Check for uninhabited types in sub-patterns (#12609) #36476
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r? @arielb1 (rust_highfive has picked a reviewer for you, use r? to override) |
canndrew
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☔ The latest upstream changes (presumably #36551) made this pull request unmergeable. Please resolve the merge conflicts. |
canndrew
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☔ The latest upstream changes (presumably #36857) made this pull request unmergeable. Please resolve the merge conflicts. |
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I would prefer that people on the lang team to look on this. |
This alters the exhaustiveness-checking algorithm for pattern matches to avoid raising spurious errors about cases not being covered for uninhabited types. Specifically, the construct_witness function now returns an Option. If it sees that DUMMY_WILD_PAT is being used to match on an uninhabited type it returns None to indicate that there is no witness. We look for DUMMY_WILD_PAT specifically and not any wildcard pattern so that wildcard patterns explicitly written by the programmer continue to work without raising errors about unreachability.
canndrew
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☔ The latest upstream changes (presumably #36695) made this pull request unmergeable. Please resolve the merge conflicts. |
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Looks like the code that this touched went through a major refactor and this PR will have to be rewritten. |
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/cc @rust-lang/lang @rust-lang/compiler |
aturon
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@canndrew shall we close the PR then and you can re-open when ready? |
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@nikomatsakis Sure |
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There's another, more complete and correct attempt at fixing this here: #38069 |
This alters the exhaustiveness-checking algorithm for pattern matches to
avoid raising spurious errors about cases not being covered for
uninhabited types.
Specifically, the construct_witness function now returns an Option. If
it sees that DUMMY_WILD_PAT is being used to match on an uninhabited
type it returns None to indicate that there is no witness. We look for
DUMMY_WILD_PAT specifically and not any wildcard pattern so that
wildcard patterns explicitly written by the programmer continue to work
without raising errors about unreachability.