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
    }

1 files changed, 12 insertions, 0 deletions

diff --git a/railties/test/rails_info_test.rb b/railties/test/rails_info_test.rb
index 50522c1be6..d167a86e56 100644
--- a/railties/test/rails_info_test.rb
+++ b/railties/test/rails_info_test.rb
@@ -43,6 +43,18 @@ class InfoTest < ActiveSupport::TestCase
     end
   end
 
+  def test_json_includes_middleware
+    Rails::Info.module_eval do
+      property "Middleware", ["Rack::Lock", "Rack::Static"]
+    end
+
+    hash = JSON.parse(Rails::Info.to_json)
+    assert_includes hash.keys, "Middleware"
+    properties.value_for("Middleware").each do |value|
+      assert_includes hash["Middleware"], value
+    end
+  end
+
   private
     def properties
       Rails::Info.properties