Don't ignore all generic self tail calls when collecting the return type of a function

[Mateusz Burzyński (Andarist)]

fixes #63990 (a bug introduced with #53995 )

This PR avoids ignoring recursive self calls when the arguments list is not assignable to the parameter list of the signature declaration.

So this errors:

const f = <T>(a: T, p: number) => {
    if (!p) return a;
    return f(p, p - 1);
};

But this continues to work:

function h<T>(value: T, count: number) {
    if (!count) return value;
    return h(value, count - 1);
}

It also ignores generic calls with type argument lists because that can lead to other instantiations of the signature declaration.

[Copilot]

Pull request overview

Tightens generic recursive return-type inference so only same-instantiation tail calls are ignored.

Changes:

• Checks recursive arguments against the current generic signature.
• Adds regression coverage and generated baselines.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
tsc/internal/checker/checker.go	Refines recursive-call inference handling.
tsc/testdata/tests/cases/compiler/genericRecursiveFunctionReturn.ts	Adds regression scenarios.
tsc/testdata/baselines/reference/compiler/genericRecursiveFunctionReturn.errors.txt	Records expected diagnostics.
tsc/testdata/baselines/reference/compiler/genericRecursiveFunctionReturn.types	Records inferred types.
tsc/testdata/baselines/reference/compiler/genericRecursiveFunctionReturn.symbols	Records symbols.
tsc/testdata/baselines/reference/compiler/genericRecursiveFunctionReturn.js	Records emitted JavaScript.

---

💡 Add a code-review agent skill for context-aware, tailored reviews. Learn more in the docs.