Consistent narrowing by discriminant #38311
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@typescript-bot test this |
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Heya @ahejlsberg, I've started to run the parallelized community code test suite on this PR at 88025e6. You can monitor the build here. |
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Heya @ahejlsberg, I've started to run the perf test suite on this PR at 88025e6. You can monitor the build here. Update: The results are in! |
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Heya @ahejlsberg, I've started to run the parallelized Definitely Typed test suite on this PR at 88025e6. You can monitor the build here. |
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Heya @ahejlsberg, I've started to run the extended test suite on this PR at 88025e6. You can monitor the build here. |
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The user suite test run you requested has finished and failed. I've opened a PR with the baseline diff from master. |
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@ahejlsberg Here they are:Comparison Report - master..38311
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Tests all look good (nothing but preexisting conditions). |
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@weswigham I think it pretty much replaces the second: this is so much simpler. I don’t believe this is quite as general as the other PR aims to be, but I went through all the duplicates on the original issue and this fixes them. I think my only comment here is whether it’s worth filter the declared type for non-object types. I’m not sure this approach works if the declared type is something like The first PR you link was some tidying I haven’t updated yet (sorry). I don’t think it’s changed by this. |
RyanCavanaugh
approved these changes
May 5, 2020
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With this PR we fix inconsistencies in our narrowing logic for discriminated unions. Previously we required the declared type of a reference to be a union type before we'd narrow by discriminants. This meant narrowing by discriminant wouldn't work in conjunction with user defined type predicate narrowing, with the notable (and inconsistent) exception of
switchstatements. We now consistently allow narrowing by discriminant of a reference with a declared type that isn't a union but a control flow type that is (which, for example, might result from first narrowing anunknownto a union type using a user defined type predicate and then narrowing the union type by a discriminant).Fixes #30557.
Fixes #36777.