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Preserve widening literals when narrowing primitive unions by equality - #64771
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Mateusz Burzyński (Andarist) wants to merge 1 commit into
Open
Mateusz Burzyński (Andarist) wants to merge 1 commit into
Mateusz Burzyński (Andarist) wants to merge 1 commit into
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🟢 Approval recommended
The targeted fix matches the previous general-path behavior and is covered by focused regression and negative-control tests.
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What changed in this PR
Fixes equality narrowing so primitive unions retain widening literal freshness while explicit literal unions remain non-widening.
Changes:
- Distinguishes exact literal constituents from primitive containment.
- Adds regression coverage for strings, numbers, bigints, mutable inference, and
flatMap.
| File | Description |
|---|---|
tsc/internal/checker/flow.go |
Preserves literal freshness during equality narrowing. |
tsc/testdata/tests/cases/compiler/narrowingByEqualityPreservesWideningLiterals.ts |
Adds regression and control cases. |
tsc/testdata/baselines/reference/compiler/narrowingByEqualityPreservesWideningLiterals.types |
Records inferred types. |
tsc/testdata/baselines/reference/compiler/narrowingByEqualityPreservesWideningLiterals.symbols |
Records resolved symbols. |
tsc/testdata/baselines/reference/compiler/narrowingByEqualityPreservesWideningLiterals.errors.txt |
Records expected control-case diagnostics. |
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Ryan Cavanaugh (RyanCavanaugh)
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from Anders Hejlsberg (ahejlsberg)
October 13, 2026 17:24
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fixes #64766