PERF: Client side triggering multiple requests when opening composer (#21823)

What is the problem?

There are two problems being fixed here:

1. When opening the composer, we are seeing multiple requests made to
   the `/composer_messages` endpoint. This is due to our use of the
   `transitionend` event on the `#reply-control` element. The event is
   fired once for each transition event and the `#reply-control` element
   has multiple transition events.

2. System tests have animations disabled so the `transitionend` event
   does not fire at all.

What is the solution?

Instead of relying on the `transitionend` event, we can instead just
observer the `composerState` property of the `ComposerBody` component
and trigger the `composer:opened` appEvent with a delay that is similar
to the transition duration used for the `ComposerBody` component.

app/assets/javascripts/discourse/app/components/composer-body.js

@@ -170,20 +170,7 @@ export default Component.extend(KeyEnterEscape, {
 
   didInsertElement() {
     this._super(...arguments);
-
     this.setupComposerResizeEvents();
-
-    const triggerOpen = () => {
-      if (this.get("composer.composeState") === Composer.OPEN) {
-        this.appEvents.trigger("composer:opened");
-      }
-    };
-    triggerOpen();
-
-    this.element.addEventListener("transitionend", () => {
-      triggerOpen();
-    });
-
     positioningWorkaround(this.element);
   },
 

app/assets/javascripts/discourse/app/models/composer.js

@@ -5,6 +5,7 @@ import discourseComputed, {
   observes,
   on,
 } from "discourse-common/utils/decorators";
+import discourseLater from "discourse-common/lib/later";
 import {
   emailValid,
   escapeExpression,
@@ -225,6 +226,12 @@ const Composer = RestModel.extend({
     if (this.composeState === OPEN) {
       this.set("composerOpened", oldOpen || new Date());
       elem.classList.add("composer-open");
+
+      // If the duration changes here, it must also be changed in `stylesheets/common/base/compose.scss` which is where
+      // the transition duration is defined. A delay is added here as we only want to fire the event after the transition ends.
+      discourseLater(() => {
+        this.appEvents.trigger("composer:opened");
+      }, 250);
     } else {
       if (oldOpen) {
         const oldTotal = this.composerTotalOpened || 0;

app/assets/javascripts/discourse/tests/acceptance/composer-messages-test.js

@@ -138,9 +138,6 @@ acceptance("Composer - Messages - Duplicate links", function (needs) {
     await visit("/t/internationalization-localization/280");
     await click("button.create");
 
-    // Work around the lack of CSS transitions in the test env
-    query("#reply-control").dispatchEvent(new Event("transitionend"));
-
     assert
       .dom(".composer-popup")
       .doesNotExist("composer warning is not shown by default");

app/assets/stylesheets/common/base/compose.scss

@@ -23,8 +23,11 @@ html.composer-open {
     min-width: 0;
   }
   z-index: z("composer", "content");
+
+  // If the transition duration is changed here, it must also be changed in the `composeStateChanged` function of models/composer.js
   transition: height 250ms ease, background 250ms ease, transform 250ms ease,
     max-width 250ms ease, padding-bottom 250ms ease;
+
   background-color: var(--secondary);
   box-shadow: shadow("composer");
 

spec/system/composer/dont_feed_the_trolls_popup_spec.rb

@@ -12,10 +12,6 @@ describe "Composer don't feed the trolls popup", type: :system, js: true do
   before { sign_in user }
 
   it "shows a popup when about to reply to a troll" do
-    skip(
-      "TGX: This does not work when Capybara.disable_animation is set to true. We're in the midst of fixing this.",
-    )
-
     SiteSetting.educate_until_posts = 0
 
     topic_page.visit_topic(topic)