.every() .find() .filter() methods fail with "This expression is not callable." error on union of array types

Bug Report

🔎 Search Terms

• This expression is not callable
• none of those signatures are compatible with each other

🕗 Version & Regression Information

• This is the behavior in every version I tried, and I reviewed the FAQ for entries about union types. I also reviewed previous related issues.

⏯ Playground Link

• .every() does not work
• .filter() does not work
• .find() does not work
• .reduce() also doesn’t work, but there is already an issue for that one. (Perhaps we should merge it into this?)

💻 Code

interface Fizz {
    id: number;
    fizz: string;
}

interface Buzz {
    id: number;
    buzz: string;
}

([] as Fizz[] | Buzz[]).filter(item => item.id < 5); 

🙁 Actual behavior

Compilation fails with the following error:

This expression is not callable.
  Each member of the union type '{ <S extends Fizz>(predicate: (value: Fizz, index: number, array: Fizz[]) => value is S, thisArg?: any): S[]; (predicate: (value: Fizz, index: number, array: Fizz[]) => unknown, thisArg?: any): Fizz[]; } | { ...; }' has signatures, but none of those signatures are compatible with each other.

🙂 Expected behavior

Compilation succeeds, as it does for map and several other array functions.

🔖 Useful links

• Original issue
• PR that closed original issue

[jcalz]

Maybe something could be done specifically for arrays instead of worrying about merging arbitrary signatures? Like, widen A[] | B[] to readonly (A | B)[] for these failing method calls? 🤷‍♂️

[weswigham]

Well, we’d need to come up with sensible rules for merging overload lists. Conceptually, we could (attempt to) make a list of 4 overloads by combining each of the input signatures, except there’s no inherent ordering to those 4 signatures, unlike a normal overload set, so it’s unclear how we’d choose which signature to resolve against, ultimately.