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::{CombinedSnapshot, InferOk, TyCtxtInferExt};
8 use crate::traits::query::evaluate_obligation::InferCtxtExt;
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_ast::Attribute;
17 use rustc_hir::def_id::{DefId, LOCAL_CRATE};
18 use rustc_middle::ty::fast_reject::{self, SimplifyParams, StripReferences};
19 use rustc_middle::ty::fold::TypeFoldable;
20 use rustc_middle::ty::subst::Subst;
21 use rustc_middle::ty::{self, Ty, TyCtxt};
22 use rustc_span::symbol::sym;
23 use rustc_span::DUMMY_SP;
26 /// Whether we do the orphan check relative to this crate or
27 /// to some remote crate.
28 #[derive(Copy, Clone, Debug)]
34 #[derive(Debug, Copy, Clone)]
40 pub struct OverlapResult<'tcx> {
41 pub impl_header: ty::ImplHeader<'tcx>,
42 pub intercrate_ambiguity_causes: Vec<IntercrateAmbiguityCause>,
44 /// `true` if the overlap might've been permitted before the shift
46 pub involves_placeholder: bool,
49 pub fn add_placeholder_note(err: &mut rustc_errors::DiagnosticBuilder<'_>) {
51 "this behavior recently changed as a result of a bug fix; \
52 see rust-lang/rust#56105 for details",
56 /// If there are types that satisfy both impls, invokes `on_overlap`
57 /// with a suitably-freshened `ImplHeader` with those types
58 /// substituted. Otherwise, invokes `no_overlap`.
59 #[instrument(skip(tcx, skip_leak_check, on_overlap, no_overlap), level = "debug")]
60 pub fn overlapping_impls<F1, F2, R>(
64 skip_leak_check: SkipLeakCheck,
69 F1: FnOnce(OverlapResult<'_>) -> R,
72 // Before doing expensive operations like entering an inference context, do
73 // a quick check via fast_reject to tell if the impl headers could possibly
75 let impl1_ref = tcx.impl_trait_ref(impl1_def_id);
76 let impl2_ref = tcx.impl_trait_ref(impl2_def_id);
78 // Check if any of the input types definitely do not unify.
80 impl1_ref.iter().flat_map(|tref| tref.substs.types()),
81 impl2_ref.iter().flat_map(|tref| tref.substs.types()),
84 let t1 = fast_reject::simplify_type(tcx, ty1, SimplifyParams::No, StripReferences::No);
85 let t2 = fast_reject::simplify_type(tcx, ty2, SimplifyParams::No, StripReferences::No);
87 if let (Some(t1), Some(t2)) = (t1, t2) {
88 // Simplified successfully
95 // Some types involved are definitely different, so the impls couldn't possibly overlap.
96 debug!("overlapping_impls: fast_reject early-exit");
100 let overlaps = tcx.infer_ctxt().enter(|infcx| {
101 let selcx = &mut SelectionContext::intercrate(&infcx);
102 overlap(selcx, skip_leak_check, impl1_def_id, impl2_def_id).is_some()
109 // In the case where we detect an error, run the check again, but
110 // this time tracking intercrate ambuiguity causes for better
111 // diagnostics. (These take time and can lead to false errors.)
112 tcx.infer_ctxt().enter(|infcx| {
113 let selcx = &mut SelectionContext::intercrate(&infcx);
114 selcx.enable_tracking_intercrate_ambiguity_causes();
115 on_overlap(overlap(selcx, skip_leak_check, impl1_def_id, impl2_def_id).unwrap())
119 fn with_fresh_ty_vars<'cx, 'tcx>(
120 selcx: &mut SelectionContext<'cx, 'tcx>,
121 param_env: ty::ParamEnv<'tcx>,
123 ) -> ty::ImplHeader<'tcx> {
124 let tcx = selcx.tcx();
125 let impl_substs = selcx.infcx().fresh_substs_for_item(DUMMY_SP, impl_def_id);
127 let header = ty::ImplHeader {
129 self_ty: tcx.type_of(impl_def_id).subst(tcx, impl_substs),
130 trait_ref: tcx.impl_trait_ref(impl_def_id).subst(tcx, impl_substs),
131 predicates: tcx.predicates_of(impl_def_id).instantiate(tcx, impl_substs).predicates,
134 let Normalized { value: mut header, obligations } =
135 traits::normalize(selcx, param_env, ObligationCause::dummy(), header);
137 header.predicates.extend(obligations.into_iter().map(|o| o.predicate));
141 /// What kind of overlap check are we doing -- this exists just for testing and feature-gating
143 #[derive(Copy, Clone, PartialEq, Eq, Hash, Debug)]
145 /// The 1.0 rules (either types fail to unify, or where clauses are not implemented for crate-local types)
147 /// Feature-gated test: Stable, *or* there is an explicit negative impl that rules out one of the where-clauses.
149 /// Just check for negative impls, not for "where clause not implemented": used for testing.
154 fn use_negative_impl(&self) -> bool {
155 *self == OverlapMode::Strict || *self == OverlapMode::WithNegative
158 fn use_implicit_negative(&self) -> bool {
159 *self == OverlapMode::Stable || *self == OverlapMode::WithNegative
163 fn overlap_mode<'tcx>(tcx: TyCtxt<'tcx>, impl1_def_id: DefId, impl2_def_id: DefId) -> OverlapMode {
164 // Find the possible coherence mode override opt-in attributes for each `DefId`
165 let find_coherence_attr = |attr: &Attribute| {
166 let name = attr.name_or_empty();
168 sym::rustc_with_negative_coherence | sym::rustc_strict_coherence => Some(name),
172 let impl1_coherence_mode = tcx.get_attrs(impl1_def_id).iter().find_map(find_coherence_attr);
173 let impl2_coherence_mode = tcx.get_attrs(impl2_def_id).iter().find_map(find_coherence_attr);
175 // If there are any (that currently happens in tests), they need to match. Otherwise, the
176 // default 1.0 rules are used.
177 match (impl1_coherence_mode, impl2_coherence_mode) {
178 (None, None) => OverlapMode::Stable,
179 (Some(sym::rustc_with_negative_coherence), Some(sym::rustc_with_negative_coherence)) => {
180 OverlapMode::WithNegative
182 (Some(sym::rustc_strict_coherence), Some(sym::rustc_strict_coherence)) => {
185 (Some(mode), _) | (_, Some(mode)) => {
186 bug!("Use the same coherence mode on both impls: {}", mode)
191 /// Can both impl `a` and impl `b` be satisfied by a common type (including
192 /// where-clauses)? If so, returns an `ImplHeader` that unifies the two impls.
193 fn overlap<'cx, 'tcx>(
194 selcx: &mut SelectionContext<'cx, 'tcx>,
195 skip_leak_check: SkipLeakCheck,
198 ) -> Option<OverlapResult<'tcx>> {
199 debug!("overlap(impl1_def_id={:?}, impl2_def_id={:?})", impl1_def_id, impl2_def_id);
201 selcx.infcx().probe_maybe_skip_leak_check(skip_leak_check.is_yes(), |snapshot| {
202 overlap_within_probe(selcx, skip_leak_check, impl1_def_id, impl2_def_id, snapshot)
206 fn overlap_within_probe<'cx, 'tcx>(
207 selcx: &mut SelectionContext<'cx, 'tcx>,
208 skip_leak_check: SkipLeakCheck,
211 snapshot: &CombinedSnapshot<'_, 'tcx>,
212 ) -> Option<OverlapResult<'tcx>> {
213 let infcx = selcx.infcx();
216 let overlap_mode = overlap_mode(tcx, impl1_def_id, impl2_def_id);
218 if overlap_mode.use_negative_impl() {
219 if negative_impl(selcx, impl1_def_id, impl2_def_id)
220 || negative_impl(selcx, impl2_def_id, impl1_def_id)
226 // For the purposes of this check, we don't bring any placeholder
227 // types into scope; instead, we replace the generic types with
228 // fresh type variables, and hence we do our evaluations in an
229 // empty environment.
230 let param_env = ty::ParamEnv::empty();
232 let impl1_header = with_fresh_ty_vars(selcx, param_env, impl1_def_id);
233 let impl2_header = with_fresh_ty_vars(selcx, param_env, impl2_def_id);
235 debug!("overlap: impl1_header={:?}", impl1_header);
236 debug!("overlap: impl2_header={:?}", impl2_header);
238 let obligations = equate_impl_headers(selcx, &impl1_header, &impl2_header)?;
239 debug!("overlap: unification check succeeded");
241 if overlap_mode.use_implicit_negative() {
242 if implicit_negative(selcx, param_env, &impl1_header, impl2_header, obligations) {
247 if !skip_leak_check.is_yes() {
248 if infcx.leak_check(true, snapshot).is_err() {
249 debug!("overlap: leak check failed");
254 let intercrate_ambiguity_causes = selcx.take_intercrate_ambiguity_causes();
255 debug!("overlap: intercrate_ambiguity_causes={:#?}", intercrate_ambiguity_causes);
257 let involves_placeholder =
258 matches!(selcx.infcx().region_constraints_added_in_snapshot(snapshot), Some(true));
260 let impl_header = selcx.infcx().resolve_vars_if_possible(impl1_header);
261 Some(OverlapResult { impl_header, intercrate_ambiguity_causes, involves_placeholder })
264 fn equate_impl_headers<'cx, 'tcx>(
265 selcx: &mut SelectionContext<'cx, 'tcx>,
266 impl1_header: &ty::ImplHeader<'tcx>,
267 impl2_header: &ty::ImplHeader<'tcx>,
268 ) -> Option<PredicateObligations<'tcx>> {
269 // Do `a` and `b` unify? If not, no overlap.
272 .at(&ObligationCause::dummy(), ty::ParamEnv::empty())
273 .eq_impl_headers(impl1_header, impl2_header)
274 .map(|infer_ok| infer_ok.obligations)
278 /// Given impl1 and impl2 check if both impls can be satisfied by a common type (including
279 /// where-clauses) If so, return false, otherwise return true, they are disjoint.
280 fn implicit_negative<'cx, 'tcx>(
281 selcx: &mut SelectionContext<'cx, 'tcx>,
282 param_env: ty::ParamEnv<'tcx>,
283 impl1_header: &ty::ImplHeader<'tcx>,
284 impl2_header: ty::ImplHeader<'tcx>,
285 obligations: PredicateObligations<'tcx>,
287 // There's no overlap if obligations are unsatisfiable or if the obligation negated is
290 // For example, given these two impl headers:
292 // `impl<'a> From<&'a str> for Box<dyn Error>`
293 // `impl<E> From<E> for Box<dyn Error> where E: Error`
297 // `Box<dyn Error>: From<&'?a str>`
298 // `Box<dyn Error>: From<?E>`
300 // After equating the two headers:
302 // `Box<dyn Error> = Box<dyn Error>`
303 // So, `?E = &'?a str` and then given the where clause `&'?a str: Error`.
305 // If the obligation `&'?a str: Error` holds, it means that there's overlap. If that doesn't
306 // hold we need to check if `&'?a str: !Error` holds, if doesn't hold there's overlap because
307 // at some point an impl for `&'?a str: Error` could be added.
308 let infcx = selcx.infcx();
310 let opt_failing_obligation = impl1_header
314 .chain(impl2_header.predicates)
315 .map(|p| infcx.resolve_vars_if_possible(p))
316 .map(|p| Obligation {
317 cause: ObligationCause::dummy(),
324 loose_check(selcx, o) || tcx.features().negative_impls && negative_impl_exists(selcx, o)
326 // FIXME: the call to `selcx.predicate_may_hold_fatal` above should be ported
327 // to the canonical trait query form, `infcx.predicate_may_hold`, once
328 // the new system supports intercrate mode (which coherence needs).
330 if let Some(failing_obligation) = opt_failing_obligation {
331 debug!("overlap: obligation unsatisfiable {:?}", failing_obligation);
338 /// Given impl1 and impl2 check if both impls are never satisfied by a common type (including
339 /// where-clauses) If so, return true, they are disjoint and false otherwise.
340 fn negative_impl<'cx, 'tcx>(
341 selcx: &mut SelectionContext<'cx, 'tcx>,
345 let tcx = selcx.infcx().tcx;
347 // create a parameter environment corresponding to a (placeholder) instantiation of impl1
348 let impl1_env = tcx.param_env(impl1_def_id);
349 let impl1_trait_ref = tcx.impl_trait_ref(impl1_def_id).unwrap();
351 // Create an infcx, taking the predicates of impl1 as assumptions:
352 tcx.infer_ctxt().enter(|infcx| {
353 // Normalize the trait reference. The WF rules ought to ensure
354 // that this always succeeds.
355 let impl1_trait_ref = match traits::fully_normalize(
357 FulfillmentContext::new(),
358 ObligationCause::dummy(),
362 Ok(impl1_trait_ref) => impl1_trait_ref,
364 bug!("failed to fully normalize {:?}: {:?}", impl1_trait_ref, err);
368 // Attempt to prove that impl2 applies, given all of the above.
369 let selcx = &mut SelectionContext::new(&infcx);
370 let impl2_substs = infcx.fresh_substs_for_item(DUMMY_SP, impl2_def_id);
371 let (impl2_trait_ref, obligations) =
372 impl_trait_ref_and_oblig(selcx, impl1_env, impl2_def_id, impl2_substs);
374 // do the impls unify? If not, not disjoint.
375 let more_obligations = match infcx
376 .at(&ObligationCause::dummy(), impl1_env)
377 .eq(impl1_trait_ref, impl2_trait_ref)
379 Ok(InferOk { obligations, .. }) => obligations,
382 "explicit_disjoint: {:?} does not unify with {:?}",
383 impl1_trait_ref, impl2_trait_ref
389 let opt_failing_obligation = obligations
391 .chain(more_obligations)
392 .find(|o| negative_impl_exists(selcx, o));
394 if let Some(failing_obligation) = opt_failing_obligation {
395 debug!("overlap: obligation unsatisfiable {:?}", failing_obligation);
403 fn loose_check<'cx, 'tcx>(
404 selcx: &mut SelectionContext<'cx, 'tcx>,
405 o: &PredicateObligation<'tcx>,
407 !selcx.predicate_may_hold_fatal(o)
410 fn negative_impl_exists<'cx, 'tcx>(
411 selcx: &SelectionContext<'cx, 'tcx>,
412 o: &PredicateObligation<'tcx>,
414 let infcx = selcx.infcx();
419 // FIXME This isn't quite correct, regions should be included
420 selcx.infcx().predicate_must_hold_modulo_regions(o)
425 pub fn trait_ref_is_knowable<'tcx>(
427 trait_ref: ty::TraitRef<'tcx>,
428 ) -> Option<Conflict> {
429 debug!("trait_ref_is_knowable(trait_ref={:?})", trait_ref);
430 if orphan_check_trait_ref(tcx, trait_ref, InCrate::Remote).is_ok() {
431 // A downstream or cousin crate is allowed to implement some
432 // substitution of this trait-ref.
433 return Some(Conflict::Downstream);
436 if trait_ref_is_local_or_fundamental(tcx, trait_ref) {
437 // This is a local or fundamental trait, so future-compatibility
438 // is no concern. We know that downstream/cousin crates are not
439 // allowed to implement a substitution of this trait ref, which
440 // means impls could only come from dependencies of this crate,
441 // which we already know about.
445 // This is a remote non-fundamental trait, so if another crate
446 // can be the "final owner" of a substitution of this trait-ref,
447 // they are allowed to implement it future-compatibly.
449 // However, if we are a final owner, then nobody else can be,
450 // and if we are an intermediate owner, then we don't care
451 // about future-compatibility, which means that we're OK if
453 if orphan_check_trait_ref(tcx, trait_ref, InCrate::Local).is_ok() {
454 debug!("trait_ref_is_knowable: orphan check passed");
457 debug!("trait_ref_is_knowable: nonlocal, nonfundamental, unowned");
458 Some(Conflict::Upstream)
462 pub fn trait_ref_is_local_or_fundamental<'tcx>(
464 trait_ref: ty::TraitRef<'tcx>,
466 trait_ref.def_id.krate == LOCAL_CRATE || tcx.has_attr(trait_ref.def_id, sym::fundamental)
469 pub enum OrphanCheckErr<'tcx> {
470 NonLocalInputType(Vec<(Ty<'tcx>, bool /* Is this the first input type? */)>),
471 UncoveredTy(Ty<'tcx>, Option<Ty<'tcx>>),
474 /// Checks the coherence orphan rules. `impl_def_id` should be the
475 /// `DefId` of a trait impl. To pass, either the trait must be local, or else
476 /// two conditions must be satisfied:
478 /// 1. All type parameters in `Self` must be "covered" by some local type constructor.
479 /// 2. Some local type must appear in `Self`.
480 pub fn orphan_check(tcx: TyCtxt<'_>, impl_def_id: DefId) -> Result<(), OrphanCheckErr<'_>> {
481 debug!("orphan_check({:?})", impl_def_id);
483 // We only except this routine to be invoked on implementations
484 // of a trait, not inherent implementations.
485 let trait_ref = tcx.impl_trait_ref(impl_def_id).unwrap();
486 debug!("orphan_check: trait_ref={:?}", trait_ref);
488 // If the *trait* is local to the crate, ok.
489 if trait_ref.def_id.is_local() {
490 debug!("trait {:?} is local to current crate", trait_ref.def_id);
494 orphan_check_trait_ref(tcx, trait_ref, InCrate::Local)
497 /// Checks whether a trait-ref is potentially implementable by a crate.
499 /// The current rule is that a trait-ref orphan checks in a crate C:
501 /// 1. Order the parameters in the trait-ref in subst order - Self first,
502 /// others linearly (e.g., `<U as Foo<V, W>>` is U < V < W).
503 /// 2. Of these type parameters, there is at least one type parameter
504 /// in which, walking the type as a tree, you can reach a type local
505 /// to C where all types in-between are fundamental types. Call the
506 /// first such parameter the "local key parameter".
507 /// - e.g., `Box<LocalType>` is OK, because you can visit LocalType
508 /// going through `Box`, which is fundamental.
509 /// - similarly, `FundamentalPair<Vec<()>, Box<LocalType>>` is OK for
511 /// - but (knowing that `Vec<T>` is non-fundamental, and assuming it's
512 /// not local), `Vec<LocalType>` is bad, because `Vec<->` is between
513 /// the local type and the type parameter.
514 /// 3. Before this local type, no generic type parameter of the impl must
515 /// be reachable through fundamental types.
516 /// - e.g. `impl<T> Trait<LocalType> for Vec<T>` is fine, as `Vec` is not fundamental.
517 /// - while `impl<T> Trait<LocalType for Box<T>` results in an error, as `T` is
518 /// reachable through the fundamental type `Box`.
519 /// 4. Every type in the local key parameter not known in C, going
520 /// through the parameter's type tree, must appear only as a subtree of
521 /// a type local to C, with only fundamental types between the type
522 /// local to C and the local key parameter.
523 /// - e.g., `Vec<LocalType<T>>>` (or equivalently `Box<Vec<LocalType<T>>>`)
524 /// is bad, because the only local type with `T` as a subtree is
525 /// `LocalType<T>`, and `Vec<->` is between it and the type parameter.
526 /// - similarly, `FundamentalPair<LocalType<T>, T>` is bad, because
527 /// the second occurrence of `T` is not a subtree of *any* local type.
528 /// - however, `LocalType<Vec<T>>` is OK, because `T` is a subtree of
529 /// `LocalType<Vec<T>>`, which is local and has no types between it and
530 /// the type parameter.
532 /// The orphan rules actually serve several different purposes:
534 /// 1. They enable link-safety - i.e., 2 mutually-unknowing crates (where
535 /// every type local to one crate is unknown in the other) can't implement
536 /// the same trait-ref. This follows because it can be seen that no such
537 /// type can orphan-check in 2 such crates.
539 /// To check that a local impl follows the orphan rules, we check it in
540 /// InCrate::Local mode, using type parameters for the "generic" types.
542 /// 2. They ground negative reasoning for coherence. If a user wants to
543 /// write both a conditional blanket impl and a specific impl, we need to
544 /// make sure they do not overlap. For example, if we write
546 /// impl<T> IntoIterator for Vec<T>
547 /// impl<T: Iterator> IntoIterator for T
549 /// We need to be able to prove that `Vec<$0>: !Iterator` for every type $0.
550 /// We can observe that this holds in the current crate, but we need to make
551 /// sure this will also hold in all unknown crates (both "independent" crates,
552 /// which we need for link-safety, and also child crates, because we don't want
553 /// child crates to get error for impl conflicts in a *dependency*).
555 /// For that, we only allow negative reasoning if, for every assignment to the
556 /// inference variables, every unknown crate would get an orphan error if they
557 /// try to implement this trait-ref. To check for this, we use InCrate::Remote
558 /// mode. That is sound because we already know all the impls from known crates.
560 /// 3. For non-`#[fundamental]` traits, they guarantee that parent crates can
561 /// add "non-blanket" impls without breaking negative reasoning in dependent
562 /// crates. This is the "rebalancing coherence" (RFC 1023) restriction.
564 /// For that, we only a allow crate to perform negative reasoning on
565 /// non-local-non-`#[fundamental]` only if there's a local key parameter as per (2).
567 /// Because we never perform negative reasoning generically (coherence does
568 /// not involve type parameters), this can be interpreted as doing the full
569 /// orphan check (using InCrate::Local mode), substituting non-local known
570 /// types for all inference variables.
572 /// This allows for crates to future-compatibly add impls as long as they
573 /// can't apply to types with a key parameter in a child crate - applying
574 /// the rules, this basically means that every type parameter in the impl
575 /// must appear behind a non-fundamental type (because this is not a
576 /// type-system requirement, crate owners might also go for "semantic
577 /// future-compatibility" involving things such as sealed traits, but
578 /// the above requirement is sufficient, and is necessary in "open world"
581 /// Note that this function is never called for types that have both type
582 /// parameters and inference variables.
583 fn orphan_check_trait_ref<'tcx>(
585 trait_ref: ty::TraitRef<'tcx>,
587 ) -> Result<(), OrphanCheckErr<'tcx>> {
588 debug!("orphan_check_trait_ref(trait_ref={:?}, in_crate={:?})", trait_ref, in_crate);
590 if trait_ref.needs_infer() && trait_ref.needs_subst() {
592 "can't orphan check a trait ref with both params and inference variables {:?}",
597 // Given impl<P1..=Pn> Trait<T1..=Tn> for T0, an impl is valid only
598 // if at least one of the following is true:
600 // - Trait is a local trait
601 // (already checked in orphan_check prior to calling this function)
603 // - At least one of the types T0..=Tn must be a local type.
604 // Let Ti be the first such type.
605 // - No uncovered type parameters P1..=Pn may appear in T0..Ti (excluding Ti)
607 fn uncover_fundamental_ty<'tcx>(
612 // FIXME: this is currently somewhat overly complicated,
613 // but fixing this requires a more complicated refactor.
614 if !contained_non_local_types(tcx, ty, in_crate).is_empty() {
615 if let Some(inner_tys) = fundamental_ty_inner_tys(tcx, ty) {
617 .flat_map(|ty| uncover_fundamental_ty(tcx, ty, in_crate))
625 let mut non_local_spans = vec![];
626 for (i, input_ty) in trait_ref
629 .flat_map(|ty| uncover_fundamental_ty(tcx, ty, in_crate))
632 debug!("orphan_check_trait_ref: check ty `{:?}`", input_ty);
633 let non_local_tys = contained_non_local_types(tcx, input_ty, in_crate);
634 if non_local_tys.is_empty() {
635 debug!("orphan_check_trait_ref: ty_is_local `{:?}`", input_ty);
637 } else if let ty::Param(_) = input_ty.kind() {
638 debug!("orphan_check_trait_ref: uncovered ty: `{:?}`", input_ty);
639 let local_type = trait_ref
642 .flat_map(|ty| uncover_fundamental_ty(tcx, ty, in_crate))
643 .find(|ty| ty_is_local_constructor(ty, in_crate));
645 debug!("orphan_check_trait_ref: uncovered ty local_type: `{:?}`", local_type);
647 return Err(OrphanCheckErr::UncoveredTy(input_ty, local_type));
650 non_local_spans.extend(non_local_tys.into_iter().map(|input_ty| (input_ty, i == 0)));
652 // If we exit above loop, never found a local type.
653 debug!("orphan_check_trait_ref: no local type");
654 Err(OrphanCheckErr::NonLocalInputType(non_local_spans))
657 /// Returns a list of relevant non-local types for `ty`.
659 /// This is just `ty` itself unless `ty` is `#[fundamental]`,
660 /// in which case we recursively look into this type.
662 /// If `ty` is local itself, this method returns an empty `Vec`.
666 /// - `u32` is not local, so this returns `[u32]`.
667 /// - for `Foo<u32>`, where `Foo` is a local type, this returns `[]`.
668 /// - `&mut u32` returns `[u32]`, as `&mut` is a fundamental type, similar to `Box`.
669 /// - `Box<Foo<u32>>` returns `[]`, as `Box` is a fundamental type and `Foo` is local.
670 fn contained_non_local_types<'tcx>(
675 if ty_is_local_constructor(ty, in_crate) {
678 match fundamental_ty_inner_tys(tcx, ty) {
680 inner_tys.flat_map(|ty| contained_non_local_types(tcx, ty, in_crate)).collect()
687 /// For `#[fundamental]` ADTs and `&T` / `&mut T`, returns `Some` with the
688 /// type parameters of the ADT, or `T`, respectively. For non-fundamental
689 /// types, returns `None`.
690 fn fundamental_ty_inner_tys<'tcx>(
693 ) -> Option<impl Iterator<Item = Ty<'tcx>>> {
694 let (first_ty, rest_tys) = match *ty.kind() {
695 ty::Ref(_, ty, _) => (ty, ty::subst::InternalSubsts::empty().types()),
696 ty::Adt(def, substs) if def.is_fundamental() => {
697 let mut types = substs.types();
699 // FIXME(eddyb) actually validate `#[fundamental]` up-front.
703 tcx.def_span(def.did),
704 "`#[fundamental]` requires at least one type parameter",
710 Some(first_ty) => (first_ty, types),
716 Some(iter::once(first_ty).chain(rest_tys))
719 fn def_id_is_local(def_id: DefId, in_crate: InCrate) -> bool {
721 // The type is local to *this* crate - it will not be
722 // local in any other crate.
723 InCrate::Remote => false,
724 InCrate::Local => def_id.is_local(),
728 fn ty_is_local_constructor(ty: Ty<'_>, in_crate: InCrate) -> bool {
729 debug!("ty_is_local_constructor({:?})", ty);
747 | ty::Projection(..) => false,
749 ty::Placeholder(..) | ty::Bound(..) | ty::Infer(..) => match in_crate {
750 InCrate::Local => false,
751 // The inference variable might be unified with a local
752 // type in that remote crate.
753 InCrate::Remote => true,
756 ty::Adt(def, _) => def_id_is_local(def.did, in_crate),
757 ty::Foreign(did) => def_id_is_local(did, in_crate),
759 // This merits some explanation.
760 // Normally, opaque types are not involed when performing
761 // coherence checking, since it is illegal to directly
762 // implement a trait on an opaque type. However, we might
763 // end up looking at an opaque type during coherence checking
764 // if an opaque type gets used within another type (e.g. as
765 // a type parameter). This requires us to decide whether or
766 // not an opaque type should be considered 'local' or not.
768 // We choose to treat all opaque types as non-local, even
769 // those that appear within the same crate. This seems
770 // somewhat surprising at first, but makes sense when
771 // you consider that opaque types are supposed to hide
772 // the underlying type *within the same crate*. When an
773 // opaque type is used from outside the module
774 // where it is declared, it should be impossible to observe
775 // anything about it other than the traits that it implements.
777 // The alternative would be to look at the underlying type
778 // to determine whether or not the opaque type itself should
779 // be considered local. However, this could make it a breaking change
780 // to switch the underlying ('defining') type from a local type
781 // to a remote type. This would violate the rule that opaque
782 // types should be completely opaque apart from the traits
783 // that they implement, so we don't use this behavior.
788 // Similar to the `Opaque` case (#83613).
792 ty::Dynamic(ref tt, ..) => {
793 if let Some(principal) = tt.principal() {
794 def_id_is_local(principal.def_id(), in_crate)
800 ty::Error(_) => true,
802 ty::Generator(..) | ty::GeneratorWitness(..) => {
803 bug!("ty_is_local invoked on unexpected type: {:?}", ty)