`no-array-callback-reference` rule is not compatible with TypeScript type guards

function isDefined<T>(argument: T | undefined): argument is T {
  return typeof argument !== 'undefined'
}

const items = [1, 2, undefined]

items.filter(isDefined).map((number) => {
  // number is now type guarded and undefined is eliminated
  console.log(number)
})

items.filter((num) => isDefined(num)).map((number) => {
  // however, this way it does not work, and "number" can still be undefined
  console.log(number)
})

I am not sure why TypeScript is not inferring the results in the second way.

[oss6]

Hi, the issue is described here: https://github.com/microsoft/TypeScript/issues/10734 and here: https://github.com/microsoft/TypeScript/issues/16069. Would it be sensible to add an exception for functions with type guards (either by default or through an option)?

[Vages]

With an experienced eslint-rulemaker like you, @RebeccaStevens, making the extension, I’m quite certain that the lint-rule should just ignore type-guards by default (in hindsight, I think I only suggested it due to a lack of confidence in my lint-rule abilities 😅). Having an option for it seems bloated, and if this actually affects someone negatively (which I really doubt), we could add the option in later.

I’m only an ordinary contributor myself, but if you make a PR, I could test it and give some feedback. Just tag me when you add it. PS: I use eslint-plugin-functional; good work!