no_private_function_fat_arrows rule doesn't seem right

[aseemk]

Moved from https://github.com/clutchski/coffeelint/pull/444#issuecomment-202578186:

I use a little helper for convenient getter/setter syntax, and it seems a fat arrow is needed.

class Test
    # With a fat arrow, `@` inside evaluates to the class:
    get1 = (props) =>
         console.log @

    # Without a fat arrow, `@` inside evaluates to just `this`:
    get2 = (props) ->
        console.log @

    # But either way, calling these helpers does nothing special with `this`,
    # hence it'll be "lost" in the second case:
    get1 foo: -> bar
    get2 foo: -> baz

http://coffeescript.org/#try:class%20Test%0A%20%20%20%20get1%20%3D%20(props)%20%3D%3E%0A%20%20%20%20%20%20%20%20%20console.log%20%40%0A%20%20%20%20get2%20%3D%20(props)%20-%3E%0A%20%20%20%20%20%20%20%20console.log%20%40%0A%0A%20%20%20%20get1%20foo%3A%20-%3E%20bar%0A%20%20%20%20get2%20foo%3A%20-%3E%20baz

cc @mitar

[swang]

I don't think the code is any deeper than, 'is there a fat arrow in front of a function in a class?'. There's not much deep static analysis determining whether something later on gets called internally/privately.

It does seems like fat arrows in local/private functions should be valid as it returns the class/object rather than this, so maybe the rule should have been sussed out better.

That said, I suppose you should just turn this off in your case, or directly call it as URL::. If I'm interpreting this issue wrong feel free to point that out. Otherwise I'm not sure what else can be done to fix this.