FIX: Prevent infinite loop of automations triggering each other (#26814)

It's currently possible to setup multiple automation rules that trigger each other resulting in an infinite loop. To prevent that, this commit adds a global "circuit breaker" that prevents all automations from triggering while an automation rule is executing.

Internal topic: t/124365.

plugins/automation/app/models/discourse_automation/automation.rb

@@ -134,11 +134,23 @@ module DiscourseAutomation
 
     def trigger!(context = {})
       if enabled
-        if scriptable.background && !running_in_background
-          trigger_in_background!(context)
-        else
-          triggerable&.on_call&.call(self, serialized_fields)
-          scriptable.script.call(context, serialized_fields, self)
+        if active_id = DiscourseAutomation.get_active_automation
+          Rails.logger.warn(<<~TEXT.strip)
+            [automation] potential automations infinite loop detected: skipping automation #{self.id} because automation #{active_id} is still executing.")
+          TEXT
+          return
+        end
+
+        begin
+          DiscourseAutomation.set_active_automation(self.id)
+          if scriptable.background && !running_in_background
+            trigger_in_background!(context)
+          else
+            triggerable&.on_call&.call(self, serialized_fields)
+            scriptable.script.call(context, serialized_fields, self)
+          end
+        ensure
+          DiscourseAutomation.set_active_automation(nil)
         end
       end
     end

plugins/automation/plugin.rb

@@ -28,6 +28,14 @@ module ::DiscourseAutomation
 
   AUTO_RESPONDER_TRIGGERED_IDS = "auto_responder_triggered_ids"
   USER_GROUP_MEMBERSHIP_THROUGH_BADGE_BULK_MODIFY_START_COUNT = 1000
+
+  def self.set_active_automation(id)
+    @active_automation_id = id
+  end
+
+  def self.get_active_automation
+    @active_automation_id
+  end
 end
 
 require_relative "lib/discourse_automation/engine"

plugins/automation/spec/integration/infinite_loop_protection_spec.rb

@@ -0,0 +1,47 @@
+# frozen_string_literal: true
+
+require_relative "../discourse_automation_helper"
+
+describe "Infinite loop protection" do
+  fab!(:automation_1) do
+    Fabricate(:automation, script: "auto_responder", trigger: "post_created_edited", enabled: true)
+  end
+
+  fab!(:automation_2) do
+    Fabricate(:automation, script: "auto_responder", trigger: "post_created_edited", enabled: true)
+  end
+
+  before do
+    SiteSetting.discourse_automation_enabled = true
+
+    automation_1.upsert_field!(
+      "word_answer_list",
+      "key-value",
+      { value: [{ key: "", value: "this is the reply" }].to_json },
+    )
+    automation_2.upsert_field!(
+      "word_answer_list",
+      "key-value",
+      { value: [{ key: "", value: "this is the reply" }].to_json },
+    )
+
+    automation_1.upsert_field!(
+      "answering_user",
+      "user",
+      { value: Fabricate(:user).username },
+      target: "script",
+    )
+    automation_2.upsert_field!(
+      "answering_user",
+      "user",
+      { value: Fabricate(:user).username },
+      target: "script",
+    )
+  end
+
+  it "prevents infinite loop of 2 auto_responder automations triggering each other" do
+    expect do
+      PostCreator.create!(Fabricate(:user), raw: "post", title: "topic", skip_validations: true)
+    end.to change { Post.count }.by(3)
+  end
+end

plugins/automation/spec/models/automation_spec.rb

@@ -46,16 +46,6 @@ describe DiscourseAutomation::Automation do
         Jobs::DiscourseAutomationTrigger.jobs.size
       }.by(1)
     end
-
-    it "also runs the script properly" do
-      Jobs.run_immediately!
-      post = Fabricate(:post)
-      user = post.user
-      list = capture_contexts { automation.trigger!({ post: post, user: user, test: :test }) }
-      expect(list[0]["post"].id).to eq(post.id)
-      expect(list[0]["user"].id).to eq(user.id)
-      expect(list[0]["test"]).to eq(:test)
-    end
   end
 
   describe "#detach_custom_field" do