Add new rule no-controllers

[bmish]

Some people may want to avoid the use of controllers in their applications.

Controllers are only truly necessary for specifying queryParams today, so this rule only allows controllers if queryParams are present.

While controllers are not currently deprecrated, the Ember 2019-2020 Roadmap RFC does mention:

Perhaps the longest-awaited simplification is eliminating controllers from the Ember programming model, which we will do this year. This will require us to find a new home for query parameters.

Fixes #660. CC: @mehulkar.

[mehulkar]

Awesome!

[mehulkar]

Would the rule prevent code other than queryParams and the category property?

[bmish]

Currently no. I'm enforcing the following simplified rule: If queryParams is defined inside the controller, then the controller and any other code in it is allowed. If queryParams is not defined inside the controller, then the controller is not allowed.

Why? Because it's non-trivial to determine if a particular line of code/function/property/observer/action handler/service injection/etc inside a controller is involved in or needed for reading or modifying a query parameter value.

For example, all the code below is needed for managing a query parameter value, but it would be very difficult for the lint rule to determine that.

export default Controller.extend({
  queryParams: ['sortType'],
  sortType: null,

  hasDefaultSortType: equal('model.sortType', DEFAULT_SORT_TYPE),

  sortObserver: observer('hasDefaultSortType', function() {
    if (this.hasDefaultSortType) {
      this.set('sortType', null);
    } else {
      this.set('sortType', this.model.sortType);
    }
  }),
});

[mehulkar]

makes sense. what happens if queryParams = [] is defined?

[bmish]

If you're asking if the rule handles native class syntax, then yes, it will allow a native class controller as long as it has queryParams = [...].

[rwjblue]

Seems good to me, though we shouldn't enable it by default.