Added prefer_fat_arrows_in_methods rule

[mitar]

Tests don't pass because I have no idea how to detect assigning to the prototype.

[mitar]

Any suggestions here?

[za-creature]

Not 100%, but the AST should look very similar to this:

Assign(
  variable: Value(
    base: Literal("className"),
    properties: [
      Access(
        name=Literal("prototype")
      ),
      Access(
        name=Literal("methodName")
      )
    ]
  ),
  value: Code(...)
)

Sometimes the Literals are replaced by plain strings so you should probably check for that as well.

So basically, find code that assigns a method to something.prototype.something and scan that method's code using your existing implementation.

Some food for thought:

1. What about requiring:

   class Foo
     bar: =>
       console.log("I'm exclusively foo")
   

2. How does this interact with no_unnecessary_fat_arrows ? I think you'll also need to check if this is used inside the function body and don't enforce any constraints if it isn't

3. What happens here:

   class Foo
     bar: ->
       class Baz
         constructor: ->
           # can't ever have a bound constructor so will this fail?  
   

If you need help, I'm happy to take this over. However I'd like to resurrect the community behind coffeelint as the project needs a lot of love.

[mitar]

I would also love to help with coffeelint.

[UziTech]

@mitar if you still want to help with coffeelint I have moved the repo to https://github.com/coffeelint/coffeelint

[UziTech]

Further development on coffeelint will be on coffeelint/coffeelint and will be released as @coffeelint/cli.

This PR will be tracked at coffeelint/coffeelint#15