Prefer ObjectCandidate to ImplCandidate if both apply #24056
Merged
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If we find a blanket impl for
Trait
but we're matching on an objectTrait
, prefer the object (I think we could perhaps go either way, but this seems safer). Also give a nice error for attempts to manuallyimpl Trait for Trait
, since they will be ineffectual.This fixes the problems around ambiguity ICEs relating to
Any
andMarkerTrait
that were cropping up all over the place. There may still be similar ICEs reported in #21756 that this PR does not address.Fixes #24015.
Fixes #24051.
Fixes #24037.
Fixes #23853.
Fixes #21942.
cc #21756.
cc @alexcrichton (this fixes crates.io)
r? @aturon