Fix keyof deferred for non-generic substitution types (#2186)

[adavila0703]

Summary

getIndexTypeEx was deferring keyof for substitution types when shouldDeferIndexType applied. For substitution types whose baseType and constraint are both non-generic, that deferral is incorrect, it breaks assignability for indexed access types like Test["rejectClose"] and leaves quick info unsimplified.

This change resolves keyof immediately for non-generic substitution types by returning the union of getIndexTypeEx on the substitution's baseType and constraint.

This matches the behavior from microsoft/TypeScript#61999 for microsoft/TypeScript#61728. NoInfer substitution types are still handled first, unchanged.

Tests

• Added local compiler cases substitutionTypeNonGenericIndexType1.ts and substitutionTypeNonGenericIndexType2.ts under testdata/tests/cases/compiler/ with committed .symbols and .types baselines.
• Ran: go test ./internal/testrunner/ -run "TestLocal/substitutionTypeNonGenericIndexType" -count=1

Notes

I noticed #2186 is currently in the Post-7.0 milestone. I am submitting this as a checker bug fix / parity change with upstream TypeScript behavior rather than a new feature, but I am happy to defer or retarget if you prefer to keep this for after 7.0.

[adavila0703]

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[Copilot]

Pull request overview

Fixes keyof/index-type computation for substitution types in the Go port of the TypeScript checker. Previously, getIndexTypeEx would incorrectly defer keyof for some substitution types (even when both baseType and constraint are non-generic), which broke indexed-access assignability and produced unsimplified quick info; this aligns behavior with upstream TypeScript’s fix for microsoft/TypeScript#61999 / #61728.

Changes:

• Resolve keyof immediately for non-generic substitution types by returning the union of index types from the substitution’s baseType and constraint.
• Add two local compiler test cases covering the regression scenarios (quick info simplification and assignability).
• Commit new .types and .symbols baselines for the added tests.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
internal/checker/checker.go	Updates getIndexTypeEx to avoid deferring keyof for non-generic substitution types and compute a concrete index-type union.
testdata/tests/cases/compiler/substitutionTypeNonGenericIndexType1.ts	Regression test for quick info / simplification behavior involving substitution types.
testdata/tests/cases/compiler/substitutionTypeNonGenericIndexType2.ts	Regression test for assignability of indexed access through a conditional/substitution scenario.
testdata/baselines/reference/compiler/substitutionTypeNonGenericIndexType1.types	Baseline for type display output for test case 1.
testdata/baselines/reference/compiler/substitutionTypeNonGenericIndexType1.symbols	Baseline for symbol output for test case 1.
testdata/baselines/reference/compiler/substitutionTypeNonGenericIndexType2.types	Baseline for type display output for test case 2.
testdata/baselines/reference/compiler/substitutionTypeNonGenericIndexType2.symbols	Baseline for symbol output for test case 2.

[adavila0703]

Done

[jakebailey]

If this fixes #2186, can you write "Fixes #2186" in the description?