When subclassing incorrectly, the compiler error suggests changing base class rather than the derived one

[parzhitsky]

🔎 Search Terms

override method compiler error confusing message Target signature too few

🕗 Version & Regression Information

• This is the behavior in every version I tried, and I reviewed the FAQ for entries about Why are functions with fewer parameters assignable to functions that take more parameters?

⏯ Playground Link

https://www.typescriptlang.org/play/?#code/CYUwxgNghgTiAEkoGdnwGIHtPwN4Ch4j4BbEAFwAtNgAKASgC54A3TAS2HwF999QkcRNFTwAQrHggAHuRAA7YGiw4CxeJhYgYMTgjJUatWAHNm8gK4kARtqasOXXkA

💻 Code

declare class Foo {
    method(): void
}

declare class Bar extends Foo {
    override method(arg: number): void
    //       ~~~~~~
    // Error! Target signature provides too few arguments. Expected 1 or more, but got 0.
}

🙁 Actual behavior

An error message explains how base class has less arguments than expected

🙂 Expected behavior

An error message explains how derived class has more arguments than expected

Additional information about the issue

I understand that the compiler can't know whether the base class or the derived class is defined incorrectly. But:

• normally, deriving from a class means that the developer wants to encapsulate the scope of work within this class and avoid changing the base class; also
• seeing an error related to base class on a method of the derived class is unexpected and confusing.

[RyanCavanaugh]

What it's saying here is "You will be called with too few arguments here, thus can't have this parameter (non-optionally)". It's two sides of the same coin.

I can see how you can arrive at the opposite interpretation but this doesn't seem to have confused anyone else so far, so I don't think it merits changing and possibly making worse.