External class resolve

[nzakas]

This allows a matchClass function to be passed on the options object that will override the default class matching behavior when present.

I had to change the PEG.js grammar to allow arbitrary identifiers after the :. Everything still appears to work correctly, but do let me know if there is a better way to make this change.

[michaelficarra]

This looks fine, but any reason for only a single predicate over an object with separate predicates?

Given the single-predicate option, I imagine almost all passed predicates will be of the form

function(name, node) {
  switch (name) {
    case ...:
      return ...;
    case ...:
      return ...;
    // .. and so on
  }
}

So it might be simpler to pass an object whose keys are the allowed class names.

[nzakas]

My thinking was that we might want to manipulate the class name before comparing. For instance, the default in esquery is that it converts the class name to lowercase. We might not want that for all languages, or we might want to otherwise alter how a class name is interpreted. To that end, it seemed like a better choice to just pass the raw class name and let us decide on the other end how we'd prefer to handle it.

[michaelficarra]

@nzakas Sure, simple transforms on the class name seem like a good enough reason.

[nzakas]

Thanks so much!

[marvinhagemeister]

Nit: Reading the code it looks like the selector name doesn't change. Moving that call back into the closure leads to .toLowerCase() being called repeatedly with the same value. That's work that can be avoided and I guess that was the reason it was hoisted outside of the function closure here.

[nzakas]

Probably left from the multiple rounds of refactoring. 👍