Consider index signatures as optional properties in contextual type discrimination #54596
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typescript-bot
added
Author: Team
For Milestone Bug
gabritto
commented
Jun 10, 2023
src/compiler/checker.ts
Outdated
| @@ -22719,6 +22719,15 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker { | |||
| } | |||
| const filtered = contains(include, Ternary.False) ? getUnionType(types.filter((_, i) => include[i])) : target; | |||
| return filtered.flags & TypeFlags.Never ? target : filtered; | |||
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| function getTypeOfPropertyOrOptionalIndexSignature(type: Type, name: __String): Type | undefined { | |||
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I feel like this function might already exist, but I couldn't find it.
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There's getTypeOfPropertyOrIndexSignature (used by narrowTypeByDiscriminant!). Consider replacing that function and making it take a parameter on whether to add optionality for index signatures.
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@typescript-bot test this |
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Heya @gabritto, I've started to run the parallelized Definitely Typed test suite on this PR at c66c0d1. You can monitor the build here. Update: The results are in! |
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Heya @gabritto, I've started to run the diff-based user code test suite on this PR at c66c0d1. You can monitor the build here. Update: The results are in! |
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Heya @gabritto, I've started to run the perf test suite on this PR at c66c0d1. You can monitor the build here. Update: The results are in! |
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Heya @gabritto, I've started to run the diff-based top-repos suite on this PR at c66c0d1. You can monitor the build here. Update: The results are in! |
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@gabritto Here are the results of running the user test suite comparing There were infrastructure failures potentially unrelated to your change:
Otherwise... Something interesting changed - please have a look. Details
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@gabritto Here they are:
CompilerComparison Report - main..54596
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TSServerComparison Report - main..54596
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StartupComparison Report - main..54596
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Developer Information: |
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@gabritto Here are the results of running the top-repos suite comparing Everything looks good! |
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Hey @gabritto, the results of running the DT tests are ready. |
jakebailey
approved these changes
Jun 12, 2023
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This didn't land in 5.1.6 right? When is it expected to be released? |
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This is in the 5.2 beta (also noted in the issue's milestone). |
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Fixes #54498.
The fix is suggested and described by @nebkat in this comment: #54498 (comment).
When we try to discriminate a contextual type, we consider the omission of a property to be a factor to discriminate in
discriminateTypeByDiscriminableItems's implementation, but then during that process, when looking up a property in one of the candidate types, we would not consider matching index signatures and therefore we would discard the type with the index signature. Now, when looking up a property in one of the candidate types, we also consider matching on index signatures.