FIX: when subcategories with the same name exist, filtering by tags might use the wrong subcategory

app/controllers/tags_controller.rb

@@ -270,7 +270,7 @@ class TagsController < ::ApplicationController
         page: params[:page],
         topic_ids: param_to_integer_list(:topic_ids),
         exclude_category_ids: params[:exclude_category_ids],
-        category: params[:category],
+        category: @filter_on_category ? @filter_on_category.id : params[:category],
         order: params[:order],
         ascending: params[:ascending],
         min_posts: params[:min_posts],

spec/controllers/tags_controller_spec.rb

@@ -68,6 +68,19 @@ describe TagsController do
         xhr :get, :show_latest, tag_id: tag.name, category: 'none', parent_category: category.slug
         expect(response).to be_success
       end
+
+      it "can handle subcategories with the same name" do
+        category2 = Fabricate(:category)
+        subcategory2 = Fabricate(:category,
+          parent_category_id: category2.id,
+          name: subcategory.name,
+          slug: subcategory.slug
+        )
+        t = Fabricate(:topic, category_id: subcategory2.id, tags: [other_tag])
+        xhr :get, :show_latest, tag_id: other_tag.name, category: subcategory2.slug, parent_category: category2.slug
+        expect(response).to be_success
+        expect(assigns(:list).topics).to include(t)
+      end
     end
   end