FIX: Incorrect title and chevron when filtering by post number. (#14985)

The widget's state did not reflect the state of the controller.

app/assets/javascripts/discourse/app/widgets/post.js

@@ -388,8 +388,20 @@ createWidget("post-group-request", {
 createWidget("post-contents", {
   buildKey: (attrs) => `post-contents-${attrs.id}`,
 
-  defaultState() {
-    return { expandedFirstPost: false, repliesBelow: [] };
+  defaultState(attrs) {
+    const defaultState = {
+      expandedFirstPost: false,
+      repliesBelow: [],
+    };
+
+    if (this.siteSettings.enable_filtered_replies_view) {
+      const topicController = this.register.lookup("controller:topic");
+
+      defaultState.filteredRepliesShown =
+        topicController.replies_to_post_number === attrs.post_number.toString();
+    }
+
+    return defaultState;
   },
 
   buildClasses(attrs) {

app/assets/javascripts/discourse/tests/acceptance/topic-test.js

@@ -546,3 +546,28 @@ acceptance("Topic last visit line", function (needs) {
     );
   });
 });
+
+acceptance("Topic filter replies to post number", function (needs) {
+  needs.settings({
+    enable_filtered_replies_view: true,
+  });
+
+  test("visit topic", async function (assert) {
+    await visit("/t/-/280");
+
+    assert.equal(
+      query("#post_3 .show-replies").title,
+      I18n.t("post.filtered_replies_hint", { count: 3 }),
+      "it displays the right title for filtering by replies"
+    );
+
+    await visit("/");
+    await visit("/t/-/280?replies_to_post_number=3");
+
+    assert.equal(
+      query("#post_3 .show-replies").title,
+      I18n.t("post.view_all_posts"),
+      "it displays the right title when filtered by replies"
+    );
+  });
+});