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;
15 pub mod outlives_bounds;
18 pub(crate) mod relationships;
25 use crate::errors::DumpVTableEntries;
26 use crate::infer::outlives::env::OutlivesEnvironment;
27 use crate::infer::{InferCtxt, TyCtxtInferExt};
28 use crate::traits::error_reporting::TypeErrCtxtExt as _;
29 use crate::traits::query::evaluate_obligation::InferCtxtExt as _;
30 use rustc_errors::ErrorGuaranteed;
32 use rustc_hir::def_id::DefId;
33 use rustc_hir::lang_items::LangItem;
34 use rustc_infer::traits::TraitEngineExt as _;
35 use rustc_middle::ty::fold::TypeFoldable;
36 use rustc_middle::ty::visit::TypeVisitable;
37 use rustc_middle::ty::{
38 self, DefIdTree, GenericParamDefKind, ToPredicate, Ty, TyCtxt, TypeSuperVisitable, VtblEntry,
40 use rustc_middle::ty::{InternalSubsts, SubstsRef};
41 use rustc_span::{sym, Span};
42 use smallvec::SmallVec;
45 use std::ops::ControlFlow;
47 pub use self::FulfillmentErrorCode::*;
48 pub use self::ImplSource::*;
49 pub use self::ObligationCauseCode::*;
50 pub use self::SelectionError::*;
52 pub use self::coherence::{add_placeholder_note, orphan_check, overlapping_impls};
53 pub use self::coherence::{OrphanCheckErr, OverlapResult};
54 pub use self::engine::{ObligationCtxt, TraitEngineExt};
55 pub use self::fulfill::{FulfillmentContext, PendingPredicateObligation};
56 pub use self::object_safety::astconv_object_safety_violations;
57 pub use self::object_safety::is_vtable_safe_method;
58 pub use self::object_safety::MethodViolationCode;
59 pub use self::object_safety::ObjectSafetyViolation;
60 pub use self::project::{normalize, normalize_projection_type, normalize_to};
61 pub use self::select::{EvaluationCache, SelectionCache, SelectionContext};
62 pub use self::select::{EvaluationResult, IntercrateAmbiguityCause, OverflowError};
63 pub use self::specialize::specialization_graph::FutureCompatOverlapError;
64 pub use self::specialize::specialization_graph::FutureCompatOverlapErrorKind;
65 pub use self::specialize::{specialization_graph, translate_substs, OverlapError};
66 pub use self::structural_match::{
67 search_for_adt_const_param_violation, search_for_structural_match_violation,
70 elaborate_obligations, elaborate_predicates, elaborate_predicates_with_span,
71 elaborate_trait_ref, elaborate_trait_refs,
73 pub use self::util::{expand_trait_aliases, TraitAliasExpander};
75 get_vtable_index_of_object_method, impl_item_is_final, predicate_for_trait_def, upcast_choices,
78 supertrait_def_ids, supertraits, transitive_bounds, transitive_bounds_that_define_assoc_type,
79 SupertraitDefIds, Supertraits,
82 pub use self::chalk_fulfill::FulfillmentContext as ChalkFulfillmentContext;
84 pub use rustc_infer::traits::*;
86 /// Whether to skip the leak check, as part of a future compatibility warning step.
88 /// The "default" for skip-leak-check corresponds to the current
89 /// behavior (do not skip the leak check) -- not the behavior we are
90 /// transitioning into.
91 #[derive(Copy, Clone, PartialEq, Eq, Debug, Default)]
92 pub enum SkipLeakCheck {
99 fn is_yes(self) -> bool {
100 self == SkipLeakCheck::Yes
104 /// The mode that trait queries run in.
105 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
106 pub enum TraitQueryMode {
107 /// Standard/un-canonicalized queries get accurate
108 /// spans etc. passed in and hence can do reasonable
109 /// error reporting on their own.
111 /// Canonicalized queries get dummy spans and hence
112 /// must generally propagate errors to
113 /// pre-canonicalization callsites.
117 /// Creates predicate obligations from the generic bounds.
118 #[instrument(level = "debug", skip(cause, param_env))]
119 pub fn predicates_for_generics<'tcx>(
120 cause: impl Fn(usize, Span) -> ObligationCause<'tcx>,
121 param_env: ty::ParamEnv<'tcx>,
122 generic_bounds: ty::InstantiatedPredicates<'tcx>,
123 ) -> impl Iterator<Item = PredicateObligation<'tcx>> {
124 std::iter::zip(generic_bounds.predicates, generic_bounds.spans).enumerate().map(
125 move |(idx, (predicate, span))| Obligation {
126 cause: cause(idx, span),
134 /// Determines whether the type `ty` is known to meet `bound` and
135 /// returns true if so. Returns false if `ty` either does not meet
136 /// `bound` or is not known to meet bound (note that this is
137 /// conservative towards *no impl*, which is the opposite of the
138 /// `evaluate` methods).
139 pub fn type_known_to_meet_bound_modulo_regions<'tcx>(
140 infcx: &InferCtxt<'tcx>,
141 param_env: ty::ParamEnv<'tcx>,
146 let trait_ref = ty::Binder::dummy(infcx.tcx.mk_trait_ref(def_id, [ty]));
147 pred_known_to_hold_modulo_regions(infcx, param_env, trait_ref.without_const(), span)
150 #[instrument(level = "debug", skip(infcx, param_env, span, pred), ret)]
151 fn pred_known_to_hold_modulo_regions<'tcx>(
152 infcx: &InferCtxt<'tcx>,
153 param_env: ty::ParamEnv<'tcx>,
154 pred: impl ToPredicate<'tcx, ty::Predicate<'tcx>> + TypeVisitable<'tcx>,
157 let has_non_region_infer = pred.has_non_region_infer();
158 let obligation = Obligation {
160 // We can use a dummy node-id here because we won't pay any mind
161 // to region obligations that arise (there shouldn't really be any
163 cause: ObligationCause::misc(span, hir::CRATE_HIR_ID),
165 predicate: pred.to_predicate(infcx.tcx),
168 let result = infcx.predicate_must_hold_modulo_regions(&obligation);
171 if result && has_non_region_infer {
172 // Because of inference "guessing", selection can sometimes claim
173 // to succeed while the success requires a guess. To ensure
174 // this function's result remains infallible, we must confirm
175 // that guess. While imperfect, I believe this is sound.
177 // FIXME(@lcnr): this function doesn't seem right.
178 // The handling of regions in this area of the code is terrible,
179 // see issue #29149. We should be able to improve on this with
181 let errors = fully_solve_obligation(infcx, obligation);
183 // Note: we only assume something is `Copy` if we can
184 // *definitively* show that it implements `Copy`. Otherwise,
185 // assume it is move; linear is always ok.
198 #[instrument(level = "debug", skip(tcx, elaborated_env))]
199 fn do_normalize_predicates<'tcx>(
201 cause: ObligationCause<'tcx>,
202 elaborated_env: ty::ParamEnv<'tcx>,
203 predicates: Vec<ty::Predicate<'tcx>>,
204 ) -> Result<Vec<ty::Predicate<'tcx>>, ErrorGuaranteed> {
205 let span = cause.span;
206 // FIXME. We should really... do something with these region
207 // obligations. But this call just continues the older
208 // behavior (i.e., doesn't cause any new bugs), and it would
209 // take some further refactoring to actually solve them. In
210 // particular, we would have to handle implied bounds
211 // properly, and that code is currently largely confined to
212 // regionck (though I made some efforts to extract it
215 // @arielby: In any case, these obligations are checked
216 // by wfcheck anyway, so I'm not sure we have to check
217 // them here too, and we will remove this function when
218 // we move over to lazy normalization *anyway*.
219 let infcx = tcx.infer_ctxt().ignoring_regions().build();
220 let predicates = match fully_normalize(&infcx, cause, elaborated_env, predicates) {
221 Ok(predicates) => predicates,
223 let reported = infcx.err_ctxt().report_fulfillment_errors(&errors, None);
224 return Err(reported);
228 debug!("do_normalize_predictes: normalized predicates = {:?}", predicates);
230 // We can use the `elaborated_env` here; the region code only
231 // cares about declarations like `'a: 'b`.
232 let outlives_env = OutlivesEnvironment::new(elaborated_env);
234 // FIXME: It's very weird that we ignore region obligations but apparently
235 // still need to use `resolve_regions` as we need the resolved regions in
236 // the normalized predicates.
237 let errors = infcx.resolve_regions(&outlives_env);
238 if !errors.is_empty() {
239 tcx.sess.delay_span_bug(
241 format!("failed region resolution while normalizing {elaborated_env:?}: {errors:?}"),
245 match infcx.fully_resolve(predicates) {
246 Ok(predicates) => Ok(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.
255 // @lcnr: Let's still ICE here for now. I want a test case
259 "inference variables in normalized parameter environment: {}",
266 // FIXME: this is gonna need to be removed ...
267 /// Normalizes the parameter environment, reporting errors if they occur.
268 #[instrument(level = "debug", skip(tcx))]
269 pub fn normalize_param_env_or_error<'tcx>(
271 unnormalized_env: ty::ParamEnv<'tcx>,
272 cause: ObligationCause<'tcx>,
273 ) -> ty::ParamEnv<'tcx> {
274 // I'm not wild about reporting errors here; I'd prefer to
275 // have the errors get reported at a defined place (e.g.,
276 // during typeck). Instead I have all parameter
277 // environments, in effect, going through this function
278 // and hence potentially reporting errors. This ensures of
279 // course that we never forget to normalize (the
280 // alternative seemed like it would involve a lot of
281 // manual invocations of this fn -- and then we'd have to
282 // deal with the errors at each of those sites).
284 // In any case, in practice, typeck constructs all the
285 // parameter environments once for every fn as it goes,
286 // and errors will get reported then; so outside of type inference we
287 // can be sure that no errors should occur.
288 let mut predicates: Vec<_> =
289 util::elaborate_predicates(tcx, unnormalized_env.caller_bounds().into_iter())
290 .map(|obligation| obligation.predicate)
293 debug!("normalize_param_env_or_error: elaborated-predicates={:?}", predicates);
295 let elaborated_env = ty::ParamEnv::new(
296 tcx.intern_predicates(&predicates),
297 unnormalized_env.reveal(),
298 unnormalized_env.constness(),
301 // HACK: we are trying to normalize the param-env inside *itself*. The problem is that
302 // normalization expects its param-env to be already normalized, which means we have
305 // The way we handle this is by normalizing the param-env inside an unnormalized version
306 // of the param-env, which means that if the param-env contains unnormalized projections,
307 // we'll have some normalization failures. This is unfortunate.
309 // Lazy normalization would basically handle this by treating just the
310 // normalizing-a-trait-ref-requires-itself cycles as evaluation failures.
312 // Inferred outlives bounds can create a lot of `TypeOutlives` predicates for associated
313 // types, so to make the situation less bad, we normalize all the predicates *but*
314 // the `TypeOutlives` predicates first inside the unnormalized parameter environment, and
315 // then we normalize the `TypeOutlives` bounds inside the normalized parameter environment.
317 // This works fairly well because trait matching does not actually care about param-env
318 // TypeOutlives predicates - these are normally used by regionck.
319 let outlives_predicates: Vec<_> = predicates
320 .drain_filter(|predicate| {
321 matches!(predicate.kind().skip_binder(), ty::PredicateKind::TypeOutlives(..))
326 "normalize_param_env_or_error: predicates=(non-outlives={:?}, outlives={:?})",
327 predicates, outlives_predicates
329 let Ok(non_outlives_predicates) = do_normalize_predicates(
335 // An unnormalized env is better than nothing.
336 debug!("normalize_param_env_or_error: errored resolving non-outlives predicates");
337 return elaborated_env;
340 debug!("normalize_param_env_or_error: non-outlives predicates={:?}", non_outlives_predicates);
342 // Not sure whether it is better to include the unnormalized TypeOutlives predicates
343 // here. I believe they should not matter, because we are ignoring TypeOutlives param-env
344 // predicates here anyway. Keeping them here anyway because it seems safer.
345 let outlives_env: Vec<_> =
346 non_outlives_predicates.iter().chain(&outlives_predicates).cloned().collect();
347 let outlives_env = ty::ParamEnv::new(
348 tcx.intern_predicates(&outlives_env),
349 unnormalized_env.reveal(),
350 unnormalized_env.constness(),
352 let Ok(outlives_predicates) = do_normalize_predicates(
358 // An unnormalized env is better than nothing.
359 debug!("normalize_param_env_or_error: errored resolving outlives predicates");
360 return elaborated_env;
362 debug!("normalize_param_env_or_error: outlives predicates={:?}", outlives_predicates);
364 let mut predicates = non_outlives_predicates;
365 predicates.extend(outlives_predicates);
366 debug!("normalize_param_env_or_error: final predicates={:?}", predicates);
368 tcx.intern_predicates(&predicates),
369 unnormalized_env.reveal(),
370 unnormalized_env.constness(),
374 /// Normalize a type and process all resulting obligations, returning any errors
375 #[instrument(skip_all)]
376 pub fn fully_normalize<'tcx, T>(
377 infcx: &InferCtxt<'tcx>,
378 cause: ObligationCause<'tcx>,
379 param_env: ty::ParamEnv<'tcx>,
381 ) -> Result<T, Vec<FulfillmentError<'tcx>>>
383 T: TypeFoldable<'tcx>,
385 let ocx = ObligationCtxt::new(infcx);
387 let normalized_value = ocx.normalize(cause, param_env, value);
388 debug!(?normalized_value);
389 debug!("select_all_or_error start");
390 let errors = ocx.select_all_or_error();
391 if !errors.is_empty() {
394 debug!("select_all_or_error complete");
395 let resolved_value = infcx.resolve_vars_if_possible(normalized_value);
396 debug!(?resolved_value);
400 /// Process an obligation (and any nested obligations that come from it) to
401 /// completion, returning any errors
402 pub fn fully_solve_obligation<'tcx>(
403 infcx: &InferCtxt<'tcx>,
404 obligation: PredicateObligation<'tcx>,
405 ) -> Vec<FulfillmentError<'tcx>> {
406 let mut engine = <dyn TraitEngine<'tcx>>::new(infcx.tcx);
407 engine.register_predicate_obligation(infcx, obligation);
408 engine.select_all_or_error(infcx)
411 /// Process a set of obligations (and any nested obligations that come from them)
413 pub fn fully_solve_obligations<'tcx>(
414 infcx: &InferCtxt<'tcx>,
415 obligations: impl IntoIterator<Item = PredicateObligation<'tcx>>,
416 ) -> Vec<FulfillmentError<'tcx>> {
417 let mut engine = <dyn TraitEngine<'tcx>>::new(infcx.tcx);
418 engine.register_predicate_obligations(infcx, obligations);
419 engine.select_all_or_error(infcx)
422 /// Process a bound (and any nested obligations that come from it) to completion.
423 /// This is a convenience function for traits that have no generic arguments, such
424 /// as auto traits, and builtin traits like Copy or Sized.
425 pub fn fully_solve_bound<'tcx>(
426 infcx: &InferCtxt<'tcx>,
427 cause: ObligationCause<'tcx>,
428 param_env: ty::ParamEnv<'tcx>,
431 ) -> Vec<FulfillmentError<'tcx>> {
432 let mut engine = <dyn TraitEngine<'tcx>>::new(infcx.tcx);
433 engine.register_bound(infcx, param_env, ty, bound, cause);
434 engine.select_all_or_error(infcx)
437 /// Normalizes the predicates and checks whether they hold in an empty environment. If this
438 /// returns true, then either normalize encountered an error or one of the predicates did not
439 /// hold. Used when creating vtables to check for unsatisfiable methods.
440 pub fn impossible_predicates<'tcx>(
442 predicates: Vec<ty::Predicate<'tcx>>,
444 debug!("impossible_predicates(predicates={:?})", predicates);
446 let infcx = tcx.infer_ctxt().build();
447 let param_env = ty::ParamEnv::reveal_all();
448 let ocx = ObligationCtxt::new(&infcx);
449 let predicates = ocx.normalize(ObligationCause::dummy(), param_env, predicates);
450 for predicate in predicates {
451 let obligation = Obligation::new(tcx, ObligationCause::dummy(), param_env, predicate);
452 ocx.register_obligation(obligation);
454 let errors = ocx.select_all_or_error();
456 // Clean up after ourselves
457 let _ = infcx.inner.borrow_mut().opaque_type_storage.take_opaque_types();
459 let result = !errors.is_empty();
460 debug!("impossible_predicates = {:?}", result);
464 fn subst_and_check_impossible_predicates<'tcx>(
466 key: (DefId, SubstsRef<'tcx>),
468 debug!("subst_and_check_impossible_predicates(key={:?})", key);
470 let mut predicates = tcx.predicates_of(key.0).instantiate(tcx, key.1).predicates;
472 // Specifically check trait fulfillment to avoid an error when trying to resolve
474 if let Some(trait_def_id) = tcx.trait_of_item(key.0) {
475 let trait_ref = ty::TraitRef::from_method(tcx, trait_def_id, key.1);
476 predicates.push(ty::Binder::dummy(trait_ref).to_poly_trait_predicate().to_predicate(tcx));
479 predicates.retain(|predicate| !predicate.needs_subst());
480 let result = impossible_predicates(tcx, predicates);
482 debug!("subst_and_check_impossible_predicates(key={:?}) = {:?}", key, result);
486 /// Checks whether a trait's method is impossible to call on a given impl.
488 /// This only considers predicates that reference the impl's generics, and not
489 /// those that reference the method's generics.
490 fn is_impossible_method<'tcx>(
492 (impl_def_id, trait_item_def_id): (DefId, DefId),
494 struct ReferencesOnlyParentGenerics<'tcx> {
496 generics: &'tcx ty::Generics,
497 trait_item_def_id: DefId,
499 impl<'tcx> ty::TypeVisitor<'tcx> for ReferencesOnlyParentGenerics<'tcx> {
501 fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
502 // If this is a parameter from the trait item's own generics, then bail
503 if let ty::Param(param) = t.kind()
504 && let param_def_id = self.generics.type_param(param, self.tcx).def_id
505 && self.tcx.parent(param_def_id) == self.trait_item_def_id
507 return ControlFlow::BREAK;
509 t.super_visit_with(self)
511 fn visit_region(&mut self, r: ty::Region<'tcx>) -> ControlFlow<Self::BreakTy> {
512 if let ty::ReEarlyBound(param) = r.kind()
513 && let param_def_id = self.generics.region_param(¶m, self.tcx).def_id
514 && self.tcx.parent(param_def_id) == self.trait_item_def_id
516 return ControlFlow::BREAK;
518 r.super_visit_with(self)
520 fn visit_const(&mut self, ct: ty::Const<'tcx>) -> ControlFlow<Self::BreakTy> {
521 if let ty::ConstKind::Param(param) = ct.kind()
522 && let param_def_id = self.generics.const_param(¶m, self.tcx).def_id
523 && self.tcx.parent(param_def_id) == self.trait_item_def_id
525 return ControlFlow::BREAK;
527 ct.super_visit_with(self)
531 let generics = tcx.generics_of(trait_item_def_id);
532 let predicates = tcx.predicates_of(trait_item_def_id);
534 tcx.impl_trait_ref(impl_def_id).expect("expected impl to correspond to trait");
535 let param_env = tcx.param_env(impl_def_id);
537 let mut visitor = ReferencesOnlyParentGenerics { tcx, generics, trait_item_def_id };
538 let predicates_for_trait = predicates.predicates.iter().filter_map(|(pred, span)| {
539 if pred.visit_with(&mut visitor).is_continue() {
540 Some(Obligation::new(
542 ObligationCause::dummy_with_span(*span),
544 ty::EarlyBinder(*pred).subst(tcx, impl_trait_ref.substs),
551 let infcx = tcx.infer_ctxt().ignoring_regions().build();
552 for obligation in predicates_for_trait {
553 // Ignore overflow error, to be conservative.
554 if let Ok(result) = infcx.evaluate_obligation(&obligation)
555 && !result.may_apply()
563 #[derive(Clone, Debug)]
564 enum VtblSegment<'tcx> {
566 TraitOwnEntries { trait_ref: ty::PolyTraitRef<'tcx>, emit_vptr: bool },
569 /// Prepare the segments for a vtable
570 fn prepare_vtable_segments<'tcx, T>(
572 trait_ref: ty::PolyTraitRef<'tcx>,
573 mut segment_visitor: impl FnMut(VtblSegment<'tcx>) -> ControlFlow<T>,
575 // The following constraints holds for the final arrangement.
576 // 1. The whole virtual table of the first direct super trait is included as the
577 // the prefix. If this trait doesn't have any super traits, then this step
578 // consists of the dsa metadata.
579 // 2. Then comes the proper pointer metadata(vptr) and all own methods for all
580 // other super traits except those already included as part of the first
581 // direct super trait virtual table.
582 // 3. finally, the own methods of this trait.
584 // This has the advantage that trait upcasting to the first direct super trait on each level
585 // is zero cost, and to another trait includes only replacing the pointer with one level indirection,
586 // while not using too much extra memory.
588 // For a single inheritance relationship like this,
589 // D --> C --> B --> A
590 // The resulting vtable will consists of these segments:
593 // For a multiple inheritance relationship like this,
596 // The resulting vtable will consists of these segments:
597 // DSA, A, B, B-vptr, C, D
599 // For a diamond inheritance relationship like this,
602 // The resulting vtable will consists of these segments:
603 // DSA, A, B, C, C-vptr, D
605 // For a more complex inheritance relationship like this:
606 // O --> G --> C --> A
614 // The resulting vtable will consists of these segments:
615 // DSA, A, B, B-vptr, C, D, D-vptr, E, E-vptr, F, F-vptr, G,
616 // H, H-vptr, I, I-vptr, J, J-vptr, K, K-vptr, L, L-vptr, M, M-vptr,
619 // emit dsa segment first.
620 if let ControlFlow::Break(v) = (segment_visitor)(VtblSegment::MetadataDSA) {
624 let mut emit_vptr_on_new_entry = false;
625 let mut visited = util::PredicateSet::new(tcx);
626 let predicate = trait_ref.without_const().to_predicate(tcx);
627 let mut stack: SmallVec<[(ty::PolyTraitRef<'tcx>, _, _); 5]> =
628 smallvec![(trait_ref, emit_vptr_on_new_entry, None)];
629 visited.insert(predicate);
631 // the main traversal loop:
632 // basically we want to cut the inheritance directed graph into a few non-overlapping slices of nodes
633 // that each node is emitted after all its descendents have been emitted.
634 // so we convert the directed graph into a tree by skipping all previously visited nodes using a visited set.
635 // this is done on the fly.
636 // Each loop run emits a slice - it starts by find a "childless" unvisited node, backtracking upwards, and it
637 // stops after it finds a node that has a next-sibling node.
638 // This next-sibling node will used as the starting point of next slice.
641 // For a diamond inheritance relationship like this,
642 // D#1 --> B#0 --> A#0
645 // Starting point 0 stack [D]
646 // Loop run #0: Stack after diving in is [D B A], A is "childless"
647 // after this point, all newly visited nodes won't have a vtable that equals to a prefix of this one.
648 // Loop run #0: Emitting the slice [B A] (in reverse order), B has a next-sibling node, so this slice stops here.
649 // Loop run #0: Stack after exiting out is [D C], C is the next starting point.
650 // Loop run #1: Stack after diving in is [D C], C is "childless", since its child A is skipped(already emitted).
651 // Loop run #1: Emitting the slice [D C] (in reverse order). No one has a next-sibling node.
652 // Loop run #1: Stack after exiting out is []. Now the function exits.
655 // dive deeper into the stack, recording the path
657 if let Some((inner_most_trait_ref, _, _)) = stack.last() {
658 let inner_most_trait_ref = *inner_most_trait_ref;
659 let mut direct_super_traits_iter = tcx
660 .super_predicates_of(inner_most_trait_ref.def_id())
663 .filter_map(move |(pred, _)| {
664 pred.subst_supertrait(tcx, &inner_most_trait_ref).to_opt_poly_trait_pred()
667 'diving_in_skip_visited_traits: loop {
668 if let Some(next_super_trait) = direct_super_traits_iter.next() {
669 if visited.insert(next_super_trait.to_predicate(tcx)) {
670 // We're throwing away potential constness of super traits here.
671 // FIXME: handle ~const super traits
672 let next_super_trait = next_super_trait.map_bound(|t| t.trait_ref);
675 emit_vptr_on_new_entry,
676 Some(direct_super_traits_iter),
678 break 'diving_in_skip_visited_traits;
680 continue 'diving_in_skip_visited_traits;
689 // Other than the left-most path, vptr should be emitted for each trait.
690 emit_vptr_on_new_entry = true;
692 // emit innermost item, move to next sibling and stop there if possible, otherwise jump to outer level.
694 if let Some((inner_most_trait_ref, emit_vptr, siblings_opt)) = stack.last_mut() {
695 if let ControlFlow::Break(v) = (segment_visitor)(VtblSegment::TraitOwnEntries {
696 trait_ref: *inner_most_trait_ref,
697 emit_vptr: *emit_vptr,
702 'exiting_out_skip_visited_traits: loop {
703 if let Some(siblings) = siblings_opt {
704 if let Some(next_inner_most_trait_ref) = siblings.next() {
705 if visited.insert(next_inner_most_trait_ref.to_predicate(tcx)) {
706 // We're throwing away potential constness of super traits here.
707 // FIXME: handle ~const super traits
708 let next_inner_most_trait_ref =
709 next_inner_most_trait_ref.map_bound(|t| t.trait_ref);
710 *inner_most_trait_ref = next_inner_most_trait_ref;
711 *emit_vptr = emit_vptr_on_new_entry;
714 continue 'exiting_out_skip_visited_traits;
719 continue 'exiting_out;
728 fn dump_vtable_entries<'tcx>(
731 trait_ref: ty::PolyTraitRef<'tcx>,
732 entries: &[VtblEntry<'tcx>],
734 tcx.sess.emit_err(DumpVTableEntries {
737 entries: format!("{:#?}", entries),
741 fn own_existential_vtable_entries<'tcx>(tcx: TyCtxt<'tcx>, trait_def_id: DefId) -> &'tcx [DefId] {
742 let trait_methods = tcx
743 .associated_items(trait_def_id)
744 .in_definition_order()
745 .filter(|item| item.kind == ty::AssocKind::Fn);
746 // Now list each method's DefId (for within its trait).
747 let own_entries = trait_methods.filter_map(move |trait_method| {
748 debug!("own_existential_vtable_entry: trait_method={:?}", trait_method);
749 let def_id = trait_method.def_id;
751 // Some methods cannot be called on an object; skip those.
752 if !is_vtable_safe_method(tcx, trait_def_id, &trait_method) {
753 debug!("own_existential_vtable_entry: not vtable safe");
760 tcx.arena.alloc_from_iter(own_entries.into_iter())
763 /// Given a trait `trait_ref`, iterates the vtable entries
764 /// that come from `trait_ref`, including its supertraits.
765 fn vtable_entries<'tcx>(
767 trait_ref: ty::PolyTraitRef<'tcx>,
768 ) -> &'tcx [VtblEntry<'tcx>] {
769 debug!("vtable_entries({:?})", trait_ref);
771 let mut entries = vec![];
773 let vtable_segment_callback = |segment| -> ControlFlow<()> {
775 VtblSegment::MetadataDSA => {
776 entries.extend(TyCtxt::COMMON_VTABLE_ENTRIES);
778 VtblSegment::TraitOwnEntries { trait_ref, emit_vptr } => {
779 let existential_trait_ref = trait_ref
780 .map_bound(|trait_ref| ty::ExistentialTraitRef::erase_self_ty(tcx, trait_ref));
782 // Lookup the shape of vtable for the trait.
783 let own_existential_entries =
784 tcx.own_existential_vtable_entries(existential_trait_ref.def_id());
786 let own_entries = own_existential_entries.iter().copied().map(|def_id| {
787 debug!("vtable_entries: trait_method={:?}", def_id);
789 // The method may have some early-bound lifetimes; add regions for those.
790 let substs = trait_ref.map_bound(|trait_ref| {
791 InternalSubsts::for_item(tcx, def_id, |param, _| match param.kind {
792 GenericParamDefKind::Lifetime => tcx.lifetimes.re_erased.into(),
793 GenericParamDefKind::Type { .. }
794 | GenericParamDefKind::Const { .. } => {
795 trait_ref.substs[param.index as usize]
800 // The trait type may have higher-ranked lifetimes in it;
801 // erase them if they appear, so that we get the type
802 // at some particular call site.
804 .normalize_erasing_late_bound_regions(ty::ParamEnv::reveal_all(), substs);
806 // It's possible that the method relies on where-clauses that
807 // do not hold for this particular set of type parameters.
808 // Note that this method could then never be called, so we
809 // do not want to try and codegen it, in that case (see #23435).
810 let predicates = tcx.predicates_of(def_id).instantiate_own(tcx, substs);
811 if impossible_predicates(tcx, predicates.predicates) {
812 debug!("vtable_entries: predicates do not hold");
813 return VtblEntry::Vacant;
816 let instance = ty::Instance::resolve_for_vtable(
818 ty::ParamEnv::reveal_all(),
822 .expect("resolution failed during building vtable representation");
823 VtblEntry::Method(instance)
826 entries.extend(own_entries);
829 entries.push(VtblEntry::TraitVPtr(trait_ref));
834 ControlFlow::Continue(())
837 let _ = prepare_vtable_segments(tcx, trait_ref, vtable_segment_callback);
839 if tcx.has_attr(trait_ref.def_id(), sym::rustc_dump_vtable) {
840 let sp = tcx.def_span(trait_ref.def_id());
841 dump_vtable_entries(tcx, sp, trait_ref, &entries);
844 tcx.arena.alloc_from_iter(entries.into_iter())
847 /// Find slot base for trait methods within vtable entries of another trait
848 fn vtable_trait_first_method_offset<'tcx>(
851 ty::PolyTraitRef<'tcx>, // trait_to_be_found
852 ty::PolyTraitRef<'tcx>, // trait_owning_vtable
855 let (trait_to_be_found, trait_owning_vtable) = key;
858 let trait_to_be_found_erased = tcx.erase_regions(trait_to_be_found);
860 let vtable_segment_callback = {
861 let mut vtable_base = 0;
865 VtblSegment::MetadataDSA => {
866 vtable_base += TyCtxt::COMMON_VTABLE_ENTRIES.len();
868 VtblSegment::TraitOwnEntries { trait_ref, emit_vptr } => {
869 if tcx.erase_regions(trait_ref) == trait_to_be_found_erased {
870 return ControlFlow::Break(vtable_base);
872 vtable_base += util::count_own_vtable_entries(tcx, trait_ref);
878 ControlFlow::Continue(())
882 if let Some(vtable_base) =
883 prepare_vtable_segments(tcx, trait_owning_vtable, vtable_segment_callback)
887 bug!("Failed to find info for expected trait in vtable");
891 /// Find slot offset for trait vptr within vtable entries of another trait
892 pub fn vtable_trait_upcasting_coercion_new_vptr_slot<'tcx>(
895 Ty<'tcx>, // trait object type whose trait owning vtable
896 Ty<'tcx>, // trait object for supertrait
899 let (source, target) = key;
900 assert!(matches!(&source.kind(), &ty::Dynamic(..)) && !source.needs_infer());
901 assert!(matches!(&target.kind(), &ty::Dynamic(..)) && !target.needs_infer());
903 // this has been typecked-before, so diagnostics is not really needed.
904 let unsize_trait_did = tcx.require_lang_item(LangItem::Unsize, None);
906 let trait_ref = tcx.mk_trait_ref(unsize_trait_did, [source, target]);
908 match tcx.codegen_select_candidate((ty::ParamEnv::reveal_all(), ty::Binder::dummy(trait_ref))) {
909 Ok(ImplSource::TraitUpcasting(implsrc_traitcasting)) => {
910 implsrc_traitcasting.vtable_vptr_slot
912 otherwise => bug!("expected TraitUpcasting candidate, got {otherwise:?}"),
916 pub fn provide(providers: &mut ty::query::Providers) {
917 object_safety::provide(providers);
918 structural_match::provide(providers);
919 *providers = ty::query::Providers {
920 specialization_graph_of: specialize::specialization_graph_provider,
921 specializes: specialize::specializes,
922 codegen_select_candidate: codegen::codegen_select_candidate,
923 own_existential_vtable_entries,
925 vtable_trait_upcasting_coercion_new_vptr_slot,
926 subst_and_check_impossible_predicates,
927 is_impossible_method,
928 try_unify_abstract_consts: |tcx, param_env_and| {
929 let (param_env, (a, b)) = param_env_and.into_parts();
930 const_evaluatable::try_unify_abstract_consts(tcx, (a, b), param_env)