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avoid double-unsizing arrays in bytestring match lowering - #47503
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The match lowering code, when lowering matches against bytestrings, works by coercing both the scrutinee and the pattern to `&[u8]` and then comparing them using `<[u8] as Eq>::eq`. If the scrutinee is already of type `&[u8]`, then unsizing it is both unneccessary and a trait error caught by the new and updated MIR typeck, so this PR changes lowering to avoid doing that (match lowering tried to avoid that before, but that attempt was quite broken). Fixesrust-lang#46920.
arielb1
commented
Jan 16, 2018
ContributorAuthor
beta-nominating because this is a regression |
eddyb
approved these changes
Jan 17, 2018
eddyb
commented
Jan 17, 2018
Contributor
@bors r+ |
bors
commented
Jan 17, 2018
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📌 Commit 06e32d0 has been approved by |
alexcrichton
commented
Jan 18, 2018
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@bors: p=1 (this'll get backported to beta once merged) |
bors
commented
Jan 19, 2018
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bors added a commit
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Jan 19, 2018
avoid double-unsizing arrays in bytestring match lowering The match lowering code, when lowering matches against bytestrings, works by coercing both the scrutinee and the pattern to `&[u8]` and then comparing them using `<[u8] as Eq>::eq`. If the scrutinee is already of type `&[u8]`, then unsizing it is both unneccessary and a trait error caught by the new and updated MIR typeck, so this PR changes lowering to avoid doing that (match lowering tried to avoid that before, but that attempt was quite broken). Fixes#46920. r? @eddyb
bors
commented
Jan 19, 2018
Collaborator
☀️ Test successful - status-appveyor, status-travis |
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The match lowering code, when lowering matches against bytestrings,
works by coercing both the scrutinee and the pattern to
&[u8]andthen comparing them using
<[u8] as Eq>::eq.If the scrutinee is already of type
&[u8], then unsizing it is bothunneccessary and a trait error caught by the new and updated MIR typeck,
so this PR changes lowering to avoid doing that (match lowering tried to
avoid that before, but that attempt was quite broken).
Fixes#46920.
r? @eddyb