FEATURE: add the ability to add tagging automation on topic closed (#38134)

Topic closed target is (obviously) a topic.
Auto tag topic currently targets a (first) post's topic.

Adds support to also pass a topic directly to auto_tag_topic automation.

In turn, allows adding `topic_closed` triggerable to the auto_tag_topic
automation.

plugins/automation/lib/discourse_automation/scripts/auto_tag_topic.rb

@@ -5,14 +5,19 @@ DiscourseAutomation::Scriptable.add(DiscourseAutomation::Scripts::AUTO_TAG_TOPIC
 
   version 1
 
-  triggerables %i[post_created_edited pm_created]
+  triggerables %i[post_created_edited pm_created topic_closed]
 
   script do |context, fields|
-    post = context["post"]
+    topic = nil
+    if context["topic"]
+      topic = context["topic"]
+    else
+      post = context["post"]
 
-    next if !post.is_first_post?
-    next if !post.topic
-    next unless topic = Topic.find_by(id: post.topic.id)
+      next if !post.is_first_post?
+      next if !post.topic
+      next unless topic = Topic.find_by(id: post.topic.id)
+    end
 
     tags = fields.dig("tags", "value")
 

plugins/automation/spec/scripts/auto_tag_topic_spec.rb

@@ -75,4 +75,22 @@ describe "AutoTagTopic" do
       end
     end
   end
+
+  context "with a topic" do
+    context "when tags list is empty" do
+      it "exits early with no error" do
+        expect { automation.trigger!("topic" => topic) }.to_not raise_error
+      end
+    end
+
+    context "when there are tags" do
+      before { automation.upsert_field!("tags", "tags", { value: %w[tag1 tag2] }) }
+
+      it "works" do
+        automation.trigger!("topic" => topic)
+
+        expect(topic.reload.tags.pluck(:name)).to match_array(%w[tag1 tag2])
+      end
+    end
+  end
 end