FIX: Ensure composer also filters tags when searching (#37555)

When editing a topic via the composer, tags with parent tag requirements
weren't appearing in search results, even though the parent tag was
already selected on the topic. When the composer opens for editing, it
was using these serialized string tags. The mini-tag-chooser couldn't
extract tag IDs from strings

This commit fixes that. Also adds a system spec testing the composer and
title header scenarios.

frontend/discourse/app/models/composer.js

@@ -989,6 +989,7 @@ export default class Composer extends RestModel {
     if (isEdit(opts.action) && this.post) {
       const topicProps = this.serialize(_edit_topic_serializer);
       topicProps.loading = true;
+      topicProps.tags = this.topic.tags;
 
       // When editing a shared draft, use its category
       if (opts.action === EDIT_SHARED_DRAFT && opts.destinationCategoryId) {

frontend/discourse/tests/fixtures/topic.js

@@ -4009,7 +4009,7 @@ export default {
     chunk_size: 20,
     bookmarked: null,
     bookmarks: [],
-    tags: ["foo"],
+    tags: [{ id: 1, name: "foo", slug: "foo" }],
   },
   "/t/9/1.json": {
     post_stream: {
@@ -5805,7 +5805,10 @@ export default {
         avatar_template: "/images/avatar.png",
       },
     },
-    tags: ["foo", "baz"],
+    tags: [
+      { id: 1, name: "foo", slug: "foo" },
+      { id: 2, name: "baz", slug: "baz" },
+    ],
   },
   "/t/2481/1.json": {
     post_stream: {

spec/system/tags/tags_spec.rb

@@ -263,5 +263,54 @@ describe "Tags", type: :system do
       original_tag_ids = draft_data["original_tags"].map { |t| t["id"] }
       expect(original_tag_ids).to contain_exactly(tag_one.id, tag_two.id)
     end
+
+    it "shows child tags when parent tag is selected in topic title editor and composer" do
+      parent_tag = Fabricate(:tag, name: "cap")
+      child_tag_approved = Fabricate(:tag, name: "cap-approved")
+      child_tag_closed = Fabricate(:tag, name: "cap-closed")
+      child_tag_open = Fabricate(:tag, name: "cap-open")
+
+      tag_group =
+        Fabricate(
+          :tag_group,
+          name: "Corrective Action Plans",
+          parent_tag: parent_tag,
+          one_per_topic: true,
+          tags: [child_tag_approved, child_tag_closed, child_tag_open],
+        )
+
+      topic = Fabricate(:topic, user: admin, tags: [parent_tag])
+      Fabricate(:post, topic: topic, user: admin)
+
+      sign_in(admin)
+      visit topic.url
+
+      topic_page.click_topic_edit_title
+      expect(topic_page).to have_topic_title_editor
+
+      mini_tag_chooser.expand
+      mini_tag_chooser.search("cap-")
+
+      expect(mini_tag_chooser).to have_option_name("cap-approved")
+      expect(mini_tag_chooser).to have_option_name("cap-closed")
+      expect(mini_tag_chooser).to have_option_name("cap-open")
+
+      mini_tag_chooser.collapse_with_escape
+      topic_page.click_topic_title_cancel_edit
+
+      find("#post_1 .post-controls .edit").click
+      expect(composer).to be_opened
+
+      expect(page).to have_css(".mini-tag-chooser", text: "cap")
+
+      composer_tag_chooser =
+        PageObjects::Components::SelectKit.new(".composer-fields .mini-tag-chooser")
+      composer_tag_chooser.expand
+      composer_tag_chooser.search("cap-")
+
+      expect(composer_tag_chooser).to have_option_name("cap-approved")
+      expect(composer_tag_chooser).to have_option_name("cap-closed")
+      expect(composer_tag_chooser).to have_option_name("cap-open")
+    end
   end
 end