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Rollup merge of #109447 - lcnr:coherence, r=compiler-errors

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new solver cleanup + implement coherence

the cleanup:
- change `Certainty::unify_and` to consider ambig + overflow to be ambig
- rename `trait_candidate_should_be_dropped_in_favor_of` to `candidate_should_be_dropped_in_favor_of`
- remove outdated fixme

For coherence I mostly just add an ambiguous candidate if the current trait ref is unknowable. I am doing the same for reservation impl where I also just add an ambiguous candidate.
This commit is contained in:
Matthias Krüger 2023-03-22 22:44:43 +01:00 • committed by GitHub
commit 28b9354bf6
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20 changed files with 226 additions and 62 deletions
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13
compiler/rustc_middle/src/traits/solve.rs
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@ -63,15 +63,14 @@ impl Certainty {
(Certainty::Yes, Certainty::Yes) => Certainty::Yes,
(Certainty::Yes, Certainty::Maybe(_)) => other,
(Certainty::Maybe(_), Certainty::Yes) => self,
(Certainty::Maybe(MaybeCause::Overflow), Certainty::Maybe(MaybeCause::Overflow)) => {
Certainty::Maybe(MaybeCause::Overflow)
}
// If at least one of the goals is ambiguous, hide the overflow as the ambiguous goal
// may still result in failure.
(Certainty::Maybe(MaybeCause::Ambiguity), Certainty::Maybe(_))
| (Certainty::Maybe(_), Certainty::Maybe(MaybeCause::Ambiguity)) => {
(Certainty::Maybe(MaybeCause::Ambiguity), Certainty::Maybe(MaybeCause::Ambiguity)) => {
Certainty::Maybe(MaybeCause::Ambiguity)
}
(Certainty::Maybe(MaybeCause::Ambiguity), Certainty::Maybe(MaybeCause::Overflow))
| (Certainty::Maybe(MaybeCause::Overflow), Certainty::Maybe(MaybeCause::Ambiguity))
| (Certainty::Maybe(MaybeCause::Overflow), Certainty::Maybe(MaybeCause::Overflow)) => {
Certainty::Maybe(MaybeCause::Overflow)
}
}
}
}