Add prefer-optional-catch-binding rule

[fisker]

Fixes #670

Note: I'm not check destructuring, so the following code will pass

try {} catch({message}) {}

This can get really complicated,

Case 1:

try {} catch({nonExistsProperty = thisWillExecute()}) {}

In this case nonExistsProperty is not used, removing thisWillExecute() is not safe.

Case 2:

try {} catch({a, b = a}) {}

I'm not sure we can track both a and b.

Note2: white spaces not removed.

[fisker]

@sindresorhus This is ready, have to land in v20 now :(

[sindresorhus]

Sorry, I misunderstood. I thought you intended to fix https://github.com/sindresorhus/eslint-plugin-unicorn/pull/671/files#diff-52502d7490c2a15f41e0def7598c29a4R109 in this PR and I was waiting for that.

[fisker]

Right. I forgot that, now we have time, I'll try to fix it.

[fisker]

try {
} catch(error) {
	var error = 1;
}

This one seems hard to fix, the core rule no-unused-vars has lots of code to check, really too complicated. And it's only about var because you can't

try {
} catch(error) {
	const error = 1;
}
// VM170:3 Uncaught SyntaxError: Identifier 'error' has already been declared

OR

try {
} catch(error) {
	function error(){}
}
// VM191:3 Uncaught SyntaxError: Identifier 'error' has already been declared

I'm going to give up.

If people really want that, we can improve later.

[sindresorhus]

And it's only about var because you can't

Just leave it. I really don't care about var.

In general, just ignore any legacy syntax. We should not waste time on that.

[fisker]

I alway try to to better, if it's not hard . :)

[fisker]

Integration test failure due to https://github.com/then/is-promise/issues?q=is%3Aissue+is%3Aopen+sort%3Aupdated-desc , they publish a module:type package with wrong main field.

[fisker]

Are we good to merge?