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, RegionckMode};
9 use crate::traits::select::IntercrateAmbiguityCause;
10 use crate::traits::util::impl_trait_ref_and_oblig;
11 use crate::traits::SkipLeakCheck;
13 self, FulfillmentContext, Normalized, Obligation, ObligationCause, PredicateObligation,
14 PredicateObligations, SelectionContext,
16 //use rustc_data_structures::fx::FxHashMap;
17 use rustc_errors::Diagnostic;
18 use rustc_hir::def_id::{DefId, LOCAL_CRATE};
19 use rustc_hir::CRATE_HIR_ID;
20 use rustc_infer::infer::at::ToTrace;
21 use rustc_infer::infer::{InferCtxt, TyCtxtInferExt};
22 use rustc_infer::traits::{util, TraitEngine};
23 use rustc_middle::traits::specialization_graph::OverlapMode;
24 use rustc_middle::ty::fast_reject::{self, TreatParams};
25 use rustc_middle::ty::fold::TypeFoldable;
26 use rustc_middle::ty::subst::Subst;
27 use rustc_middle::ty::{self, ImplSubject, Ty, TyCtxt};
28 use rustc_span::symbol::sym;
29 use rustc_span::DUMMY_SP;
33 /// Whether we do the orphan check relative to this crate or
34 /// to some remote crate.
35 #[derive(Copy, Clone, Debug)]
41 #[derive(Debug, Copy, Clone)]
47 pub struct OverlapResult<'tcx> {
48 pub impl_header: ty::ImplHeader<'tcx>,
49 pub intercrate_ambiguity_causes: Vec<IntercrateAmbiguityCause>,
51 /// `true` if the overlap might've been permitted before the shift
53 pub involves_placeholder: bool,
56 pub fn add_placeholder_note(err: &mut Diagnostic) {
58 "this behavior recently changed as a result of a bug fix; \
59 see rust-lang/rust#56105 for details",
63 /// If there are types that satisfy both impls, invokes `on_overlap`
64 /// with a suitably-freshened `ImplHeader` with those types
65 /// substituted. Otherwise, invokes `no_overlap`.
66 #[instrument(skip(tcx, skip_leak_check, on_overlap, no_overlap), level = "debug")]
67 pub fn overlapping_impls<F1, F2, R>(
71 skip_leak_check: SkipLeakCheck,
72 overlap_mode: OverlapMode,
77 F1: FnOnce(OverlapResult<'_>) -> R,
80 // Before doing expensive operations like entering an inference context, do
81 // a quick check via fast_reject to tell if the impl headers could possibly
83 let impl1_ref = tcx.impl_trait_ref(impl1_def_id);
84 let impl2_ref = tcx.impl_trait_ref(impl2_def_id);
86 // Check if any of the input types definitely do not unify.
88 impl1_ref.iter().flat_map(|tref| tref.substs.types()),
89 impl2_ref.iter().flat_map(|tref| tref.substs.types()),
92 let t1 = fast_reject::simplify_type(tcx, ty1, TreatParams::AsPlaceholders);
93 let t2 = fast_reject::simplify_type(tcx, ty2, TreatParams::AsPlaceholders);
95 if let (Some(t1), Some(t2)) = (t1, t2) {
96 // Simplified successfully
103 // Some types involved are definitely different, so the impls couldn't possibly overlap.
104 debug!("overlapping_impls: fast_reject early-exit");
108 let overlaps = tcx.infer_ctxt().enter(|infcx| {
109 let selcx = &mut SelectionContext::intercrate(&infcx);
110 overlap(selcx, skip_leak_check, impl1_def_id, impl2_def_id, overlap_mode).is_some()
117 // In the case where we detect an error, run the check again, but
118 // this time tracking intercrate ambuiguity causes for better
119 // diagnostics. (These take time and can lead to false errors.)
120 tcx.infer_ctxt().enter(|infcx| {
121 let selcx = &mut SelectionContext::intercrate(&infcx);
122 selcx.enable_tracking_intercrate_ambiguity_causes();
124 overlap(selcx, skip_leak_check, impl1_def_id, impl2_def_id, overlap_mode).unwrap(),
129 fn with_fresh_ty_vars<'cx, 'tcx>(
130 selcx: &mut SelectionContext<'cx, 'tcx>,
131 param_env: ty::ParamEnv<'tcx>,
133 ) -> ty::ImplHeader<'tcx> {
134 let tcx = selcx.tcx();
135 let impl_substs = selcx.infcx().fresh_substs_for_item(DUMMY_SP, impl_def_id);
137 let header = ty::ImplHeader {
139 self_ty: tcx.type_of(impl_def_id).subst(tcx, impl_substs),
140 trait_ref: tcx.impl_trait_ref(impl_def_id).subst(tcx, impl_substs),
141 predicates: tcx.predicates_of(impl_def_id).instantiate(tcx, impl_substs).predicates,
144 let Normalized { value: mut header, obligations } =
145 traits::normalize(selcx, param_env, ObligationCause::dummy(), header);
147 header.predicates.extend(obligations.into_iter().map(|o| o.predicate));
151 /// Can both impl `a` and impl `b` be satisfied by a common type (including
152 /// where-clauses)? If so, returns an `ImplHeader` that unifies the two impls.
153 fn overlap<'cx, 'tcx>(
154 selcx: &mut SelectionContext<'cx, 'tcx>,
155 skip_leak_check: SkipLeakCheck,
158 overlap_mode: OverlapMode,
159 ) -> Option<OverlapResult<'tcx>> {
161 "overlap(impl1_def_id={:?}, impl2_def_id={:?}, overlap_mode={:?})",
162 impl1_def_id, impl2_def_id, overlap_mode
165 selcx.infcx().probe_maybe_skip_leak_check(skip_leak_check.is_yes(), |snapshot| {
166 overlap_within_probe(selcx, impl1_def_id, impl2_def_id, overlap_mode, snapshot)
170 fn overlap_within_probe<'cx, 'tcx>(
171 selcx: &mut SelectionContext<'cx, 'tcx>,
174 overlap_mode: OverlapMode,
175 snapshot: &CombinedSnapshot<'_, 'tcx>,
176 ) -> Option<OverlapResult<'tcx>> {
177 let infcx = selcx.infcx();
179 if overlap_mode.use_negative_impl() {
180 if negative_impl(selcx, impl1_def_id, impl2_def_id)
181 || negative_impl(selcx, impl2_def_id, impl1_def_id)
187 // For the purposes of this check, we don't bring any placeholder
188 // types into scope; instead, we replace the generic types with
189 // fresh type variables, and hence we do our evaluations in an
190 // empty environment.
191 let param_env = ty::ParamEnv::empty();
193 let impl1_header = with_fresh_ty_vars(selcx, param_env, impl1_def_id);
194 let impl2_header = with_fresh_ty_vars(selcx, param_env, impl2_def_id);
196 let obligations = equate_impl_headers(selcx, &impl1_header, &impl2_header)?;
197 debug!("overlap: unification check succeeded");
199 if overlap_mode.use_implicit_negative() {
200 if implicit_negative(selcx, param_env, &impl1_header, impl2_header, obligations) {
205 // We disable the leak when when creating the `snapshot` by using
206 // `infcx.probe_maybe_disable_leak_check`.
207 if infcx.leak_check(true, snapshot).is_err() {
208 debug!("overlap: leak check failed");
212 let intercrate_ambiguity_causes = selcx.take_intercrate_ambiguity_causes();
213 debug!("overlap: intercrate_ambiguity_causes={:#?}", intercrate_ambiguity_causes);
215 let involves_placeholder =
216 matches!(selcx.infcx().region_constraints_added_in_snapshot(snapshot), Some(true));
218 let impl_header = selcx.infcx().resolve_vars_if_possible(impl1_header);
219 Some(OverlapResult { impl_header, intercrate_ambiguity_causes, involves_placeholder })
222 fn equate_impl_headers<'cx, 'tcx>(
223 selcx: &mut SelectionContext<'cx, 'tcx>,
224 impl1_header: &ty::ImplHeader<'tcx>,
225 impl2_header: &ty::ImplHeader<'tcx>,
226 ) -> Option<PredicateObligations<'tcx>> {
227 // Do `a` and `b` unify? If not, no overlap.
228 debug!("equate_impl_headers(impl1_header={:?}, impl2_header={:?}", impl1_header, impl2_header);
231 .at(&ObligationCause::dummy(), ty::ParamEnv::empty())
232 .eq_impl_headers(impl1_header, impl2_header)
233 .map(|infer_ok| infer_ok.obligations)
237 /// Given impl1 and impl2 check if both impls can be satisfied by a common type (including
238 /// where-clauses) If so, return false, otherwise return true, they are disjoint.
239 fn implicit_negative<'cx, 'tcx>(
240 selcx: &mut SelectionContext<'cx, 'tcx>,
241 param_env: ty::ParamEnv<'tcx>,
242 impl1_header: &ty::ImplHeader<'tcx>,
243 impl2_header: ty::ImplHeader<'tcx>,
244 obligations: PredicateObligations<'tcx>,
246 // There's no overlap if obligations are unsatisfiable or if the obligation negated is
249 // For example, given these two impl headers:
251 // `impl<'a> From<&'a str> for Box<dyn Error>`
252 // `impl<E> From<E> for Box<dyn Error> where E: Error`
256 // `Box<dyn Error>: From<&'?a str>`
257 // `Box<dyn Error>: From<?E>`
259 // After equating the two headers:
261 // `Box<dyn Error> = Box<dyn Error>`
262 // So, `?E = &'?a str` and then given the where clause `&'?a str: Error`.
264 // If the obligation `&'?a str: Error` holds, it means that there's overlap. If that doesn't
265 // hold we need to check if `&'?a str: !Error` holds, if doesn't hold there's overlap because
266 // at some point an impl for `&'?a str: Error` could be added.
268 "implicit_negative(impl1_header={:?}, impl2_header={:?}, obligations={:?})",
269 impl1_header, impl2_header, obligations
271 let infcx = selcx.infcx();
272 let opt_failing_obligation = impl1_header
276 .chain(impl2_header.predicates)
277 .map(|p| infcx.resolve_vars_if_possible(p))
278 .map(|p| Obligation {
279 cause: ObligationCause::dummy(),
285 .find(|o| !selcx.predicate_may_hold_fatal(o));
287 if let Some(failing_obligation) = opt_failing_obligation {
288 debug!("overlap: obligation unsatisfiable {:?}", failing_obligation);
295 /// Given impl1 and impl2 check if both impls are never satisfied by a common type (including
296 /// where-clauses) If so, return true, they are disjoint and false otherwise.
297 fn negative_impl<'cx, 'tcx>(
298 selcx: &mut SelectionContext<'cx, 'tcx>,
302 debug!("negative_impl(impl1_def_id={:?}, impl2_def_id={:?})", impl1_def_id, impl2_def_id);
303 let tcx = selcx.infcx().tcx;
305 // Create an infcx, taking the predicates of impl1 as assumptions:
306 tcx.infer_ctxt().enter(|infcx| {
307 // create a parameter environment corresponding to a (placeholder) instantiation of impl1
308 let impl1_env = tcx.param_env(impl1_def_id);
310 match tcx.impl_subject(impl1_def_id) {
311 ImplSubject::Trait(impl1_trait_ref) => {
312 // Normalize the trait reference. The WF rules ought to ensure
313 // that this always succeeds.
314 let impl1_trait_ref = match traits::fully_normalize(
316 FulfillmentContext::new(),
317 ObligationCause::dummy(),
321 Ok(impl1_trait_ref) => impl1_trait_ref,
323 bug!("failed to fully normalize {:?}: {:?}", impl1_trait_ref, err);
327 // Attempt to prove that impl2 applies, given all of the above.
328 let selcx = &mut SelectionContext::new(&infcx);
329 let impl2_substs = infcx.fresh_substs_for_item(DUMMY_SP, impl2_def_id);
330 let (impl2_trait_ref, obligations) =
331 impl_trait_ref_and_oblig(selcx, impl1_env, impl2_def_id, impl2_substs);
342 ImplSubject::Inherent(ty1) => {
343 let ty2 = tcx.type_of(impl2_def_id);
344 !equate(&infcx, impl1_env, impl1_def_id, ty1, ty2, iter::empty())
350 fn equate<'cx, 'tcx, T: Debug + ToTrace<'tcx>>(
351 infcx: &InferCtxt<'cx, 'tcx>,
352 impl1_env: ty::ParamEnv<'tcx>,
356 obligations: impl Iterator<Item = PredicateObligation<'tcx>>,
358 // do the impls unify? If not, not disjoint.
359 let Ok(InferOk { obligations: more_obligations, .. }) = infcx
360 .at(&ObligationCause::dummy(), impl1_env)
361 .eq(impl1, impl2) else {
363 "explicit_disjoint: {:?} does not unify with {:?}",
369 let selcx = &mut SelectionContext::new(&infcx);
370 let opt_failing_obligation = obligations
372 .chain(more_obligations)
373 .find(|o| negative_impl_exists(selcx, impl1_env, impl1_def_id, o));
375 if let Some(failing_obligation) = opt_failing_obligation {
376 debug!("overlap: obligation unsatisfiable {:?}", failing_obligation);
383 /// Try to prove that a negative impl exist for the given obligation and its super predicates.
384 #[instrument(level = "debug", skip(selcx))]
385 fn negative_impl_exists<'cx, 'tcx>(
386 selcx: &SelectionContext<'cx, 'tcx>,
387 param_env: ty::ParamEnv<'tcx>,
388 region_context: DefId,
389 o: &PredicateObligation<'tcx>,
391 let infcx = &selcx.infcx().fork();
393 if resolve_negative_obligation(infcx, param_env, region_context, o) {
397 // Try to prove a negative obligation exists for super predicates
398 for o in util::elaborate_predicates(infcx.tcx, iter::once(o.predicate)) {
399 if resolve_negative_obligation(infcx, param_env, region_context, &o) {
407 #[instrument(level = "debug", skip(infcx))]
408 fn resolve_negative_obligation<'cx, 'tcx>(
409 infcx: &InferCtxt<'cx, 'tcx>,
410 param_env: ty::ParamEnv<'tcx>,
411 region_context: DefId,
412 o: &PredicateObligation<'tcx>,
416 let Some(o) = o.flip_polarity(tcx) else {
420 let mut fulfillment_cx = FulfillmentContext::new();
421 fulfillment_cx.register_predicate_obligation(infcx, o);
423 let errors = fulfillment_cx.select_all_or_error(infcx);
425 if !errors.is_empty() {
429 let mut outlives_env = OutlivesEnvironment::new(param_env);
430 // FIXME -- add "assumed to be well formed" types into the `outlives_env`
432 // "Save" the accumulated implied bounds into the outlives environment
433 // (due to the FIXME above, there aren't any, but this step is still needed).
434 // The "body id" is given as `CRATE_HIR_ID`, which is the same body-id used
435 // by the "dummy" causes elsewhere (body-id is only relevant when checking
436 // function bodies with closures).
437 outlives_env.save_implied_bounds(CRATE_HIR_ID);
439 infcx.process_registered_region_obligations(
440 outlives_env.region_bound_pairs_map(),
441 Some(tcx.lifetimes.re_root_empty),
445 let errors = infcx.resolve_regions(region_context, &outlives_env, RegionckMode::default());
447 if !errors.is_empty() {
454 pub fn trait_ref_is_knowable<'tcx>(
456 trait_ref: ty::TraitRef<'tcx>,
457 ) -> Option<Conflict> {
458 debug!("trait_ref_is_knowable(trait_ref={:?})", trait_ref);
459 if orphan_check_trait_ref(tcx, trait_ref, InCrate::Remote).is_ok() {
460 // A downstream or cousin crate is allowed to implement some
461 // substitution of this trait-ref.
462 return Some(Conflict::Downstream);
465 if trait_ref_is_local_or_fundamental(tcx, trait_ref) {
466 // This is a local or fundamental trait, so future-compatibility
467 // is no concern. We know that downstream/cousin crates are not
468 // allowed to implement a substitution of this trait ref, which
469 // means impls could only come from dependencies of this crate,
470 // which we already know about.
474 // This is a remote non-fundamental trait, so if another crate
475 // can be the "final owner" of a substitution of this trait-ref,
476 // they are allowed to implement it future-compatibly.
478 // However, if we are a final owner, then nobody else can be,
479 // and if we are an intermediate owner, then we don't care
480 // about future-compatibility, which means that we're OK if
482 if orphan_check_trait_ref(tcx, trait_ref, InCrate::Local).is_ok() {
483 debug!("trait_ref_is_knowable: orphan check passed");
486 debug!("trait_ref_is_knowable: nonlocal, nonfundamental, unowned");
487 Some(Conflict::Upstream)
491 pub fn trait_ref_is_local_or_fundamental<'tcx>(
493 trait_ref: ty::TraitRef<'tcx>,
495 trait_ref.def_id.krate == LOCAL_CRATE || tcx.has_attr(trait_ref.def_id, sym::fundamental)
498 pub enum OrphanCheckErr<'tcx> {
499 NonLocalInputType(Vec<(Ty<'tcx>, bool /* Is this the first input type? */)>),
500 UncoveredTy(Ty<'tcx>, Option<Ty<'tcx>>),
503 /// Checks the coherence orphan rules. `impl_def_id` should be the
504 /// `DefId` of a trait impl. To pass, either the trait must be local, or else
505 /// two conditions must be satisfied:
507 /// 1. All type parameters in `Self` must be "covered" by some local type constructor.
508 /// 2. Some local type must appear in `Self`.
509 pub fn orphan_check(tcx: TyCtxt<'_>, impl_def_id: DefId) -> Result<(), OrphanCheckErr<'_>> {
510 debug!("orphan_check({:?})", impl_def_id);
512 // We only except this routine to be invoked on implementations
513 // of a trait, not inherent implementations.
514 let trait_ref = tcx.impl_trait_ref(impl_def_id).unwrap();
515 debug!("orphan_check: trait_ref={:?}", trait_ref);
517 // If the *trait* is local to the crate, ok.
518 if trait_ref.def_id.is_local() {
519 debug!("trait {:?} is local to current crate", trait_ref.def_id);
523 orphan_check_trait_ref(tcx, trait_ref, InCrate::Local)
526 /// Checks whether a trait-ref is potentially implementable by a crate.
528 /// The current rule is that a trait-ref orphan checks in a crate C:
530 /// 1. Order the parameters in the trait-ref in subst order - Self first,
531 /// others linearly (e.g., `<U as Foo<V, W>>` is U < V < W).
532 /// 2. Of these type parameters, there is at least one type parameter
533 /// in which, walking the type as a tree, you can reach a type local
534 /// to C where all types in-between are fundamental types. Call the
535 /// first such parameter the "local key parameter".
536 /// - e.g., `Box<LocalType>` is OK, because you can visit LocalType
537 /// going through `Box`, which is fundamental.
538 /// - similarly, `FundamentalPair<Vec<()>, Box<LocalType>>` is OK for
540 /// - but (knowing that `Vec<T>` is non-fundamental, and assuming it's
541 /// not local), `Vec<LocalType>` is bad, because `Vec<->` is between
542 /// the local type and the type parameter.
543 /// 3. Before this local type, no generic type parameter of the impl must
544 /// be reachable through fundamental types.
545 /// - e.g. `impl<T> Trait<LocalType> for Vec<T>` is fine, as `Vec` is not fundamental.
546 /// - while `impl<T> Trait<LocalType for Box<T>` results in an error, as `T` is
547 /// reachable through the fundamental type `Box`.
548 /// 4. Every type in the local key parameter not known in C, going
549 /// through the parameter's type tree, must appear only as a subtree of
550 /// a type local to C, with only fundamental types between the type
551 /// local to C and the local key parameter.
552 /// - e.g., `Vec<LocalType<T>>>` (or equivalently `Box<Vec<LocalType<T>>>`)
553 /// is bad, because the only local type with `T` as a subtree is
554 /// `LocalType<T>`, and `Vec<->` is between it and the type parameter.
555 /// - similarly, `FundamentalPair<LocalType<T>, T>` is bad, because
556 /// the second occurrence of `T` is not a subtree of *any* local type.
557 /// - however, `LocalType<Vec<T>>` is OK, because `T` is a subtree of
558 /// `LocalType<Vec<T>>`, which is local and has no types between it and
559 /// the type parameter.
561 /// The orphan rules actually serve several different purposes:
563 /// 1. They enable link-safety - i.e., 2 mutually-unknowing crates (where
564 /// every type local to one crate is unknown in the other) can't implement
565 /// the same trait-ref. This follows because it can be seen that no such
566 /// type can orphan-check in 2 such crates.
568 /// To check that a local impl follows the orphan rules, we check it in
569 /// InCrate::Local mode, using type parameters for the "generic" types.
571 /// 2. They ground negative reasoning for coherence. If a user wants to
572 /// write both a conditional blanket impl and a specific impl, we need to
573 /// make sure they do not overlap. For example, if we write
575 /// impl<T> IntoIterator for Vec<T>
576 /// impl<T: Iterator> IntoIterator for T
578 /// We need to be able to prove that `Vec<$0>: !Iterator` for every type $0.
579 /// We can observe that this holds in the current crate, but we need to make
580 /// sure this will also hold in all unknown crates (both "independent" crates,
581 /// which we need for link-safety, and also child crates, because we don't want
582 /// child crates to get error for impl conflicts in a *dependency*).
584 /// For that, we only allow negative reasoning if, for every assignment to the
585 /// inference variables, every unknown crate would get an orphan error if they
586 /// try to implement this trait-ref. To check for this, we use InCrate::Remote
587 /// mode. That is sound because we already know all the impls from known crates.
589 /// 3. For non-`#[fundamental]` traits, they guarantee that parent crates can
590 /// add "non-blanket" impls without breaking negative reasoning in dependent
591 /// crates. This is the "rebalancing coherence" (RFC 1023) restriction.
593 /// For that, we only a allow crate to perform negative reasoning on
594 /// non-local-non-`#[fundamental]` only if there's a local key parameter as per (2).
596 /// Because we never perform negative reasoning generically (coherence does
597 /// not involve type parameters), this can be interpreted as doing the full
598 /// orphan check (using InCrate::Local mode), substituting non-local known
599 /// types for all inference variables.
601 /// This allows for crates to future-compatibly add impls as long as they
602 /// can't apply to types with a key parameter in a child crate - applying
603 /// the rules, this basically means that every type parameter in the impl
604 /// must appear behind a non-fundamental type (because this is not a
605 /// type-system requirement, crate owners might also go for "semantic
606 /// future-compatibility" involving things such as sealed traits, but
607 /// the above requirement is sufficient, and is necessary in "open world"
610 /// Note that this function is never called for types that have both type
611 /// parameters and inference variables.
612 fn orphan_check_trait_ref<'tcx>(
614 trait_ref: ty::TraitRef<'tcx>,
616 ) -> Result<(), OrphanCheckErr<'tcx>> {
617 debug!("orphan_check_trait_ref(trait_ref={:?}, in_crate={:?})", trait_ref, in_crate);
619 if trait_ref.needs_infer() && trait_ref.needs_subst() {
621 "can't orphan check a trait ref with both params and inference variables {:?}",
626 // Given impl<P1..=Pn> Trait<T1..=Tn> for T0, an impl is valid only
627 // if at least one of the following is true:
629 // - Trait is a local trait
630 // (already checked in orphan_check prior to calling this function)
632 // - At least one of the types T0..=Tn must be a local type.
633 // Let Ti be the first such type.
634 // - No uncovered type parameters P1..=Pn may appear in T0..Ti (excluding Ti)
636 fn uncover_fundamental_ty<'tcx>(
641 // FIXME: this is currently somewhat overly complicated,
642 // but fixing this requires a more complicated refactor.
643 if !contained_non_local_types(tcx, ty, in_crate).is_empty() {
644 if let Some(inner_tys) = fundamental_ty_inner_tys(tcx, ty) {
646 .flat_map(|ty| uncover_fundamental_ty(tcx, ty, in_crate))
654 let mut non_local_spans = vec![];
655 for (i, input_ty) in trait_ref
658 .flat_map(|ty| uncover_fundamental_ty(tcx, ty, in_crate))
661 debug!("orphan_check_trait_ref: check ty `{:?}`", input_ty);
662 let non_local_tys = contained_non_local_types(tcx, input_ty, in_crate);
663 if non_local_tys.is_empty() {
664 debug!("orphan_check_trait_ref: ty_is_local `{:?}`", input_ty);
666 } else if let ty::Param(_) = input_ty.kind() {
667 debug!("orphan_check_trait_ref: uncovered ty: `{:?}`", input_ty);
668 let local_type = trait_ref
671 .flat_map(|ty| uncover_fundamental_ty(tcx, ty, in_crate))
672 .find(|ty| ty_is_local_constructor(*ty, in_crate));
674 debug!("orphan_check_trait_ref: uncovered ty local_type: `{:?}`", local_type);
676 return Err(OrphanCheckErr::UncoveredTy(input_ty, local_type));
679 non_local_spans.extend(non_local_tys.into_iter().map(|input_ty| (input_ty, i == 0)));
681 // If we exit above loop, never found a local type.
682 debug!("orphan_check_trait_ref: no local type");
683 Err(OrphanCheckErr::NonLocalInputType(non_local_spans))
686 /// Returns a list of relevant non-local types for `ty`.
688 /// This is just `ty` itself unless `ty` is `#[fundamental]`,
689 /// in which case we recursively look into this type.
691 /// If `ty` is local itself, this method returns an empty `Vec`.
695 /// - `u32` is not local, so this returns `[u32]`.
696 /// - for `Foo<u32>`, where `Foo` is a local type, this returns `[]`.
697 /// - `&mut u32` returns `[u32]`, as `&mut` is a fundamental type, similar to `Box`.
698 /// - `Box<Foo<u32>>` returns `[]`, as `Box` is a fundamental type and `Foo` is local.
699 fn contained_non_local_types<'tcx>(
704 if ty_is_local_constructor(ty, in_crate) {
707 match fundamental_ty_inner_tys(tcx, ty) {
709 inner_tys.flat_map(|ty| contained_non_local_types(tcx, ty, in_crate)).collect()
716 /// For `#[fundamental]` ADTs and `&T` / `&mut T`, returns `Some` with the
717 /// type parameters of the ADT, or `T`, respectively. For non-fundamental
718 /// types, returns `None`.
719 fn fundamental_ty_inner_tys<'tcx>(
722 ) -> Option<impl Iterator<Item = Ty<'tcx>>> {
723 let (first_ty, rest_tys) = match *ty.kind() {
724 ty::Ref(_, ty, _) => (ty, ty::subst::InternalSubsts::empty().types()),
725 ty::Adt(def, substs) if def.is_fundamental() => {
726 let mut types = substs.types();
728 // FIXME(eddyb) actually validate `#[fundamental]` up-front.
732 tcx.def_span(def.did()),
733 "`#[fundamental]` requires at least one type parameter",
739 Some(first_ty) => (first_ty, types),
745 Some(iter::once(first_ty).chain(rest_tys))
748 fn def_id_is_local(def_id: DefId, in_crate: InCrate) -> bool {
750 // The type is local to *this* crate - it will not be
751 // local in any other crate.
752 InCrate::Remote => false,
753 InCrate::Local => def_id.is_local(),
757 fn ty_is_local_constructor(ty: Ty<'_>, in_crate: InCrate) -> bool {
758 debug!("ty_is_local_constructor({:?})", ty);
776 | ty::Projection(..) => false,
778 ty::Placeholder(..) | ty::Bound(..) | ty::Infer(..) => match in_crate {
779 InCrate::Local => false,
780 // The inference variable might be unified with a local
781 // type in that remote crate.
782 InCrate::Remote => true,
785 ty::Adt(def, _) => def_id_is_local(def.did(), in_crate),
786 ty::Foreign(did) => def_id_is_local(did, in_crate),
788 // This merits some explanation.
789 // Normally, opaque types are not involed when performing
790 // coherence checking, since it is illegal to directly
791 // implement a trait on an opaque type. However, we might
792 // end up looking at an opaque type during coherence checking
793 // if an opaque type gets used within another type (e.g. as
794 // a type parameter). This requires us to decide whether or
795 // not an opaque type should be considered 'local' or not.
797 // We choose to treat all opaque types as non-local, even
798 // those that appear within the same crate. This seems
799 // somewhat surprising at first, but makes sense when
800 // you consider that opaque types are supposed to hide
801 // the underlying type *within the same crate*. When an
802 // opaque type is used from outside the module
803 // where it is declared, it should be impossible to observe
804 // anything about it other than the traits that it implements.
806 // The alternative would be to look at the underlying type
807 // to determine whether or not the opaque type itself should
808 // be considered local. However, this could make it a breaking change
809 // to switch the underlying ('defining') type from a local type
810 // to a remote type. This would violate the rule that opaque
811 // types should be completely opaque apart from the traits
812 // that they implement, so we don't use this behavior.
817 // Similar to the `Opaque` case (#83613).
821 ty::Dynamic(ref tt, ..) => {
822 if let Some(principal) = tt.principal() {
823 def_id_is_local(principal.def_id(), in_crate)
829 ty::Error(_) => true,
831 ty::Generator(..) | ty::GeneratorWitness(..) => {
832 bug!("ty_is_local invoked on unexpected type: {:?}", ty)