[CS2] fix for “do super in constructor” bug

[zdenko]

A small fix for the #4623 (do super in constructor)

class b extends a
  constructor: ->
    do super

b = class b extends a {
    constructor() {
      super();
    }
}

[GeoffreyBooth]

Should use test instead of exec.

[zdenko]

I improved RegExp and used exec so I can catch whitespace between do and super, and return correct length.

[GeoffreyBooth]

When would sup.length not be 5? And 3 is the length of do plus a space? What if someone types do super with two or more spaces between the words?

[zdenko]

Yes, 3 is the length of do plus a space.
The \s* in \s*super was added to catch all spaces between do and super.
So, when do is detected, the regex will match zero or more spaces before super, starting from third characters of current match e.g. do␣.

If you change line 144 in lexer to return 8 it will work for one space, but will fail when you add more spaces, e.g. do␣␣␣␣super.

[GeoffreyBooth]

Verified that this works with any number of whitespace characters between do and super.