316 // of the param-env, which means that if the param-env contains unnormalized projections,
317 // we'll have some normalization failures. This is unfortunate.
319 // Lazy normalization would basically handle this by treating just the
320 // normalizing-a-trait-ref-requires-itself cycles as evaluation failures.
322 // Inferred outlives bounds can create a lot of `TypeOutlives` predicates for associated
323 // types, so to make the situation less bad, we normalize all the predicates *but*
324 // the `TypeOutlives` predicates first inside the unnormalized parameter environment, and
325 // then we normalize the `TypeOutlives` bounds inside the normalized parameter environment.
327 // This works fairly well because trait matching does not actually care about param-env
328 // TypeOutlives predicates - these are normally used by regionck.
329 let outlives_predicates: Vec<_> = predicates
330 .drain_filter(|predicate| {
331 matches!(predicate.kind().skip_binder(), ty::PredicateKind::TypeOutlives(..))
336 "normalize_param_env_or_error: predicates=(non-outlives={:?}, outlives={:?})",
337 predicates, outlives_predicates
339 let Ok(non_outlives_predicates) = do_normalize_predicates(
346 // An unnormalized env is better than nothing.
347 debug!("normalize_param_env_or_error: errored resolving non-outlives predicates");
348 return elaborated_env;
351 debug!("normalize_param_env_or_error: non-outlives predicates={:?}", non_outlives_predicates);
353 // Not sure whether it is better to include the unnormalized TypeOutlives predicates
354 // here. I believe they should not matter, because we are ignoring TypeOutlives param-env
355 // predicates here anyway. Keeping them here anyway because it seems safer.
356 let outlives_env: Vec<_> =
357 non_outlives_predicates.iter().chain(&outlives_predicates).cloned().collect();
358 let outlives_env = ty::ParamEnv::new(
359 tcx.intern_predicates(&outlives_env),
360 unnormalized_env.reveal(),
361 unnormalized_env.constness(),
363 let Ok(outlives_predicates) = do_normalize_predicates(
370 // An unnormalized env is better than nothing.
371 debug!("normalize_param_env_or_error: errored resolving outlives predicates");
372 return elaborated_env;
374 debug!("normalize_param_env_or_error: outlives predicates={:?}", outlives_predicates);
376 let mut predicates = non_outlives_predicates;
377 predicates.extend(outlives_predicates);
378 debug!("normalize_param_env_or_error: final predicates={:?}", predicates);
380 tcx.intern_predicates(&predicates),
381 unnormalized_env.reveal(),
382 unnormalized_env.constness(),
386 pub fn fully_normalize<'a, 'tcx, T>(
387 infcx: &InferCtxt<'a, 'tcx>,
388 mut fulfill_cx: FulfillmentContext<'tcx>,
389 cause: ObligationCause<'tcx>,
390 param_env: ty::ParamEnv<'tcx>,
392 ) -> Result<T, Vec<FulfillmentError<'tcx>>>
394 T: TypeFoldable<'tcx>,
396 debug!("fully_normalize_with_fulfillcx(value={:?})", value);
397 let selcx = &mut SelectionContext::new(infcx);
398 let Normalized { value: normalized_value, obligations } =
399 project::normalize(selcx, param_env, cause, value);
401 "fully_normalize: normalized_value={:?} obligations={:?}",
402 normalized_value, obligations
404 for obligation in obligations {
405 fulfill_cx.register_predicate_obligation(selcx.infcx(), obligation);
408 debug!("fully_normalize: select_all_or_error start");
409 let errors = fulfill_cx.select_all_or_error(infcx);
410 if !errors.is_empty() {
413 debug!("fully_normalize: select_all_or_error complete");
414 let resolved_value = infcx.resolve_vars_if_possible(normalized_value);
415 debug!("fully_normalize: resolved_value={:?}", resolved_value);
419 /// Normalizes the predicates and checks whether they hold in an empty environment. If this
420 /// returns true, then either normalize encountered an error or one of the predicates did not
421 /// hold. Used when creating vtables to check for unsatisfiable methods.
422 pub fn impossible_predicates<'tcx>(
424 predicates: Vec<ty::Predicate<'tcx>>,
426 debug!("impossible_predicates(predicates={:?})", predicates);
428 let result = tcx.infer_ctxt().enter(|infcx| {
429 // HACK: Set tainted by errors to gracefully exit in case of overflow.
430 infcx.set_tainted_by_errors();
432 let param_env = ty::ParamEnv::reveal_all();
433 let mut selcx = SelectionContext::new(&infcx);
434 let mut fulfill_cx = FulfillmentContext::new();
435 let cause = ObligationCause::dummy();
436 let Normalized { value: predicates, obligations } =
437 normalize(&mut selcx, param_env, cause.clone(), predicates);
438 for obligation in obligations {
439 fulfill_cx.register_predicate_obligation(&infcx, obligation);
441 for predicate in predicates {
442 let obligation = Obligation::new(cause.clone(), param_env, predicate);
443 fulfill_cx.register_predicate_obligation(&infcx, obligation);
446 let errors = fulfill_cx.select_all_or_error(&infcx);
448 // Clean up after ourselves
449 let _ = infcx.inner.borrow_mut().opaque_type_storage.take_opaque_types();
453 debug!("impossible_predicates = {:?}", result);
457 fn subst_and_check_impossible_predicates<'tcx>(
459 key: (DefId, SubstsRef<'tcx>),
461 debug!("subst_and_check_impossible_predicates(key={:?})", key);
463 let mut predicates = tcx.predicates_of(key.0).instantiate(tcx, key.1).predicates;
465 // Specifically check trait fulfillment to avoid an error when trying to resolve
467 if let Some(trait_def_id) = tcx.trait_of_item(key.0) {
468 let trait_ref = ty::TraitRef::from_method(tcx, trait_def_id, key.1);
469 predicates.push(ty::Binder::dummy(trait_ref).to_poly_trait_predicate().to_predicate(tcx));
472 predicates.retain(|predicate| !predicate.needs_subst());
473 let result = impossible_predicates(tcx, predicates);
475 debug!("subst_and_check_impossible_predicates(key={:?}) = {:?}", key, result);
479 #[derive(Clone, Debug)]
480 enum VtblSegment<'tcx> {
482 TraitOwnEntries { trait_ref: ty::PolyTraitRef<'tcx>, emit_vptr: bool },
485 /// Prepare the segments for a vtable
486 fn prepare_vtable_segments<'tcx, T>(
488 trait_ref: ty::PolyTraitRef<'tcx>,
489 mut segment_visitor: impl FnMut(VtblSegment<'tcx>) -> ControlFlow<T>,
491 // The following constraints holds for the final arrangement.
492 // 1. The whole virtual table of the first direct super trait is included as the
493 // the prefix. If this trait doesn't have any super traits, then this step
494 // consists of the dsa metadata.
495 // 2. Then comes the proper pointer metadata(vptr) and all own methods for all
496 // other super traits except those already included as part of the first
497 // direct super trait virtual table.
498 // 3. finally, the own methods of this trait.
500 // This has the advantage that trait upcasting to the first direct super trait on each level
501 // is zero cost, and to another trait includes only replacing the pointer with one level indirection,
502 // while not using too much extra memory.
504 // For a single inheritance relationship like this,
505 // D --> C --> B --> A
506 // The resulting vtable will consists of these segments:
509 // For a multiple inheritance relationship like this,
512 // The resulting vtable will consists of these segments:
513 // DSA, A, B, B-vptr, C, D
515 // For a diamond inheritance relationship like this,
518 // The resulting vtable will consists of these segments:
519 // DSA, A, B, C, C-vptr, D
521 // For a more complex inheritance relationship like this:
522 // O --> G --> C --> A
530 // The resulting vtable will consists of these segments:
531 // DSA, A, B, B-vptr, C, D, D-vptr, E, E-vptr, F, F-vptr, G,
532 // H, H-vptr, I, I-vptr, J, J-vptr, K, K-vptr, L, L-vptr, M, M-vptr,
535 // emit dsa segment first.
536 if let ControlFlow::Break(v) = (segment_visitor)(VtblSegment::MetadataDSA) {
540 let mut emit_vptr_on_new_entry = false;
541 let mut visited = util::PredicateSet::new(tcx);
542 let predicate = trait_ref.without_const().to_predicate(tcx);
543 let mut stack: SmallVec<[(ty::PolyTraitRef<'tcx>, _, _); 5]> =
544 smallvec![(trait_ref, emit_vptr_on_new_entry, None)];
545 visited.insert(predicate);
547 // the main traversal loop:
548 // basically we want to cut the inheritance directed graph into a few non-overlapping slices of nodes
549 // that each node is emitted after all its descendents have been emitted.
550 // so we convert the directed graph into a tree by skipping all previously visited nodes using a visited set.
551 // this is done on the fly.
552 // Each loop run emits a slice - it starts by find a "childless" unvisited node, backtracking upwards, and it
553 // stops after it finds a node that has a next-sibling node.
554 // This next-sibling node will used as the starting point of next slice.
557 // For a diamond inheritance relationship like this,
558 // D#1 --> B#0 --> A#0
561 // Starting point 0 stack [D]
562 // Loop run #0: Stack after diving in is [D B A], A is "childless"
563 // after this point, all newly visited nodes won't have a vtable that equals to a prefix of this one.
564 // Loop run #0: Emitting the slice [B A] (in reverse order), B has a next-sibling node, so this slice stops here.
565 // Loop run #0: Stack after exiting out is [D C], C is the next starting point.
566 // Loop run #1: Stack after diving in is [D C], C is "childless", since its child A is skipped(already emitted).
567 // Loop run #1: Emitting the slice [D C] (in reverse order). No one has a next-sibling node.
568 // Loop run #1: Stack after exiting out is []. Now the function exits.
571 // dive deeper into the stack, recording the path
573 if let Some((inner_most_trait_ref, _, _)) = stack.last() {
574 let inner_most_trait_ref = *inner_most_trait_ref;
575 let mut direct_super_traits_iter = tcx
576 .super_predicates_of(inner_most_trait_ref.def_id())
579 .filter_map(move |(pred, _)| {
580 pred.subst_supertrait(tcx, &inner_most_trait_ref).to_opt_poly_trait_pred()
583 'diving_in_skip_visited_traits: loop {
584 if let Some(next_super_trait) = direct_super_traits_iter.next() {
585 if visited.insert(next_super_trait.to_predicate(tcx)) {
586 // We're throwing away potential constness of super traits here.
587 // FIXME: handle ~const super traits
588 let next_super_trait = next_super_trait.map_bound(|t| t.trait_ref);
591 emit_vptr_on_new_entry,
592 Some(direct_super_traits_iter),
594 break 'diving_in_skip_visited_traits;
596 continue 'diving_in_skip_visited_traits;
605 // Other than the left-most path, vptr should be emitted for each trait.
606 emit_vptr_on_new_entry = true;
608 // emit innermost item, move to next sibling and stop there if possible, otherwise jump to outer level.
610 if let Some((inner_most_trait_ref, emit_vptr, siblings_opt)) = stack.last_mut() {
611 if let ControlFlow::Break(v) = (segment_visitor)(VtblSegment::TraitOwnEntries {
612 trait_ref: *inner_most_trait_ref,
613 emit_vptr: *emit_vptr,
618 'exiting_out_skip_visited_traits: loop {
619 if let Some(siblings) = siblings_opt {
620 if let Some(next_inner_most_trait_ref) = siblings.next() {
621 if visited.insert(next_inner_most_trait_ref.to_predicate(tcx)) {
622 // We're throwing away potential constness of super traits here.
623 // FIXME: handle ~const super traits
624 let next_inner_most_trait_ref =
625 next_inner_most_trait_ref.map_bound(|t| t.trait_ref);
626 *inner_most_trait_ref = next_inner_most_trait_ref;
627 *emit_vptr = emit_vptr_on_new_entry;
630 continue 'exiting_out_skip_visited_traits;
635 continue 'exiting_out;
644 fn dump_vtable_entries<'tcx>(
647 trait_ref: ty::PolyTraitRef<'tcx>,
648 entries: &[VtblEntry<'tcx>],
650 let msg = format!("vtable entries for `{}`: {:#?}", trait_ref, entries);
651 tcx.sess.struct_span_err(sp, &msg).emit();
654 fn own_existential_vtable_entries<'tcx>(
656 trait_ref: ty::PolyExistentialTraitRef<'tcx>,
658 let trait_methods = tcx
659 .associated_items(trait_ref.def_id())
660 .in_definition_order()
661 .filter(|item| item.kind == ty::AssocKind::Fn);
662 // Now list each method's DefId (for within its trait).
663 let own_entries = trait_methods.filter_map(move |trait_method| {
664 debug!("own_existential_vtable_entry: trait_method={:?}", trait_method);
665 let def_id = trait_method.def_id;
667 // Some methods cannot be called on an object; skip those.
668 if !is_vtable_safe_method(tcx, trait_ref.def_id(), &trait_method) {
669 debug!("own_existential_vtable_entry: not vtable safe");
676 tcx.arena.alloc_from_iter(own_entries.into_iter())
679 /// Given a trait `trait_ref`, iterates the vtable entries
680 /// that come from `trait_ref`, including its supertraits.
681 fn vtable_entries<'tcx>(
683 trait_ref: ty::PolyTraitRef<'tcx>,
684 ) -> &'tcx [VtblEntry<'tcx>] {
685 debug!("vtable_entries({:?})", trait_ref);
687 let mut entries = vec![];
689 let vtable_segment_callback = |segment| -> ControlFlow<()> {
691 VtblSegment::MetadataDSA => {
692 entries.extend(TyCtxt::COMMON_VTABLE_ENTRIES);
694 VtblSegment::TraitOwnEntries { trait_ref, emit_vptr } => {
695 let existential_trait_ref = trait_ref
696 .map_bound(|trait_ref| ty::ExistentialTraitRef::erase_self_ty(tcx, trait_ref));
698 // Lookup the shape of vtable for the trait.
699 let own_existential_entries =
700 tcx.own_existential_vtable_entries(existential_trait_ref);
702 let own_entries = own_existential_entries.iter().copied().map(|def_id| {
703 debug!("vtable_entries: trait_method={:?}", def_id);
705 // The method may have some early-bound lifetimes; add regions for those.
706 let substs = trait_ref.map_bound(|trait_ref| {
707 InternalSubsts::for_item(tcx, def_id, |param, _| match param.kind {
708 GenericParamDefKind::Lifetime => tcx.lifetimes.re_erased.into(),
709 GenericParamDefKind::Type { .. }
710 | GenericParamDefKind::Const { .. } => {
711 trait_ref.substs[param.index as usize]
716 // The trait type may have higher-ranked lifetimes in it;
717 // erase them if they appear, so that we get the type
718 // at some particular call site.
720 .normalize_erasing_late_bound_regions(ty::ParamEnv::reveal_all(), substs);
722 // It's possible that the method relies on where-clauses that
723 // do not hold for this particular set of type parameters.
724 // Note that this method could then never be called, so we
725 // do not want to try and codegen it, in that case (see #23435).
726 let predicates = tcx.predicates_of(def_id).instantiate_own(tcx, substs);
727 if impossible_predicates(tcx, predicates.predicates) {
728 debug!("vtable_entries: predicates do not hold");
729 return VtblEntry::Vacant;
732 let instance = ty::Instance::resolve_for_vtable(
734 ty::ParamEnv::reveal_all(),
738 .expect("resolution failed during building vtable representation");
739 VtblEntry::Method(instance)
742 entries.extend(own_entries);
745 entries.push(VtblEntry::TraitVPtr(trait_ref));
750 ControlFlow::Continue(())
753 let _ = prepare_vtable_segments(tcx, trait_ref, vtable_segment_callback);
755 if tcx.has_attr(trait_ref.def_id(), sym::rustc_dump_vtable) {
756 let sp = tcx.def_span(trait_ref.def_id());
757 dump_vtable_entries(tcx, sp, trait_ref, &entries);
760 tcx.arena.alloc_from_iter(entries.into_iter())
763 /// Find slot base for trait methods within vtable entries of another trait
764 fn vtable_trait_first_method_offset<'tcx>(
767 ty::PolyTraitRef<'tcx>, // trait_to_be_found
768 ty::PolyTraitRef<'tcx>, // trait_owning_vtable
771 let (trait_to_be_found, trait_owning_vtable) = key;
774 let trait_to_be_found_erased = tcx.erase_regions(trait_to_be_found);
776 let vtable_segment_callback = {
777 let mut vtable_base = 0;
781 VtblSegment::MetadataDSA => {
782 vtable_base += TyCtxt::COMMON_VTABLE_ENTRIES.len();
784 VtblSegment::TraitOwnEntries { trait_ref, emit_vptr } => {
785 if tcx.erase_regions(trait_ref) == trait_to_be_found_erased {
786 return ControlFlow::Break(vtable_base);
788 vtable_base += util::count_own_vtable_entries(tcx, trait_ref);
794 ControlFlow::Continue(())
798 if let Some(vtable_base) =
799 prepare_vtable_segments(tcx, trait_owning_vtable, vtable_segment_callback)
803 bug!("Failed to find info for expected trait in vtable");
807 /// Find slot offset for trait vptr within vtable entries of another trait
808 pub fn vtable_trait_upcasting_coercion_new_vptr_slot<'tcx>(
811 Ty<'tcx>, // trait object type whose trait owning vtable
812 Ty<'tcx>, // trait object for supertrait
815 let (source, target) = key;
816 assert!(matches!(&source.kind(), &ty::Dynamic(..)) && !source.needs_infer());
817 assert!(matches!(&target.kind(), &ty::Dynamic(..)) && !target.needs_infer());
819 // this has been typecked-before, so diagnostics is not really needed.
820 let unsize_trait_did = tcx.require_lang_item(LangItem::Unsize, None);
822 let trait_ref = ty::TraitRef {
823 def_id: unsize_trait_did,
824 substs: tcx.mk_substs_trait(source, &[target.into()]),
826 let obligation = Obligation::new(
827 ObligationCause::dummy(),
828 ty::ParamEnv::reveal_all(),
829 ty::Binder::dummy(ty::TraitPredicate {
831 constness: ty::BoundConstness::NotConst,
832 polarity: ty::ImplPolarity::Positive,
836 let implsrc = tcx.infer_ctxt().enter(|infcx| {
837 let mut selcx = SelectionContext::new(&infcx);
838 selcx.select(&obligation).unwrap()
841 let Some(ImplSource::TraitUpcasting(implsrc_traitcasting)) = implsrc else {
845 implsrc_traitcasting.vtable_vptr_slot
848 pub fn provide(providers: &mut ty::query::Providers) {
849 object_safety::provide(providers);
850 structural_match::provide(providers);
851 *providers = ty::query::Providers {
852 specialization_graph_of: specialize::specialization_graph_provider,
853 specializes: specialize::specializes,
854 codegen_fulfill_obligation: codegen::codegen_fulfill_obligation,
855 own_existential_vtable_entries,
857 vtable_trait_upcasting_coercion_new_vptr_slot,
858 subst_and_check_impossible_predicates,
859 thir_abstract_const: |tcx, def_id| {
860 let def_id = def_id.expect_local();
861 if let Some(def) = ty::WithOptConstParam::try_lookup(def_id, tcx) {
862 tcx.thir_abstract_const_of_const_arg(def)
864 const_evaluatable::thir_abstract_const(tcx, ty::WithOptConstParam::unknown(def_id))
867 thir_abstract_const_of_const_arg: |tcx, (did, param_did)| {
868 const_evaluatable::thir_abstract_const(
870 ty::WithOptConstParam { did, const_param_did: Some(param_did) },
873 try_unify_abstract_consts: |tcx, param_env_and| {
874 let (param_env, (a, b)) = param_env_and.into_parts();
875 const_evaluatable::try_unify_abstract_consts(tcx, (a, b), param_env)