Permit expando property function with return type annotation as assertion #1787
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Pull Request Overview
This PR fixes a TypeScript assertion function bug by allowing expando property functions with return type annotations to be used as assertions. The fix addresses issue #1774 by updating the type checker to recognize when a function assigned to an object property has an explicit return type annotation (like assertion signatures).
- Adds logic to recognize expando property functions with return type annotations as valid for assertions
- Updates the explicit type annotation detection to include this case
- Removes a duplicate error diagnostic call
Reviewed Changes
Copilot reviewed 5 out of 5 changed files in this pull request and generated no comments.
Show a summary per file
| File | Description |
|---|---|
| testdata/tests/cases/compiler/expandoFunctionAsAssertion.ts | Test case demonstrating expando function with assertion signature |
| testdata/baselines/reference/compiler/expandoFunctionAsAssertion.types | Expected type output baseline for the new test |
| testdata/baselines/reference/compiler/expandoFunctionAsAssertion.symbols | Expected symbol output baseline for the new test |
| internal/checker/flow.go | Adds detection logic for expando property functions with return type annotations |
| internal/checker/checker.go | Removes duplicate error diagnostic call |
jakebailey
approved these changes
Oct 1, 2025
|
Thanks for the quick fix! 🙇🏻 |
wincent
added a commit
to wincent/wincent
that referenced
this pull request
Oct 2, 2025
To obtain this fix: - microsoft/typescript-go#1787 With this, we have a clean build with no errors and can switch over to the preview.
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Fixes #1774.