Normalize distributed type parameters in conditional type relationships - #64307
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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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Mateusz Burzyński (Andarist)
September 17, 2026 10:22
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🟢 Approval recommended
The focused normalization fix is consistent with the mapper behavior and has bidirectional regression coverage.
Pull request overview
Normalizes both sides of conditional true-branch relationships, restoring assignability for equivalent distributive conditional types.
Changes:
- Instantiates the target true type with the inference mapper.
- Adds a bidirectional regression test and generated baselines.
File summaries
| File | Description |
|---|---|
tsc/internal/checker/relater.go |
Normalizes the target conditional branch. |
tsc/testdata/tests/cases/conformance/types/conditional/conditionalTypes1.ts |
Adds regression coverage. |
tsc/testdata/baselines/reference/conformance/conditionalTypes1.types |
Updates type baseline. |
tsc/testdata/baselines/reference/conformance/conditionalTypes1.symbols |
Updates symbol baseline. |
tsc/testdata/baselines/reference/conformance/conditionalTypes1.js |
Updates emit and declaration baseline. |
tsc/testdata/baselines/reference/conformance/conditionalTypes1.errors.txt |
Confirms no new diagnostics. |
Review details
- Files reviewed: 6/6 changed files
- Comments generated: 0
- Review effort level: Balanced
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fixes a regression from #64237 , cc Anders Hejlsberg (@ahejlsberg)
The target type here needs to be instantiated too - so the
Tcan be mapped back to the non-distributed type parameter. The source type already does that mapping so the distributed type param on that side becomes non-distributed. But that creates an assymetry without mapping the target side too.