Debug Failure with strictFunctionTypes: type provided should not be a non-generic 'promise'-like

[frigus02]

🔎 Search Terms

type provided should not be a non-generic 'promise'-like

🕗 Version & Regression Information

• This is a crash
• This is the behavior in every version I tried: v5.2.2 and v5.3.2

⏯ Playground Link

Playground link

Note: Because this is a crash, the playground looks broken. The browser console has the stack trace.

💻 Code

// @strict
type NotPromise<T> = T extends Thennable<unknown>
  ? T
  : T extends PromiseLike<unknown>
  ? never
  : T;

type Receiver<T> = (value: NotPromise<T>) => void;

class Thennable<T> {
  then(a: Receiver<T>) {}

  private handleResolve<TResult>(
    result: NotPromise<TResult> | Thennable<NotPromise<TResult>>,
    resolve: Receiver<TResult>,
  ) {
    if (result instanceof Thennable) {
      // Error: Debug Failure. False expression: type provided should not be a non-generic 'promise'-like.
      this.resolvePromise(result, resolve);
    }
  }

  private resolvePromise<TResult>(
    result: Thennable<TResult>,
    resolve: Receiver<TResult>,
  ) {}
}

🙁 Actual behavior

Error: Debug Failure. False expression: type provided should not be a non-generic 'promise'-like.
    at createAwaitedTypeIfNeeded (/test-ts-debug-assert-promise-like/node_modules/typescript/lib/tsc.js:76671:11)
    at getAwaitedType (/test-ts-debug-assert-promise-like/node_modules/typescript/lib/tsc.js:76676:27)
    at getAwaitedTypeOfPromise (/test-ts-debug-assert-promise-like/node_modules/typescript/lib/tsc.js:76554:28)
    at maybeAddMissingAwaitInfo (/test-ts-debug-assert-promise-like/node_modules/typescript/lib/tsc.js:70872:13)
    at getSignatureApplicabilityError (/test-ts-debug-assert-promise-like/node_modules/typescript/lib/tsc.js:70837:11)
    at resolveCall (/test-ts-debug-assert-promise-like/node_modules/typescript/lib/tsc.js:71232:25)
    at resolveCallExpression (/test-ts-debug-assert-promise-like/node_modules/typescript/lib/tsc.js:71633:12)
    at resolveSignature (/test-ts-debug-assert-promise-like/node_modules/typescript/lib/tsc.js:72037:16)
    at getResolvedSignature (/test-ts-debug-assert-promise-like/node_modules/typescript/lib/tsc.js:72059:18)
    at checkCallExpression (/test-ts-debug-assert-promise-like/node_modules/typescript/lib/tsc.js:72171:23)

at the node this.resolvePromise(result, resolve);

🙂 Expected behavior

No crash.

Additional information about the issue

Found this when migrating to ts.transpileModule. As far as I can tell it's triggered by 2 conditions, which all have to be true:

• strictFunctionTypes: true
• The type PromiseLike must not exist, e.g. by using noLib: true

[typescript-bot]

The change between v4.7.4 and v4.8.4 occurred at a614119.

[jakebailey]

FWIW I tested this and it's just always happened (as noted in the issue), so a bisect is gonna do something funky.

[andrewbranch]

The crash doesn't show up in the playground in 4.7, at least not on page load

[jakebailey]

Ah, I must have done something wrong.