Add JSON support to rails properties route (`/rails/info/properties`).

Added json format, like this:

    {
      "Rails version": "6.0.0.alpha",
      "Ruby version": "2.5.1-p57 (x86_64-darwin17)",
      "RubyGems version": "2.7.6",
      "Rack version": "2.0.6",
      "JavaScript Runtime": "Node.js (V8)",
      "Middleware": ["Rack::Sendfile", "ActionDispatch::Static", "ActionDispatch::Executor", "ActiveSupport::Cache::Strategy::LocalCache::Middleware", "Rack::Runtime", "Rack::MethodOverride", "ActionDispatch::RequestId", "ActionDispatch::RemoteIp", "Sprockets::Rails::QuietAssets", "Rails::Rack::Logger", "ActionDispatch::ShowExceptions", "WebConsole::Middleware", "ActionDispatch::DebugExceptions", "ActionDispatch::Reloader", "ActionDispatch::Callbacks", "ActiveRecord::Migration::CheckPending", "ActionDispatch::Cookies", "ActionDispatch::Session::CookieStore", "ActionDispatch::Flash", "ActionDispatch::ContentSecurityPolicy::Middleware", "Rack::Head", "Rack::ConditionalGet", "Rack::ETag", "Rack::TempfileReaper"],
      "Application root": "/path/to/app",
      "Environment": "development",
      "Database adapter": "sqlite3",
      "Database schema version": 0
    }

2 files changed, 14 insertions, 2 deletions

diff --git a/railties/lib/rails/info.rb b/railties/lib/rails/info.rb
index 3df36efc4c..b8173c8d11 100644
--- a/railties/lib/rails/info.rb
+++ b/railties/lib/rails/info.rb
@@ -54,6 +54,10 @@ module Rails
           table << "</table>"
         end
       end
+
+      def to_json
+        Hash[properties].to_json
+      end
     end
 
     # The Rails version.
diff --git a/railties/lib/rails/info_controller.rb b/railties/lib/rails/info_controller.rb
index b4f4a5922a..50fe176946 100644
--- a/railties/lib/rails/info_controller.rb
+++ b/railties/lib/rails/info_controller.rb
@@ -14,8 +14,16 @@ class Rails::InfoController < Rails::ApplicationController # :nodoc:
   end
 
   def properties
-    @info = Rails::Info.to_html
-    @page_title = "Properties"
+    respond_to do |format|
+      format.html do
+        @info = Rails::Info.to_html
+        @page_title = "Properties"
+      end
+
+      format.json do
+        render json: Rails::Info.to_json
+      end
+    end
   end
 
   def routes