List-patterns: list-patterns may be always-true #59478
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RikkiGibson
reviewed
Feb 11, 2022
| comp.VerifyEmitDiagnostics( | ||
| // (2,5): warning CS8794: An expression of type 'S' always matches the provided pattern. | ||
| // _ = new S() is [..var y]; | ||
| Diagnostic(ErrorCode.WRN_IsPatternAlways, "new S() is [..var y]").WithArguments("S").WithLocation(2, 5), |
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Is the expectation here that user should simplify to var y?
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The user should simply write is var y (which would not warn).
List and slice patterns make assumptions about collections being well-behaved. If you grab the entire range, you should get the same collection, so that dicing wasn't necessary.
alrz
reviewed
Feb 11, 2022
| public void AlwaysTruePattern() | ||
| { | ||
| var source = @" | ||
| _ = new S() is [..var y]; |
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I think you could verify y is definitely assigned after this statement.
RikkiGibson
approved these changes
Feb 11, 2022
cston
approved these changes
Feb 11, 2022
ghost
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Fixes #59466
Relates to test plan #51289
FYI @alrz