FEATURE: New site setting embed_unlisted (#9391)

If enabled, posts imported to discourse via embeddings will default to
unlisted until they receive a reply.

spec/models/topic_embed_spec.rb

@@ -41,6 +41,7 @@ describe TopicEmbed do
         expect(TopicEmbed.where(topic_id: post.topic_id)).to be_present
 
         expect(post.topic.category).to eq(embeddable_host.category)
+        expect(post.topic).to be_visible
       end
 
       it "Supports updating the post content" do
@@ -71,6 +72,20 @@ describe TopicEmbed do
         post = TopicEmbed.import(user, cased_url, title, "some random content")
         expect(post.cooked).to match(/#{cased_url}/)
       end
+
+      it "will make the topic unlisted if `embed_unlisted` is set until someone replies" do
+        SiteSetting.embed_unlisted = true
+        imported_post = TopicEmbed.import(user, "http://eviltrout.com/abcd", title, "some random content")
+        expect(imported_post.topic).not_to be_visible
+        pc = PostCreator.new(
+          Fabricate(:user),
+          raw: "this is a reply that will make the topic visible",
+          topic_id: imported_post.topic_id,
+          reply_to_post_number: 1
+        )
+        pc.create
+        expect(imported_post.topic.reload).to be_visible
+      end
     end
 
     context "post creation supports markdown rendering" do