fix(eslint-plugin): [explicit-module-boundary-types] don't check returned functions if parent function has return type

[ifiokjr]

Description

Version 3.0.0 of the plugin enabled explicit-module-boundary-types by default. Unfortunately it doesn't currently handle the case where the parent function has a type signature. The following correct code produces an error.

export const foo = (a: string): (n: number) => string => {
  return (n) => String(n)
}

This fixes the problem by checking the parent nodes of exported declarations to see if they are already typed. If they are typed it doesn't show the error for child functions.

Fixes #1845

[typescript-eslint]

Thanks for the PR, @ifiokjr!

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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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[codecov]

Codecov Report

Merging #2084 into master will increase coverage by 0.00%.
The diff coverage is 92.85%.

@@           Coverage Diff           @@
##           master    #2084   +/-   ##
=======================================
  Coverage   93.42%   93.42%           
=======================================
  Files         171      171           
  Lines        7755     7774   +19     
  Branches     2215     2222    +7     
=======================================
+ Hits         7245     7263   +18     
  Misses        244      244           
- Partials      266      267    +1     

Flag	Coverage Δ
#unittest	93.42% <92.85%> (+<0.01%)	⬆️

Impacted Files	Coverage Δ
...plugin/src/rules/explicit-module-boundary-types.ts	82.75% <50.00%> (+0.14%)	⬆️
.../eslint-plugin/src/util/explicitReturnTypeUtils.ts	98.85% <96.15%> (-1.15%)	⬇️

[bradzacher]

Mostly LGTM - thanks!

One comment that needs addressing.

[ifiokjr]

I've just pushed again to:

• Exit early when the type of the ancestor of the node being checked is not a return statement.
• Immediately return the value from FunctionExpression ancestor checks.
• Remove comments from the test source code.
• Add one more deeply nested test case.

[bradzacher]

LGTM - thanks!