bug(lib): Explicitly stating wrong return type of `Promise.then` without arguments results in no error

🔎 Search Terms

• silenced Promise resolution type mismatch
• Promise generic explicit no error
• no error when Promise type is specified explicitly
• generic inside optional argument

🕗 Version & Regression Information

TS v3.3.3 correctly detects the error, which is the earliest Playground version. All other Playground versions silence the error.

⏯ Playground Link

https://www.typescriptlang.org/play/?ts=6.0.0-dev.20260312#code/MYewdgzgLgBFCm0BcMAKAnEBbAlheAPNOjmAOYB8MAvGprvgHTqIgA2AbvABQCMAlIygALeGG78A3EA

💻 Code

const test: Promise<string> = Promise.resolve(1).then();

🙁 Actual behavior

No TypeScript errors.

🙂 Expected behavior

I expected a similar error to what TS v3.3.3 yields:

Type Promise<number> is not assignable to type Promise<string>. Type number is not assignable to type string.

Additional information about the issue

No response

Reproduce el ejemplo reportado en el TypeScript Playground enlazado y compara el comportamiento actual con el resultado de TypeScript 3.3.3 descrito en el issue. Traza el flujo de comprobación de tipos de Promise.then llamado sin argumentos; se considera terminado cuando la asignación explícita a Promise informa de la incompatibilidad con Promise.