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Add rustc_strict_coherence attribute and use it to check overlap

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Santiago Pastorino 2021-10-22 15:44:28 -03:00
parent 74454c4888
commit da79fa964c
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6 changed files with 64 additions and 2 deletions
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15
compiler/rustc_trait_selection/src/traits/coherence.rs
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@ -222,11 +222,22 @@ fn overlap_within_probe(
})
.chain(obligations)
.find(|o| {
!selcx.predicate_may_hold_fatal(o)
|| o.flip_polarity(tcx)
// 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 tcx.has_attr(a_def_id, sym::rustc_strict_coherence)
&& tcx.has_attr(b_def_id, sym::rustc_strict_coherence)
{
o.flip_polarity(tcx)
.as_ref()
.map(|o| selcx.infcx().predicate_must_hold_modulo_regions(o))
.unwrap_or(false)
} else {
!selcx.predicate_may_hold_fatal(o)
|| o.flip_polarity(tcx)
.as_ref()
.map(|o| selcx.infcx().predicate_must_hold_modulo_regions(o))
.unwrap_or(false)
}
});
// FIXME: the call to `selcx.predicate_may_hold_fatal` above should be ported
// to the canonical trait query form, `infcx.predicate_may_hold`, once