Query params in loading substates

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  appName: 'Ember Twiddle'
});

controllers.index-loading.js

import Ember from 'ember';
import { inject as service } from '@ember/service';
import { readOnly } from '@ember/object/computed';

export default Ember.Controller.extend({
  queryParams: ['bar'],
  foo: '42',
  bar: '',
  baz: ''
});

controllers.index.js

import Ember from 'ember';

export default Ember.Controller.extend({
});

routes.index-loading.js

import Ember from 'ember';
import { get } from '@ember/object';

export default Ember.Route.extend({
  setupController(controller) {
    controller.set('baz', get(this.paramsFor('index-loading'), 'bar'));
  }
});

routes.index.js

import Ember from 'ember';
import RSVP from 'rsvp';

export default Ember.Route.extend({
  queryParams: {
    bar: {
      refreshModel: true
    }
  },
  model() {
    let defer = RSVP.defer();
    setTimeout(()=>defer.resolve(), 3000);
    return defer.promise;
  }
});

templates.application.hbs

<h1>Welcome to {{appName}}</h1>
<br>
<br>
{{outlet}}
<br>
<br>

templates.index-loading.hbs

<div>index-loading...</div>
<div>foo is {{foo}} (just a static property)</div>
<div>bar is {{bar}} (direct QP)</div>
<div>baz is {{baz}} (set via paramsFor)</div>

templates.index.hbs

index
{{#link-to "index" (query-params bar="IT_WORKED")}}add qps{{/link-to}}
{{#link-to "index" (query-params bar="")}}clear qps{{/link-to}}

twiddle.json

{
  "version": "0.15.0",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.js",
    "ember": "3.2.2",
    "ember-template-compiler": "3.2.2",
    "ember-testing": "3.2.2"
  },
  "addons": {
    "ember-data": "3.2.0"
  }
}