Repro 18969

components.demo\.hbs

<ol>
  <li>Open browser dev tools</li>
  <li>click "Make True"</li>
  <li>click "Make False"</li>
  <li>Notice an error in the console</li>
</ol>

<button {{on 'click' this.makeTrue}}>
  Make True
</button>

<button {{on 'click' this.makeFalse}}>
  Make False
</button>

<hr>

{{#if (eq this.data.kind 'foo')}}
  <em>Some Deep Render Requiring nested Data, based on the assumpting that kind is "foo"</em><br>
  
  <pre {{data-attributes-from this.derivedData}}>
    this.derivedData: {{this.derivedData}}
  </pre>
{{else}}
  Click "Make True"
{{/if}}

<hr>

<pre>this.data =
{{as-formatted-string this.data}}
</pre>

components.demo\.js

import Component from '@glimmer/component';
import { action } from '@ember/object';
import { tracked } from '@glimmer/tracking';

class Data {
  @tracked kind;
  @tracked nestedData;
  
  constructor(kind, nestedData) {
    this.kind = kind;
    this.nestedData = nestedData;
  }
  
  toJSON() {
    let { kind, nestedData } = this;
    return { kind, nestedData }; 
  }
}

export default class DemoRoot extends Component {
  @tracked data;
  
  get derivedData() {
    return this.data.nestedData.kind;
  }
  
  @action
  makeTrue() {
    this.data = new Data('foo', new Data('baz'));
  }
  
  @action
  makeFalse() {
    this.data = new Data('bar');
  }
}

components.link\.hbs

<a ...attributes target="_blank">
  {{yield}}
</a>

components.title\.hbs

<h1>
	Reproduction of 
  
  <Link href="https://github.com/emberjs/ember.js/issues/18969">
  	emberjs/ember.js#18969
  </Link>
</h1>
<Link href="https://github.com/NullVoxPopuli/repro-repo-emberjs-18969">Repro Repo</Link>

controllers.application\.js

import Controller from '@ember/controller';

export default class ApplicationController extends Controller {
  appName = 'Ember Twiddle';
}

helpers.as-formatted-string\.js

import { helper } from '@ember/component/helper';

export default helper(function asFormattedString([a]/*, hash*/) {
  return a ? JSON.stringify(a, null, 2) : `${a}`;
});

helpers.eq\.js

import { helper } from '@ember/component/helper';

export default helper(function eq([a, b]/*, hash*/) {
  return a === b;
});

modifiers.data-attributes-from\.js

import Modifier from 'ember-modifier';

export default class DataAttributesFrom extends Modifier {
}

styles.app\.css

body {
  padding: 1rem;
}

templates.application\.hbs

<link rel="stylesheet" href="https://cdn.shoelace.style/1.0.0-beta.25/shoelace.css">


<Title />

<br><br>

<Demo />

twiddle\.json

{
  "version": "0.17.1",
  "EmberENV": {
    "FEATURES": {},
    "_TEMPLATE_ONLY_GLIMMER_COMPONENTS": false,
    "_APPLICATION_TEMPLATE_WRAPPER": true,
    "_JQUERY_INTEGRATION": true
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/3.5.1/jquery.js",
    "ember": "3.18.1",
    "ember-template-compiler": "3.18.1",
    "ember-testing": "3.18.1"
  },
  "addons": {
    "@glimmer/component": "1.0.0",
    "ember-modifier": "1.0.3"
  }
}