1use std::ops::ControlFlow;
11
12use rustc_ast::Mutability;
13use rustc_data_structures::stack::ensure_sufficient_stack;
14use rustc_hir::lang_items::LangItem;
15use rustc_infer::infer::{DefineOpaqueTypes, HigherRankedType, InferOk};
16use rustc_infer::traits::ObligationCauseCode;
17use rustc_middle::traits::{BuiltinImplSource, SignatureMismatchData};
18use rustc_middle::ty::{self, GenericArgsRef, Ty, TyCtxt, Upcast};
19use rustc_middle::{bug, span_bug};
20use rustc_span::def_id::DefId;
21use rustc_type_ir::elaborate;
22use thin_vec::thin_vec;
23use tracing::{debug, instrument};
24
25use super::SelectionCandidate::{self, *};
26use super::{BuiltinImplConditions, PredicateObligations, SelectionContext};
27use crate::traits::normalize::{normalize_with_depth, normalize_with_depth_to};
28use crate::traits::util::{self, closure_trait_ref_and_return_type};
29use crate::traits::{
30 ImplSource, ImplSourceUserDefinedData, Normalized, Obligation, ObligationCause,
31 PolyTraitObligation, PredicateObligation, Selection, SelectionError, SignatureMismatch,
32 TraitDynIncompatible, TraitObligation, Unimplemented,
33};
34
35impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
36 #[instrument(level = "debug", skip(self))]
37 pub(super) fn confirm_candidate(
38 &mut self,
39 obligation: &PolyTraitObligation<'tcx>,
40 candidate: SelectionCandidate<'tcx>,
41 ) -> Result<Selection<'tcx>, SelectionError<'tcx>> {
42 let mut impl_src = match candidate {
43 BuiltinCandidate { has_nested } => {
44 let data = self.confirm_builtin_candidate(obligation, has_nested);
45 ImplSource::Builtin(BuiltinImplSource::Misc, data)
46 }
47
48 TransmutabilityCandidate => {
49 let data = self.confirm_transmutability_candidate(obligation)?;
50 ImplSource::Builtin(BuiltinImplSource::Misc, data)
51 }
52
53 ParamCandidate(param) => {
54 let obligations =
55 self.confirm_param_candidate(obligation, param.map_bound(|t| t.trait_ref));
56 ImplSource::Param(obligations)
57 }
58
59 ImplCandidate(impl_def_id) => {
60 ImplSource::UserDefined(self.confirm_impl_candidate(obligation, impl_def_id))
61 }
62
63 AutoImplCandidate => {
64 let data = self.confirm_auto_impl_candidate(obligation)?;
65 ImplSource::Builtin(BuiltinImplSource::Misc, data)
66 }
67
68 ProjectionCandidate(idx) => {
69 let obligations = self.confirm_projection_candidate(obligation, idx)?;
70 ImplSource::Param(obligations)
71 }
72
73 ObjectCandidate(idx) => self.confirm_object_candidate(obligation, idx)?,
74
75 ClosureCandidate { .. } => {
76 let vtable_closure = self.confirm_closure_candidate(obligation)?;
77 ImplSource::Builtin(BuiltinImplSource::Misc, vtable_closure)
78 }
79
80 AsyncClosureCandidate => {
81 let vtable_closure = self.confirm_async_closure_candidate(obligation)?;
82 ImplSource::Builtin(BuiltinImplSource::Misc, vtable_closure)
83 }
84
85 AsyncFnKindHelperCandidate => {
88 ImplSource::Builtin(BuiltinImplSource::Misc, PredicateObligations::new())
89 }
90
91 CoroutineCandidate => {
92 let vtable_coroutine = self.confirm_coroutine_candidate(obligation)?;
93 ImplSource::Builtin(BuiltinImplSource::Misc, vtable_coroutine)
94 }
95
96 FutureCandidate => {
97 let vtable_future = self.confirm_future_candidate(obligation)?;
98 ImplSource::Builtin(BuiltinImplSource::Misc, vtable_future)
99 }
100
101 IteratorCandidate => {
102 let vtable_iterator = self.confirm_iterator_candidate(obligation)?;
103 ImplSource::Builtin(BuiltinImplSource::Misc, vtable_iterator)
104 }
105
106 AsyncIteratorCandidate => {
107 let vtable_iterator = self.confirm_async_iterator_candidate(obligation)?;
108 ImplSource::Builtin(BuiltinImplSource::Misc, vtable_iterator)
109 }
110
111 FnPointerCandidate => {
112 let data = self.confirm_fn_pointer_candidate(obligation)?;
113 ImplSource::Builtin(BuiltinImplSource::Misc, data)
114 }
115
116 TraitAliasCandidate => {
117 let data = self.confirm_trait_alias_candidate(obligation);
118 ImplSource::Builtin(BuiltinImplSource::Misc, data)
119 }
120
121 BuiltinObjectCandidate => {
122 ImplSource::Builtin(BuiltinImplSource::Misc, PredicateObligations::new())
126 }
127
128 BuiltinUnsizeCandidate => self.confirm_builtin_unsize_candidate(obligation)?,
129
130 TraitUpcastingUnsizeCandidate(idx) => {
131 self.confirm_trait_upcasting_unsize_candidate(obligation, idx)?
132 }
133
134 BikeshedGuaranteedNoDropCandidate => {
135 self.confirm_bikeshed_guaranteed_no_drop_candidate(obligation)
136 }
137 };
138
139 for subobligation in impl_src.borrow_nested_obligations_mut() {
142 subobligation.set_depth_from_parent(obligation.recursion_depth);
143 }
144
145 Ok(impl_src)
146 }
147
148 fn confirm_projection_candidate(
149 &mut self,
150 obligation: &PolyTraitObligation<'tcx>,
151 idx: usize,
152 ) -> Result<PredicateObligations<'tcx>, SelectionError<'tcx>> {
153 let tcx = self.tcx();
154
155 let placeholder_trait_predicate =
156 self.infcx.enter_forall_and_leak_universe(obligation.predicate).trait_ref;
157 let placeholder_self_ty = self.infcx.shallow_resolve(placeholder_trait_predicate.self_ty());
158 let candidate_predicate = self
159 .for_each_item_bound(
160 placeholder_self_ty,
161 |_, clause, clause_idx| {
162 if clause_idx == idx {
163 ControlFlow::Break(clause)
164 } else {
165 ControlFlow::Continue(())
166 }
167 },
168 || unreachable!(),
169 )
170 .break_value()
171 .expect("expected to index into clause that exists");
172 let candidate = candidate_predicate
173 .as_trait_clause()
174 .expect("projection candidate is not a trait predicate")
175 .map_bound(|t| t.trait_ref);
176
177 let candidate = self.infcx.instantiate_binder_with_fresh_vars(
178 obligation.cause.span,
179 HigherRankedType,
180 candidate,
181 );
182 let mut obligations = PredicateObligations::new();
183 let candidate = normalize_with_depth_to(
184 self,
185 obligation.param_env,
186 obligation.cause.clone(),
187 obligation.recursion_depth + 1,
188 candidate,
189 &mut obligations,
190 );
191
192 obligations.extend(
193 self.infcx
194 .at(&obligation.cause, obligation.param_env)
195 .eq(DefineOpaqueTypes::No, placeholder_trait_predicate, candidate)
196 .map(|InferOk { obligations, .. }| obligations)
197 .map_err(|_| Unimplemented)?,
198 );
199
200 if let ty::Alias(ty::Projection, alias_ty) = placeholder_self_ty.kind() {
202 let predicates = tcx.predicates_of(alias_ty.def_id).instantiate_own(tcx, alias_ty.args);
203 for (predicate, _) in predicates {
204 let normalized = normalize_with_depth_to(
205 self,
206 obligation.param_env,
207 obligation.cause.clone(),
208 obligation.recursion_depth + 1,
209 predicate,
210 &mut obligations,
211 );
212 obligations.push(Obligation::with_depth(
213 self.tcx(),
214 obligation.cause.clone(),
215 obligation.recursion_depth + 1,
216 obligation.param_env,
217 normalized,
218 ));
219 }
220 }
221
222 Ok(obligations)
223 }
224
225 fn confirm_param_candidate(
226 &mut self,
227 obligation: &PolyTraitObligation<'tcx>,
228 param: ty::PolyTraitRef<'tcx>,
229 ) -> PredicateObligations<'tcx> {
230 debug!(?obligation, ?param, "confirm_param_candidate");
231
232 match self.match_where_clause_trait_ref(obligation, param) {
237 Ok(obligations) => obligations,
238 Err(()) => {
239 bug!(
240 "Where clause `{:?}` was applicable to `{:?}` but now is not",
241 param,
242 obligation
243 );
244 }
245 }
246 }
247
248 fn confirm_builtin_candidate(
249 &mut self,
250 obligation: &PolyTraitObligation<'tcx>,
251 has_nested: bool,
252 ) -> PredicateObligations<'tcx> {
253 debug!(?obligation, ?has_nested, "confirm_builtin_candidate");
254
255 let tcx = self.tcx();
256 let obligations = if has_nested {
257 let trait_def = obligation.predicate.def_id();
258 let conditions = if tcx.is_lang_item(trait_def, LangItem::Sized) {
259 self.sized_conditions(obligation)
260 } else if tcx.is_lang_item(trait_def, LangItem::Copy) {
261 self.copy_clone_conditions(obligation)
262 } else if tcx.is_lang_item(trait_def, LangItem::Clone) {
263 self.copy_clone_conditions(obligation)
264 } else if tcx.is_lang_item(trait_def, LangItem::FusedIterator) {
265 self.fused_iterator_conditions(obligation)
266 } else {
267 bug!("unexpected builtin trait {:?}", trait_def)
268 };
269 let BuiltinImplConditions::Where(types) = conditions else {
270 bug!("obligation {:?} had matched a builtin impl but now doesn't", obligation);
271 };
272 let types = self.infcx.enter_forall_and_leak_universe(types);
273
274 let cause = obligation.derived_cause(ObligationCauseCode::BuiltinDerived);
275 self.collect_predicates_for_types(
276 obligation.param_env,
277 cause,
278 obligation.recursion_depth + 1,
279 trait_def,
280 types,
281 )
282 } else {
283 PredicateObligations::new()
284 };
285
286 debug!(?obligations);
287
288 obligations
289 }
290
291 #[instrument(level = "debug", skip(self))]
292 fn confirm_transmutability_candidate(
293 &mut self,
294 obligation: &PolyTraitObligation<'tcx>,
295 ) -> Result<PredicateObligations<'tcx>, SelectionError<'tcx>> {
296 use rustc_transmute::{Answer, Assume, Condition};
297
298 fn reference_obligations<'tcx>(
300 tcx: TyCtxt<'tcx>,
301 obligation: &PolyTraitObligation<'tcx>,
302 (src_lifetime, src_ty, src_mut): (ty::Region<'tcx>, Ty<'tcx>, Mutability),
303 (dst_lifetime, dst_ty, dst_mut): (ty::Region<'tcx>, Ty<'tcx>, Mutability),
304 assume: Assume,
305 ) -> PredicateObligations<'tcx> {
306 let make_transmute_obl = |src, dst| {
307 let transmute_trait = obligation.predicate.def_id();
308 let assume = obligation.predicate.skip_binder().trait_ref.args.const_at(2);
309 let trait_ref = ty::TraitRef::new(
310 tcx,
311 transmute_trait,
312 [
313 ty::GenericArg::from(dst),
314 ty::GenericArg::from(src),
315 ty::GenericArg::from(assume),
316 ],
317 );
318 Obligation::with_depth(
319 tcx,
320 obligation.cause.clone(),
321 obligation.recursion_depth + 1,
322 obligation.param_env,
323 obligation.predicate.rebind(trait_ref),
324 )
325 };
326
327 let make_freeze_obl = |ty| {
328 let trait_ref = ty::TraitRef::new(
329 tcx,
330 tcx.require_lang_item(LangItem::Freeze, None),
331 [ty::GenericArg::from(ty)],
332 );
333 Obligation::with_depth(
334 tcx,
335 obligation.cause.clone(),
336 obligation.recursion_depth + 1,
337 obligation.param_env,
338 trait_ref,
339 )
340 };
341
342 let make_outlives_obl = |target, region| {
343 let outlives = ty::OutlivesPredicate(target, region);
344 Obligation::with_depth(
345 tcx,
346 obligation.cause.clone(),
347 obligation.recursion_depth + 1,
348 obligation.param_env,
349 obligation.predicate.rebind(outlives),
350 )
351 };
352
353 let mut obls = PredicateObligations::with_capacity(1);
357 obls.push(make_transmute_obl(src_ty, dst_ty));
358 if !assume.lifetimes {
359 obls.push(make_outlives_obl(src_lifetime, dst_lifetime));
360 }
361
362 if src_mut == Mutability::Not {
366 obls.extend([make_freeze_obl(src_ty), make_freeze_obl(dst_ty)])
367 }
368
369 if dst_mut == Mutability::Mut {
376 obls.push(make_transmute_obl(dst_ty, src_ty));
377 if !assume.lifetimes {
378 obls.push(make_outlives_obl(dst_lifetime, src_lifetime));
379 }
380 }
381
382 obls
383 }
384
385 #[instrument(level = "debug", skip(tcx, obligation))]
387 fn flatten_answer_tree<'tcx>(
388 tcx: TyCtxt<'tcx>,
389 obligation: &PolyTraitObligation<'tcx>,
390 cond: Condition<rustc_transmute::layout::rustc::Ref<'tcx>>,
391 assume: Assume,
392 ) -> PredicateObligations<'tcx> {
393 match cond {
394 Condition::IfAll(conds) | Condition::IfAny(conds) => conds
397 .into_iter()
398 .flat_map(|cond| flatten_answer_tree(tcx, obligation, cond, assume))
399 .collect(),
400 Condition::IfTransmutable { src, dst } => reference_obligations(
401 tcx,
402 obligation,
403 (src.lifetime, src.ty, src.mutability),
404 (dst.lifetime, dst.ty, dst.mutability),
405 assume,
406 ),
407 }
408 }
409
410 let predicate = obligation.predicate.skip_binder();
411
412 let mut assume = predicate.trait_ref.args.const_at(2);
413 if self.tcx().features().generic_const_exprs() {
415 assume = crate::traits::evaluate_const(self.infcx, assume, obligation.param_env)
416 }
417 let Some(assume) = rustc_transmute::Assume::from_const(self.infcx.tcx, assume) else {
418 return Err(Unimplemented);
419 };
420
421 let dst = predicate.trait_ref.args.type_at(0);
422 let src = predicate.trait_ref.args.type_at(1);
423
424 debug!(?src, ?dst);
425 let mut transmute_env = rustc_transmute::TransmuteTypeEnv::new(self.infcx.tcx);
426 let maybe_transmutable =
427 transmute_env.is_transmutable(rustc_transmute::Types { dst, src }, assume);
428
429 let fully_flattened = match maybe_transmutable {
430 Answer::No(_) => Err(Unimplemented)?,
431 Answer::If(cond) => flatten_answer_tree(self.tcx(), obligation, cond, assume),
432 Answer::Yes => PredicateObligations::new(),
433 };
434
435 debug!(?fully_flattened);
436 Ok(fully_flattened)
437 }
438
439 fn confirm_auto_impl_candidate(
445 &mut self,
446 obligation: &PolyTraitObligation<'tcx>,
447 ) -> Result<PredicateObligations<'tcx>, SelectionError<'tcx>> {
448 ensure_sufficient_stack(|| {
449 assert_eq!(obligation.predicate.polarity(), ty::PredicatePolarity::Positive);
450
451 let self_ty =
452 obligation.predicate.self_ty().map_bound(|ty| self.infcx.shallow_resolve(ty));
453
454 let types = self.constituent_types_for_ty(self_ty)?;
455 let types = self.infcx.enter_forall_and_leak_universe(types);
456
457 let cause = obligation.derived_cause(ObligationCauseCode::BuiltinDerived);
458 let obligations = self.collect_predicates_for_types(
459 obligation.param_env,
460 cause,
461 obligation.recursion_depth + 1,
462 obligation.predicate.def_id(),
463 types,
464 );
465
466 Ok(obligations)
467 })
468 }
469
470 fn confirm_impl_candidate(
471 &mut self,
472 obligation: &PolyTraitObligation<'tcx>,
473 impl_def_id: DefId,
474 ) -> ImplSourceUserDefinedData<'tcx, PredicateObligation<'tcx>> {
475 debug!(?obligation, ?impl_def_id, "confirm_impl_candidate");
476
477 let args = self.rematch_impl(impl_def_id, obligation);
480 debug!(?args, "impl args");
481 ensure_sufficient_stack(|| {
482 self.vtable_impl(
483 impl_def_id,
484 args,
485 &obligation.cause,
486 obligation.recursion_depth + 1,
487 obligation.param_env,
488 obligation.predicate,
489 )
490 })
491 }
492
493 fn vtable_impl(
494 &mut self,
495 impl_def_id: DefId,
496 args: Normalized<'tcx, GenericArgsRef<'tcx>>,
497 cause: &ObligationCause<'tcx>,
498 recursion_depth: usize,
499 param_env: ty::ParamEnv<'tcx>,
500 parent_trait_pred: ty::Binder<'tcx, ty::TraitPredicate<'tcx>>,
501 ) -> ImplSourceUserDefinedData<'tcx, PredicateObligation<'tcx>> {
502 debug!(?impl_def_id, ?args, ?recursion_depth, "vtable_impl");
503
504 let mut impl_obligations = self.impl_or_trait_obligations(
505 cause,
506 recursion_depth,
507 param_env,
508 impl_def_id,
509 args.value,
510 parent_trait_pred,
511 );
512
513 debug!(?impl_obligations, "vtable_impl");
514
515 impl_obligations.extend(args.obligations);
521
522 ImplSourceUserDefinedData { impl_def_id, args: args.value, nested: impl_obligations }
523 }
524
525 fn confirm_object_candidate(
526 &mut self,
527 obligation: &PolyTraitObligation<'tcx>,
528 index: usize,
529 ) -> Result<ImplSource<'tcx, PredicateObligation<'tcx>>, SelectionError<'tcx>> {
530 let tcx = self.tcx();
531 debug!(?obligation, ?index, "confirm_object_candidate");
532
533 let trait_predicate = self.infcx.enter_forall_and_leak_universe(obligation.predicate);
534 let self_ty = self.infcx.shallow_resolve(trait_predicate.self_ty());
535 let ty::Dynamic(data, ..) = *self_ty.kind() else {
536 span_bug!(obligation.cause.span, "object candidate with non-object");
537 };
538
539 let object_trait_ref = data.principal().unwrap_or_else(|| {
540 span_bug!(obligation.cause.span, "object candidate with no principal")
541 });
542 let object_trait_ref = self.infcx.instantiate_binder_with_fresh_vars(
543 obligation.cause.span,
544 HigherRankedType,
545 object_trait_ref,
546 );
547 let object_trait_ref = object_trait_ref.with_self_ty(self.tcx(), self_ty);
548
549 let mut nested = PredicateObligations::new();
550
551 let mut supertraits = util::supertraits(tcx, ty::Binder::dummy(object_trait_ref));
552 let unnormalized_upcast_trait_ref =
553 supertraits.nth(index).expect("supertraits iterator no longer has as many elements");
554
555 let upcast_trait_ref = self.infcx.instantiate_binder_with_fresh_vars(
556 obligation.cause.span,
557 HigherRankedType,
558 unnormalized_upcast_trait_ref,
559 );
560 let upcast_trait_ref = normalize_with_depth_to(
561 self,
562 obligation.param_env,
563 obligation.cause.clone(),
564 obligation.recursion_depth + 1,
565 upcast_trait_ref,
566 &mut nested,
567 );
568
569 nested.extend(
570 self.infcx
571 .at(&obligation.cause, obligation.param_env)
572 .eq(DefineOpaqueTypes::No, trait_predicate.trait_ref, upcast_trait_ref)
573 .map(|InferOk { obligations, .. }| obligations)
574 .map_err(|_| Unimplemented)?,
575 );
576
577 for (supertrait, _) in tcx
580 .explicit_super_predicates_of(trait_predicate.def_id())
581 .iter_instantiated_copied(tcx, trait_predicate.trait_ref.args)
582 {
583 let normalized_supertrait = normalize_with_depth_to(
584 self,
585 obligation.param_env,
586 obligation.cause.clone(),
587 obligation.recursion_depth + 1,
588 supertrait,
589 &mut nested,
590 );
591 nested.push(obligation.with(tcx, normalized_supertrait));
592 }
593
594 let assoc_types: Vec<_> = tcx
595 .associated_items(trait_predicate.def_id())
596 .in_definition_order()
597 .filter(|item| !tcx.generics_require_sized_self(item.def_id))
600 .filter_map(
601 |item| if item.kind == ty::AssocKind::Type { Some(item.def_id) } else { None },
602 )
603 .collect();
604
605 for assoc_type in assoc_types {
606 let defs: &ty::Generics = tcx.generics_of(assoc_type);
607
608 if !defs.own_params.is_empty() {
609 tcx.dcx().span_delayed_bug(
610 obligation.cause.span,
611 "GATs in trait object shouldn't have been considered",
612 );
613 return Err(SelectionError::TraitDynIncompatible(trait_predicate.trait_ref.def_id));
614 }
615
616 for bound in self.tcx().item_bounds(assoc_type).transpose_iter() {
620 let normalized_bound = normalize_with_depth_to(
621 self,
622 obligation.param_env,
623 obligation.cause.clone(),
624 obligation.recursion_depth + 1,
625 bound.instantiate(tcx, trait_predicate.trait_ref.args),
626 &mut nested,
627 );
628 nested.push(obligation.with(tcx, normalized_bound));
629 }
630 }
631
632 debug!(?nested, "object nested obligations");
633
634 Ok(ImplSource::Builtin(BuiltinImplSource::Object(index), nested))
635 }
636
637 fn confirm_fn_pointer_candidate(
638 &mut self,
639 obligation: &PolyTraitObligation<'tcx>,
640 ) -> Result<PredicateObligations<'tcx>, SelectionError<'tcx>> {
641 debug!(?obligation, "confirm_fn_pointer_candidate");
642 let placeholder_predicate = self.infcx.enter_forall_and_leak_universe(obligation.predicate);
643 let self_ty = self.infcx.shallow_resolve(placeholder_predicate.self_ty());
644
645 let tcx = self.tcx();
646 let sig = self_ty.fn_sig(tcx);
647 let trait_ref = closure_trait_ref_and_return_type(
648 tcx,
649 obligation.predicate.def_id(),
650 self_ty,
651 sig,
652 util::TupleArgumentsFlag::Yes,
653 )
654 .map_bound(|(trait_ref, _)| trait_ref);
655
656 let mut nested =
657 self.equate_trait_refs(obligation.with(tcx, placeholder_predicate), trait_ref)?;
658 let cause = obligation.derived_cause(ObligationCauseCode::BuiltinDerived);
659
660 let output_ty = self.infcx.enter_forall_and_leak_universe(sig.output());
662 let output_ty = normalize_with_depth_to(
663 self,
664 obligation.param_env,
665 cause.clone(),
666 obligation.recursion_depth,
667 output_ty,
668 &mut nested,
669 );
670 let tr = ty::TraitRef::new(
671 self.tcx(),
672 self.tcx().require_lang_item(LangItem::Sized, Some(cause.span)),
673 [output_ty],
674 );
675 nested.push(Obligation::new(self.infcx.tcx, cause, obligation.param_env, tr));
676
677 Ok(nested)
678 }
679
680 fn confirm_trait_alias_candidate(
681 &mut self,
682 obligation: &PolyTraitObligation<'tcx>,
683 ) -> PredicateObligations<'tcx> {
684 debug!(?obligation, "confirm_trait_alias_candidate");
685
686 let predicate = self.infcx.enter_forall_and_leak_universe(obligation.predicate);
687 let trait_ref = predicate.trait_ref;
688 let trait_def_id = trait_ref.def_id;
689 let args = trait_ref.args;
690
691 let trait_obligations = self.impl_or_trait_obligations(
692 &obligation.cause,
693 obligation.recursion_depth,
694 obligation.param_env,
695 trait_def_id,
696 args,
697 obligation.predicate,
698 );
699
700 debug!(?trait_def_id, ?trait_obligations, "trait alias obligations");
701
702 trait_obligations
703 }
704
705 fn confirm_coroutine_candidate(
706 &mut self,
707 obligation: &PolyTraitObligation<'tcx>,
708 ) -> Result<PredicateObligations<'tcx>, SelectionError<'tcx>> {
709 let placeholder_predicate = self.infcx.enter_forall_and_leak_universe(obligation.predicate);
710 let self_ty = self.infcx.shallow_resolve(placeholder_predicate.self_ty());
711 let ty::Coroutine(coroutine_def_id, args) = *self_ty.kind() else {
712 bug!("closure candidate for non-closure {:?}", obligation);
713 };
714
715 debug!(?obligation, ?coroutine_def_id, ?args, "confirm_coroutine_candidate");
716
717 let coroutine_sig = args.as_coroutine().sig();
718
719 let (trait_ref, _, _) = super::util::coroutine_trait_ref_and_outputs(
720 self.tcx(),
721 obligation.predicate.def_id(),
722 self_ty,
723 coroutine_sig,
724 );
725
726 let nested = self.equate_trait_refs(
727 obligation.with(self.tcx(), placeholder_predicate),
728 ty::Binder::dummy(trait_ref),
729 )?;
730 debug!(?trait_ref, ?nested, "coroutine candidate obligations");
731
732 Ok(nested)
733 }
734
735 fn confirm_future_candidate(
736 &mut self,
737 obligation: &PolyTraitObligation<'tcx>,
738 ) -> Result<PredicateObligations<'tcx>, SelectionError<'tcx>> {
739 let placeholder_predicate = self.infcx.enter_forall_and_leak_universe(obligation.predicate);
740 let self_ty = self.infcx.shallow_resolve(placeholder_predicate.self_ty());
741 let ty::Coroutine(coroutine_def_id, args) = *self_ty.kind() else {
742 bug!("closure candidate for non-closure {:?}", obligation);
743 };
744
745 debug!(?obligation, ?coroutine_def_id, ?args, "confirm_future_candidate");
746
747 let coroutine_sig = args.as_coroutine().sig();
748
749 let (trait_ref, _) = super::util::future_trait_ref_and_outputs(
750 self.tcx(),
751 obligation.predicate.def_id(),
752 self_ty,
753 coroutine_sig,
754 );
755
756 let nested = self.equate_trait_refs(
757 obligation.with(self.tcx(), placeholder_predicate),
758 ty::Binder::dummy(trait_ref),
759 )?;
760 debug!(?trait_ref, ?nested, "future candidate obligations");
761
762 Ok(nested)
763 }
764
765 fn confirm_iterator_candidate(
766 &mut self,
767 obligation: &PolyTraitObligation<'tcx>,
768 ) -> Result<PredicateObligations<'tcx>, SelectionError<'tcx>> {
769 let placeholder_predicate = self.infcx.enter_forall_and_leak_universe(obligation.predicate);
770 let self_ty = self.infcx.shallow_resolve(placeholder_predicate.self_ty());
771 let ty::Coroutine(coroutine_def_id, args) = *self_ty.kind() else {
772 bug!("closure candidate for non-closure {:?}", obligation);
773 };
774
775 debug!(?obligation, ?coroutine_def_id, ?args, "confirm_iterator_candidate");
776
777 let gen_sig = args.as_coroutine().sig();
778
779 let (trait_ref, _) = super::util::iterator_trait_ref_and_outputs(
780 self.tcx(),
781 obligation.predicate.def_id(),
782 self_ty,
783 gen_sig,
784 );
785
786 let nested = self.equate_trait_refs(
787 obligation.with(self.tcx(), placeholder_predicate),
788 ty::Binder::dummy(trait_ref),
789 )?;
790 debug!(?trait_ref, ?nested, "iterator candidate obligations");
791
792 Ok(nested)
793 }
794
795 fn confirm_async_iterator_candidate(
796 &mut self,
797 obligation: &PolyTraitObligation<'tcx>,
798 ) -> Result<PredicateObligations<'tcx>, SelectionError<'tcx>> {
799 let placeholder_predicate = self.infcx.enter_forall_and_leak_universe(obligation.predicate);
800 let self_ty = self.infcx.shallow_resolve(placeholder_predicate.self_ty());
801 let ty::Coroutine(coroutine_def_id, args) = *self_ty.kind() else {
802 bug!("closure candidate for non-closure {:?}", obligation);
803 };
804
805 debug!(?obligation, ?coroutine_def_id, ?args, "confirm_async_iterator_candidate");
806
807 let gen_sig = args.as_coroutine().sig();
808
809 let (trait_ref, _) = super::util::async_iterator_trait_ref_and_outputs(
810 self.tcx(),
811 obligation.predicate.def_id(),
812 self_ty,
813 gen_sig,
814 );
815
816 let nested = self.equate_trait_refs(
817 obligation.with(self.tcx(), placeholder_predicate),
818 ty::Binder::dummy(trait_ref),
819 )?;
820 debug!(?trait_ref, ?nested, "iterator candidate obligations");
821
822 Ok(nested)
823 }
824
825 #[instrument(skip(self), level = "debug")]
826 fn confirm_closure_candidate(
827 &mut self,
828 obligation: &PolyTraitObligation<'tcx>,
829 ) -> Result<PredicateObligations<'tcx>, SelectionError<'tcx>> {
830 let placeholder_predicate = self.infcx.enter_forall_and_leak_universe(obligation.predicate);
831 let self_ty: Ty<'_> = self.infcx.shallow_resolve(placeholder_predicate.self_ty());
832
833 let trait_ref = match *self_ty.kind() {
834 ty::Closure(..) => {
835 self.closure_trait_ref_unnormalized(self_ty, obligation.predicate.def_id())
836 }
837 ty::CoroutineClosure(_, args) => {
838 args.as_coroutine_closure().coroutine_closure_sig().map_bound(|sig| {
839 ty::TraitRef::new(
840 self.tcx(),
841 obligation.predicate.def_id(),
842 [self_ty, sig.tupled_inputs_ty],
843 )
844 })
845 }
846 _ => {
847 bug!("closure candidate for non-closure {:?}", obligation);
848 }
849 };
850
851 self.equate_trait_refs(obligation.with(self.tcx(), placeholder_predicate), trait_ref)
852 }
853
854 #[instrument(skip(self), level = "debug")]
855 fn confirm_async_closure_candidate(
856 &mut self,
857 obligation: &PolyTraitObligation<'tcx>,
858 ) -> Result<PredicateObligations<'tcx>, SelectionError<'tcx>> {
859 let placeholder_predicate = self.infcx.enter_forall_and_leak_universe(obligation.predicate);
860 let self_ty = self.infcx.shallow_resolve(placeholder_predicate.self_ty());
861
862 let tcx = self.tcx();
863
864 let mut nested = PredicateObligations::new();
865 let (trait_ref, kind_ty) = match *self_ty.kind() {
866 ty::CoroutineClosure(_, args) => {
867 let args = args.as_coroutine_closure();
868 let trait_ref = args.coroutine_closure_sig().map_bound(|sig| {
869 ty::TraitRef::new(
870 self.tcx(),
871 obligation.predicate.def_id(),
872 [self_ty, sig.tupled_inputs_ty],
873 )
874 });
875
876 (trait_ref, args.kind_ty())
880 }
881 ty::FnDef(..) | ty::FnPtr(..) => {
882 let sig = self_ty.fn_sig(tcx);
883 let trait_ref = sig.map_bound(|sig| {
884 ty::TraitRef::new(
885 self.tcx(),
886 obligation.predicate.def_id(),
887 [self_ty, Ty::new_tup(tcx, sig.inputs())],
888 )
889 });
890
891 let future_trait_def_id = tcx.require_lang_item(LangItem::Future, None);
893 nested.push(obligation.with(
894 tcx,
895 sig.output().map_bound(|output_ty| {
896 ty::TraitRef::new(tcx, future_trait_def_id, [output_ty])
897 }),
898 ));
899 let sized_trait_def_id = tcx.require_lang_item(LangItem::Sized, None);
900 nested.push(obligation.with(
901 tcx,
902 sig.output().map_bound(|output_ty| {
903 ty::TraitRef::new(tcx, sized_trait_def_id, [output_ty])
904 }),
905 ));
906
907 (trait_ref, Ty::from_closure_kind(tcx, ty::ClosureKind::Fn))
908 }
909 ty::Closure(_, args) => {
910 let args = args.as_closure();
911 let sig = args.sig();
912 let trait_ref = sig.map_bound(|sig| {
913 ty::TraitRef::new(
914 self.tcx(),
915 obligation.predicate.def_id(),
916 [self_ty, sig.inputs()[0]],
917 )
918 });
919
920 let future_trait_def_id = tcx.require_lang_item(LangItem::Future, None);
922 let placeholder_output_ty = self.infcx.enter_forall_and_leak_universe(sig.output());
923 nested.push(obligation.with(
924 tcx,
925 ty::TraitRef::new(tcx, future_trait_def_id, [placeholder_output_ty]),
926 ));
927 let sized_trait_def_id = tcx.require_lang_item(LangItem::Sized, None);
928 nested.push(obligation.with(
929 tcx,
930 sig.output().map_bound(|output_ty| {
931 ty::TraitRef::new(tcx, sized_trait_def_id, [output_ty])
932 }),
933 ));
934
935 (trait_ref, args.kind_ty())
936 }
937 _ => bug!("expected callable type for AsyncFn candidate"),
938 };
939
940 nested.extend(
941 self.equate_trait_refs(obligation.with(tcx, placeholder_predicate), trait_ref)?,
942 );
943
944 let goal_kind =
945 self.tcx().async_fn_trait_kind_from_def_id(obligation.predicate.def_id()).unwrap();
946
947 if let Some(closure_kind) = self.infcx.shallow_resolve(kind_ty).to_opt_closure_kind() {
951 if !closure_kind.extends(goal_kind) {
952 return Err(SelectionError::Unimplemented);
953 }
954 } else {
955 nested.push(Obligation::new(
956 self.tcx(),
957 obligation.derived_cause(ObligationCauseCode::BuiltinDerived),
958 obligation.param_env,
959 ty::TraitRef::new(
960 self.tcx(),
961 self.tcx().require_lang_item(
962 LangItem::AsyncFnKindHelper,
963 Some(obligation.cause.span),
964 ),
965 [kind_ty, Ty::from_closure_kind(self.tcx(), goal_kind)],
966 ),
967 ));
968 }
969
970 Ok(nested)
971 }
972
973 #[instrument(skip(self), level = "trace")]
999 fn equate_trait_refs(
1000 &mut self,
1001 obligation: TraitObligation<'tcx>,
1002 found_trait_ref: ty::PolyTraitRef<'tcx>,
1003 ) -> Result<PredicateObligations<'tcx>, SelectionError<'tcx>> {
1004 let found_trait_ref = self.infcx.instantiate_binder_with_fresh_vars(
1005 obligation.cause.span,
1006 HigherRankedType,
1007 found_trait_ref,
1008 );
1009 let Normalized { obligations: nested, value: (obligation_trait_ref, found_trait_ref) } =
1011 ensure_sufficient_stack(|| {
1012 normalize_with_depth(
1013 self,
1014 obligation.param_env,
1015 obligation.cause.clone(),
1016 obligation.recursion_depth + 1,
1017 (obligation.predicate.trait_ref, found_trait_ref),
1018 )
1019 });
1020
1021 self.infcx
1023 .at(&obligation.cause, obligation.param_env)
1024 .eq(DefineOpaqueTypes::Yes, obligation_trait_ref, found_trait_ref)
1025 .map(|InferOk { mut obligations, .. }| {
1026 obligations.extend(nested);
1027 obligations
1028 })
1029 .map_err(|terr| {
1030 SignatureMismatch(Box::new(SignatureMismatchData {
1031 expected_trait_ref: obligation_trait_ref,
1032 found_trait_ref,
1033 terr,
1034 }))
1035 })
1036 }
1037
1038 fn confirm_trait_upcasting_unsize_candidate(
1039 &mut self,
1040 obligation: &PolyTraitObligation<'tcx>,
1041 idx: usize,
1042 ) -> Result<ImplSource<'tcx, PredicateObligation<'tcx>>, SelectionError<'tcx>> {
1043 let tcx = self.tcx();
1044
1045 let predicate = obligation.predicate.no_bound_vars().unwrap();
1048 let a_ty = self.infcx.shallow_resolve(predicate.self_ty());
1049 let b_ty = self.infcx.shallow_resolve(predicate.trait_ref.args.type_at(1));
1050
1051 let ty::Dynamic(a_data, a_region, ty::Dyn) = *a_ty.kind() else {
1052 bug!("expected `dyn` type in `confirm_trait_upcasting_unsize_candidate`")
1053 };
1054 let ty::Dynamic(b_data, b_region, ty::Dyn) = *b_ty.kind() else {
1055 bug!("expected `dyn` type in `confirm_trait_upcasting_unsize_candidate`")
1056 };
1057
1058 let source_principal = a_data.principal().unwrap().with_self_ty(tcx, a_ty);
1059 let unnormalized_upcast_principal =
1060 util::supertraits(tcx, source_principal).nth(idx).unwrap();
1061
1062 let nested = self
1063 .match_upcast_principal(
1064 obligation,
1065 unnormalized_upcast_principal,
1066 a_data,
1067 b_data,
1068 a_region,
1069 b_region,
1070 )?
1071 .expect("did not expect ambiguity during confirmation");
1072
1073 Ok(ImplSource::Builtin(BuiltinImplSource::TraitUpcasting(idx), nested))
1074 }
1075
1076 fn confirm_builtin_unsize_candidate(
1077 &mut self,
1078 obligation: &PolyTraitObligation<'tcx>,
1079 ) -> Result<ImplSource<'tcx, PredicateObligation<'tcx>>, SelectionError<'tcx>> {
1080 let tcx = self.tcx();
1081
1082 let source = self.infcx.shallow_resolve(obligation.self_ty().no_bound_vars().unwrap());
1085 let target = obligation.predicate.skip_binder().trait_ref.args.type_at(1);
1086 let target = self.infcx.shallow_resolve(target);
1087 debug!(?source, ?target, "confirm_builtin_unsize_candidate");
1088
1089 Ok(match (source.kind(), target.kind()) {
1090 (&ty::Dynamic(data_a, r_a, dyn_a), &ty::Dynamic(data_b, r_b, dyn_b))
1092 if dyn_a == dyn_b =>
1093 {
1094 let iter = data_a
1097 .principal()
1098 .filter(|_| {
1099 data_b.principal().is_some()
1101 })
1102 .map(|b| b.map_bound(ty::ExistentialPredicate::Trait))
1103 .into_iter()
1104 .chain(
1105 data_a
1106 .projection_bounds()
1107 .map(|b| b.map_bound(ty::ExistentialPredicate::Projection)),
1108 )
1109 .chain(
1110 data_b
1111 .auto_traits()
1112 .map(ty::ExistentialPredicate::AutoTrait)
1113 .map(ty::Binder::dummy),
1114 );
1115 let existential_predicates = tcx.mk_poly_existential_predicates_from_iter(iter);
1116 let source_trait = Ty::new_dynamic(tcx, existential_predicates, r_b, dyn_a);
1117
1118 let InferOk { mut obligations, .. } = self
1121 .infcx
1122 .at(&obligation.cause, obligation.param_env)
1123 .sup(DefineOpaqueTypes::Yes, target, source_trait)
1124 .map_err(|_| Unimplemented)?;
1125
1126 let outlives = ty::OutlivesPredicate(r_a, r_b);
1128 obligations.push(Obligation::with_depth(
1129 tcx,
1130 obligation.cause.clone(),
1131 obligation.recursion_depth + 1,
1132 obligation.param_env,
1133 obligation.predicate.rebind(outlives),
1134 ));
1135
1136 ImplSource::Builtin(BuiltinImplSource::Misc, obligations)
1137 }
1138
1139 (_, &ty::Dynamic(data, r, ty::Dyn)) => {
1141 let mut object_dids = data.auto_traits().chain(data.principal_def_id());
1142 if let Some(did) = object_dids.find(|did| !tcx.is_dyn_compatible(*did)) {
1143 return Err(TraitDynIncompatible(did));
1144 }
1145
1146 let predicate_to_obligation = |predicate| {
1147 Obligation::with_depth(
1148 tcx,
1149 obligation.cause.clone(),
1150 obligation.recursion_depth + 1,
1151 obligation.param_env,
1152 predicate,
1153 )
1154 };
1155
1156 let mut nested: PredicateObligations<'_> = data
1163 .iter()
1164 .map(|predicate| predicate_to_obligation(predicate.with_self_ty(tcx, source)))
1165 .collect();
1166
1167 let tr = ty::TraitRef::new(
1169 tcx,
1170 tcx.require_lang_item(LangItem::Sized, Some(obligation.cause.span)),
1171 [source],
1172 );
1173 nested.push(predicate_to_obligation(tr.upcast(tcx)));
1174
1175 let outlives = ty::OutlivesPredicate(source, r);
1178 nested.push(predicate_to_obligation(
1179 ty::ClauseKind::TypeOutlives(outlives).upcast(tcx),
1180 ));
1181
1182 if let Some(principal) = data.principal() {
1185 for supertrait in
1186 elaborate::supertraits(tcx, principal.with_self_ty(tcx, source))
1187 {
1188 if tcx.is_trait_alias(supertrait.def_id()) {
1189 continue;
1190 }
1191
1192 for &assoc_item in tcx.associated_item_def_ids(supertrait.def_id()) {
1193 if !tcx.is_impl_trait_in_trait(assoc_item) {
1194 continue;
1195 }
1196
1197 if tcx.generics_require_sized_self(assoc_item) {
1199 continue;
1200 }
1201
1202 let pointer_like_goal = pointer_like_goal_for_rpitit(
1203 tcx,
1204 supertrait,
1205 assoc_item,
1206 &obligation.cause,
1207 );
1208
1209 nested.push(predicate_to_obligation(pointer_like_goal.upcast(tcx)));
1210 }
1211 }
1212 }
1213
1214 ImplSource::Builtin(BuiltinImplSource::Misc, nested)
1215 }
1216
1217 (&ty::Array(a, _), &ty::Slice(b)) => {
1219 let InferOk { obligations, .. } = self
1220 .infcx
1221 .at(&obligation.cause, obligation.param_env)
1222 .eq(DefineOpaqueTypes::Yes, b, a)
1223 .map_err(|_| Unimplemented)?;
1224
1225 ImplSource::Builtin(BuiltinImplSource::Misc, obligations)
1226 }
1227
1228 (&ty::Adt(def, args_a), &ty::Adt(_, args_b)) => {
1230 let unsizing_params = tcx.unsizing_params_for_adt(def.did());
1231 if unsizing_params.is_empty() {
1232 return Err(Unimplemented);
1233 }
1234
1235 let tail_field = def.non_enum_variant().tail();
1236 let tail_field_ty = tcx.type_of(tail_field.did);
1237
1238 let mut nested = PredicateObligations::new();
1239
1240 let source_tail = normalize_with_depth_to(
1244 self,
1245 obligation.param_env,
1246 obligation.cause.clone(),
1247 obligation.recursion_depth + 1,
1248 tail_field_ty.instantiate(tcx, args_a),
1249 &mut nested,
1250 );
1251 let target_tail = normalize_with_depth_to(
1252 self,
1253 obligation.param_env,
1254 obligation.cause.clone(),
1255 obligation.recursion_depth + 1,
1256 tail_field_ty.instantiate(tcx, args_b),
1257 &mut nested,
1258 );
1259
1260 let args =
1263 tcx.mk_args_from_iter(args_a.iter().enumerate().map(|(i, k)| {
1264 if unsizing_params.contains(i as u32) { args_b[i] } else { k }
1265 }));
1266 let new_struct = Ty::new_adt(tcx, def, args);
1267 let InferOk { obligations, .. } = self
1268 .infcx
1269 .at(&obligation.cause, obligation.param_env)
1270 .eq(DefineOpaqueTypes::Yes, target, new_struct)
1271 .map_err(|_| Unimplemented)?;
1272 nested.extend(obligations);
1273
1274 let tail_unsize_obligation = obligation.with(
1276 tcx,
1277 ty::TraitRef::new(
1278 tcx,
1279 obligation.predicate.def_id(),
1280 [source_tail, target_tail],
1281 ),
1282 );
1283 nested.push(tail_unsize_obligation);
1284
1285 ImplSource::Builtin(BuiltinImplSource::Misc, nested)
1286 }
1287
1288 _ => bug!("source: {source}, target: {target}"),
1289 })
1290 }
1291
1292 fn confirm_bikeshed_guaranteed_no_drop_candidate(
1293 &mut self,
1294 obligation: &PolyTraitObligation<'tcx>,
1295 ) -> ImplSource<'tcx, PredicateObligation<'tcx>> {
1296 let mut obligations = thin_vec![];
1297
1298 let tcx = self.tcx();
1299 let self_ty = obligation.predicate.self_ty();
1300 match *self_ty.skip_binder().kind() {
1301 ty::Ref(..) => {}
1303 ty::Adt(def, _) if def.is_manually_drop() => {}
1305 ty::Tuple(tys) => {
1308 obligations.extend(tys.iter().map(|elem_ty| {
1309 obligation.with(
1310 tcx,
1311 self_ty.rebind(ty::TraitRef::new(
1312 tcx,
1313 obligation.predicate.def_id(),
1314 [elem_ty],
1315 )),
1316 )
1317 }));
1318 }
1319 ty::Array(elem_ty, _) => {
1320 obligations.push(obligation.with(
1321 tcx,
1322 self_ty.rebind(ty::TraitRef::new(
1323 tcx,
1324 obligation.predicate.def_id(),
1325 [elem_ty],
1326 )),
1327 ));
1328 }
1329
1330 ty::FnDef(..)
1334 | ty::FnPtr(..)
1335 | ty::Error(_)
1336 | ty::Uint(_)
1337 | ty::Int(_)
1338 | ty::Infer(ty::IntVar(_) | ty::FloatVar(_))
1339 | ty::Bool
1340 | ty::Float(_)
1341 | ty::Char
1342 | ty::RawPtr(..)
1343 | ty::Never
1344 | ty::Pat(..)
1345 | ty::Dynamic(..)
1346 | ty::Str
1347 | ty::Slice(_)
1348 | ty::Foreign(..)
1349 | ty::Adt(..)
1350 | ty::Alias(..)
1351 | ty::Param(_)
1352 | ty::Placeholder(..)
1353 | ty::Closure(..)
1354 | ty::CoroutineClosure(..)
1355 | ty::Coroutine(..)
1356 | ty::UnsafeBinder(_)
1357 | ty::CoroutineWitness(..)
1358 | ty::Bound(..) => {
1359 obligations.push(obligation.with(
1360 tcx,
1361 self_ty.map_bound(|ty| {
1362 ty::TraitRef::new(
1363 tcx,
1364 tcx.require_lang_item(LangItem::Copy, Some(obligation.cause.span)),
1365 [ty],
1366 )
1367 }),
1368 ));
1369 }
1370
1371 ty::Infer(ty::TyVar(_) | ty::FreshTy(_) | ty::FreshIntTy(_) | ty::FreshFloatTy(_)) => {
1372 panic!("unexpected type `{self_ty:?}`")
1373 }
1374 }
1375
1376 ImplSource::Builtin(BuiltinImplSource::Misc, obligations)
1377 }
1378}
1379
1380fn pointer_like_goal_for_rpitit<'tcx>(
1390 tcx: TyCtxt<'tcx>,
1391 supertrait: ty::PolyTraitRef<'tcx>,
1392 rpitit_item: DefId,
1393 cause: &ObligationCause<'tcx>,
1394) -> ty::PolyTraitRef<'tcx> {
1395 let mut bound_vars = supertrait.bound_vars().to_vec();
1396
1397 let args = supertrait.skip_binder().args.extend_to(tcx, rpitit_item, |arg, _| match arg.kind {
1398 ty::GenericParamDefKind::Lifetime => {
1399 let kind = ty::BoundRegionKind::Named(arg.def_id, tcx.item_name(arg.def_id));
1400 bound_vars.push(ty::BoundVariableKind::Region(kind));
1401 ty::Region::new_bound(
1402 tcx,
1403 ty::INNERMOST,
1404 ty::BoundRegion { var: ty::BoundVar::from_usize(bound_vars.len() - 1), kind },
1405 )
1406 .into()
1407 }
1408 ty::GenericParamDefKind::Type { .. } | ty::GenericParamDefKind::Const { .. } => {
1409 unreachable!()
1410 }
1411 });
1412
1413 ty::Binder::bind_with_vars(
1414 ty::TraitRef::new(
1415 tcx,
1416 tcx.require_lang_item(LangItem::PointerLike, Some(cause.span)),
1417 [Ty::new_projection_from_args(tcx, rpitit_item, args)],
1418 ),
1419 tcx.mk_bound_variable_kinds(&bound_vars),
1420 )
1421}