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_subject_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::{InferCtxt, TyCtxtInferExt};
21 use rustc_infer::traits::{util, TraitEngine};
22 use rustc_middle::traits::specialization_graph::OverlapMode;
23 use rustc_middle::ty::fast_reject::{self, TreatParams};
24 use rustc_middle::ty::fold::TypeFoldable;
25 use rustc_middle::ty::subst::Subst;
26 use rustc_middle::ty::{self, ImplSubject, Ty, TyCtxt};
27 use rustc_span::symbol::sym;
28 use rustc_span::DUMMY_SP;
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: Vec<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 impl1_ref = tcx.impl_trait_ref(impl1_def_id);
83 let impl2_ref = tcx.impl_trait_ref(impl2_def_id);
85 // Check if any of the input types definitely do not unify.
87 impl1_ref.iter().flat_map(|tref| tref.substs.types()),
88 impl2_ref.iter().flat_map(|tref| tref.substs.types()),
91 let t1 = fast_reject::simplify_type(tcx, ty1, TreatParams::AsPlaceholders);
92 let t2 = fast_reject::simplify_type(tcx, ty2, TreatParams::AsPlaceholders);
94 if let (Some(t1), Some(t2)) = (t1, t2) {
95 // Simplified successfully
102 // Some types involved are definitely different, so the impls couldn't possibly overlap.
103 debug!("overlapping_impls: fast_reject early-exit");
107 let overlaps = tcx.infer_ctxt().enter(|infcx| {
108 let selcx = &mut SelectionContext::intercrate(&infcx);
109 overlap(selcx, skip_leak_check, impl1_def_id, impl2_def_id, overlap_mode).is_some()
116 // In the case where we detect an error, run the check again, but
117 // this time tracking intercrate ambiguity causes for better
118 // diagnostics. (These take time and can lead to false errors.)
119 tcx.infer_ctxt().enter(|infcx| {
120 let selcx = &mut SelectionContext::intercrate(&infcx);
121 selcx.enable_tracking_intercrate_ambiguity_causes();
123 overlap(selcx, skip_leak_check, impl1_def_id, impl2_def_id, overlap_mode).unwrap(),
128 fn with_fresh_ty_vars<'cx, 'tcx>(
129 selcx: &mut SelectionContext<'cx, 'tcx>,
130 param_env: ty::ParamEnv<'tcx>,
132 ) -> ty::ImplHeader<'tcx> {
133 let tcx = selcx.tcx();
134 let impl_substs = selcx.infcx().fresh_substs_for_item(DUMMY_SP, impl_def_id);
136 let header = ty::ImplHeader {
138 self_ty: tcx.type_of(impl_def_id).subst(tcx, impl_substs),
139 trait_ref: tcx.impl_trait_ref(impl_def_id).subst(tcx, impl_substs),
140 predicates: tcx.predicates_of(impl_def_id).instantiate(tcx, impl_substs).predicates,
143 let Normalized { value: mut header, obligations } =
144 traits::normalize(selcx, param_env, ObligationCause::dummy(), header);
146 header.predicates.extend(obligations.into_iter().map(|o| o.predicate));
150 /// Can both impl `a` and impl `b` be satisfied by a common type (including
151 /// where-clauses)? If so, returns an `ImplHeader` that unifies the two impls.
152 fn overlap<'cx, 'tcx>(
153 selcx: &mut SelectionContext<'cx, 'tcx>,
154 skip_leak_check: SkipLeakCheck,
157 overlap_mode: OverlapMode,
158 ) -> Option<OverlapResult<'tcx>> {
160 "overlap(impl1_def_id={:?}, impl2_def_id={:?}, overlap_mode={:?})",
161 impl1_def_id, impl2_def_id, overlap_mode
164 selcx.infcx().probe_maybe_skip_leak_check(skip_leak_check.is_yes(), |snapshot| {
165 overlap_within_probe(selcx, impl1_def_id, impl2_def_id, overlap_mode, snapshot)
169 fn overlap_within_probe<'cx, 'tcx>(
170 selcx: &mut SelectionContext<'cx, 'tcx>,
173 overlap_mode: OverlapMode,
174 snapshot: &CombinedSnapshot<'_, 'tcx>,
175 ) -> Option<OverlapResult<'tcx>> {
176 let infcx = selcx.infcx();
178 if overlap_mode.use_negative_impl() {
179 if negative_impl(selcx, impl1_def_id, impl2_def_id)
180 || negative_impl(selcx, impl2_def_id, impl1_def_id)
186 // For the purposes of this check, we don't bring any placeholder
187 // types into scope; instead, we replace the generic types with
188 // fresh type variables, and hence we do our evaluations in an
189 // empty environment.
190 let param_env = ty::ParamEnv::empty();
192 let impl1_header = with_fresh_ty_vars(selcx, param_env, impl1_def_id);
193 let impl2_header = with_fresh_ty_vars(selcx, param_env, impl2_def_id);
195 let obligations = equate_impl_headers(selcx, &impl1_header, &impl2_header)?;
196 debug!("overlap: unification check succeeded");
198 if overlap_mode.use_implicit_negative() {
199 if implicit_negative(selcx, param_env, &impl1_header, impl2_header, obligations) {
204 // We disable the leak when when creating the `snapshot` by using
205 // `infcx.probe_maybe_disable_leak_check`.
206 if infcx.leak_check(true, snapshot).is_err() {
207 debug!("overlap: leak check failed");
211 let intercrate_ambiguity_causes = selcx.take_intercrate_ambiguity_causes();
212 debug!("overlap: intercrate_ambiguity_causes={:#?}", intercrate_ambiguity_causes);
214 let involves_placeholder =
215 matches!(selcx.infcx().region_constraints_added_in_snapshot(snapshot), Some(true));
217 let impl_header = selcx.infcx().resolve_vars_if_possible(impl1_header);
218 Some(OverlapResult { impl_header, intercrate_ambiguity_causes, involves_placeholder })
221 fn equate_impl_headers<'cx, 'tcx>(
222 selcx: &mut SelectionContext<'cx, 'tcx>,
223 impl1_header: &ty::ImplHeader<'tcx>,
224 impl2_header: &ty::ImplHeader<'tcx>,
225 ) -> Option<PredicateObligations<'tcx>> {
226 // Do `a` and `b` unify? If not, no overlap.
227 debug!("equate_impl_headers(impl1_header={:?}, impl2_header={:?}", impl1_header, impl2_header);
230 .at(&ObligationCause::dummy(), ty::ParamEnv::empty())
231 .eq_impl_headers(impl1_header, impl2_header)
232 .map(|infer_ok| infer_ok.obligations)
236 /// Given impl1 and impl2 check if both impls can be satisfied by a common type (including
237 /// where-clauses) If so, return false, otherwise return true, they are disjoint.
238 fn implicit_negative<'cx, 'tcx>(
239 selcx: &mut SelectionContext<'cx, 'tcx>,
240 param_env: ty::ParamEnv<'tcx>,
241 impl1_header: &ty::ImplHeader<'tcx>,
242 impl2_header: ty::ImplHeader<'tcx>,
243 obligations: PredicateObligations<'tcx>,
245 // There's no overlap if obligations are unsatisfiable or if the obligation negated is
248 // For example, given these two impl headers:
250 // `impl<'a> From<&'a str> for Box<dyn Error>`
251 // `impl<E> From<E> for Box<dyn Error> where E: Error`
255 // `Box<dyn Error>: From<&'?a str>`
256 // `Box<dyn Error>: From<?E>`
258 // After equating the two headers:
260 // `Box<dyn Error> = Box<dyn Error>`
261 // So, `?E = &'?a str` and then given the where clause `&'?a str: Error`.
263 // If the obligation `&'?a str: Error` holds, it means that there's overlap. If that doesn't
264 // hold we need to check if `&'?a str: !Error` holds, if doesn't hold there's overlap because
265 // at some point an impl for `&'?a str: Error` could be added.
267 "implicit_negative(impl1_header={:?}, impl2_header={:?}, obligations={:?})",
268 impl1_header, impl2_header, obligations
270 let infcx = selcx.infcx();
271 let opt_failing_obligation = impl1_header
275 .chain(impl2_header.predicates)
276 .map(|p| infcx.resolve_vars_if_possible(p))
277 .map(|p| Obligation {
278 cause: ObligationCause::dummy(),
284 .find(|o| !selcx.predicate_may_hold_fatal(o));
286 if let Some(failing_obligation) = opt_failing_obligation {
287 debug!("overlap: obligation unsatisfiable {:?}", failing_obligation);
294 /// Given impl1 and impl2 check if both impls are never satisfied by a common type (including
295 /// where-clauses) If so, return true, they are disjoint and false otherwise.
296 fn negative_impl<'cx, 'tcx>(
297 selcx: &mut SelectionContext<'cx, 'tcx>,
301 debug!("negative_impl(impl1_def_id={:?}, impl2_def_id={:?})", impl1_def_id, impl2_def_id);
302 let tcx = selcx.infcx().tcx;
304 // Create an infcx, taking the predicates of impl1 as assumptions:
305 tcx.infer_ctxt().enter(|infcx| {
306 // create a parameter environment corresponding to a (placeholder) instantiation of impl1
307 let impl_env = tcx.param_env(impl1_def_id);
308 let subject1 = match traits::fully_normalize(
310 FulfillmentContext::new(),
311 ObligationCause::dummy(),
313 tcx.impl_subject(impl1_def_id),
316 Err(err) => bug!("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, impl1_def_id, subject1, subject2, obligations)
329 fn equate<'cx, 'tcx>(
330 infcx: &InferCtxt<'cx, 'tcx>,
331 impl_env: ty::ParamEnv<'tcx>,
333 subject1: ImplSubject<'tcx>,
334 subject2: ImplSubject<'tcx>,
335 obligations: impl Iterator<Item = PredicateObligation<'tcx>>,
337 // do the impls unify? If not, not disjoint.
338 let Ok(InferOk { obligations: more_obligations, .. }) =
339 infcx.at(&ObligationCause::dummy(), impl_env).eq(subject1, subject2)
341 debug!("explicit_disjoint: {:?} does not unify with {:?}", subject1, subject2);
345 let selcx = &mut SelectionContext::new(&infcx);
346 let opt_failing_obligation = obligations
348 .chain(more_obligations)
349 .find(|o| negative_impl_exists(selcx, impl_env, impl1_def_id, o));
351 if let Some(failing_obligation) = opt_failing_obligation {
352 debug!("overlap: obligation unsatisfiable {:?}", failing_obligation);
359 /// Try to prove that a negative impl exist for the given obligation and its super predicates.
360 #[instrument(level = "debug", skip(selcx))]
361 fn negative_impl_exists<'cx, 'tcx>(
362 selcx: &SelectionContext<'cx, 'tcx>,
363 param_env: ty::ParamEnv<'tcx>,
364 region_context: DefId,
365 o: &PredicateObligation<'tcx>,
367 let infcx = &selcx.infcx().fork();
369 if resolve_negative_obligation(infcx, param_env, region_context, o) {
373 // Try to prove a negative obligation exists for super predicates
374 for o in util::elaborate_predicates(infcx.tcx, iter::once(o.predicate)) {
375 if resolve_negative_obligation(infcx, param_env, region_context, &o) {
383 #[instrument(level = "debug", skip(infcx))]
384 fn resolve_negative_obligation<'cx, 'tcx>(
385 infcx: &InferCtxt<'cx, 'tcx>,
386 param_env: ty::ParamEnv<'tcx>,
387 region_context: DefId,
388 o: &PredicateObligation<'tcx>,
392 let Some(o) = o.flip_polarity(tcx) else {
396 let mut fulfillment_cx = FulfillmentContext::new();
397 fulfillment_cx.register_predicate_obligation(infcx, o);
399 let errors = fulfillment_cx.select_all_or_error(infcx);
401 if !errors.is_empty() {
405 let mut outlives_env = OutlivesEnvironment::new(param_env);
406 // FIXME -- add "assumed to be well formed" types into the `outlives_env`
408 // "Save" the accumulated implied bounds into the outlives environment
409 // (due to the FIXME above, there aren't any, but this step is still needed).
410 // The "body id" is given as `CRATE_HIR_ID`, which is the same body-id used
411 // by the "dummy" causes elsewhere (body-id is only relevant when checking
412 // function bodies with closures).
413 outlives_env.save_implied_bounds(CRATE_HIR_ID);
415 infcx.process_registered_region_obligations(
416 outlives_env.region_bound_pairs_map(),
417 Some(tcx.lifetimes.re_root_empty),
421 let errors = infcx.resolve_regions(region_context, &outlives_env, RegionckMode::default());
423 if !errors.is_empty() {
430 pub fn trait_ref_is_knowable<'tcx>(
432 trait_ref: ty::TraitRef<'tcx>,
433 ) -> Option<Conflict> {
434 debug!("trait_ref_is_knowable(trait_ref={:?})", trait_ref);
435 if orphan_check_trait_ref(tcx, trait_ref, InCrate::Remote).is_ok() {
436 // A downstream or cousin crate is allowed to implement some
437 // substitution of this trait-ref.
438 return Some(Conflict::Downstream);
441 if trait_ref_is_local_or_fundamental(tcx, trait_ref) {
442 // This is a local or fundamental trait, so future-compatibility
443 // is no concern. We know that downstream/cousin crates are not
444 // allowed to implement a substitution of this trait ref, which
445 // means impls could only come from dependencies of this crate,
446 // which we already know about.
450 // This is a remote non-fundamental trait, so if another crate
451 // can be the "final owner" of a substitution of this trait-ref,
452 // they are allowed to implement it future-compatibly.
454 // However, if we are a final owner, then nobody else can be,
455 // and if we are an intermediate owner, then we don't care
456 // about future-compatibility, which means that we're OK if
458 if orphan_check_trait_ref(tcx, trait_ref, InCrate::Local).is_ok() {
459 debug!("trait_ref_is_knowable: orphan check passed");
462 debug!("trait_ref_is_knowable: nonlocal, nonfundamental, unowned");
463 Some(Conflict::Upstream)
467 pub fn trait_ref_is_local_or_fundamental<'tcx>(
469 trait_ref: ty::TraitRef<'tcx>,
471 trait_ref.def_id.krate == LOCAL_CRATE || tcx.has_attr(trait_ref.def_id, sym::fundamental)
474 pub enum OrphanCheckErr<'tcx> {
475 NonLocalInputType(Vec<(Ty<'tcx>, bool /* Is this the first input type? */)>),
476 UncoveredTy(Ty<'tcx>, Option<Ty<'tcx>>),
479 /// Checks the coherence orphan rules. `impl_def_id` should be the
480 /// `DefId` of a trait impl. To pass, either the trait must be local, or else
481 /// two conditions must be satisfied:
483 /// 1. All type parameters in `Self` must be "covered" by some local type constructor.
484 /// 2. Some local type must appear in `Self`.
485 pub fn orphan_check(tcx: TyCtxt<'_>, impl_def_id: DefId) -> Result<(), OrphanCheckErr<'_>> {
486 debug!("orphan_check({:?})", impl_def_id);
488 // We only except this routine to be invoked on implementations
489 // of a trait, not inherent implementations.
490 let trait_ref = tcx.impl_trait_ref(impl_def_id).unwrap();
491 debug!("orphan_check: trait_ref={:?}", trait_ref);
493 // If the *trait* is local to the crate, ok.
494 if trait_ref.def_id.is_local() {
495 debug!("trait {:?} is local to current crate", trait_ref.def_id);
499 orphan_check_trait_ref(tcx, trait_ref, InCrate::Local)
502 /// Checks whether a trait-ref is potentially implementable by a crate.
504 /// The current rule is that a trait-ref orphan checks in a crate C:
506 /// 1. Order the parameters in the trait-ref in subst order - Self first,
507 /// others linearly (e.g., `<U as Foo<V, W>>` is U < V < W).
508 /// 2. Of these type parameters, there is at least one type parameter
509 /// in which, walking the type as a tree, you can reach a type local
510 /// to C where all types in-between are fundamental types. Call the
511 /// first such parameter the "local key parameter".
512 /// - e.g., `Box<LocalType>` is OK, because you can visit LocalType
513 /// going through `Box`, which is fundamental.
514 /// - similarly, `FundamentalPair<Vec<()>, Box<LocalType>>` is OK for
516 /// - but (knowing that `Vec<T>` is non-fundamental, and assuming it's
517 /// not local), `Vec<LocalType>` is bad, because `Vec<->` is between
518 /// the local type and the type parameter.
519 /// 3. Before this local type, no generic type parameter of the impl must
520 /// be reachable through fundamental types.
521 /// - e.g. `impl<T> Trait<LocalType> for Vec<T>` is fine, as `Vec` is not fundamental.
522 /// - while `impl<T> Trait<LocalType for Box<T>` results in an error, as `T` is
523 /// reachable through the fundamental type `Box`.
524 /// 4. Every type in the local key parameter not known in C, going
525 /// through the parameter's type tree, must appear only as a subtree of
526 /// a type local to C, with only fundamental types between the type
527 /// local to C and the local key parameter.
528 /// - e.g., `Vec<LocalType<T>>>` (or equivalently `Box<Vec<LocalType<T>>>`)
529 /// is bad, because the only local type with `T` as a subtree is
530 /// `LocalType<T>`, and `Vec<->` is between it and the type parameter.
531 /// - similarly, `FundamentalPair<LocalType<T>, T>` is bad, because
532 /// the second occurrence of `T` is not a subtree of *any* local type.
533 /// - however, `LocalType<Vec<T>>` is OK, because `T` is a subtree of
534 /// `LocalType<Vec<T>>`, which is local and has no types between it and
535 /// the type parameter.
537 /// The orphan rules actually serve several different purposes:
539 /// 1. They enable link-safety - i.e., 2 mutually-unknowing crates (where
540 /// every type local to one crate is unknown in the other) can't implement
541 /// the same trait-ref. This follows because it can be seen that no such
542 /// type can orphan-check in 2 such crates.
544 /// To check that a local impl follows the orphan rules, we check it in
545 /// InCrate::Local mode, using type parameters for the "generic" types.
547 /// 2. They ground negative reasoning for coherence. If a user wants to
548 /// write both a conditional blanket impl and a specific impl, we need to
549 /// make sure they do not overlap. For example, if we write
551 /// impl<T> IntoIterator for Vec<T>
552 /// impl<T: Iterator> IntoIterator for T
554 /// We need to be able to prove that `Vec<$0>: !Iterator` for every type $0.
555 /// We can observe that this holds in the current crate, but we need to make
556 /// sure this will also hold in all unknown crates (both "independent" crates,
557 /// which we need for link-safety, and also child crates, because we don't want
558 /// child crates to get error for impl conflicts in a *dependency*).
560 /// For that, we only allow negative reasoning if, for every assignment to the
561 /// inference variables, every unknown crate would get an orphan error if they
562 /// try to implement this trait-ref. To check for this, we use InCrate::Remote
563 /// mode. That is sound because we already know all the impls from known crates.
565 /// 3. For non-`#[fundamental]` traits, they guarantee that parent crates can
566 /// add "non-blanket" impls without breaking negative reasoning in dependent
567 /// crates. This is the "rebalancing coherence" (RFC 1023) restriction.
569 /// For that, we only a allow crate to perform negative reasoning on
570 /// non-local-non-`#[fundamental]` only if there's a local key parameter as per (2).
572 /// Because we never perform negative reasoning generically (coherence does
573 /// not involve type parameters), this can be interpreted as doing the full
574 /// orphan check (using InCrate::Local mode), substituting non-local known
575 /// types for all inference variables.
577 /// This allows for crates to future-compatibly add impls as long as they
578 /// can't apply to types with a key parameter in a child crate - applying
579 /// the rules, this basically means that every type parameter in the impl
580 /// must appear behind a non-fundamental type (because this is not a
581 /// type-system requirement, crate owners might also go for "semantic
582 /// future-compatibility" involving things such as sealed traits, but
583 /// the above requirement is sufficient, and is necessary in "open world"
586 /// Note that this function is never called for types that have both type
587 /// parameters and inference variables.
588 fn orphan_check_trait_ref<'tcx>(
590 trait_ref: ty::TraitRef<'tcx>,
592 ) -> Result<(), OrphanCheckErr<'tcx>> {
593 debug!("orphan_check_trait_ref(trait_ref={:?}, in_crate={:?})", trait_ref, in_crate);
595 if trait_ref.needs_infer() && trait_ref.needs_subst() {
597 "can't orphan check a trait ref with both params and inference variables {:?}",
602 // Given impl<P1..=Pn> Trait<T1..=Tn> for T0, an impl is valid only
603 // if at least one of the following is true:
605 // - Trait is a local trait
606 // (already checked in orphan_check prior to calling this function)
608 // - At least one of the types T0..=Tn must be a local type.
609 // Let Ti be the first such type.
610 // - No uncovered type parameters P1..=Pn may appear in T0..Ti (excluding Ti)
612 fn uncover_fundamental_ty<'tcx>(
617 // FIXME: this is currently somewhat overly complicated,
618 // but fixing this requires a more complicated refactor.
619 if !contained_non_local_types(tcx, ty, in_crate).is_empty() {
620 if let Some(inner_tys) = fundamental_ty_inner_tys(tcx, ty) {
622 .flat_map(|ty| uncover_fundamental_ty(tcx, ty, in_crate))
630 let mut non_local_spans = vec![];
631 for (i, input_ty) in trait_ref
634 .flat_map(|ty| uncover_fundamental_ty(tcx, ty, in_crate))
637 debug!("orphan_check_trait_ref: check ty `{:?}`", input_ty);
638 let non_local_tys = contained_non_local_types(tcx, input_ty, in_crate);
639 if non_local_tys.is_empty() {
640 debug!("orphan_check_trait_ref: ty_is_local `{:?}`", input_ty);
642 } else if let ty::Param(_) = input_ty.kind() {
643 debug!("orphan_check_trait_ref: uncovered ty: `{:?}`", input_ty);
644 let local_type = trait_ref
647 .flat_map(|ty| uncover_fundamental_ty(tcx, ty, in_crate))
648 .find(|ty| ty_is_local_constructor(*ty, in_crate));
650 debug!("orphan_check_trait_ref: uncovered ty local_type: `{:?}`", local_type);
652 return Err(OrphanCheckErr::UncoveredTy(input_ty, local_type));
655 non_local_spans.extend(non_local_tys.into_iter().map(|input_ty| (input_ty, i == 0)));
657 // If we exit above loop, never found a local type.
658 debug!("orphan_check_trait_ref: no local type");
659 Err(OrphanCheckErr::NonLocalInputType(non_local_spans))
662 /// Returns a list of relevant non-local types for `ty`.
664 /// This is just `ty` itself unless `ty` is `#[fundamental]`,
665 /// in which case we recursively look into this type.
667 /// If `ty` is local itself, this method returns an empty `Vec`.
671 /// - `u32` is not local, so this returns `[u32]`.
672 /// - for `Foo<u32>`, where `Foo` is a local type, this returns `[]`.
673 /// - `&mut u32` returns `[u32]`, as `&mut` is a fundamental type, similar to `Box`.
674 /// - `Box<Foo<u32>>` returns `[]`, as `Box` is a fundamental type and `Foo` is local.
675 fn contained_non_local_types<'tcx>(
680 if ty_is_local_constructor(ty, in_crate) {
683 match fundamental_ty_inner_tys(tcx, ty) {
685 inner_tys.flat_map(|ty| contained_non_local_types(tcx, ty, in_crate)).collect()
692 /// For `#[fundamental]` ADTs and `&T` / `&mut T`, returns `Some` with the
693 /// type parameters of the ADT, or `T`, respectively. For non-fundamental
694 /// types, returns `None`.
695 fn fundamental_ty_inner_tys<'tcx>(
698 ) -> Option<impl Iterator<Item = Ty<'tcx>>> {
699 let (first_ty, rest_tys) = match *ty.kind() {
700 ty::Ref(_, ty, _) => (ty, ty::subst::InternalSubsts::empty().types()),
701 ty::Adt(def, substs) if def.is_fundamental() => {
702 let mut types = substs.types();
704 // FIXME(eddyb) actually validate `#[fundamental]` up-front.
708 tcx.def_span(def.did()),
709 "`#[fundamental]` requires at least one type parameter",
715 Some(first_ty) => (first_ty, types),
721 Some(iter::once(first_ty).chain(rest_tys))
724 fn def_id_is_local(def_id: DefId, in_crate: InCrate) -> bool {
726 // The type is local to *this* crate - it will not be
727 // local in any other crate.
728 InCrate::Remote => false,
729 InCrate::Local => def_id.is_local(),
733 fn ty_is_local_constructor(ty: Ty<'_>, in_crate: InCrate) -> bool {
734 debug!("ty_is_local_constructor({:?})", ty);
752 | ty::Projection(..) => false,
754 ty::Placeholder(..) | ty::Bound(..) | ty::Infer(..) => match in_crate {
755 InCrate::Local => false,
756 // The inference variable might be unified with a local
757 // type in that remote crate.
758 InCrate::Remote => true,
761 ty::Adt(def, _) => def_id_is_local(def.did(), in_crate),
762 ty::Foreign(did) => def_id_is_local(did, in_crate),
764 // This merits some explanation.
765 // Normally, opaque types are not involved when performing
766 // coherence checking, since it is illegal to directly
767 // implement a trait on an opaque type. However, we might
768 // end up looking at an opaque type during coherence checking
769 // if an opaque type gets used within another type (e.g. as
770 // a type parameter). This requires us to decide whether or
771 // not an opaque type should be considered 'local' or not.
773 // We choose to treat all opaque types as non-local, even
774 // those that appear within the same crate. This seems
775 // somewhat surprising at first, but makes sense when
776 // you consider that opaque types are supposed to hide
777 // the underlying type *within the same crate*. When an
778 // opaque type is used from outside the module
779 // where it is declared, it should be impossible to observe
780 // anything about it other than the traits that it implements.
782 // The alternative would be to look at the underlying type
783 // to determine whether or not the opaque type itself should
784 // be considered local. However, this could make it a breaking change
785 // to switch the underlying ('defining') type from a local type
786 // to a remote type. This would violate the rule that opaque
787 // types should be completely opaque apart from the traits
788 // that they implement, so we don't use this behavior.
793 // Similar to the `Opaque` case (#83613).
797 ty::Dynamic(ref tt, ..) => {
798 if let Some(principal) = tt.principal() {
799 def_id_is_local(principal.def_id(), in_crate)
805 ty::Error(_) => true,
807 ty::Generator(..) | ty::GeneratorWitness(..) => {
808 bug!("ty_is_local invoked on unexpected type: {:?}", ty)