FIX: prevent 💥 when selecting replies to posts quoting themselves

app/models/post.rb

@@ -654,6 +654,8 @@ class Post < ActiveRecord::Base
     Post.secured(guardian).where(id: post_ids).includes(:user, :topic).order(:id).to_a
   end
 
+  MAX_REPLY_LEVEL ||= 1000
+
   def reply_ids(guardian = nil)
     replies = Post.exec_sql("
       WITH RECURSIVE breadcrumb(id, level) AS (
@@ -662,6 +664,8 @@ class Post < ActiveRecord::Base
         SELECT reply_id, level + 1
           FROM post_replies, breadcrumb
          WHERE post_id = id
+           AND post_id <> reply_id
+           AND level < #{MAX_REPLY_LEVEL}
       ), breadcrumb_with_count AS (
         SELECT id, level, COUNT(*)
           FROM post_replies, breadcrumb

spec/models/post_spec.rb

@@ -786,6 +786,7 @@ describe Post do
     let!(:p4) { Fabricate(:post, topic: topic, post_number: 4, reply_to_post_number: 2) }
     let!(:p5) { Fabricate(:post, topic: topic, post_number: 5, reply_to_post_number: 4) }
     let!(:p6) { Fabricate(:post, topic: topic, post_number: 6) }
+    let!(:p7) { Fabricate(:post, topic: topic, post_number: 7) }
 
     before {
       PostReply.create!(post: p1, reply: p2)
@@ -793,6 +794,7 @@ describe Post do
       PostReply.create!(post: p2, reply: p6) # simulates p6 quoting p2
       PostReply.create!(post: p3, reply: p5) # simulates p5 quoting p3
       PostReply.create!(post: p4, reply: p5)
+      PostReply.create!(post: p7, reply: p7) # https://meta.discourse.org/t/topic-quoting-itself-displays-reply-indicator/76085
     }
 
     it "returns the reply ids and their level" do
@@ -801,7 +803,8 @@ describe Post do
       expect(p3.reply_ids).to be_empty # has no replies
       expect(p4.reply_ids).to be_empty # p5 replies to 2 posts (p4 and p3)
       expect(p5.reply_ids).to be_empty # has no replies
-      expect(p6.reply_ids).to be_empty # last post
+      expect(p6.reply_ids).to be_empty # has no replies
+      expect(p7.reply_ids).to be_empty # quotes itself
     end
 
   end