Matching Strada order of operations in recursive signature resolution

[Ryan Cavanaugh (RyanCavanaugh)]

Fixes #63949

(Copilot fix + manual guidance)

When resolving a nested generic call inside a callback passed to another generic function, signature resolution can reenter for the same call node. The recursive resolution computes and caches the correct source-order signature.

The Go checker still reused this cached signature late in getResolvedSignature. By that point, the local resolution had already used an incomplete contextual type derived from the containing callback. This allowed the callback’s inferred string return type to flow backward into the nested call:

identity((data: { value: number }) => request(data));

request consequently inferred T = string instead of applying its default type, making its parameter type undefined and producing TS2345.

Current Strada handles this reentrancy earlier in resolveCall, returning the recursively cached source-order signature before the incomplete contextual result can affect resolution.

[Copilot]

Pull request overview

Aligns recursive signature resolution with Strada, preventing incomplete contextual types from overriding correctly cached signatures.

Changes:

• Reuses cached signatures earlier in resolveCall.
• Adds regression coverage for generic defaults in callbacks.
• Records expected symbol and type baselines.

Show a summary per file

File	Description
tsc/internal/checker/checker.go	Moves cached-signature handling into call resolution.
tsc/testdata/tests/cases/compiler/genericDefaultInContextSensitiveCallback.ts	Adds the regression test.
tsc/testdata/baselines/reference/compiler/genericDefaultInContextSensitiveCallback.types	Verifies inferred types.
tsc/testdata/baselines/reference/compiler/genericDefaultInContextSensitiveCallback.symbols	Records symbol resolution.

Review details

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• Files reviewed: 4/4 changed files
• Comments generated: 0
• Review effort level: Balanced

[Mateusz Burzyński (Andarist)]

Moving it like this here breaks:

declare const example: (f: (a: string) => number) => string;

const f = (a: string) => g();

const g = () => {
  return example(f);
};

The above should error but IIRC it doesn't with this fix. Note that I'm mainly speaking from my memory right now - but this change basically ports my own #60208 and I was looking into this whole issue yesterday (and still thinking about how to fix it to satisfy all the cases) so I hope my memory serves me well ;p