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Add a regression test for narrowing NoInfer union constituents of non-generic aliases - #64969
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Jake Bailey (jakebailey) merged 1 commit intoOct 28, 2026
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🟢 Approval recommended
The focused test-only additions have consistent baselines and no identified blocking issues.
No open issues 🎉
What changed in this PR
Adds compiler regression coverage for narrowing NoInfer union constituents in non-generic aliases, without changing compiler behavior.
Changes:
- Tests discriminant narrowing directly and after accessing an alias through
Box<string>. - Adds type and symbol baselines recording the expected results.
| File | Description |
|---|---|
tsc/testdata/tests/cases/compiler/narrowingNoInfer2.ts |
Adds both narrowing scenarios under strict checking. |
tsc/testdata/baselines/reference/compiler/narrowingNoInfer2.types |
Records expected narrowed types and property types. |
tsc/testdata/baselines/reference/compiler/narrowingNoInfer2.symbols |
Records expected symbol bindings. |
Review effort: Balanced
Jake Bailey (jakebailey)
approved these changes
Oct 28, 2026
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I found this missing~ coverage when playing around with: #64958 . I think the gains from that experiment are too little to justify pulling this in but the tests coverage is nice