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TS 3.9 - No overload matches this call #38241
Description
Activity
It is a breaking changed covered in #37195.
async?being optional is causing your problem. It was unsound code before that is now being caught.This convoluted typing was created because we could not work out a better way to support a function that if invoked with
async: truewould return aPromiseorvoidotherwise.Kitson Kelly (@kitsonk) - do you have a suggestion for how we can support this scenario?
I think we just need to define one extra overload (although I would expect TS to be able to infer that on its own 😞):
export function mainNgcc(options: AsyncNgccOptions): Promise<void>; export function mainNgcc(options: SyncNgccOptions): void; +export function mainNgcc(options: AsyncNgccOptions | SyncNgccOptions): void | Promise<void>; export function mainNgcc(options: AsyncNgccOptions | SyncNgccOptions): void | Promise<void> { // ... }Reacted by spiffytechI'm tempted to mark
Working as Intendedbut I'm not totally clear exactly whyOmit<..., "async"> & { async: true }causes issues. Anders Hejlsberg (@ahejlsberg) care to weigh in?Daniel Rosenwasser (@DanielRosenwasser) not to step on Ander's toes, but I believe it is very intentional, because #37195 was specifically to fix unsafe situations with
Omitand intersection types brought up in #36604.Oh, I see - I wasn't looking at where the error was being issued. This makes sense.
George Kalpakas (@gkalpak) technically you could condense the whole thing down to
// Overload export function process<T extends AsyncNgccOptions | SyncNgccOptions>(options: T): T extends AsyncNgccOptions ? Promise<void> : void; // Implementation export function process(options: AsyncNgccOptions | SyncNgccOptions): void | Promise<void> { return mainNgcc(options); }
Thanks guys for your input.
Thx, Daniel Rosenwasser (@DanielRosenwasser)!
FWIW, I still find overloads more readable (and wish TypeScript would recognize the 3rd overload signature from the implementation):
function process(options: SyncNgccOptions): void; function process(options: AsyncNgccOptions): Promise<void>; function process(options: SyncNgccOptions | AsyncNgccOptions): void | Promise<void> { // ... }
Reacted by Samuel TLG- locked as resolved and limited conversation to collaborators
on Oct 21, 2025
TypeScript Version: 3.9.1-rc
Search Terms:
No overload matches this call
Code
Expected behavior:
No error as per TS 3.8
Actual behavior:
Error
No overload matches this call. Overload 1 of 2, '(options: AsyncNgccOptions): Promise', gave the following error. Argument of type 'SyncNgccOptions | AsyncNgccOptions' is not assignable to parameter of type 'AsyncNgccOptions'. Type 'SyncNgccOptions' is not assignable to type 'AsyncNgccOptions'. Type 'SyncNgccOptions' is not assignable to type '{ async: true; }'. Types of property 'async' are incompatible. Type 'false | undefined' is not assignable to type 'true'. Type 'undefined' is not assignable to type 'true'. Overload 2 of 2, '(options: SyncNgccOptions): void', gave the following error. Argument of type 'SyncNgccOptions | AsyncNgccOptions' is not assignable to parameter of type 'SyncNgccOptions'. Type 'AsyncNgccOptions' is not assignable to type 'SyncNgccOptions'. Types of property 'async' are incompatible. Type 'true' is not assignable to type 'false | undefined'.
Playground Link: https://www.typescriptlang.org/v2/en/play?ts=3.9.0-beta#code/KYDwDg9gTgLgBASwHY2FAZgQwMbDgZQE8lsA5Ac22wHkwYEIkBnOAbwCg4u4AjTJ4AAVMMABYAuOExhRk5ANyduMTFHLAYAURRRCgiMhjCxAfknTZSBUq79i2M3CwAbAYoC+7dqEiw4MQjA8AEEmewoqWnpGFgBeOGoAWwQYAB4iEgiaOgZmABo4AHI7EkKAPjgAMjY4EuxJGQBXPHdFb3BoeHRGkmikODAoCFwmJgAKCByYyVDwymy+pgBKSUEh5IFUgDcDABMyxR9Opx7sPoGhkfHJxckMsnmo3OXJHYRdw46-bt7ci+HgKMJlNmDMwplHiCWAAfAhzSJQlZwN67OCwtYQDbAbZ7CocbhwKAaRpQfqJTDILLAxZLDxedq+Lqnc7kynzanPMHwhbPJEYrE494HBnHH5nP6spBUm6cuEQhE0157T6Mk6-RhwSXSqFc+U8mJouUPBW8pXvQ38hCbFF49ieIA
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