feat(eslint-plugin): [explicit-function-return-type] allow as const arrow functions

[Zzzen]

add an option allowDirectConstAssertionInArrowFunctions to allow bodyless arrow functions which return as const.

closes #653

[typescript-eslint]

Thanks for the PR, @Zzzen!

typescript-eslint is a 100% community driven project, and we are incredibly grateful that you are contributing to that community.

The core maintainers work on this in their personal time, so please understand that it may not be possible for them to review your work immediately.

Thanks again!

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[JamesHenry]

LGTM, thanks!

[JamesHenry]

Actually, sorry might have changed my mind:

Currently in this PR:

This would be fine:

const foo = () => {
  return {
    bar: true
  } as const;
}

But this wouldn't:

function foo() {
  return {
    bar: true
  } as const;
}

This feels very arbitrary to me... Why do we want to limit this to ArrowFunctionExpressions?

cc @bradzacher as you did also explicitly mention arrow functions on the original issue

[Zzzen]

IMO, this is tricky.
if this one is fine,

function foo() {
  return {
    bar: true
  } as const;
}

should this one pass too?

function foo() {
  if (x) {
    return { bar: true } as const;
  } else {
    return { foo: true } as const;
  }
}

[JamesHenry]

@Zzzen Apologies, I was actually incorrect with my previous comment:

const foo = () => {
  return {
    bar: true
  } as const;
}

This would not actually be ok with your PR, because the body would be a BlockStatement, so the PR is fine for what it is trying to achieve. Sorry for the confusion!

[codecov]

Codecov Report

Merging #876 into master will increase coverage by 0.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #876      +/-   ##
==========================================
+ Coverage   94.16%   94.18%   +0.01%     
==========================================
  Files         113      113              
  Lines        4870     4882      +12     
  Branches     1355     1361       +6     
==========================================
+ Hits         4586     4598      +12     
  Misses        163      163              
  Partials      121      121

Impacted Files	Coverage Δ
...-plugin/src/rules/explicit-function-return-type.ts	100% <100%> (ø)	⬆️