Post-build validation of typescript files

[mrginglymus]

Is your feature request related to a problem? Please describe.

In #31527, I observed tsup generating malformed typescript definitions.

This is a known risk of using tsup - they recommend testing the output with either tsc or @arethetypeswrong/cli after generation.

Describe the solution you'd like

A post-bundle validation step that type-checks generated .d.ts files.

In theory this could be done with a tsconfig file that looks something like:

{
  "extends": "../../tsconfig.json",
  "compilerOptions": {
    "skipLibCheck": false
  },
  "include": ["dist/**/*.d.ts"],
  "exclude": [ "../../**/node_modules"]
}

However! In order to test definition files, it requires skipLibCheck to be false. This will precipitate a whole bunch of unrelated errors in downstream packages that have invalid or incompatible types.

Describe alternatives you've considered

No response

Are you able to assist to bring the feature to reality?

yes, I can

Additional context

No response

[mrginglymus]

Possibly fixed by #31555