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). Fixes rust-lang#46920.
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beta-nominating because this is a regression |
eddyb
approved these changes
Jan 17, 2018
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@bors r+ |
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📌 Commit 06e32d0 has been approved by |
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@bors: p=1 (this'll get backported to beta once merged) |
bors
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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
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☀️ Test successful - status-appveyor, status-travis |
Merged
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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