[RXVEN-1907 (RXVEN-1907)]

When comparing a generic constructor type against a concrete constructor, the checker reports TS2367 even though the comparison is valid: func(Child) in the linked issue accepts Child as Constructor<T>, so constructor === Child can legitimately be true. Reproduced on current main (7.1.0-dev) and on typescript@7.0.2: if (constructor === Child) fails with "the types 'Constructor' and 'typeof Child' have no overlap".

The comparable relation already treats a type parameter appearing as the source as comparable through its constraint, but when a free type parameter appears as the target of a comparison (here: Base<T>.Item: T inside the constructor's return type), a non-type-parameter source is reported as having no overlap. That asymmetry only becomes visible when the type parameter is nested inside a property or a construct signature return type, because there the top-level equality check never retries in the other direction.

This change adds the mirrored fallback: under the comparable relation, when the target is an unconstrained type parameter (its constraint is unknown), a non-type-parameter source is also checked against unknown, so it is treated as potentially overlapping. Type parameters with an object constraint keep their current strict behavior, so the existing TS2352/TS2367 expectations in genericTypeAssertions4/5 and unknownControlFlow are unchanged.

I added tests/cases/compiler/comparableRelationTypeParameterTarget.ts with its generated baseline, and ran the full go test ./... suite under tsc/ locally with no failures.

Disclosure: this PR was prepared with AI assistance and reviewed by me.

Fixes #27910

[Copilot]

🟢 Approval recommended

Static review identified no blocking issues in the narrowly guarded fallback or regression baselines; tests were not run during this review.

No open issues 🎉

What changed in this PR

Fixes #27910 by allowing valid comparisons between generic constructor types and concrete constructors in the native TypeScript checker.

Changes:

• Adds a comparable-relation fallback for unconstrained target type parameters.
• Adds regression coverage for constructor comparisons while preserving errors for unrelated type parameters.

File	Description
tsc/​internal/​checker/​relater.go	Adds the guarded comparability fallback.
tsc/​testdata/​tests/​cases/​compiler/​comparableRelationTypeParameterTarget.ts	Tests valid constructor and invalid unrelated-parameter comparisons.
tsc/​testdata/​baselines/​reference/​compiler/​comparableRelationTypeParameterTarget.types	Records expected types.
tsc/​testdata/​baselines/​reference/​compiler/​comparableRelationTypeParameterTarget.symbols	Records expected symbols.
tsc/​testdata/​baselines/​reference/​compiler/​comparableRelationTypeParameterTarget.errors.txt	Records the remaining expected TS2367 diagnostic.

_{Review effort: Balanced}