Use singular array element variable name in autofix for no-for-loop rule

[bmish]

If the loop is iterating an array with a plural name (such as plugins), the generated element variable in the autofix could use the singular version of the array name (plugin), instead of just the generic name element.

Fixes #743. CC: @mongoose700

[fisker]

https://github.com/facebook/react/blob/3ca1904b37ad1f527ff5e31b51373caea67478c5/packages/react-devtools-shared/src/__tests__/storeStressSync-test.js#L117

[bmish]

@fisker just updated to avoid using reserved JavaScript keywords.

[fisker]

for (const case_ of cases) {}

for (const element of cases) {}

Which one do you prefer?

[bmish]

@fisker no strong preference, either works for me.

[fisker]

I prefer

for (const case_ of cases) {}

over

for (const element of cases) {}

And

for (const function_ of functions) {}

over

for (const element of functions) {}

If we decide to use case_, we need fix #747 first, then we can use avoidCapture to change case to case_

[sindresorhus]

I also prefer case_.

[snowteamer]

I kinda dislike both of them, since I think one should try not using identifiers like cases or functions in the first place.

That being said, I also prefer the case_ form, because I think the trailing underscore may serve as a nice visual reminder to the user that she should think about renaming the variable.

[bmish]

Rebased to take advantage of the avoidCapture improvement from #749 for producing the case_ variable name.

[fisker]

invalid: [
	...[
	  ['plugin', 'plugins'],
	  ['person', 'people'],
	  ['element', 'list'],
	].map(([elementName, arrayName]) => 
	  testCase(
	    `for(const i = 0; i < ${arrayName}.length; i++) {console.log(${arrayName}[i])}`,
	    `for(const ${elementName} of ${arrayName}) {console.log(${elementName})}`,
	  )
	),
]

Can you rewrite tests to this? So we can test more cases easier.

[fisker]

I ask you again, don't squash!

[bmish]

@fisker good idea, updated test cases. Sorry, squashing is a habit, I will try to avoid it.

[fisker]

Add some words ends with s? Even if it was wrong.
Also add one test that uses i.

[fisker]

Add a word that has more than one plural, girlsAndBoys?

[fisker]

Looks good.

[sindresorhus]

Nice work :)

[fisker]

@bmish Do you interested in improving no-fn-reference-in-iterator rule? We use element there too. No pressure.

[bmish]

@fisker I'll see if I have a chance sometime, thanks for the idea. Can you file a ticket for now?

[fisker]

@bmish #754