FEATURE: add max_reply_history to limit number of replies

that can be expanded, when clicking "in-reply-to"

app/assets/javascripts/discourse/models/post_stream.js

@@ -649,7 +649,7 @@ Discourse.PostStream = Em.Object.extend({
   **/
   findReplyHistory: function(post) {
     var postStream = this,
-        url = "/posts/" + post.get('id') + "/reply-history.json";
+        url = "/posts/" + post.get('id') + "/reply-history.json?max_replies=" + Discourse.SiteSettings.max_reply_history;
 
     return Discourse.ajax(url).then(function(result) {
       return result.map(function (p) {

app/controllers/posts_controller.rb

@@ -158,7 +158,7 @@ class PostsController < ApplicationController
 
   def reply_history
     post = find_post_from_params
-    render_serialized(post.reply_history, PostSerializer)
+    render_serialized(post.reply_history(params[:max_replies].to_i), PostSerializer)
   end
 
   def destroy

app/models/post.rb

@@ -476,7 +476,7 @@ class Post < ActiveRecord::Base
   end
 
 
-  def reply_history
+  def reply_history(max_replies=100)
     post_ids = Post.exec_sql("WITH RECURSIVE breadcrumb(id, reply_to_post_number) AS (
                               SELECT p.id, p.reply_to_post_number FROM posts AS p
                                 WHERE p.id = :post_id
@@ -486,7 +486,12 @@ class Post < ActiveRecord::Base
                                      AND p.topic_id = :topic_id
                             ) SELECT id from breadcrumb ORDER by id", post_id: id, topic_id: topic_id).to_a
 
-    post_ids.map! {|r| r['id'].to_i }.reject! {|post_id| post_id == id}
+    post_ids.map! {|r| r['id'].to_i }
+            .reject! {|post_id| post_id == id}
+
+    # [1,2,3][-10,-1] => nil
+    post_ids = (post_ids[(0-max_replies)..-1] || post_ids)
+
     Post.where(id: post_ids).includes(:user, :topic).order(:id).to_a
   end
 

config/locales/server.en.yml

@@ -741,6 +741,7 @@ en:
     suppress_reply_directly_below: "Don't show the expandable reply count on a post when there is only a single reply directly below this post."
     suppress_reply_directly_above: "Don't show the expandable in-reply-to on a post when there is only a single reply directly above this post."
     suppress_reply_when_quoting: "Don't show the expandable in-reply-to on a post when post quotes reply."
+    max_reply_history: "Maximum number of replies to expand when expanding in-reply-to"
 
     experimental_reply_expansion: "Hide intermediate replies when expanding a reply to (experimental)"
 

config/site_settings.yml

@@ -347,6 +347,9 @@ posting:
     default: true
   suppress_reply_when_quoting:
     default: true
+  max_reply_history:
+    default: 1
+    client: true
   experimental_reply_expansion:
     default: false
     client: true

spec/models/post_spec.rb

@@ -715,6 +715,7 @@ describe Post do
 
     it "returns the posts in reply to this post" do
       p4.reply_history.should == [p1, p2]
+      p4.reply_history(1).should == [p2]
       p3.reply_history.should be_blank
       p2.reply_history.should == [p1]
     end