Use impl obligations as initial environment for specialization #37541
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This fixes a regression. Backport? Perhaps best would be to backport a less aggressive version (basically drop the 3rd commit). cc @rust-lang/compiler |
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The `specializes()` function was trying to normalize the impl trait in an empty environment. This could lead to inexplicable failures.
This seems better because I want to avoid the situation where unresolved inference variables make it into the environment. On the other hand, I am not 100% sure that this is correct. My assumption was that the WF check should ensure that this normalization can succeed. But it occurs to me that the WF checks may need to make use of the `specializes` predicate themselves, and hence we may have a kind of cycle here (this is a bigger problem with spec in any case that we need to resolve). On the other hand, this should just cause extra errors I think, so it seems like a safe thing to attempt. Certainly all tests pass.
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@bors r+ p=1 (need to get backports done) |
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📌 Commit b4f910d has been approved by |
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Use impl obligations as initial environment for specialization This corrects a small regression in specialization that crept in, I think as part of the refactoring to introduce arenas. I also made an experiment (in the last commit) to cleanup the code to be more aggressive about normalization. As the commit log notes, I am not 100% sure that this is correct, but it feels safer, and I think that at worst it yields *more* ICEs (as opposed to admitting faulty code). I'll schedule a crater run to check beyond the testbase. Fixes #37291. r? @aturon
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Approving for backport w/o the 3rd commit, which is a bit more conservative. The first part is definitely wrong and this fixes a regression. cc @rust-lang/compiler |
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This corrects a small regression in specialization that crept in, I think as part of the refactoring to introduce arenas. I also made an experiment (in the last commit) to cleanup the code to be more aggressive about normalization. As the commit log notes, I am not 100% sure that this is correct, but it feels safer, and I think that at worst it yields more ICEs (as opposed to admitting faulty code). I'll schedule a crater run to check beyond the testbase.
Fixes #37291.
r? @aturon