761 lines
30 KiB
Rust
761 lines
30 KiB
Rust
//! See Rustc Dev Guide chapters on [trait-resolution] and [trait-specialization] for more info on
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//! how this works.
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//!
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//! [trait-resolution]: https://rustc-dev-guide.rust-lang.org/traits/resolution.html
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//! [trait-specialization]: https://rustc-dev-guide.rust-lang.org/traits/specialization.html
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use crate::infer::outlives::env::OutlivesEnvironment;
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use crate::infer::{CombinedSnapshot, InferOk};
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use crate::traits::outlives_bounds::InferCtxtExt as _;
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use crate::traits::select::IntercrateAmbiguityCause;
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use crate::traits::util::impl_subject_and_oblig;
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use crate::traits::SkipLeakCheck;
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use crate::traits::{
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self, Obligation, ObligationCause, ObligationCtxt, PredicateObligation, PredicateObligations,
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SelectionContext,
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};
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use rustc_data_structures::fx::FxIndexSet;
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use rustc_errors::Diagnostic;
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use rustc_hir::def_id::{DefId, CRATE_DEF_ID, LOCAL_CRATE};
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use rustc_hir::CRATE_HIR_ID;
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use rustc_infer::infer::{DefiningAnchor, InferCtxt, TyCtxtInferExt};
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use rustc_infer::traits::util;
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use rustc_middle::traits::specialization_graph::OverlapMode;
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use rustc_middle::ty::fast_reject::{DeepRejectCtxt, TreatParams};
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use rustc_middle::ty::visit::TypeVisitable;
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use rustc_middle::ty::{self, ImplSubject, Ty, TyCtxt, TypeVisitor};
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use rustc_span::symbol::sym;
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use rustc_span::DUMMY_SP;
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use std::fmt::Debug;
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use std::iter;
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use std::ops::ControlFlow;
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use super::NormalizeExt;
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/// Whether we do the orphan check relative to this crate or
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/// to some remote crate.
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#[derive(Copy, Clone, Debug)]
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enum InCrate {
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Local,
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Remote,
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}
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#[derive(Debug, Copy, Clone)]
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pub enum Conflict {
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Upstream,
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Downstream,
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}
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pub struct OverlapResult<'tcx> {
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pub impl_header: ty::ImplHeader<'tcx>,
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pub intercrate_ambiguity_causes: FxIndexSet<IntercrateAmbiguityCause>,
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/// `true` if the overlap might've been permitted before the shift
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/// to universes.
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pub involves_placeholder: bool,
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}
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pub fn add_placeholder_note(err: &mut Diagnostic) {
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err.note(
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"this behavior recently changed as a result of a bug fix; \
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see rust-lang/rust#56105 for details",
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);
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}
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/// If there are types that satisfy both impls, returns `Some`
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/// with a suitably-freshened `ImplHeader` with those types
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/// substituted. Otherwise, returns `None`.
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#[instrument(skip(tcx, skip_leak_check), level = "debug")]
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pub fn overlapping_impls(
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tcx: TyCtxt<'_>,
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impl1_def_id: DefId,
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impl2_def_id: DefId,
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skip_leak_check: SkipLeakCheck,
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overlap_mode: OverlapMode,
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) -> Option<OverlapResult<'_>> {
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// Before doing expensive operations like entering an inference context, do
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// a quick check via fast_reject to tell if the impl headers could possibly
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// unify.
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let drcx = DeepRejectCtxt { treat_obligation_params: TreatParams::AsInfer };
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let impl1_ref = tcx.impl_trait_ref(impl1_def_id);
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let impl2_ref = tcx.impl_trait_ref(impl2_def_id);
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let may_overlap = match (impl1_ref, impl2_ref) {
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(Some(a), Some(b)) => iter::zip(a.substs, b.substs)
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.all(|(arg1, arg2)| drcx.generic_args_may_unify(arg1, arg2)),
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(None, None) => {
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let self_ty1 = tcx.type_of(impl1_def_id);
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let self_ty2 = tcx.type_of(impl2_def_id);
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drcx.types_may_unify(self_ty1, self_ty2)
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}
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_ => bug!("unexpected impls: {impl1_def_id:?} {impl2_def_id:?}"),
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};
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if !may_overlap {
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// Some types involved are definitely different, so the impls couldn't possibly overlap.
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debug!("overlapping_impls: fast_reject early-exit");
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return None;
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}
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let infcx =
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tcx.infer_ctxt().with_opaque_type_inference(DefiningAnchor::Bubble).intercrate().build();
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let selcx = &mut SelectionContext::new(&infcx);
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let overlaps =
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overlap(selcx, skip_leak_check, impl1_def_id, impl2_def_id, overlap_mode).is_some();
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if !overlaps {
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return None;
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}
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// In the case where we detect an error, run the check again, but
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// this time tracking intercrate ambiguity causes for better
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// diagnostics. (These take time and can lead to false errors.)
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let infcx =
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tcx.infer_ctxt().with_opaque_type_inference(DefiningAnchor::Bubble).intercrate().build();
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let selcx = &mut SelectionContext::new(&infcx);
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selcx.enable_tracking_intercrate_ambiguity_causes();
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Some(overlap(selcx, skip_leak_check, impl1_def_id, impl2_def_id, overlap_mode).unwrap())
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}
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fn with_fresh_ty_vars<'cx, 'tcx>(
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selcx: &mut SelectionContext<'cx, 'tcx>,
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param_env: ty::ParamEnv<'tcx>,
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impl_def_id: DefId,
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) -> ty::ImplHeader<'tcx> {
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let tcx = selcx.tcx();
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let impl_substs = selcx.infcx.fresh_substs_for_item(DUMMY_SP, impl_def_id);
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let header = ty::ImplHeader {
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impl_def_id,
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self_ty: tcx.bound_type_of(impl_def_id).subst(tcx, impl_substs),
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trait_ref: tcx.bound_impl_trait_ref(impl_def_id).map(|i| i.subst(tcx, impl_substs)),
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predicates: tcx.predicates_of(impl_def_id).instantiate(tcx, impl_substs).predicates,
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};
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let InferOk { value: mut header, obligations } =
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selcx.infcx.at(&ObligationCause::dummy(), param_env).normalize(header);
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header.predicates.extend(obligations.into_iter().map(|o| o.predicate));
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header
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}
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/// Can both impl `a` and impl `b` be satisfied by a common type (including
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/// where-clauses)? If so, returns an `ImplHeader` that unifies the two impls.
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fn overlap<'cx, 'tcx>(
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selcx: &mut SelectionContext<'cx, 'tcx>,
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skip_leak_check: SkipLeakCheck,
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impl1_def_id: DefId,
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impl2_def_id: DefId,
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overlap_mode: OverlapMode,
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) -> Option<OverlapResult<'tcx>> {
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debug!(
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"overlap(impl1_def_id={:?}, impl2_def_id={:?}, overlap_mode={:?})",
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impl1_def_id, impl2_def_id, overlap_mode
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);
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selcx.infcx.probe_maybe_skip_leak_check(skip_leak_check.is_yes(), |snapshot| {
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overlap_within_probe(selcx, impl1_def_id, impl2_def_id, overlap_mode, snapshot)
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})
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}
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fn overlap_within_probe<'cx, 'tcx>(
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selcx: &mut SelectionContext<'cx, 'tcx>,
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impl1_def_id: DefId,
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impl2_def_id: DefId,
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overlap_mode: OverlapMode,
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snapshot: &CombinedSnapshot<'tcx>,
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) -> Option<OverlapResult<'tcx>> {
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let infcx = selcx.infcx;
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if overlap_mode.use_negative_impl() {
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if negative_impl(infcx.tcx, impl1_def_id, impl2_def_id)
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|| negative_impl(infcx.tcx, impl2_def_id, impl1_def_id)
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{
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return None;
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}
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}
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// For the purposes of this check, we don't bring any placeholder
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// types into scope; instead, we replace the generic types with
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// fresh type variables, and hence we do our evaluations in an
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// empty environment.
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let param_env = ty::ParamEnv::empty();
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let impl1_header = with_fresh_ty_vars(selcx, param_env, impl1_def_id);
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let impl2_header = with_fresh_ty_vars(selcx, param_env, impl2_def_id);
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let obligations = equate_impl_headers(selcx, &impl1_header, &impl2_header)?;
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debug!("overlap: unification check succeeded");
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if overlap_mode.use_implicit_negative() {
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if implicit_negative(selcx, param_env, &impl1_header, impl2_header, obligations) {
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return None;
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}
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}
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// We disable the leak when creating the `snapshot` by using
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// `infcx.probe_maybe_disable_leak_check`.
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if infcx.leak_check(true, snapshot).is_err() {
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debug!("overlap: leak check failed");
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return None;
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}
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let intercrate_ambiguity_causes = selcx.take_intercrate_ambiguity_causes();
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debug!("overlap: intercrate_ambiguity_causes={:#?}", intercrate_ambiguity_causes);
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let involves_placeholder =
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matches!(selcx.infcx.region_constraints_added_in_snapshot(snapshot), Some(true));
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let impl_header = selcx.infcx.resolve_vars_if_possible(impl1_header);
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Some(OverlapResult { impl_header, intercrate_ambiguity_causes, involves_placeholder })
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}
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fn equate_impl_headers<'cx, 'tcx>(
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selcx: &mut SelectionContext<'cx, 'tcx>,
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impl1_header: &ty::ImplHeader<'tcx>,
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impl2_header: &ty::ImplHeader<'tcx>,
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) -> Option<PredicateObligations<'tcx>> {
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// Do `a` and `b` unify? If not, no overlap.
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debug!("equate_impl_headers(impl1_header={:?}, impl2_header={:?}", impl1_header, impl2_header);
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selcx
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.infcx
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.at(&ObligationCause::dummy(), ty::ParamEnv::empty())
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.eq_impl_headers(impl1_header, impl2_header)
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.map(|infer_ok| infer_ok.obligations)
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.ok()
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}
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/// Given impl1 and impl2 check if both impls can be satisfied by a common type (including
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/// where-clauses) If so, return false, otherwise return true, they are disjoint.
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fn implicit_negative<'cx, 'tcx>(
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selcx: &mut SelectionContext<'cx, 'tcx>,
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param_env: ty::ParamEnv<'tcx>,
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impl1_header: &ty::ImplHeader<'tcx>,
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impl2_header: ty::ImplHeader<'tcx>,
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obligations: PredicateObligations<'tcx>,
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) -> bool {
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// There's no overlap if obligations are unsatisfiable or if the obligation negated is
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// satisfied.
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//
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// For example, given these two impl headers:
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//
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// `impl<'a> From<&'a str> for Box<dyn Error>`
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// `impl<E> From<E> for Box<dyn Error> where E: Error`
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//
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// So we have:
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//
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// `Box<dyn Error>: From<&'?a str>`
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// `Box<dyn Error>: From<?E>`
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//
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// After equating the two headers:
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//
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// `Box<dyn Error> = Box<dyn Error>`
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// So, `?E = &'?a str` and then given the where clause `&'?a str: Error`.
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//
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// If the obligation `&'?a str: Error` holds, it means that there's overlap. If that doesn't
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// hold we need to check if `&'?a str: !Error` holds, if doesn't hold there's overlap because
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// at some point an impl for `&'?a str: Error` could be added.
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debug!(
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"implicit_negative(impl1_header={:?}, impl2_header={:?}, obligations={:?})",
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impl1_header, impl2_header, obligations
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);
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let infcx = selcx.infcx;
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let opt_failing_obligation = impl1_header
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.predicates
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.iter()
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.copied()
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.chain(impl2_header.predicates)
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.map(|p| infcx.resolve_vars_if_possible(p))
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.map(|p| Obligation {
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cause: ObligationCause::dummy(),
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param_env,
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recursion_depth: 0,
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predicate: p,
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})
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.chain(obligations)
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.find(|o| !selcx.predicate_may_hold_fatal(o));
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if let Some(failing_obligation) = opt_failing_obligation {
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debug!("overlap: obligation unsatisfiable {:?}", failing_obligation);
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true
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} else {
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false
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}
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}
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/// Given impl1 and impl2 check if both impls are never satisfied by a common type (including
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/// where-clauses) If so, return true, they are disjoint and false otherwise.
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fn negative_impl(tcx: TyCtxt<'_>, impl1_def_id: DefId, impl2_def_id: DefId) -> bool {
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debug!("negative_impl(impl1_def_id={:?}, impl2_def_id={:?})", impl1_def_id, impl2_def_id);
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// Create an infcx, taking the predicates of impl1 as assumptions:
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let infcx = tcx.infer_ctxt().build();
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// create a parameter environment corresponding to a (placeholder) instantiation of impl1
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let impl_env = tcx.param_env(impl1_def_id);
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let subject1 = match traits::fully_normalize(
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&infcx,
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ObligationCause::dummy(),
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impl_env,
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tcx.impl_subject(impl1_def_id),
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) {
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Ok(s) => s,
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Err(err) => {
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tcx.sess.delay_span_bug(
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tcx.def_span(impl1_def_id),
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format!("failed to fully normalize {:?}: {:?}", impl1_def_id, err),
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);
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return false;
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}
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};
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// Attempt to prove that impl2 applies, given all of the above.
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let selcx = &mut SelectionContext::new(&infcx);
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let impl2_substs = infcx.fresh_substs_for_item(DUMMY_SP, impl2_def_id);
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let (subject2, obligations) =
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impl_subject_and_oblig(selcx, impl_env, impl2_def_id, impl2_substs);
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!equate(&infcx, impl_env, subject1, subject2, obligations, impl1_def_id)
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}
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fn equate<'tcx>(
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infcx: &InferCtxt<'tcx>,
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impl_env: ty::ParamEnv<'tcx>,
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subject1: ImplSubject<'tcx>,
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subject2: ImplSubject<'tcx>,
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obligations: impl Iterator<Item = PredicateObligation<'tcx>>,
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body_def_id: DefId,
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) -> bool {
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// do the impls unify? If not, not disjoint.
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let Ok(InferOk { obligations: more_obligations, .. }) =
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infcx.at(&ObligationCause::dummy(), impl_env).eq(subject1, subject2)
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else {
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debug!("explicit_disjoint: {:?} does not unify with {:?}", subject1, subject2);
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return true;
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};
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let opt_failing_obligation = obligations
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.into_iter()
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.chain(more_obligations)
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.find(|o| negative_impl_exists(infcx, o, body_def_id));
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if let Some(failing_obligation) = opt_failing_obligation {
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debug!("overlap: obligation unsatisfiable {:?}", failing_obligation);
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false
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} else {
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true
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}
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}
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/// Try to prove that a negative impl exist for the given obligation and its super predicates.
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#[instrument(level = "debug", skip(infcx))]
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fn negative_impl_exists<'tcx>(
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infcx: &InferCtxt<'tcx>,
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o: &PredicateObligation<'tcx>,
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body_def_id: DefId,
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) -> bool {
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if resolve_negative_obligation(infcx.fork(), o, body_def_id) {
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return true;
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}
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// Try to prove a negative obligation exists for super predicates
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for o in util::elaborate_predicates(infcx.tcx, iter::once(o.predicate)) {
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if resolve_negative_obligation(infcx.fork(), &o, body_def_id) {
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return true;
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}
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}
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false
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}
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#[instrument(level = "debug", skip(infcx))]
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fn resolve_negative_obligation<'tcx>(
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infcx: InferCtxt<'tcx>,
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o: &PredicateObligation<'tcx>,
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body_def_id: DefId,
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) -> bool {
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let tcx = infcx.tcx;
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let Some(o) = o.flip_polarity(tcx) else {
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return false;
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};
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let param_env = o.param_env;
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if !super::fully_solve_obligation(&infcx, o).is_empty() {
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return false;
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}
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let (body_id, body_def_id) = if let Some(body_def_id) = body_def_id.as_local() {
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(tcx.hir().local_def_id_to_hir_id(body_def_id), body_def_id)
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} else {
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(CRATE_HIR_ID, CRATE_DEF_ID)
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};
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let ocx = ObligationCtxt::new(&infcx);
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let wf_tys = ocx.assumed_wf_types(param_env, DUMMY_SP, body_def_id);
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let outlives_env = OutlivesEnvironment::with_bounds(
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param_env,
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Some(&infcx),
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infcx.implied_bounds_tys(param_env, body_id, wf_tys),
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);
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infcx.process_registered_region_obligations(outlives_env.region_bound_pairs(), param_env);
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infcx.resolve_regions(&outlives_env).is_empty()
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}
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pub fn trait_ref_is_knowable<'tcx>(
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tcx: TyCtxt<'tcx>,
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trait_ref: ty::TraitRef<'tcx>,
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) -> Result<(), Conflict> {
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debug!("trait_ref_is_knowable(trait_ref={:?})", trait_ref);
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if orphan_check_trait_ref(tcx, trait_ref, InCrate::Remote).is_ok() {
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// A downstream or cousin crate is allowed to implement some
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// substitution of this trait-ref.
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return Err(Conflict::Downstream);
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}
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if trait_ref_is_local_or_fundamental(tcx, trait_ref) {
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// This is a local or fundamental trait, so future-compatibility
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// is no concern. We know that downstream/cousin crates are not
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// allowed to implement a substitution of this trait ref, which
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// means impls could only come from dependencies of this crate,
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// which we already know about.
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return Ok(());
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}
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// This is a remote non-fundamental trait, so if another crate
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// can be the "final owner" of a substitution of this trait-ref,
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// they are allowed to implement it future-compatibly.
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//
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// However, if we are a final owner, then nobody else can be,
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// and if we are an intermediate owner, then we don't care
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// about future-compatibility, which means that we're OK if
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// we are an owner.
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if orphan_check_trait_ref(tcx, trait_ref, InCrate::Local).is_ok() {
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debug!("trait_ref_is_knowable: orphan check passed");
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Ok(())
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} else {
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|
debug!("trait_ref_is_knowable: nonlocal, nonfundamental, unowned");
|
|
Err(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::Alias(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::Alias(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
|
|
}
|
|
|
|
/// All possible values for a constant parameter already exist
|
|
/// in the crate defining the trait, so they are always non-local[^1].
|
|
///
|
|
/// Because there's no way to have an impl where the first local
|
|
/// generic argument is a constant, we also don't have to fail
|
|
/// the orphan check when encountering a parameter or a generic constant.
|
|
///
|
|
/// This means that we can completely ignore constants during the orphan check.
|
|
///
|
|
/// See `src/test/ui/coherence/const-generics-orphan-check-ok.rs` for examples.
|
|
///
|
|
/// [^1]: This might not hold for function pointers or trait objects in the future.
|
|
/// As these should be quite rare as const arguments and especially rare as impl
|
|
/// parameters, allowing uncovered const parameters in impls seems more useful
|
|
/// than allowing `impl<T> Trait<local_fn_ptr, T> for i32` to compile.
|
|
fn visit_const(&mut self, _c: ty::Const<'tcx>) -> ControlFlow<Self::BreakTy> {
|
|
ControlFlow::CONTINUE
|
|
}
|
|
}
|