UX: change text of public_topic action code in login required sites. (#14764)

The wording "made this topic public" made confusion in login required forums.

app/serializers/post_serializer.rb

@@ -432,6 +432,11 @@ class PostSerializer < BasicPostSerializer
     scope.is_staff? ? object.version : object.public_version
   end
 
+  def action_code
+    return "open_topic" if object.action_code == "public_topic" && SiteSetting.login_required?
+    object.action_code
+  end
+
   def include_action_code?
     object.action_code.present?
   end

config/locales/client.en.yml

@@ -145,6 +145,7 @@ en:
 
     action_codes:
       public_topic: "made this topic public %{when}"
+      open_topic: "converted this to a topic %{when}"
       private_topic: "made this topic a personal message %{when}"
       split_topic: "split this topic %{when}"
       invited_user: "invited %{who} %{when}"

spec/serializers/post_serializer_spec.rb

@@ -282,6 +282,16 @@ describe PostSerializer do
 
   end
 
+  context "post with small action" do
+    fab!(:post) { Fabricate(:small_action, action_code: "public_topic") }
+
+    it "returns `action_code` based on `login_required` site setting" do
+      expect(serialized_post_for_user(nil)[:action_code]).to eq("public_topic")
+      SiteSetting.login_required = true
+      expect(serialized_post_for_user(nil)[:action_code]).to eq("open_topic")
+    end
+  end
+
   def serialized_post(u)
     s = PostSerializer.new(post, scope: Guardian.new(u), root: false)
     s.add_raw = true