FEATURE: Update the topic excerpt when the OP is rebaked (#9852)

* We now have a site setting "topic_excerpt_maxlength" that is used when the OP is created or revised to generate a topic excerpt.
* However, posts created before this setting was introduced cannot benefit from this change unless they are revised, and if the topic excerpt length setting is changed that situation is also not covererd.
* This PR makes a change to rebake! to update the topic excerpt IF the post is the OP.

app/models/post.rb

@@ -650,6 +650,10 @@ class Post < ActiveRecord::Base
       baked_version: BAKED_VERSION
     )
 
+    if is_first_post?
+      topic.update_excerpt(excerpt_for_topic)
+    end
+
     if invalidate_broken_images
       custom_fields.delete(BROKEN_IMAGES)
       save_custom_fields

app/models/topic.rb

@@ -1476,6 +1476,13 @@ class Topic < ActiveRecord::Base
     private_topic
   end
 
+  def update_excerpt(excerpt)
+    update_column(:excerpt, excerpt)
+    if archetype == "banner"
+      ApplicationController.banner_json_cache.clear
+    end
+  end
+
   def pm_with_non_human_user?
     sql = <<~SQL
     SELECT 1 FROM topics

lib/post_revisor.rb

@@ -567,11 +567,7 @@ class PostRevisor
   end
 
   def update_topic_excerpt
-    excerpt = @post.excerpt_for_topic
-    @topic.update_column(:excerpt, excerpt)
-    if @topic.archetype == "banner"
-      ApplicationController.banner_json_cache.clear
-    end
+    @topic.update_excerpt(@post.excerpt_for_topic)
   end
 
   def update_category_description

spec/models/post_spec.rb

@@ -1195,6 +1195,25 @@ describe Post do
       expect(post.cooked).to eq(first_cooked)
       expect(result).to eq(true)
     end
+
+    it "updates the topic excerpt at the same time if it is the OP" do
+      post = create_post
+      post.topic.update(excerpt: "test")
+      DB.exec("UPDATE posts SET cooked = 'frogs' WHERE id = ?", [ post.id ])
+      post.reload
+      result = post.rebake!
+      post.topic.reload
+      expect(post.topic.excerpt).not_to eq("test")
+    end
+
+    it "does not update the topic excerpt if the post is not the OP" do
+      post = create_post
+      post2 = create_post
+      post.topic.update(excerpt: "test")
+      result = post2.rebake!
+      post.topic.reload
+      expect(post.topic.excerpt).to eq("test")
+    end
   end
 
   describe "#set_owner" do