FEATURE: Improve "+ subcategories" option (#26086)

This commit improves the "+ X subcategories" option that shows sometimes
in the category selector. It used to show when there was a single match,
but now it also shows up on exact matches even though there are multiple
results.

It also makes it work when lazy_load_categories is enabled by searching
the subcategories before rendering them.

app/assets/javascripts/discourse/tests/integration/components/select-kit/category-selector-test.js

@@ -49,8 +49,8 @@ module(
         "Parent Category × 95"
       );
       assert.equal(
-        this.subject.rowByIndex(1).el().innerText.replace("\n", " "),
-        "Parent Category + 2 subcategories"
+        this.subject.rowByIndex(1).el().innerText.replaceAll("\n", " "),
+        "Parent Category × 95 + 2 subcategories"
       );
     });
   }

app/assets/javascripts/select-kit/addon/components/category-row.gjs

@@ -111,6 +111,9 @@ export default class CategoryRow extends Component {
           this.allowUncategorizedTopics || this.allowUncategorized,
         hideParent: !!this.parentCategory,
         topicCount: this.topicCount,
+        subcategoryCount: this.args.item?.categories
+          ? this.args.item.categories.length - 1
+          : 0,
       })
     );
   }

app/assets/javascripts/select-kit/addon/components/category-selector.js

@@ -1,6 +1,5 @@
 import EmberObject, { computed } from "@ember/object";
 import { mapBy } from "@ember/object/computed";
-import { categoryBadgeHTML } from "discourse/helpers/category-link";
 import Category from "discourse/models/category";
 import { makeArray } from "discourse-common/lib/helpers";
 import CategoryRow from "select-kit/components/category-row";
@@ -70,19 +69,30 @@ export default MultiSelectComponent.extend({
       categories = this._super(filter);
     }
 
-    // If there is a single match and it has subcategories, add a row for
-    // selecting all
-    if (categories.length === 1) {
-      const descendants = categories[0].descendants;
-      if (descendants.length > 1) {
-        categories.push(
+    // If there is a single match or an exact match and it has subcategories,
+    // add a row for selecting all subcategories
+    if (
+      categories.length === 1 ||
+      (categories.length > 0 && categories[0].name.localeCompare(filter) === 0)
+    ) {
+      // Descendants may not be loaded if lazy loading is enabled. Search for
+      // subcategories will make sure these are loaded
+      if (this.site.lazy_load_categories) {
+        await Category.asyncSearch("", {
+          parentCategoryId: categories[0].id,
+        });
+      }
+
+      if (categories[0].descendants.length > 1) {
+        categories.splice(
+          1,
+          0,
           EmberObject.create({
-            label: categoryBadgeHTML(descendants[0], {
-              link: false,
-              recursive: true,
-              subcategoryCount: descendants.length - 1,
-            }),
-            categories: [...descendants],
+            // This is just a hack to ensure the IDs are unique, but ensure
+            // that parseInt still returns a valid ID in order to generate the
+            // label
+            id: `${categories[0].id}+subcategories`,
+            categories: categories[0].descendants,
           })
         );
       }