Add docs for migrate to 9.x

docs/app/router.ts

@@ -33,6 +33,7 @@ Router.map(function () {
       // Other
       this.route('test-helpers');
       this.route('api-reference');
+      this.route('migrate-8-0-to-9-0');
     });
 
     this.route('cookbook', function () {

docs/app/routes/public-pages/docs/migrate-8-0-to-9-0.ts

@@ -0,0 +1,3 @@
+import Route from '@ember/routing/route';
+
+export default class PublicPagesDocsMigrate80To90Route extends Route {}

docs/app/templates/public-pages/docs.gts

@@ -41,6 +41,10 @@ const groupedSections = [
     id: 'upgrade',
     groupName: 'Upgrade',
     options: [
+      {
+        route: 'public-pages.docs.migrate-8-0-to-9-0',
+        text: 'Migrate from 8.0 to 9.0',
+      },
       {
         route: 'public-pages.docs.migrate-7-0-to-8-0',
         text: 'Migrate from 7.0 to 8.0',

docs/app/templates/public-pages/docs/migrate-7-0-to-8-0.gts

@@ -39,9 +39,9 @@ import { LinkTo } from '@ember/routing';
 
   <div class="doc-page-nav">
     <LinkTo
-      @route="public-pages.docs.animations"
+      @route="public-pages.docs.migrate-8-0-to-9-0"
       class="doc-page-nav-link-prev"
-    >&lt; Animations</LinkTo>
+    >&lt; Migrate from 8.0 to 9.0</LinkTo>
     <LinkTo
       @route="public-pages.docs.test-helpers"
       class="doc-page-nav-link-next"

docs/app/templates/public-pages/docs/migrate-8-0-to-9-0.gts

@@ -0,0 +1,89 @@
+import { LinkTo } from '@ember/routing';
+
+<template>
+  <h1 class="doc-page-title">Migrate from 8.0 to 9.0</h1>
+
+  <p>Before migrating to 9.x, you should first update to the latest 8.x release,
+    as most of the breaking changes were introduced in 8.x.</p>
+
+  <h2>Breaking changes</h2>
+
+  <ul>
+    <li>
+      <p>The minimum required Ember version is now 4.12.</p>
+    </li>
+    <li>
+      <p>
+        Passing
+        <code>components</code>
+        as strings is no longer supported. You must now pass all components as
+        <code>contextual components</code>.<br />
+        <small><i>(Ember deprecated passing components as strings in version
+            3.25. In line with this change, we have removed the dependency on
+            the deprecated
+            <code>@embroider/util</code>
+            package.)</i></small>
+      </p>
+    </li>
+    <li>
+      <p>
+        <code>node-sass</code>
+        has been deprecated for many years and is no longer supported. Please
+        migrate to
+        <code>sass</code>
+        or
+        <code>sass-embedded</code>.
+      </p>
+    </li>
+    <li>
+      <p>
+        Passing
+        <code>@dropdownId</code>
+        wasn't working correctly without using custom modifiers and was
+        undocumented. Remove this parameter and use the
+        <code>uniqueId</code>
+        property from the public API instead.
+        <br />
+        <small><i>(Deprecation added in 8.8)</i></small>
+      </p>
+    </li>
+    <li>
+      <p>
+        Passing configurations to
+        <code>ember-basic-dropdown</code>
+        over
+        <code>ember-cli-build.js</code>
+        was removed. You should pass them over
+        <code>setConfig</code>
+        (see the installation guide)
+        <br />
+        <small><i>(Deprecation added in 8.9)</i></small>
+      </p>
+    </li>
+    <li>
+      <p>
+        ember-basic-dropdown previously read the value of
+        <code>APP.rootElement</code>
+        from
+        <code>ember-cli-build.js</code>. According to the v2 addon
+        specification, addons should not read configurations from
+        <code>ember-cli-build.js</code>. You must now pass this value via
+        <code>setConfig</code>
+        (see the installation guide).
+        <br />
+        <small><i>(Deprecation added in 8.9)</i></small>
+      </p>
+    </li>
+  </ul>
+
+  <div class="doc-page-nav">
+    <LinkTo
+      @route="public-pages.docs.animations"
+      class="doc-page-nav-link-prev"
+    >&lt; Animations</LinkTo>
+    <LinkTo
+      @route="public-pages.docs.migrate-7-0-to-8-0"
+      class="doc-page-nav-link-next"
+    >Migrate from 7.0 to 8.0 &gt;</LinkTo>
+  </div>
+</template>

docs/tests/unit/routes/public-pages/docs/migrate-8-0-to-9-0-test.ts

@@ -0,0 +1,13 @@
+import { module, test } from 'qunit';
+import { setupTest } from 'docs/tests/helpers';
+
+module('Unit | Route | public-pages/docs/migrate-8-0-to-9-0', function (hooks) {
+  setupTest(hooks);
+
+  test('it exists', function (assert) {
+    const route = this.owner.lookup(
+      'route:public-pages/docs/migrate-8-0-to-9-0',
+    );
+    assert.ok(route);
+  });
+});