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_hir::def_id::{DefId, LOCAL_CRATE};
18 use rustc_hir::CRATE_HIR_ID;
19 use rustc_infer::infer::TyCtxtInferExt;
20 use rustc_infer::traits::TraitEngine;
21 use rustc_middle::traits::specialization_graph::OverlapMode;
22 use rustc_middle::ty::fast_reject::{self, SimplifyParams};
23 use rustc_middle::ty::fold::TypeFoldable;
24 use rustc_middle::ty::subst::Subst;
25 use rustc_middle::ty::{self, Ty, TyCtxt};
26 use rustc_span::symbol::sym;
27 use rustc_span::DUMMY_SP;
30 /// Whether we do the orphan check relative to this crate or
31 /// to some remote crate.
32 #[derive(Copy, Clone, Debug)]
38 #[derive(Debug, Copy, Clone)]
44 pub struct OverlapResult<'tcx> {
45 pub impl_header: ty::ImplHeader<'tcx>,
46 pub intercrate_ambiguity_causes: Vec<IntercrateAmbiguityCause>,
48 /// `true` if the overlap might've been permitted before the shift
50 pub involves_placeholder: bool,
53 pub fn add_placeholder_note(err: &mut rustc_errors::DiagnosticBuilder<'_>) {
55 "this behavior recently changed as a result of a bug fix; \
56 see rust-lang/rust#56105 for details",
60 /// If there are types that satisfy both impls, invokes `on_overlap`
61 /// with a suitably-freshened `ImplHeader` with those types
62 /// substituted. Otherwise, invokes `no_overlap`.
63 #[instrument(skip(tcx, skip_leak_check, on_overlap, no_overlap), level = "debug")]
64 pub fn overlapping_impls<F1, F2, R>(
68 skip_leak_check: SkipLeakCheck,
69 overlap_mode: OverlapMode,
74 F1: FnOnce(OverlapResult<'_>) -> R,
77 // Before doing expensive operations like entering an inference context, do
78 // a quick check via fast_reject to tell if the impl headers could possibly
80 let impl1_ref = tcx.impl_trait_ref(impl1_def_id);
81 let impl2_ref = tcx.impl_trait_ref(impl2_def_id);
83 // Check if any of the input types definitely do not unify.
85 impl1_ref.iter().flat_map(|tref| tref.substs.types()),
86 impl2_ref.iter().flat_map(|tref| tref.substs.types()),
89 let t1 = fast_reject::simplify_type(tcx, ty1, SimplifyParams::No);
90 let t2 = fast_reject::simplify_type(tcx, ty2, SimplifyParams::No);
92 if let (Some(t1), Some(t2)) = (t1, t2) {
93 // Simplified successfully
100 // Some types involved are definitely different, so the impls couldn't possibly overlap.
101 debug!("overlapping_impls: fast_reject early-exit");
105 let overlaps = tcx.infer_ctxt().enter(|infcx| {
106 let selcx = &mut SelectionContext::intercrate(&infcx);
107 overlap(selcx, skip_leak_check, impl1_def_id, impl2_def_id, overlap_mode).is_some()
114 // In the case where we detect an error, run the check again, but
115 // this time tracking intercrate ambuiguity causes for better
116 // diagnostics. (These take time and can lead to false errors.)
117 tcx.infer_ctxt().enter(|infcx| {
118 let selcx = &mut SelectionContext::intercrate(&infcx);
119 selcx.enable_tracking_intercrate_ambiguity_causes();
121 overlap(selcx, skip_leak_check, impl1_def_id, impl2_def_id, overlap_mode).unwrap(),
126 fn with_fresh_ty_vars<'cx, 'tcx>(
127 selcx: &mut SelectionContext<'cx, 'tcx>,
128 param_env: ty::ParamEnv<'tcx>,
130 ) -> ty::ImplHeader<'tcx> {
131 let tcx = selcx.tcx();
132 let impl_substs = selcx.infcx().fresh_substs_for_item(DUMMY_SP, impl_def_id);
134 let header = ty::ImplHeader {
136 self_ty: tcx.type_of(impl_def_id).subst(tcx, impl_substs),
137 trait_ref: tcx.impl_trait_ref(impl_def_id).subst(tcx, impl_substs),
138 predicates: tcx.predicates_of(impl_def_id).instantiate(tcx, impl_substs).predicates,
141 let Normalized { value: mut header, obligations } =
142 traits::normalize(selcx, param_env, ObligationCause::dummy(), header);
144 header.predicates.extend(obligations.into_iter().map(|o| o.predicate));
148 /// Can both impl `a` and impl `b` be satisfied by a common type (including
149 /// where-clauses)? If so, returns an `ImplHeader` that unifies the two impls.
150 fn overlap<'cx, 'tcx>(
151 selcx: &mut SelectionContext<'cx, 'tcx>,
152 skip_leak_check: SkipLeakCheck,
155 overlap_mode: OverlapMode,
156 ) -> Option<OverlapResult<'tcx>> {
158 "overlap(impl1_def_id={:?}, impl2_def_id={:?}, overlap_mode={:?})",
159 impl1_def_id, impl2_def_id, overlap_mode
162 selcx.infcx().probe_maybe_skip_leak_check(skip_leak_check.is_yes(), |snapshot| {
163 overlap_within_probe(
174 fn overlap_within_probe<'cx, 'tcx>(
175 selcx: &mut SelectionContext<'cx, 'tcx>,
176 skip_leak_check: SkipLeakCheck,
179 overlap_mode: OverlapMode,
180 snapshot: &CombinedSnapshot<'_, 'tcx>,
181 ) -> Option<OverlapResult<'tcx>> {
182 let infcx = selcx.infcx();
184 if overlap_mode.use_negative_impl() {
185 if negative_impl(selcx, impl1_def_id, impl2_def_id)
186 || negative_impl(selcx, impl2_def_id, impl1_def_id)
192 // For the purposes of this check, we don't bring any placeholder
193 // types into scope; instead, we replace the generic types with
194 // fresh type variables, and hence we do our evaluations in an
195 // empty environment.
196 let param_env = ty::ParamEnv::empty();
198 let impl1_header = with_fresh_ty_vars(selcx, param_env, impl1_def_id);
199 let impl2_header = with_fresh_ty_vars(selcx, param_env, impl2_def_id);
201 let obligations = equate_impl_headers(selcx, &impl1_header, &impl2_header)?;
202 debug!("overlap: unification check succeeded");
204 if overlap_mode.use_implicit_negative() {
205 if implicit_negative(selcx, param_env, &impl1_header, impl2_header, obligations) {
210 if !skip_leak_check.is_yes() {
211 if infcx.leak_check(true, snapshot).is_err() {
212 debug!("overlap: leak check failed");
217 let intercrate_ambiguity_causes = selcx.take_intercrate_ambiguity_causes();
218 debug!("overlap: intercrate_ambiguity_causes={:#?}", intercrate_ambiguity_causes);
220 let involves_placeholder =
221 matches!(selcx.infcx().region_constraints_added_in_snapshot(snapshot), Some(true));
223 let impl_header = selcx.infcx().resolve_vars_if_possible(impl1_header);
224 Some(OverlapResult { impl_header, intercrate_ambiguity_causes, involves_placeholder })
227 fn equate_impl_headers<'cx, 'tcx>(
228 selcx: &mut SelectionContext<'cx, 'tcx>,
229 impl1_header: &ty::ImplHeader<'tcx>,
230 impl2_header: &ty::ImplHeader<'tcx>,
231 ) -> Option<PredicateObligations<'tcx>> {
232 // Do `a` and `b` unify? If not, no overlap.
233 debug!("equate_impl_headers(impl1_header={:?}, impl2_header={:?}", impl1_header, impl2_header);
236 .at(&ObligationCause::dummy(), ty::ParamEnv::empty())
237 .eq_impl_headers(impl1_header, impl2_header)
238 .map(|infer_ok| infer_ok.obligations)
242 /// Given impl1 and impl2 check if both impls can be satisfied by a common type (including
243 /// where-clauses) If so, return false, otherwise return true, they are disjoint.
244 fn implicit_negative<'cx, 'tcx>(
245 selcx: &mut SelectionContext<'cx, 'tcx>,
246 param_env: ty::ParamEnv<'tcx>,
247 impl1_header: &ty::ImplHeader<'tcx>,
248 impl2_header: ty::ImplHeader<'tcx>,
249 obligations: PredicateObligations<'tcx>,
251 // There's no overlap if obligations are unsatisfiable or if the obligation negated is
254 // For example, given these two impl headers:
256 // `impl<'a> From<&'a str> for Box<dyn Error>`
257 // `impl<E> From<E> for Box<dyn Error> where E: Error`
261 // `Box<dyn Error>: From<&'?a str>`
262 // `Box<dyn Error>: From<?E>`
264 // After equating the two headers:
266 // `Box<dyn Error> = Box<dyn Error>`
267 // So, `?E = &'?a str` and then given the where clause `&'?a str: Error`.
269 // If the obligation `&'?a str: Error` holds, it means that there's overlap. If that doesn't
270 // hold we need to check if `&'?a str: !Error` holds, if doesn't hold there's overlap because
271 // at some point an impl for `&'?a str: Error` could be added.
273 "implicit_negative(impl1_header={:?}, impl2_header={:?}, obligations={:?})",
274 impl1_header, impl2_header, obligations
276 let infcx = selcx.infcx();
277 let opt_failing_obligation = impl1_header
281 .chain(impl2_header.predicates)
282 .map(|p| infcx.resolve_vars_if_possible(p))
283 .map(|p| Obligation {
284 cause: ObligationCause::dummy(),
290 .find(|o| !selcx.predicate_may_hold_fatal(o));
292 if let Some(failing_obligation) = opt_failing_obligation {
293 debug!("overlap: obligation unsatisfiable {:?}", failing_obligation);
300 /// Given impl1 and impl2 check if both impls are never satisfied by a common type (including
301 /// where-clauses) If so, return true, they are disjoint and false otherwise.
302 fn negative_impl<'cx, 'tcx>(
303 selcx: &mut SelectionContext<'cx, 'tcx>,
307 debug!("negative_impl(impl1_def_id={:?}, impl2_def_id={:?})", impl1_def_id, impl2_def_id);
308 let tcx = selcx.infcx().tcx;
310 // create a parameter environment corresponding to a (placeholder) instantiation of impl1
311 let impl1_env = tcx.param_env(impl1_def_id);
312 let impl1_trait_ref = tcx.impl_trait_ref(impl1_def_id).unwrap();
314 // Create an infcx, taking the predicates of impl1 as assumptions:
315 tcx.infer_ctxt().enter(|infcx| {
316 // Normalize the trait reference. The WF rules ought to ensure
317 // that this always succeeds.
318 let impl1_trait_ref = match traits::fully_normalize(
320 FulfillmentContext::new(),
321 ObligationCause::dummy(),
325 Ok(impl1_trait_ref) => impl1_trait_ref,
327 bug!("failed to fully normalize {:?}: {:?}", impl1_trait_ref, err);
331 // Attempt to prove that impl2 applies, given all of the above.
332 let selcx = &mut SelectionContext::new(&infcx);
333 let impl2_substs = infcx.fresh_substs_for_item(DUMMY_SP, impl2_def_id);
334 let (impl2_trait_ref, obligations) =
335 impl_trait_ref_and_oblig(selcx, impl1_env, impl2_def_id, impl2_substs);
337 // do the impls unify? If not, not disjoint.
338 let more_obligations = match infcx
339 .at(&ObligationCause::dummy(), impl1_env)
340 .eq(impl1_trait_ref, impl2_trait_ref)
342 Ok(InferOk { obligations, .. }) => obligations,
345 "explicit_disjoint: {:?} does not unify with {:?}",
346 impl1_trait_ref, impl2_trait_ref
352 let opt_failing_obligation = obligations
354 .chain(more_obligations)
355 .find(|o| negative_impl_exists(selcx, impl1_env, impl1_def_id, o));
357 if let Some(failing_obligation) = opt_failing_obligation {
358 debug!("overlap: obligation unsatisfiable {:?}", failing_obligation);
366 fn negative_impl_exists<'cx, 'tcx>(
367 selcx: &SelectionContext<'cx, 'tcx>,
368 param_env: ty::ParamEnv<'tcx>,
369 region_context: DefId,
370 o: &PredicateObligation<'tcx>,
372 let infcx = &selcx.infcx().fork();
376 let mut fulfillment_cx = FulfillmentContext::new();
377 fulfillment_cx.register_predicate_obligation(infcx, o);
379 let errors = fulfillment_cx.select_all_or_error(infcx);
380 if !errors.is_empty() {
384 let mut outlives_env = OutlivesEnvironment::new(param_env);
385 // FIXME -- add "assumed to be well formed" types into the `outlives_env`
387 // "Save" the accumulated implied bounds into the outlives environment
388 // (due to the FIXME above, there aren't any, but this step is still needed).
389 // The "body id" is given as `CRATE_HIR_ID`, which is the same body-id used
390 // by the "dummy" causes elsewhere (body-id is only relevant when checking
391 // function bodies with closures).
392 outlives_env.save_implied_bounds(CRATE_HIR_ID);
394 infcx.process_registered_region_obligations(
395 outlives_env.region_bound_pairs_map(),
396 Some(tcx.lifetimes.re_root_empty),
401 infcx.resolve_regions(region_context, &outlives_env, RegionckMode::default());
402 if !errors.is_empty() {
411 pub fn trait_ref_is_knowable<'tcx>(
413 trait_ref: ty::TraitRef<'tcx>,
414 ) -> Option<Conflict> {
415 debug!("trait_ref_is_knowable(trait_ref={:?})", trait_ref);
416 if orphan_check_trait_ref(tcx, trait_ref, InCrate::Remote).is_ok() {
417 // A downstream or cousin crate is allowed to implement some
418 // substitution of this trait-ref.
419 return Some(Conflict::Downstream);
422 if trait_ref_is_local_or_fundamental(tcx, trait_ref) {
423 // This is a local or fundamental trait, so future-compatibility
424 // is no concern. We know that downstream/cousin crates are not
425 // allowed to implement a substitution of this trait ref, which
426 // means impls could only come from dependencies of this crate,
427 // which we already know about.
431 // This is a remote non-fundamental trait, so if another crate
432 // can be the "final owner" of a substitution of this trait-ref,
433 // they are allowed to implement it future-compatibly.
435 // However, if we are a final owner, then nobody else can be,
436 // and if we are an intermediate owner, then we don't care
437 // about future-compatibility, which means that we're OK if
439 if orphan_check_trait_ref(tcx, trait_ref, InCrate::Local).is_ok() {
440 debug!("trait_ref_is_knowable: orphan check passed");
443 debug!("trait_ref_is_knowable: nonlocal, nonfundamental, unowned");
444 Some(Conflict::Upstream)
448 pub fn trait_ref_is_local_or_fundamental<'tcx>(
450 trait_ref: ty::TraitRef<'tcx>,
452 trait_ref.def_id.krate == LOCAL_CRATE || tcx.has_attr(trait_ref.def_id, sym::fundamental)
455 pub enum OrphanCheckErr<'tcx> {
456 NonLocalInputType(Vec<(Ty<'tcx>, bool /* Is this the first input type? */)>),
457 UncoveredTy(Ty<'tcx>, Option<Ty<'tcx>>),
460 /// Checks the coherence orphan rules. `impl_def_id` should be the
461 /// `DefId` of a trait impl. To pass, either the trait must be local, or else
462 /// two conditions must be satisfied:
464 /// 1. All type parameters in `Self` must be "covered" by some local type constructor.
465 /// 2. Some local type must appear in `Self`.
466 pub fn orphan_check(tcx: TyCtxt<'_>, impl_def_id: DefId) -> Result<(), OrphanCheckErr<'_>> {
467 debug!("orphan_check({:?})", impl_def_id);
469 // We only except this routine to be invoked on implementations
470 // of a trait, not inherent implementations.
471 let trait_ref = tcx.impl_trait_ref(impl_def_id).unwrap();
472 debug!("orphan_check: trait_ref={:?}", trait_ref);
474 // If the *trait* is local to the crate, ok.
475 if trait_ref.def_id.is_local() {
476 debug!("trait {:?} is local to current crate", trait_ref.def_id);
480 orphan_check_trait_ref(tcx, trait_ref, InCrate::Local)
483 /// Checks whether a trait-ref is potentially implementable by a crate.
485 /// The current rule is that a trait-ref orphan checks in a crate C:
487 /// 1. Order the parameters in the trait-ref in subst order - Self first,
488 /// others linearly (e.g., `<U as Foo<V, W>>` is U < V < W).
489 /// 2. Of these type parameters, there is at least one type parameter
490 /// in which, walking the type as a tree, you can reach a type local
491 /// to C where all types in-between are fundamental types. Call the
492 /// first such parameter the "local key parameter".
493 /// - e.g., `Box<LocalType>` is OK, because you can visit LocalType
494 /// going through `Box`, which is fundamental.
495 /// - similarly, `FundamentalPair<Vec<()>, Box<LocalType>>` is OK for
497 /// - but (knowing that `Vec<T>` is non-fundamental, and assuming it's
498 /// not local), `Vec<LocalType>` is bad, because `Vec<->` is between
499 /// the local type and the type parameter.
500 /// 3. Before this local type, no generic type parameter of the impl must
501 /// be reachable through fundamental types.
502 /// - e.g. `impl<T> Trait<LocalType> for Vec<T>` is fine, as `Vec` is not fundamental.
503 /// - while `impl<T> Trait<LocalType for Box<T>` results in an error, as `T` is
504 /// reachable through the fundamental type `Box`.
505 /// 4. Every type in the local key parameter not known in C, going
506 /// through the parameter's type tree, must appear only as a subtree of
507 /// a type local to C, with only fundamental types between the type
508 /// local to C and the local key parameter.
509 /// - e.g., `Vec<LocalType<T>>>` (or equivalently `Box<Vec<LocalType<T>>>`)
510 /// is bad, because the only local type with `T` as a subtree is
511 /// `LocalType<T>`, and `Vec<->` is between it and the type parameter.
512 /// - similarly, `FundamentalPair<LocalType<T>, T>` is bad, because
513 /// the second occurrence of `T` is not a subtree of *any* local type.
514 /// - however, `LocalType<Vec<T>>` is OK, because `T` is a subtree of
515 /// `LocalType<Vec<T>>`, which is local and has no types between it and
516 /// the type parameter.
518 /// The orphan rules actually serve several different purposes:
520 /// 1. They enable link-safety - i.e., 2 mutually-unknowing crates (where
521 /// every type local to one crate is unknown in the other) can't implement
522 /// the same trait-ref. This follows because it can be seen that no such
523 /// type can orphan-check in 2 such crates.
525 /// To check that a local impl follows the orphan rules, we check it in
526 /// InCrate::Local mode, using type parameters for the "generic" types.
528 /// 2. They ground negative reasoning for coherence. If a user wants to
529 /// write both a conditional blanket impl and a specific impl, we need to
530 /// make sure they do not overlap. For example, if we write
532 /// impl<T> IntoIterator for Vec<T>
533 /// impl<T: Iterator> IntoIterator for T
535 /// We need to be able to prove that `Vec<$0>: !Iterator` for every type $0.
536 /// We can observe that this holds in the current crate, but we need to make
537 /// sure this will also hold in all unknown crates (both "independent" crates,
538 /// which we need for link-safety, and also child crates, because we don't want
539 /// child crates to get error for impl conflicts in a *dependency*).
541 /// For that, we only allow negative reasoning if, for every assignment to the
542 /// inference variables, every unknown crate would get an orphan error if they
543 /// try to implement this trait-ref. To check for this, we use InCrate::Remote
544 /// mode. That is sound because we already know all the impls from known crates.
546 /// 3. For non-`#[fundamental]` traits, they guarantee that parent crates can
547 /// add "non-blanket" impls without breaking negative reasoning in dependent
548 /// crates. This is the "rebalancing coherence" (RFC 1023) restriction.
550 /// For that, we only a allow crate to perform negative reasoning on
551 /// non-local-non-`#[fundamental]` only if there's a local key parameter as per (2).
553 /// Because we never perform negative reasoning generically (coherence does
554 /// not involve type parameters), this can be interpreted as doing the full
555 /// orphan check (using InCrate::Local mode), substituting non-local known
556 /// types for all inference variables.
558 /// This allows for crates to future-compatibly add impls as long as they
559 /// can't apply to types with a key parameter in a child crate - applying
560 /// the rules, this basically means that every type parameter in the impl
561 /// must appear behind a non-fundamental type (because this is not a
562 /// type-system requirement, crate owners might also go for "semantic
563 /// future-compatibility" involving things such as sealed traits, but
564 /// the above requirement is sufficient, and is necessary in "open world"
567 /// Note that this function is never called for types that have both type
568 /// parameters and inference variables.
569 fn orphan_check_trait_ref<'tcx>(
571 trait_ref: ty::TraitRef<'tcx>,
573 ) -> Result<(), OrphanCheckErr<'tcx>> {
574 debug!("orphan_check_trait_ref(trait_ref={:?}, in_crate={:?})", trait_ref, in_crate);
576 if trait_ref.needs_infer() && trait_ref.needs_subst() {
578 "can't orphan check a trait ref with both params and inference variables {:?}",
583 // Given impl<P1..=Pn> Trait<T1..=Tn> for T0, an impl is valid only
584 // if at least one of the following is true:
586 // - Trait is a local trait
587 // (already checked in orphan_check prior to calling this function)
589 // - At least one of the types T0..=Tn must be a local type.
590 // Let Ti be the first such type.
591 // - No uncovered type parameters P1..=Pn may appear in T0..Ti (excluding Ti)
593 fn uncover_fundamental_ty<'tcx>(
598 // FIXME: this is currently somewhat overly complicated,
599 // but fixing this requires a more complicated refactor.
600 if !contained_non_local_types(tcx, ty, in_crate).is_empty() {
601 if let Some(inner_tys) = fundamental_ty_inner_tys(tcx, ty) {
603 .flat_map(|ty| uncover_fundamental_ty(tcx, ty, in_crate))
611 let mut non_local_spans = vec![];
612 for (i, input_ty) in trait_ref
615 .flat_map(|ty| uncover_fundamental_ty(tcx, ty, in_crate))
618 debug!("orphan_check_trait_ref: check ty `{:?}`", input_ty);
619 let non_local_tys = contained_non_local_types(tcx, input_ty, in_crate);
620 if non_local_tys.is_empty() {
621 debug!("orphan_check_trait_ref: ty_is_local `{:?}`", input_ty);
623 } else if let ty::Param(_) = input_ty.kind() {
624 debug!("orphan_check_trait_ref: uncovered ty: `{:?}`", input_ty);
625 let local_type = trait_ref
628 .flat_map(|ty| uncover_fundamental_ty(tcx, ty, in_crate))
629 .find(|ty| ty_is_local_constructor(*ty, in_crate));
631 debug!("orphan_check_trait_ref: uncovered ty local_type: `{:?}`", local_type);
633 return Err(OrphanCheckErr::UncoveredTy(input_ty, local_type));
636 non_local_spans.extend(non_local_tys.into_iter().map(|input_ty| (input_ty, i == 0)));
638 // If we exit above loop, never found a local type.
639 debug!("orphan_check_trait_ref: no local type");
640 Err(OrphanCheckErr::NonLocalInputType(non_local_spans))
643 /// Returns a list of relevant non-local types for `ty`.
645 /// This is just `ty` itself unless `ty` is `#[fundamental]`,
646 /// in which case we recursively look into this type.
648 /// If `ty` is local itself, this method returns an empty `Vec`.
652 /// - `u32` is not local, so this returns `[u32]`.
653 /// - for `Foo<u32>`, where `Foo` is a local type, this returns `[]`.
654 /// - `&mut u32` returns `[u32]`, as `&mut` is a fundamental type, similar to `Box`.
655 /// - `Box<Foo<u32>>` returns `[]`, as `Box` is a fundamental type and `Foo` is local.
656 fn contained_non_local_types<'tcx>(
661 if ty_is_local_constructor(ty, in_crate) {
664 match fundamental_ty_inner_tys(tcx, ty) {
666 inner_tys.flat_map(|ty| contained_non_local_types(tcx, ty, in_crate)).collect()
673 /// For `#[fundamental]` ADTs and `&T` / `&mut T`, returns `Some` with the
674 /// type parameters of the ADT, or `T`, respectively. For non-fundamental
675 /// types, returns `None`.
676 fn fundamental_ty_inner_tys<'tcx>(
679 ) -> Option<impl Iterator<Item = Ty<'tcx>>> {
680 let (first_ty, rest_tys) = match *ty.kind() {
681 ty::Ref(_, ty, _) => (ty, ty::subst::InternalSubsts::empty().types()),
682 ty::Adt(def, substs) if def.is_fundamental() => {
683 let mut types = substs.types();
685 // FIXME(eddyb) actually validate `#[fundamental]` up-front.
689 tcx.def_span(def.did),
690 "`#[fundamental]` requires at least one type parameter",
696 Some(first_ty) => (first_ty, types),
702 Some(iter::once(first_ty).chain(rest_tys))
705 fn def_id_is_local(def_id: DefId, in_crate: InCrate) -> bool {
707 // The type is local to *this* crate - it will not be
708 // local in any other crate.
709 InCrate::Remote => false,
710 InCrate::Local => def_id.is_local(),
714 fn ty_is_local_constructor(ty: Ty<'_>, in_crate: InCrate) -> bool {
715 debug!("ty_is_local_constructor({:?})", ty);
733 | ty::Projection(..) => false,
735 ty::Placeholder(..) | ty::Bound(..) | ty::Infer(..) => match in_crate {
736 InCrate::Local => false,
737 // The inference variable might be unified with a local
738 // type in that remote crate.
739 InCrate::Remote => true,
742 ty::Adt(def, _) => def_id_is_local(def.did, in_crate),
743 ty::Foreign(did) => def_id_is_local(did, in_crate),
745 // This merits some explanation.
746 // Normally, opaque types are not involed when performing
747 // coherence checking, since it is illegal to directly
748 // implement a trait on an opaque type. However, we might
749 // end up looking at an opaque type during coherence checking
750 // if an opaque type gets used within another type (e.g. as
751 // a type parameter). This requires us to decide whether or
752 // not an opaque type should be considered 'local' or not.
754 // We choose to treat all opaque types as non-local, even
755 // those that appear within the same crate. This seems
756 // somewhat surprising at first, but makes sense when
757 // you consider that opaque types are supposed to hide
758 // the underlying type *within the same crate*. When an
759 // opaque type is used from outside the module
760 // where it is declared, it should be impossible to observe
761 // anything about it other than the traits that it implements.
763 // The alternative would be to look at the underlying type
764 // to determine whether or not the opaque type itself should
765 // be considered local. However, this could make it a breaking change
766 // to switch the underlying ('defining') type from a local type
767 // to a remote type. This would violate the rule that opaque
768 // types should be completely opaque apart from the traits
769 // that they implement, so we don't use this behavior.
774 // Similar to the `Opaque` case (#83613).
778 ty::Dynamic(ref tt, ..) => {
779 if let Some(principal) = tt.principal() {
780 def_id_is_local(principal.def_id(), in_crate)
786 ty::Error(_) => true,
788 ty::Generator(..) | ty::GeneratorWitness(..) => {
789 bug!("ty_is_local invoked on unexpected type: {:?}", ty)