Fixed an issue with destructured bindings from a generic union constraint not being narrowed correctly - #50221
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…aint not being narrowed correctly
TypeScript Bot (typescript-bot)
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the
For Milestone Bug
| @@ -25762,10 +25762,11 @@ namespace ts { | |||
| if (!(links.flags & NodeCheckFlags.InCheckIdentifier)) { | |||
| links.flags |= NodeCheckFlags.InCheckIdentifier; | |||
| const parentType = getTypeForBindingElementParent(parent, CheckMode.Normal); | |||
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We are receiving T here from here:
https://github.dev/microsoft/TypeScript/blob/71e852922888337ef51a0e48416034a94a6c34d9/src/compiler/checker.ts#L9030-L9034
I've compared the code run for the second case - where those variables were destructured into a const declaration in the function's body and not directly in the parameter position and I've discovered that in that case, the returned type was Action, from here:
https://github.dev/microsoft/TypeScript/blob/71e852922888337ef51a0e48416034a94a6c34d9/src/compiler/checker.ts#L9088-L9089
That in turn could be traced back to getNarrowableTypeForReference here:
https://github.dev/microsoft/TypeScript/blob/71e852922888337ef51a0e48416034a94a6c34d9/src/compiler/checker.ts#L26001
So I've just replicated the logic from there (just slightly simplified):
https://github.dev/microsoft/TypeScript/blob/71e852922888337ef51a0e48416034a94a6c34d9/src/compiler/checker.ts#L25747
In here, we are always interested in narrowable types so it made sense to me to just unconditionally resolve through getBaseConstraintOrType
Nathan Shively-Sanders (sandersn)
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Nathan Shively-Sanders (sandersn)
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Looks reasonable to me although Anders Hejlsberg (@ahejlsberg) should take a look too.
…iables # Conflicts: # tests/baselines/reference/dependentDestructuredVariables.js
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Anders Hejlsberg (@ahejlsberg) friendly 🏓 |
4 participants
fixes #50206
cc Anders Hejlsberg (@ahejlsberg)