FEATURE: search fallback to tags when category not found

lib/search.rb

@@ -297,7 +297,12 @@ class Search
     if category_id
       posts.where("topics.category_id = ?", category_id)
     else
-      posts.where("1 = 0")
+      posts.where("topics.id IN (
+        SELECT DISTINCT(tt.topic_id)
+        FROM topic_tags tt, tags
+        WHERE tt.tag_id = tags.id
+        AND tags.name = ?
+        )", slug[0])
     end
   end
 

spec/components/search_spec.rb

@@ -536,7 +536,7 @@ describe Search do
 
     end
 
-    it 'supports category slug' do
+    it 'supports category slug and tags' do
       # main category
       category = Fabricate(:category, name: 'category 24', slug: 'category-24')
       topic = Fabricate(:topic, created_at: 3.months.ago, category: category)
@@ -552,6 +552,11 @@ describe Search do
 
       expect(Search.execute('testing again #category-24:sub-category').posts.length).to eq(1)
       expect(Search.execute('testing again #sub-category').posts.length).to eq(0)
+
+      # tags
+      topic.tags = [Fabricate(:tag, name: 'alpha')]
+      expect(Search.execute('this is a test #alpha').posts.map(&:id)).to eq([post.id])
+      expect(Search.execute('this is a test #beta').posts.size).to eq(0)
     end
 
     it "can find with tag" do