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Diffstat (limited to 'compiler/rustc_trait_selection/src/traits/coherence.rs')
| -rw-r--r-- | compiler/rustc_trait_selection/src/traits/coherence.rs | 747 |
1 files changed, 747 insertions, 0 deletions
diff --git a/compiler/rustc_trait_selection/src/traits/coherence.rs b/compiler/rustc_trait_selection/src/traits/coherence.rs new file mode 100644 index 000000000..1c8cdf4ca --- /dev/null +++ b/compiler/rustc_trait_selection/src/traits/coherence.rs @@ -0,0 +1,747 @@ +//! See Rustc Dev Guide chapters on [trait-resolution] and [trait-specialization] for more info on +//! how this works. +//! +//! [trait-resolution]: https://rustc-dev-guide.rust-lang.org/traits/resolution.html +//! [trait-specialization]: https://rustc-dev-guide.rust-lang.org/traits/specialization.html + +use crate::infer::outlives::env::OutlivesEnvironment; +use crate::infer::{CombinedSnapshot, InferOk}; +use crate::traits::select::IntercrateAmbiguityCause; +use crate::traits::util::impl_subject_and_oblig; +use crate::traits::SkipLeakCheck; +use crate::traits::{ + self, FulfillmentContext, Normalized, Obligation, ObligationCause, PredicateObligation, + PredicateObligations, SelectionContext, TraitEngineExt, +}; +use rustc_data_structures::fx::FxIndexSet; +use rustc_errors::Diagnostic; +use rustc_hir::def_id::{DefId, LOCAL_CRATE}; +use rustc_infer::infer::{InferCtxt, TyCtxtInferExt}; +use rustc_infer::traits::{util, TraitEngine}; +use rustc_middle::traits::specialization_graph::OverlapMode; +use rustc_middle::ty::fast_reject::{DeepRejectCtxt, TreatParams}; +use rustc_middle::ty::subst::Subst; +use rustc_middle::ty::visit::TypeVisitable; +use rustc_middle::ty::{self, ImplSubject, Ty, TyCtxt, TypeVisitor}; +use rustc_span::symbol::sym; +use rustc_span::DUMMY_SP; +use std::fmt::Debug; +use std::iter; +use std::ops::ControlFlow; + +/// Whether we do the orphan check relative to this crate or +/// to some remote crate. +#[derive(Copy, Clone, Debug)] +enum InCrate { + Local, + Remote, +} + +#[derive(Debug, Copy, Clone)] +pub enum Conflict { + Upstream, + Downstream, +} + +pub struct OverlapResult<'tcx> { + pub impl_header: ty::ImplHeader<'tcx>, + pub intercrate_ambiguity_causes: FxIndexSet<IntercrateAmbiguityCause>, + + /// `true` if the overlap might've been permitted before the shift + /// to universes. + pub involves_placeholder: bool, +} + +pub fn add_placeholder_note(err: &mut Diagnostic) { + err.note( + "this behavior recently changed as a result of a bug fix; \ + see rust-lang/rust#56105 for details", + ); +} + +/// If there are types that satisfy both impls, invokes `on_overlap` +/// with a suitably-freshened `ImplHeader` with those types +/// substituted. Otherwise, invokes `no_overlap`. +#[instrument(skip(tcx, skip_leak_check, on_overlap, no_overlap), level = "debug")] +pub fn overlapping_impls<F1, F2, R>( + tcx: TyCtxt<'_>, + impl1_def_id: DefId, + impl2_def_id: DefId, + skip_leak_check: SkipLeakCheck, + overlap_mode: OverlapMode, + on_overlap: F1, + no_overlap: F2, +) -> R +where + F1: FnOnce(OverlapResult<'_>) -> R, + F2: FnOnce() -> R, +{ + // Before doing expensive operations like entering an inference context, do + // a quick check via fast_reject to tell if the impl headers could possibly + // unify. + let drcx = DeepRejectCtxt { treat_obligation_params: TreatParams::AsInfer }; + let impl1_ref = tcx.impl_trait_ref(impl1_def_id); + let impl2_ref = tcx.impl_trait_ref(impl2_def_id); + let may_overlap = match (impl1_ref, impl2_ref) { + (Some(a), Some(b)) => iter::zip(a.substs, b.substs) + .all(|(arg1, arg2)| drcx.generic_args_may_unify(arg1, arg2)), + (None, None) => { + let self_ty1 = tcx.type_of(impl1_def_id); + let self_ty2 = tcx.type_of(impl2_def_id); + drcx.types_may_unify(self_ty1, self_ty2) + } + _ => bug!("unexpected impls: {impl1_def_id:?} {impl2_def_id:?}"), + }; + + if !may_overlap { + // Some types involved are definitely different, so the impls couldn't possibly overlap. + debug!("overlapping_impls: fast_reject early-exit"); + return no_overlap(); + } + + let overlaps = tcx.infer_ctxt().enter(|infcx| { + let selcx = &mut SelectionContext::intercrate(&infcx); + overlap(selcx, skip_leak_check, impl1_def_id, impl2_def_id, overlap_mode).is_some() + }); + + if !overlaps { + return no_overlap(); + } + + // In the case where we detect an error, run the check again, but + // this time tracking intercrate ambiguity causes for better + // diagnostics. (These take time and can lead to false errors.) + tcx.infer_ctxt().enter(|infcx| { + let selcx = &mut SelectionContext::intercrate(&infcx); + selcx.enable_tracking_intercrate_ambiguity_causes(); + on_overlap( + overlap(selcx, skip_leak_check, impl1_def_id, impl2_def_id, overlap_mode).unwrap(), + ) + }) +} + +fn with_fresh_ty_vars<'cx, 'tcx>( + selcx: &mut SelectionContext<'cx, 'tcx>, + param_env: ty::ParamEnv<'tcx>, + impl_def_id: DefId, +) -> ty::ImplHeader<'tcx> { + let tcx = selcx.tcx(); + let impl_substs = selcx.infcx().fresh_substs_for_item(DUMMY_SP, impl_def_id); + + let header = ty::ImplHeader { + impl_def_id, + self_ty: tcx.bound_type_of(impl_def_id).subst(tcx, impl_substs), + trait_ref: tcx.bound_impl_trait_ref(impl_def_id).map(|i| i.subst(tcx, impl_substs)), + predicates: tcx.predicates_of(impl_def_id).instantiate(tcx, impl_substs).predicates, + }; + + let Normalized { value: mut header, obligations } = + traits::normalize(selcx, param_env, ObligationCause::dummy(), header); + + header.predicates.extend(obligations.into_iter().map(|o| o.predicate)); + header +} + +/// Can both impl `a` and impl `b` be satisfied by a common type (including +/// where-clauses)? If so, returns an `ImplHeader` that unifies the two impls. +fn overlap<'cx, 'tcx>( + selcx: &mut SelectionContext<'cx, 'tcx>, + skip_leak_check: SkipLeakCheck, + impl1_def_id: DefId, + impl2_def_id: DefId, + overlap_mode: OverlapMode, +) -> Option<OverlapResult<'tcx>> { + debug!( + "overlap(impl1_def_id={:?}, impl2_def_id={:?}, overlap_mode={:?})", + impl1_def_id, impl2_def_id, overlap_mode + ); + + selcx.infcx().probe_maybe_skip_leak_check(skip_leak_check.is_yes(), |snapshot| { + overlap_within_probe(selcx, impl1_def_id, impl2_def_id, overlap_mode, snapshot) + }) +} + +fn overlap_within_probe<'cx, 'tcx>( + selcx: &mut SelectionContext<'cx, 'tcx>, + impl1_def_id: DefId, + impl2_def_id: DefId, + overlap_mode: OverlapMode, + snapshot: &CombinedSnapshot<'_, 'tcx>, +) -> Option<OverlapResult<'tcx>> { + let infcx = selcx.infcx(); + + if overlap_mode.use_negative_impl() { + if negative_impl(selcx, impl1_def_id, impl2_def_id) + || negative_impl(selcx, impl2_def_id, impl1_def_id) + { + return None; + } + } + + // For the purposes of this check, we don't bring any placeholder + // types into scope; instead, we replace the generic types with + // fresh type variables, and hence we do our evaluations in an + // empty environment. + let param_env = ty::ParamEnv::empty(); + + let impl1_header = with_fresh_ty_vars(selcx, param_env, impl1_def_id); + let impl2_header = with_fresh_ty_vars(selcx, param_env, impl2_def_id); + + let obligations = equate_impl_headers(selcx, &impl1_header, &impl2_header)?; + debug!("overlap: unification check succeeded"); + + if overlap_mode.use_implicit_negative() { + if implicit_negative(selcx, param_env, &impl1_header, impl2_header, obligations) { + return None; + } + } + + // We disable the leak when when creating the `snapshot` by using + // `infcx.probe_maybe_disable_leak_check`. + if infcx.leak_check(true, snapshot).is_err() { + debug!("overlap: leak check failed"); + return None; + } + + let intercrate_ambiguity_causes = selcx.take_intercrate_ambiguity_causes(); + debug!("overlap: intercrate_ambiguity_causes={:#?}", intercrate_ambiguity_causes); + + let involves_placeholder = + matches!(selcx.infcx().region_constraints_added_in_snapshot(snapshot), Some(true)); + + let impl_header = selcx.infcx().resolve_vars_if_possible(impl1_header); + Some(OverlapResult { impl_header, intercrate_ambiguity_causes, involves_placeholder }) +} + +fn equate_impl_headers<'cx, 'tcx>( + selcx: &mut SelectionContext<'cx, 'tcx>, + impl1_header: &ty::ImplHeader<'tcx>, + impl2_header: &ty::ImplHeader<'tcx>, +) -> Option<PredicateObligations<'tcx>> { + // Do `a` and `b` unify? If not, no overlap. + debug!("equate_impl_headers(impl1_header={:?}, impl2_header={:?}", impl1_header, impl2_header); + selcx + .infcx() + .at(&ObligationCause::dummy(), ty::ParamEnv::empty()) + .eq_impl_headers(impl1_header, impl2_header) + .map(|infer_ok| infer_ok.obligations) + .ok() +} + +/// Given impl1 and impl2 check if both impls can be satisfied by a common type (including +/// where-clauses) If so, return false, otherwise return true, they are disjoint. +fn implicit_negative<'cx, 'tcx>( + selcx: &mut SelectionContext<'cx, 'tcx>, + param_env: ty::ParamEnv<'tcx>, + impl1_header: &ty::ImplHeader<'tcx>, + impl2_header: ty::ImplHeader<'tcx>, + obligations: PredicateObligations<'tcx>, +) -> bool { + // There's no overlap if obligations are unsatisfiable or if the obligation negated is + // satisfied. + // + // For example, given these two impl headers: + // + // `impl<'a> From<&'a str> for Box<dyn Error>` + // `impl<E> From<E> for Box<dyn Error> where E: Error` + // + // So we have: + // + // `Box<dyn Error>: From<&'?a str>` + // `Box<dyn Error>: From<?E>` + // + // After equating the two headers: + // + // `Box<dyn Error> = Box<dyn Error>` + // So, `?E = &'?a str` and then given the where clause `&'?a str: Error`. + // + // If the obligation `&'?a str: Error` holds, it means that there's overlap. If that doesn't + // hold we need to check if `&'?a str: !Error` holds, if doesn't hold there's overlap because + // at some point an impl for `&'?a str: Error` could be added. + debug!( + "implicit_negative(impl1_header={:?}, impl2_header={:?}, obligations={:?})", + impl1_header, impl2_header, obligations + ); + let infcx = selcx.infcx(); + let opt_failing_obligation = impl1_header + .predicates + .iter() + .copied() + .chain(impl2_header.predicates) + .map(|p| infcx.resolve_vars_if_possible(p)) + .map(|p| Obligation { + cause: ObligationCause::dummy(), + param_env, + recursion_depth: 0, + predicate: p, + }) + .chain(obligations) + .find(|o| !selcx.predicate_may_hold_fatal(o)); + + if let Some(failing_obligation) = opt_failing_obligation { + debug!("overlap: obligation unsatisfiable {:?}", failing_obligation); + true + } else { + false + } +} + +/// Given impl1 and impl2 check if both impls are never satisfied by a common type (including +/// where-clauses) If so, return true, they are disjoint and false otherwise. +fn negative_impl<'cx, 'tcx>( + selcx: &mut SelectionContext<'cx, 'tcx>, + impl1_def_id: DefId, + impl2_def_id: DefId, +) -> bool { + debug!("negative_impl(impl1_def_id={:?}, impl2_def_id={:?})", impl1_def_id, impl2_def_id); + let tcx = selcx.infcx().tcx; + + // Create an infcx, taking the predicates of impl1 as assumptions: + tcx.infer_ctxt().enter(|infcx| { + // create a parameter environment corresponding to a (placeholder) instantiation of impl1 + let impl_env = tcx.param_env(impl1_def_id); + let subject1 = match traits::fully_normalize( + &infcx, + FulfillmentContext::new(), + ObligationCause::dummy(), + impl_env, + tcx.impl_subject(impl1_def_id), + ) { + Ok(s) => s, + Err(err) => bug!("failed to fully normalize {:?}: {:?}", impl1_def_id, err), + }; + + // Attempt to prove that impl2 applies, given all of the above. + let selcx = &mut SelectionContext::new(&infcx); + let impl2_substs = infcx.fresh_substs_for_item(DUMMY_SP, impl2_def_id); + let (subject2, obligations) = + impl_subject_and_oblig(selcx, impl_env, impl2_def_id, impl2_substs); + + !equate(&infcx, impl_env, subject1, subject2, obligations) + }) +} + +fn equate<'cx, 'tcx>( + infcx: &InferCtxt<'cx, 'tcx>, + impl_env: ty::ParamEnv<'tcx>, + subject1: ImplSubject<'tcx>, + subject2: ImplSubject<'tcx>, + obligations: impl Iterator<Item = PredicateObligation<'tcx>>, +) -> bool { + // do the impls unify? If not, not disjoint. + let Ok(InferOk { obligations: more_obligations, .. }) = + infcx.at(&ObligationCause::dummy(), impl_env).eq(subject1, subject2) + else { + debug!("explicit_disjoint: {:?} does not unify with {:?}", subject1, subject2); + return true; + }; + + let selcx = &mut SelectionContext::new(&infcx); + let opt_failing_obligation = obligations + .into_iter() + .chain(more_obligations) + .find(|o| negative_impl_exists(selcx, impl_env, o)); + + if let Some(failing_obligation) = opt_failing_obligation { + debug!("overlap: obligation unsatisfiable {:?}", failing_obligation); + false + } else { + true + } +} + +/// Try to prove that a negative impl exist for the given obligation and its super predicates. +#[instrument(level = "debug", skip(selcx))] +fn negative_impl_exists<'cx, 'tcx>( + selcx: &SelectionContext<'cx, 'tcx>, + param_env: ty::ParamEnv<'tcx>, + o: &PredicateObligation<'tcx>, +) -> bool { + let infcx = &selcx.infcx().fork(); + + if resolve_negative_obligation(infcx, param_env, o) { + return true; + } + + // Try to prove a negative obligation exists for super predicates + for o in util::elaborate_predicates(infcx.tcx, iter::once(o.predicate)) { + if resolve_negative_obligation(infcx, param_env, &o) { + return true; + } + } + + false +} + +#[instrument(level = "debug", skip(infcx))] +fn resolve_negative_obligation<'cx, 'tcx>( + infcx: &InferCtxt<'cx, 'tcx>, + param_env: ty::ParamEnv<'tcx>, + o: &PredicateObligation<'tcx>, +) -> bool { + let tcx = infcx.tcx; + + let Some(o) = o.flip_polarity(tcx) else { + return false; + }; + + let mut fulfillment_cx = <dyn TraitEngine<'tcx>>::new(infcx.tcx); + fulfillment_cx.register_predicate_obligation(infcx, o); + + let errors = fulfillment_cx.select_all_or_error(infcx); + + if !errors.is_empty() { + return false; + } + + // FIXME -- also add "assumed to be well formed" types into the `outlives_env` + let outlives_env = OutlivesEnvironment::new(param_env); + infcx.process_registered_region_obligations(outlives_env.region_bound_pairs(), param_env); + + infcx.resolve_regions(&outlives_env).is_empty() +} + +pub fn trait_ref_is_knowable<'tcx>( + tcx: TyCtxt<'tcx>, + trait_ref: ty::TraitRef<'tcx>, +) -> Option<Conflict> { + debug!("trait_ref_is_knowable(trait_ref={:?})", trait_ref); + if orphan_check_trait_ref(tcx, trait_ref, InCrate::Remote).is_ok() { + // A downstream or cousin crate is allowed to implement some + // substitution of this trait-ref. + return Some(Conflict::Downstream); + } + + if trait_ref_is_local_or_fundamental(tcx, trait_ref) { + // This is a local or fundamental trait, so future-compatibility + // is no concern. We know that downstream/cousin crates are not + // allowed to implement a substitution of this trait ref, which + // means impls could only come from dependencies of this crate, + // which we already know about. + return None; + } + + // This is a remote non-fundamental trait, so if another crate + // can be the "final owner" of a substitution of this trait-ref, + // they are allowed to implement it future-compatibly. + // + // However, if we are a final owner, then nobody else can be, + // and if we are an intermediate owner, then we don't care + // about future-compatibility, which means that we're OK if + // we are an owner. + if orphan_check_trait_ref(tcx, trait_ref, InCrate::Local).is_ok() { + debug!("trait_ref_is_knowable: orphan check passed"); + None + } else { + debug!("trait_ref_is_knowable: nonlocal, nonfundamental, unowned"); + Some(Conflict::Upstream) + } +} + +pub fn trait_ref_is_local_or_fundamental<'tcx>( + tcx: TyCtxt<'tcx>, + trait_ref: ty::TraitRef<'tcx>, +) -> bool { + trait_ref.def_id.krate == LOCAL_CRATE || tcx.has_attr(trait_ref.def_id, sym::fundamental) +} + +pub enum OrphanCheckErr<'tcx> { + NonLocalInputType(Vec<(Ty<'tcx>, bool /* Is this the first input type? */)>), + UncoveredTy(Ty<'tcx>, Option<Ty<'tcx>>), +} + +/// Checks the coherence orphan rules. `impl_def_id` should be the +/// `DefId` of a trait impl. To pass, either the trait must be local, or else +/// two conditions must be satisfied: +/// +/// 1. All type parameters in `Self` must be "covered" by some local type constructor. +/// 2. Some local type must appear in `Self`. +pub fn orphan_check(tcx: TyCtxt<'_>, impl_def_id: DefId) -> Result<(), OrphanCheckErr<'_>> { + debug!("orphan_check({:?})", impl_def_id); + + // We only except this routine to be invoked on implementations + // of a trait, not inherent implementations. + let trait_ref = tcx.impl_trait_ref(impl_def_id).unwrap(); + debug!("orphan_check: trait_ref={:?}", trait_ref); + + // If the *trait* is local to the crate, ok. + if trait_ref.def_id.is_local() { + debug!("trait {:?} is local to current crate", trait_ref.def_id); + return Ok(()); + } + + orphan_check_trait_ref(tcx, trait_ref, InCrate::Local) +} + +/// Checks whether a trait-ref is potentially implementable by a crate. +/// +/// The current rule is that a trait-ref orphan checks in a crate C: +/// +/// 1. Order the parameters in the trait-ref in subst order - Self first, +/// others linearly (e.g., `<U as Foo<V, W>>` is U < V < W). +/// 2. Of these type parameters, there is at least one type parameter +/// in which, walking the type as a tree, you can reach a type local +/// to C where all types in-between are fundamental types. Call the +/// first such parameter the "local key parameter". +/// - e.g., `Box<LocalType>` is OK, because you can visit LocalType +/// going through `Box`, which is fundamental. +/// - similarly, `FundamentalPair<Vec<()>, Box<LocalType>>` is OK for +/// the same reason. +/// - but (knowing that `Vec<T>` is non-fundamental, and assuming it's +/// not local), `Vec<LocalType>` is bad, because `Vec<->` is between +/// the local type and the type parameter. +/// 3. Before this local type, no generic type parameter of the impl must +/// be reachable through fundamental types. +/// - e.g. `impl<T> Trait<LocalType> for Vec<T>` is fine, as `Vec` is not fundamental. +/// - while `impl<T> Trait<LocalType> for Box<T>` results in an error, as `T` is +/// reachable through the fundamental type `Box`. +/// 4. Every type in the local key parameter not known in C, going +/// through the parameter's type tree, must appear only as a subtree of +/// a type local to C, with only fundamental types between the type +/// local to C and the local key parameter. +/// - e.g., `Vec<LocalType<T>>>` (or equivalently `Box<Vec<LocalType<T>>>`) +/// is bad, because the only local type with `T` as a subtree is +/// `LocalType<T>`, and `Vec<->` is between it and the type parameter. +/// - similarly, `FundamentalPair<LocalType<T>, T>` is bad, because +/// the second occurrence of `T` is not a subtree of *any* local type. +/// - however, `LocalType<Vec<T>>` is OK, because `T` is a subtree of +/// `LocalType<Vec<T>>`, which is local and has no types between it and +/// the type parameter. +/// +/// The orphan rules actually serve several different purposes: +/// +/// 1. They enable link-safety - i.e., 2 mutually-unknowing crates (where +/// every type local to one crate is unknown in the other) can't implement +/// the same trait-ref. This follows because it can be seen that no such +/// type can orphan-check in 2 such crates. +/// +/// To check that a local impl follows the orphan rules, we check it in +/// InCrate::Local mode, using type parameters for the "generic" types. +/// +/// 2. They ground negative reasoning for coherence. If a user wants to +/// write both a conditional blanket impl and a specific impl, we need to +/// make sure they do not overlap. For example, if we write +/// ```ignore (illustrative) +/// impl<T> IntoIterator for Vec<T> +/// impl<T: Iterator> IntoIterator for T +/// ``` +/// We need to be able to prove that `Vec<$0>: !Iterator` for every type $0. +/// We can observe that this holds in the current crate, but we need to make +/// sure this will also hold in all unknown crates (both "independent" crates, +/// which we need for link-safety, and also child crates, because we don't want +/// child crates to get error for impl conflicts in a *dependency*). +/// +/// For that, we only allow negative reasoning if, for every assignment to the +/// inference variables, every unknown crate would get an orphan error if they +/// try to implement this trait-ref. To check for this, we use InCrate::Remote +/// mode. That is sound because we already know all the impls from known crates. +/// +/// 3. For non-`#[fundamental]` traits, they guarantee that parent crates can +/// add "non-blanket" impls without breaking negative reasoning in dependent +/// crates. This is the "rebalancing coherence" (RFC 1023) restriction. +/// +/// For that, we only a allow crate to perform negative reasoning on +/// non-local-non-`#[fundamental]` only if there's a local key parameter as per (2). +/// +/// Because we never perform negative reasoning generically (coherence does +/// not involve type parameters), this can be interpreted as doing the full +/// orphan check (using InCrate::Local mode), substituting non-local known +/// types for all inference variables. +/// +/// This allows for crates to future-compatibly add impls as long as they +/// can't apply to types with a key parameter in a child crate - applying +/// the rules, this basically means that every type parameter in the impl +/// must appear behind a non-fundamental type (because this is not a +/// type-system requirement, crate owners might also go for "semantic +/// future-compatibility" involving things such as sealed traits, but +/// the above requirement is sufficient, and is necessary in "open world" +/// cases). +/// +/// Note that this function is never called for types that have both type +/// parameters and inference variables. +fn orphan_check_trait_ref<'tcx>( + tcx: TyCtxt<'tcx>, + trait_ref: ty::TraitRef<'tcx>, + in_crate: InCrate, +) -> Result<(), OrphanCheckErr<'tcx>> { + debug!("orphan_check_trait_ref(trait_ref={:?}, in_crate={:?})", trait_ref, in_crate); + + if trait_ref.needs_infer() && trait_ref.needs_subst() { + bug!( + "can't orphan check a trait ref with both params and inference variables {:?}", + trait_ref + ); + } + + let mut checker = OrphanChecker::new(tcx, in_crate); + match trait_ref.visit_with(&mut checker) { + ControlFlow::Continue(()) => Err(OrphanCheckErr::NonLocalInputType(checker.non_local_tys)), + ControlFlow::Break(OrphanCheckEarlyExit::ParamTy(ty)) => { + // Does there exist some local type after the `ParamTy`. + checker.search_first_local_ty = true; + if let Some(OrphanCheckEarlyExit::LocalTy(local_ty)) = + trait_ref.visit_with(&mut checker).break_value() + { + Err(OrphanCheckErr::UncoveredTy(ty, Some(local_ty))) + } else { + Err(OrphanCheckErr::UncoveredTy(ty, None)) + } + } + ControlFlow::Break(OrphanCheckEarlyExit::LocalTy(_)) => Ok(()), + } +} + +struct OrphanChecker<'tcx> { + tcx: TyCtxt<'tcx>, + in_crate: InCrate, + in_self_ty: bool, + /// Ignore orphan check failures and exclusively search for the first + /// local type. + search_first_local_ty: bool, + non_local_tys: Vec<(Ty<'tcx>, bool)>, +} + +impl<'tcx> OrphanChecker<'tcx> { + fn new(tcx: TyCtxt<'tcx>, in_crate: InCrate) -> Self { + OrphanChecker { + tcx, + in_crate, + in_self_ty: true, + search_first_local_ty: false, + non_local_tys: Vec::new(), + } + } + + fn found_non_local_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<OrphanCheckEarlyExit<'tcx>> { + self.non_local_tys.push((t, self.in_self_ty)); + ControlFlow::CONTINUE + } + + fn found_param_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<OrphanCheckEarlyExit<'tcx>> { + if self.search_first_local_ty { + ControlFlow::CONTINUE + } else { + ControlFlow::Break(OrphanCheckEarlyExit::ParamTy(t)) + } + } + + fn def_id_is_local(&mut self, def_id: DefId) -> bool { + match self.in_crate { + InCrate::Local => def_id.is_local(), + InCrate::Remote => false, + } + } +} + +enum OrphanCheckEarlyExit<'tcx> { + ParamTy(Ty<'tcx>), + LocalTy(Ty<'tcx>), +} + +impl<'tcx> TypeVisitor<'tcx> for OrphanChecker<'tcx> { + type BreakTy = OrphanCheckEarlyExit<'tcx>; + fn visit_region(&mut self, _r: ty::Region<'tcx>) -> ControlFlow<Self::BreakTy> { + ControlFlow::CONTINUE + } + + fn visit_ty(&mut self, ty: Ty<'tcx>) -> ControlFlow<Self::BreakTy> { + let result = match *ty.kind() { + ty::Bool + | ty::Char + | ty::Int(..) + | ty::Uint(..) + | ty::Float(..) + | ty::Str + | ty::FnDef(..) + | ty::FnPtr(_) + | ty::Array(..) + | ty::Slice(..) + | ty::RawPtr(..) + | ty::Never + | ty::Tuple(..) + | ty::Projection(..) => self.found_non_local_ty(ty), + + ty::Param(..) => self.found_param_ty(ty), + + ty::Placeholder(..) | ty::Bound(..) | ty::Infer(..) => match self.in_crate { + InCrate::Local => self.found_non_local_ty(ty), + // The inference variable might be unified with a local + // type in that remote crate. + InCrate::Remote => ControlFlow::Break(OrphanCheckEarlyExit::LocalTy(ty)), + }, + + // For fundamental types, we just look inside of them. + ty::Ref(_, ty, _) => ty.visit_with(self), + ty::Adt(def, substs) => { + if self.def_id_is_local(def.did()) { + ControlFlow::Break(OrphanCheckEarlyExit::LocalTy(ty)) + } else if def.is_fundamental() { + substs.visit_with(self) + } else { + self.found_non_local_ty(ty) + } + } + ty::Foreign(def_id) => { + if self.def_id_is_local(def_id) { + ControlFlow::Break(OrphanCheckEarlyExit::LocalTy(ty)) + } else { + self.found_non_local_ty(ty) + } + } + ty::Dynamic(tt, ..) => { + let principal = tt.principal().map(|p| p.def_id()); + if principal.map_or(false, |p| self.def_id_is_local(p)) { + ControlFlow::Break(OrphanCheckEarlyExit::LocalTy(ty)) + } else { + self.found_non_local_ty(ty) + } + } + ty::Error(_) => ControlFlow::Break(OrphanCheckEarlyExit::LocalTy(ty)), + ty::Closure(..) | ty::Generator(..) | ty::GeneratorWitness(..) => { + self.tcx.sess.delay_span_bug( + DUMMY_SP, + format!("ty_is_local invoked on closure or generator: {:?}", ty), + ); + ControlFlow::Break(OrphanCheckEarlyExit::LocalTy(ty)) + } + ty::Opaque(..) => { + // This merits some explanation. + // Normally, opaque types are not involved when performing + // coherence checking, since it is illegal to directly + // implement a trait on an opaque type. However, we might + // end up looking at an opaque type during coherence checking + // if an opaque type gets used within another type (e.g. as + // the type of a field) when checking for auto trait or `Sized` + // impls. This requires us to decide whether or not an opaque + // type should be considered 'local' or not. + // + // We choose to treat all opaque types as non-local, even + // those that appear within the same crate. This seems + // somewhat surprising at first, but makes sense when + // you consider that opaque types are supposed to hide + // the underlying type *within the same crate*. When an + // opaque type is used from outside the module + // where it is declared, it should be impossible to observe + // anything about it other than the traits that it implements. + // + // The alternative would be to look at the underlying type + // to determine whether or not the opaque type itself should + // be considered local. However, this could make it a breaking change + // to switch the underlying ('defining') type from a local type + // to a remote type. This would violate the rule that opaque + // types should be completely opaque apart from the traits + // that they implement, so we don't use this behavior. + self.found_non_local_ty(ty) + } + }; + // A bit of a hack, the `OrphanChecker` is only used to visit a `TraitRef`, so + // the first type we visit is always the self type. + self.in_self_ty = false; + result + } + + // FIXME: Constants should participate in orphan checking. + fn visit_const(&mut self, _c: ty::Const<'tcx>) -> ControlFlow<Self::BreakTy> { + ControlFlow::CONTINUE + } +} |