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Add overlap mode

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This commit is contained in:
Santiago Pastorino 2022-01-21 12:22:13 -03:00
parent b2a45f0645
commit c2890ed426
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GPG Key ID: 8131A24E0C79EFAF
1 changed files with 27 additions and 9 deletions
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34
compiler/rustc_trait_selection/src/traits/coherence.rs
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@ -135,6 +135,25 @@ fn with_fresh_ty_vars<'cx, 'tcx>(
header
}
enum OverlapMode {
Stable,
Strict,
}
fn overlap_mode<'tcx>(tcx: TyCtxt<'tcx>, impl1_def_id: DefId, impl2_def_id: DefId) -> OverlapMode {
if tcx.has_attr(impl1_def_id, sym::rustc_strict_coherence)
!= tcx.has_attr(impl2_def_id, sym::rustc_strict_coherence)
{
bug!("Use strict coherence on both impls",);
}
if tcx.has_attr(impl1_def_id, sym::rustc_strict_coherence) {
OverlapMode::Strict
} else {
OverlapMode::Stable
}
}
/// 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>(
@ -169,10 +188,8 @@ fn overlap_within_probe<'cx, 'tcx>(
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 strict_coherence = tcx.has_attr(impl1_def_id, sym::rustc_strict_coherence)
&& tcx.has_attr(impl2_def_id, sym::rustc_strict_coherence);
if stable_disjoint(selcx, param_env, &impl1_header, impl2_header, strict_coherence) {
let overlap_mode = overlap_mode(tcx, impl1_def_id, impl2_def_id);
if stable_disjoint(selcx, param_env, &impl1_header, impl2_header, overlap_mode) {
return None;
}
@ -200,7 +217,7 @@ fn stable_disjoint<'cx, 'tcx>(
param_env: ty::ParamEnv<'tcx>,
impl1_header: &ty::ImplHeader<'tcx>,
impl2_header: ty::ImplHeader<'tcx>,
strict_coherence: bool,
overlap_mode: OverlapMode,
) -> bool {
debug!("overlap: impl1_header={:?}", impl1_header);
debug!("overlap: impl2_header={:?}", impl2_header);
@ -258,11 +275,12 @@ fn stable_disjoint<'cx, 'tcx>(
.find(|o| {
// if both impl headers are set to strict coherence it means that this will be accepted
// only if it's stated that T: !Trait. So only prove that the negated obligation holds.
if strict_coherence {
strict_check(selcx, o)
} else {
match overlap_mode {
OverlapMode::Stable => {
loose_check(selcx, o) || tcx.features().negative_impls && strict_check(selcx, o)
}
OverlapMode::Strict => strict_check(selcx, o),
}
});
// FIXME: the call to `selcx.predicate_may_hold_fatal` above should be ported
// to the canonical trait query form, `infcx.predicate_may_hold`, once