1 //! See Rustc Dev Guide chapters on [trait-resolution] and [trait-specialization] for more info on
4 //! [trait-resolution]: https://rustc-dev-guide.rust-lang.org/traits/resolution.html
5 //! [trait-specialization]: https://rustc-dev-guide.rust-lang.org/traits/specialization.html
7 use crate::infer::outlives::env::OutlivesEnvironment;
8 use crate::infer::{CombinedSnapshot, InferOk};
9 use crate::traits::select::IntercrateAmbiguityCause;
10 use crate::traits::util::impl_subject_and_oblig;
11 use crate::traits::SkipLeakCheck;
13 self, Normalized, Obligation, ObligationCause, PredicateObligation, PredicateObligations,
16 use rustc_data_structures::fx::FxIndexSet;
17 use rustc_errors::Diagnostic;
18 use rustc_hir::def_id::{DefId, LOCAL_CRATE};
19 use rustc_infer::infer::{InferCtxt, TyCtxtInferExt};
20 use rustc_infer::traits::util;
21 use rustc_middle::traits::specialization_graph::OverlapMode;
22 use rustc_middle::ty::fast_reject::{DeepRejectCtxt, TreatParams};
23 use rustc_middle::ty::subst::Subst;
24 use rustc_middle::ty::visit::TypeVisitable;
25 use rustc_middle::ty::{self, ImplSubject, Ty, TyCtxt, TypeVisitor};
26 use rustc_span::symbol::sym;
27 use rustc_span::DUMMY_SP;
30 use std::ops::ControlFlow;
32 /// Whether we do the orphan check relative to this crate or
33 /// to some remote crate.
34 #[derive(Copy, Clone, Debug)]
40 #[derive(Debug, Copy, Clone)]
46 pub struct OverlapResult<'tcx> {
47 pub impl_header: ty::ImplHeader<'tcx>,
48 pub intercrate_ambiguity_causes: FxIndexSet<IntercrateAmbiguityCause>,
50 /// `true` if the overlap might've been permitted before the shift
52 pub involves_placeholder: bool,
55 pub fn add_placeholder_note(err: &mut Diagnostic) {
57 "this behavior recently changed as a result of a bug fix; \
58 see rust-lang/rust#56105 for details",
62 /// If there are types that satisfy both impls, invokes `on_overlap`
63 /// with a suitably-freshened `ImplHeader` with those types
64 /// substituted. Otherwise, invokes `no_overlap`.
65 #[instrument(skip(tcx, skip_leak_check, on_overlap, no_overlap), level = "debug")]
66 pub fn overlapping_impls<F1, F2, R>(
70 skip_leak_check: SkipLeakCheck,
71 overlap_mode: OverlapMode,
76 F1: FnOnce(OverlapResult<'_>) -> R,
79 // Before doing expensive operations like entering an inference context, do
80 // a quick check via fast_reject to tell if the impl headers could possibly
82 let drcx = DeepRejectCtxt { treat_obligation_params: TreatParams::AsInfer };
83 let impl1_ref = tcx.impl_trait_ref(impl1_def_id);
84 let impl2_ref = tcx.impl_trait_ref(impl2_def_id);
85 let may_overlap = match (impl1_ref, impl2_ref) {
86 (Some(a), Some(b)) => iter::zip(a.substs, b.substs)
87 .all(|(arg1, arg2)| drcx.generic_args_may_unify(arg1, arg2)),
89 let self_ty1 = tcx.type_of(impl1_def_id);
90 let self_ty2 = tcx.type_of(impl2_def_id);
91 drcx.types_may_unify(self_ty1, self_ty2)
93 _ => bug!("unexpected impls: {impl1_def_id:?} {impl2_def_id:?}"),
97 // Some types involved are definitely different, so the impls couldn't possibly overlap.
98 debug!("overlapping_impls: fast_reject early-exit");
102 let overlaps = tcx.infer_ctxt().enter(|infcx| {
103 let selcx = &mut SelectionContext::intercrate(&infcx);
104 overlap(selcx, skip_leak_check, impl1_def_id, impl2_def_id, overlap_mode).is_some()
111 // In the case where we detect an error, run the check again, but
112 // this time tracking intercrate ambiguity causes for better
113 // diagnostics. (These take time and can lead to false errors.)
114 tcx.infer_ctxt().enter(|infcx| {
115 let selcx = &mut SelectionContext::intercrate(&infcx);
116 selcx.enable_tracking_intercrate_ambiguity_causes();
118 overlap(selcx, skip_leak_check, impl1_def_id, impl2_def_id, overlap_mode).unwrap(),
123 fn with_fresh_ty_vars<'cx, 'tcx>(
124 selcx: &mut SelectionContext<'cx, 'tcx>,
125 param_env: ty::ParamEnv<'tcx>,
127 ) -> ty::ImplHeader<'tcx> {
128 let tcx = selcx.tcx();
129 let impl_substs = selcx.infcx().fresh_substs_for_item(DUMMY_SP, impl_def_id);
131 let header = ty::ImplHeader {
133 self_ty: tcx.bound_type_of(impl_def_id).subst(tcx, impl_substs),
134 trait_ref: tcx.bound_impl_trait_ref(impl_def_id).map(|i| i.subst(tcx, impl_substs)),
135 predicates: tcx.predicates_of(impl_def_id).instantiate(tcx, impl_substs).predicates,
138 let Normalized { value: mut header, obligations } =
139 traits::normalize(selcx, param_env, ObligationCause::dummy(), header);
141 header.predicates.extend(obligations.into_iter().map(|o| o.predicate));
145 /// Can both impl `a` and impl `b` be satisfied by a common type (including
146 /// where-clauses)? If so, returns an `ImplHeader` that unifies the two impls.
147 fn overlap<'cx, 'tcx>(
148 selcx: &mut SelectionContext<'cx, 'tcx>,
149 skip_leak_check: SkipLeakCheck,
152 overlap_mode: OverlapMode,
153 ) -> Option<OverlapResult<'tcx>> {
155 "overlap(impl1_def_id={:?}, impl2_def_id={:?}, overlap_mode={:?})",
156 impl1_def_id, impl2_def_id, overlap_mode
159 selcx.infcx().probe_maybe_skip_leak_check(skip_leak_check.is_yes(), |snapshot| {
160 overlap_within_probe(selcx, impl1_def_id, impl2_def_id, overlap_mode, snapshot)
164 fn overlap_within_probe<'cx, 'tcx>(
165 selcx: &mut SelectionContext<'cx, 'tcx>,
168 overlap_mode: OverlapMode,
169 snapshot: &CombinedSnapshot<'_, 'tcx>,
170 ) -> Option<OverlapResult<'tcx>> {
171 let infcx = selcx.infcx();
173 if overlap_mode.use_negative_impl() {
174 if negative_impl(selcx, impl1_def_id, impl2_def_id)
175 || negative_impl(selcx, impl2_def_id, impl1_def_id)
181 // For the purposes of this check, we don't bring any placeholder
182 // types into scope; instead, we replace the generic types with
183 // fresh type variables, and hence we do our evaluations in an
184 // empty environment.
185 let param_env = ty::ParamEnv::empty();
187 let impl1_header = with_fresh_ty_vars(selcx, param_env, impl1_def_id);
188 let impl2_header = with_fresh_ty_vars(selcx, param_env, impl2_def_id);
190 let obligations = equate_impl_headers(selcx, &impl1_header, &impl2_header)?;
191 debug!("overlap: unification check succeeded");
193 if overlap_mode.use_implicit_negative() {
194 if implicit_negative(selcx, param_env, &impl1_header, impl2_header, obligations) {
199 // We disable the leak when when creating the `snapshot` by using
200 // `infcx.probe_maybe_disable_leak_check`.
201 if infcx.leak_check(true, snapshot).is_err() {
202 debug!("overlap: leak check failed");
206 let intercrate_ambiguity_causes = selcx.take_intercrate_ambiguity_causes();
207 debug!("overlap: intercrate_ambiguity_causes={:#?}", intercrate_ambiguity_causes);
209 let involves_placeholder =
210 matches!(selcx.infcx().region_constraints_added_in_snapshot(snapshot), Some(true));
212 let impl_header = selcx.infcx().resolve_vars_if_possible(impl1_header);
213 Some(OverlapResult { impl_header, intercrate_ambiguity_causes, involves_placeholder })
216 fn equate_impl_headers<'cx, 'tcx>(
217 selcx: &mut SelectionContext<'cx, 'tcx>,
218 impl1_header: &ty::ImplHeader<'tcx>,
219 impl2_header: &ty::ImplHeader<'tcx>,
220 ) -> Option<PredicateObligations<'tcx>> {
221 // Do `a` and `b` unify? If not, no overlap.
222 debug!("equate_impl_headers(impl1_header={:?}, impl2_header={:?}", impl1_header, impl2_header);
225 .at(&ObligationCause::dummy(), ty::ParamEnv::empty())
226 .eq_impl_headers(impl1_header, impl2_header)
227 .map(|infer_ok| infer_ok.obligations)
231 /// Given impl1 and impl2 check if both impls can be satisfied by a common type (including
232 /// where-clauses) If so, return false, otherwise return true, they are disjoint.
233 fn implicit_negative<'cx, 'tcx>(
234 selcx: &mut SelectionContext<'cx, 'tcx>,
235 param_env: ty::ParamEnv<'tcx>,
236 impl1_header: &ty::ImplHeader<'tcx>,
237 impl2_header: ty::ImplHeader<'tcx>,
238 obligations: PredicateObligations<'tcx>,
240 // There's no overlap if obligations are unsatisfiable or if the obligation negated is
243 // For example, given these two impl headers:
245 // `impl<'a> From<&'a str> for Box<dyn Error>`
246 // `impl<E> From<E> for Box<dyn Error> where E: Error`
250 // `Box<dyn Error>: From<&'?a str>`
251 // `Box<dyn Error>: From<?E>`
253 // After equating the two headers:
255 // `Box<dyn Error> = Box<dyn Error>`
256 // So, `?E = &'?a str` and then given the where clause `&'?a str: Error`.
258 // If the obligation `&'?a str: Error` holds, it means that there's overlap. If that doesn't
259 // hold we need to check if `&'?a str: !Error` holds, if doesn't hold there's overlap because
260 // at some point an impl for `&'?a str: Error` could be added.
262 "implicit_negative(impl1_header={:?}, impl2_header={:?}, obligations={:?})",
263 impl1_header, impl2_header, obligations
265 let infcx = selcx.infcx();
266 let opt_failing_obligation = impl1_header
270 .chain(impl2_header.predicates)
271 .map(|p| infcx.resolve_vars_if_possible(p))
272 .map(|p| Obligation {
273 cause: ObligationCause::dummy(),
279 .find(|o| !selcx.predicate_may_hold_fatal(o));
281 if let Some(failing_obligation) = opt_failing_obligation {
282 debug!("overlap: obligation unsatisfiable {:?}", failing_obligation);
289 /// Given impl1 and impl2 check if both impls are never satisfied by a common type (including
290 /// where-clauses) If so, return true, they are disjoint and false otherwise.
291 fn negative_impl<'cx, 'tcx>(
292 selcx: &mut SelectionContext<'cx, 'tcx>,
296 debug!("negative_impl(impl1_def_id={:?}, impl2_def_id={:?})", impl1_def_id, impl2_def_id);
297 let tcx = selcx.infcx().tcx;
299 // Create an infcx, taking the predicates of impl1 as assumptions:
300 tcx.infer_ctxt().enter(|infcx| {
301 // create a parameter environment corresponding to a (placeholder) instantiation of impl1
302 let impl_env = tcx.param_env(impl1_def_id);
303 let subject1 = match traits::fully_normalize(
305 ObligationCause::dummy(),
307 tcx.impl_subject(impl1_def_id),
311 tcx.sess.delay_span_bug(
312 tcx.def_span(impl1_def_id),
313 format!("failed to fully normalize {:?}: {:?}", impl1_def_id, err),
319 // Attempt to prove that impl2 applies, given all of the above.
320 let selcx = &mut SelectionContext::new(&infcx);
321 let impl2_substs = infcx.fresh_substs_for_item(DUMMY_SP, impl2_def_id);
322 let (subject2, obligations) =
323 impl_subject_and_oblig(selcx, impl_env, impl2_def_id, impl2_substs);
325 !equate(&infcx, impl_env, subject1, subject2, obligations)
329 fn equate<'cx, 'tcx>(
330 infcx: &InferCtxt<'cx, 'tcx>,
331 impl_env: ty::ParamEnv<'tcx>,
332 subject1: ImplSubject<'tcx>,
333 subject2: ImplSubject<'tcx>,
334 obligations: impl Iterator<Item = PredicateObligation<'tcx>>,
336 // do the impls unify? If not, not disjoint.
337 let Ok(InferOk { obligations: more_obligations, .. }) =
338 infcx.at(&ObligationCause::dummy(), impl_env).eq(subject1, subject2)
340 debug!("explicit_disjoint: {:?} does not unify with {:?}", subject1, subject2);
344 let selcx = &mut SelectionContext::new(&infcx);
345 let opt_failing_obligation = obligations
347 .chain(more_obligations)
348 .find(|o| negative_impl_exists(selcx, impl_env, o));
350 if let Some(failing_obligation) = opt_failing_obligation {
351 debug!("overlap: obligation unsatisfiable {:?}", failing_obligation);
358 /// Try to prove that a negative impl exist for the given obligation and its super predicates.
359 #[instrument(level = "debug", skip(selcx))]
360 fn negative_impl_exists<'cx, 'tcx>(
361 selcx: &SelectionContext<'cx, 'tcx>,
362 param_env: ty::ParamEnv<'tcx>,
363 o: &PredicateObligation<'tcx>,
365 let infcx = &selcx.infcx().fork();
367 if resolve_negative_obligation(infcx, param_env, o) {
371 // Try to prove a negative obligation exists for super predicates
372 for o in util::elaborate_predicates(infcx.tcx, iter::once(o.predicate)) {
373 if resolve_negative_obligation(infcx, param_env, &o) {
381 #[instrument(level = "debug", skip(infcx))]
382 fn resolve_negative_obligation<'cx, 'tcx>(
383 infcx: &InferCtxt<'cx, 'tcx>,
384 param_env: ty::ParamEnv<'tcx>,
385 o: &PredicateObligation<'tcx>,
389 let Some(o) = o.flip_polarity(tcx) else {
393 let errors = super::fully_solve_obligation(infcx, o);
394 if !errors.is_empty() {
398 let outlives_env = OutlivesEnvironment::new(param_env);
399 infcx.process_registered_region_obligations(outlives_env.region_bound_pairs(), param_env);
401 infcx.resolve_regions(&outlives_env).is_empty()
404 pub fn trait_ref_is_knowable<'tcx>(
406 trait_ref: ty::TraitRef<'tcx>,
407 ) -> Result<(), Conflict> {
408 debug!("trait_ref_is_knowable(trait_ref={:?})", trait_ref);
409 if orphan_check_trait_ref(tcx, trait_ref, InCrate::Remote).is_ok() {
410 // A downstream or cousin crate is allowed to implement some
411 // substitution of this trait-ref.
412 return Err(Conflict::Downstream);
415 if trait_ref_is_local_or_fundamental(tcx, trait_ref) {
416 // This is a local or fundamental trait, so future-compatibility
417 // is no concern. We know that downstream/cousin crates are not
418 // allowed to implement a substitution of this trait ref, which
419 // means impls could only come from dependencies of this crate,
420 // which we already know about.
424 // This is a remote non-fundamental trait, so if another crate
425 // can be the "final owner" of a substitution of this trait-ref,
426 // they are allowed to implement it future-compatibly.
428 // However, if we are a final owner, then nobody else can be,
429 // and if we are an intermediate owner, then we don't care
430 // about future-compatibility, which means that we're OK if
432 if orphan_check_trait_ref(tcx, trait_ref, InCrate::Local).is_ok() {
433 debug!("trait_ref_is_knowable: orphan check passed");
436 debug!("trait_ref_is_knowable: nonlocal, nonfundamental, unowned");
437 Err(Conflict::Upstream)
441 pub fn trait_ref_is_local_or_fundamental<'tcx>(
443 trait_ref: ty::TraitRef<'tcx>,
445 trait_ref.def_id.krate == LOCAL_CRATE || tcx.has_attr(trait_ref.def_id, sym::fundamental)
448 pub enum OrphanCheckErr<'tcx> {
449 NonLocalInputType(Vec<(Ty<'tcx>, bool /* Is this the first input type? */)>),
450 UncoveredTy(Ty<'tcx>, Option<Ty<'tcx>>),
453 /// Checks the coherence orphan rules. `impl_def_id` should be the
454 /// `DefId` of a trait impl. To pass, either the trait must be local, or else
455 /// two conditions must be satisfied:
457 /// 1. All type parameters in `Self` must be "covered" by some local type constructor.
458 /// 2. Some local type must appear in `Self`.
459 pub fn orphan_check(tcx: TyCtxt<'_>, impl_def_id: DefId) -> Result<(), OrphanCheckErr<'_>> {
460 debug!("orphan_check({:?})", impl_def_id);
462 // We only except this routine to be invoked on implementations
463 // of a trait, not inherent implementations.
464 let trait_ref = tcx.impl_trait_ref(impl_def_id).unwrap();
465 debug!("orphan_check: trait_ref={:?}", trait_ref);
467 // If the *trait* is local to the crate, ok.
468 if trait_ref.def_id.is_local() {
469 debug!("trait {:?} is local to current crate", trait_ref.def_id);
473 orphan_check_trait_ref(tcx, trait_ref, InCrate::Local)
476 /// Checks whether a trait-ref is potentially implementable by a crate.
478 /// The current rule is that a trait-ref orphan checks in a crate C:
480 /// 1. Order the parameters in the trait-ref in subst order - Self first,
481 /// others linearly (e.g., `<U as Foo<V, W>>` is U < V < W).
482 /// 2. Of these type parameters, there is at least one type parameter
483 /// in which, walking the type as a tree, you can reach a type local
484 /// to C where all types in-between are fundamental types. Call the
485 /// first such parameter the "local key parameter".
486 /// - e.g., `Box<LocalType>` is OK, because you can visit LocalType
487 /// going through `Box`, which is fundamental.
488 /// - similarly, `FundamentalPair<Vec<()>, Box<LocalType>>` is OK for
490 /// - but (knowing that `Vec<T>` is non-fundamental, and assuming it's
491 /// not local), `Vec<LocalType>` is bad, because `Vec<->` is between
492 /// the local type and the type parameter.
493 /// 3. Before this local type, no generic type parameter of the impl must
494 /// be reachable through fundamental types.
495 /// - e.g. `impl<T> Trait<LocalType> for Vec<T>` is fine, as `Vec` is not fundamental.
496 /// - while `impl<T> Trait<LocalType> for Box<T>` results in an error, as `T` is
497 /// reachable through the fundamental type `Box`.
498 /// 4. Every type in the local key parameter not known in C, going
499 /// through the parameter's type tree, must appear only as a subtree of
500 /// a type local to C, with only fundamental types between the type
501 /// local to C and the local key parameter.
502 /// - e.g., `Vec<LocalType<T>>>` (or equivalently `Box<Vec<LocalType<T>>>`)
503 /// is bad, because the only local type with `T` as a subtree is
504 /// `LocalType<T>`, and `Vec<->` is between it and the type parameter.
505 /// - similarly, `FundamentalPair<LocalType<T>, T>` is bad, because
506 /// the second occurrence of `T` is not a subtree of *any* local type.
507 /// - however, `LocalType<Vec<T>>` is OK, because `T` is a subtree of
508 /// `LocalType<Vec<T>>`, which is local and has no types between it and
509 /// the type parameter.
511 /// The orphan rules actually serve several different purposes:
513 /// 1. They enable link-safety - i.e., 2 mutually-unknowing crates (where
514 /// every type local to one crate is unknown in the other) can't implement
515 /// the same trait-ref. This follows because it can be seen that no such
516 /// type can orphan-check in 2 such crates.
518 /// To check that a local impl follows the orphan rules, we check it in
519 /// InCrate::Local mode, using type parameters for the "generic" types.
521 /// 2. They ground negative reasoning for coherence. If a user wants to
522 /// write both a conditional blanket impl and a specific impl, we need to
523 /// make sure they do not overlap. For example, if we write
524 /// ```ignore (illustrative)
525 /// impl<T> IntoIterator for Vec<T>
526 /// impl<T: Iterator> IntoIterator for T
528 /// We need to be able to prove that `Vec<$0>: !Iterator` for every type $0.
529 /// We can observe that this holds in the current crate, but we need to make
530 /// sure this will also hold in all unknown crates (both "independent" crates,
531 /// which we need for link-safety, and also child crates, because we don't want
532 /// child crates to get error for impl conflicts in a *dependency*).
534 /// For that, we only allow negative reasoning if, for every assignment to the
535 /// inference variables, every unknown crate would get an orphan error if they
536 /// try to implement this trait-ref. To check for this, we use InCrate::Remote
537 /// mode. That is sound because we already know all the impls from known crates.
539 /// 3. For non-`#[fundamental]` traits, they guarantee that parent crates can
540 /// add "non-blanket" impls without breaking negative reasoning in dependent
541 /// crates. This is the "rebalancing coherence" (RFC 1023) restriction.
543 /// For that, we only a allow crate to perform negative reasoning on
544 /// non-local-non-`#[fundamental]` only if there's a local key parameter as per (2).
546 /// Because we never perform negative reasoning generically (coherence does
547 /// not involve type parameters), this can be interpreted as doing the full
548 /// orphan check (using InCrate::Local mode), substituting non-local known
549 /// types for all inference variables.
551 /// This allows for crates to future-compatibly add impls as long as they
552 /// can't apply to types with a key parameter in a child crate - applying
553 /// the rules, this basically means that every type parameter in the impl
554 /// must appear behind a non-fundamental type (because this is not a
555 /// type-system requirement, crate owners might also go for "semantic
556 /// future-compatibility" involving things such as sealed traits, but
557 /// the above requirement is sufficient, and is necessary in "open world"
560 /// Note that this function is never called for types that have both type
561 /// parameters and inference variables.
562 fn orphan_check_trait_ref<'tcx>(
564 trait_ref: ty::TraitRef<'tcx>,
566 ) -> Result<(), OrphanCheckErr<'tcx>> {
567 debug!("orphan_check_trait_ref(trait_ref={:?}, in_crate={:?})", trait_ref, in_crate);
569 if trait_ref.needs_infer() && trait_ref.needs_subst() {
571 "can't orphan check a trait ref with both params and inference variables {:?}",
576 let mut checker = OrphanChecker::new(tcx, in_crate);
577 match trait_ref.visit_with(&mut checker) {
578 ControlFlow::Continue(()) => Err(OrphanCheckErr::NonLocalInputType(checker.non_local_tys)),
579 ControlFlow::Break(OrphanCheckEarlyExit::ParamTy(ty)) => {
580 // Does there exist some local type after the `ParamTy`.
581 checker.search_first_local_ty = true;
582 if let Some(OrphanCheckEarlyExit::LocalTy(local_ty)) =
583 trait_ref.visit_with(&mut checker).break_value()
585 Err(OrphanCheckErr::UncoveredTy(ty, Some(local_ty)))
587 Err(OrphanCheckErr::UncoveredTy(ty, None))
590 ControlFlow::Break(OrphanCheckEarlyExit::LocalTy(_)) => Ok(()),
594 struct OrphanChecker<'tcx> {
598 /// Ignore orphan check failures and exclusively search for the first
600 search_first_local_ty: bool,
601 non_local_tys: Vec<(Ty<'tcx>, bool)>,
604 impl<'tcx> OrphanChecker<'tcx> {
605 fn new(tcx: TyCtxt<'tcx>, in_crate: InCrate) -> Self {
610 search_first_local_ty: false,
611 non_local_tys: Vec::new(),
615 fn found_non_local_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<OrphanCheckEarlyExit<'tcx>> {
616 self.non_local_tys.push((t, self.in_self_ty));
617 ControlFlow::CONTINUE
620 fn found_param_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<OrphanCheckEarlyExit<'tcx>> {
621 if self.search_first_local_ty {
622 ControlFlow::CONTINUE
624 ControlFlow::Break(OrphanCheckEarlyExit::ParamTy(t))
628 fn def_id_is_local(&mut self, def_id: DefId) -> bool {
629 match self.in_crate {
630 InCrate::Local => def_id.is_local(),
631 InCrate::Remote => false,
636 enum OrphanCheckEarlyExit<'tcx> {
641 impl<'tcx> TypeVisitor<'tcx> for OrphanChecker<'tcx> {
642 type BreakTy = OrphanCheckEarlyExit<'tcx>;
643 fn visit_region(&mut self, _r: ty::Region<'tcx>) -> ControlFlow<Self::BreakTy> {
644 ControlFlow::CONTINUE
647 fn visit_ty(&mut self, ty: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
648 let result = match *ty.kind() {
662 | ty::Projection(..) => self.found_non_local_ty(ty),
664 ty::Param(..) => self.found_param_ty(ty),
666 ty::Placeholder(..) | ty::Bound(..) | ty::Infer(..) => match self.in_crate {
667 InCrate::Local => self.found_non_local_ty(ty),
668 // The inference variable might be unified with a local
669 // type in that remote crate.
670 InCrate::Remote => ControlFlow::Break(OrphanCheckEarlyExit::LocalTy(ty)),
673 // For fundamental types, we just look inside of them.
674 ty::Ref(_, ty, _) => ty.visit_with(self),
675 ty::Adt(def, substs) => {
676 if self.def_id_is_local(def.did()) {
677 ControlFlow::Break(OrphanCheckEarlyExit::LocalTy(ty))
678 } else if def.is_fundamental() {
679 substs.visit_with(self)
681 self.found_non_local_ty(ty)
684 ty::Foreign(def_id) => {
685 if self.def_id_is_local(def_id) {
686 ControlFlow::Break(OrphanCheckEarlyExit::LocalTy(ty))
688 self.found_non_local_ty(ty)
691 ty::Dynamic(tt, ..) => {
692 let principal = tt.principal().map(|p| p.def_id());
693 if principal.map_or(false, |p| self.def_id_is_local(p)) {
694 ControlFlow::Break(OrphanCheckEarlyExit::LocalTy(ty))
696 self.found_non_local_ty(ty)
699 ty::Error(_) => ControlFlow::Break(OrphanCheckEarlyExit::LocalTy(ty)),
700 ty::Closure(..) | ty::Generator(..) | ty::GeneratorWitness(..) => {
701 self.tcx.sess.delay_span_bug(
703 format!("ty_is_local invoked on closure or generator: {:?}", ty),
705 ControlFlow::Break(OrphanCheckEarlyExit::LocalTy(ty))
708 // This merits some explanation.
709 // Normally, opaque types are not involved when performing
710 // coherence checking, since it is illegal to directly
711 // implement a trait on an opaque type. However, we might
712 // end up looking at an opaque type during coherence checking
713 // if an opaque type gets used within another type (e.g. as
714 // the type of a field) when checking for auto trait or `Sized`
715 // impls. This requires us to decide whether or not an opaque
716 // type should be considered 'local' or not.
718 // We choose to treat all opaque types as non-local, even
719 // those that appear within the same crate. This seems
720 // somewhat surprising at first, but makes sense when
721 // you consider that opaque types are supposed to hide
722 // the underlying type *within the same crate*. When an
723 // opaque type is used from outside the module
724 // where it is declared, it should be impossible to observe
725 // anything about it other than the traits that it implements.
727 // The alternative would be to look at the underlying type
728 // to determine whether or not the opaque type itself should
729 // be considered local. However, this could make it a breaking change
730 // to switch the underlying ('defining') type from a local type
731 // to a remote type. This would violate the rule that opaque
732 // types should be completely opaque apart from the traits
733 // that they implement, so we don't use this behavior.
734 self.found_non_local_ty(ty)
737 // A bit of a hack, the `OrphanChecker` is only used to visit a `TraitRef`, so
738 // the first type we visit is always the self type.
739 self.in_self_ty = false;
743 /// All possible values for a constant parameter already exist
744 /// in the crate defining the trait, so they are always non-local[^1].
746 /// Because there's no way to have an impl where the first local
747 /// generic argument is a constant, we also don't have to fail
748 /// the orphan check when encountering a parameter or a generic constant.
750 /// This means that we can completely ignore constants during the orphan check.
752 /// See `src/test/ui/coherence/const-generics-orphan-check-ok.rs` for examples.
754 /// [^1]: This might not hold for function pointers or trait objects in the future.
755 /// As these should be quite rare as const arguments and especially rare as impl
756 /// parameters, allowing uncovered const parameters in impls seems more useful
757 /// than allowing `impl<T> Trait<local_fn_ptr, T> for i32` to compile.
758 fn visit_const(&mut self, _c: ty::Const<'tcx>) -> ControlFlow<Self::BreakTy> {
759 ControlFlow::CONTINUE