October 26, 2013

Sinatra, Bundler, and the global namespace

Either my google-fu is waning or I ran into an issue most people haven’t so I want to quickly document it.

The scenario

A Rails 4 app mounting a modular-style Sinatra app to service a particular route, kind of like this.


MyApp::Application.routes.draw do
  mount MySubApp => 'subapp'


require 'sinatra/base'

class MySubApp < Sinatra::Base
  # stuff

The problem

The Gemfile looks like what you’d expect if you just added gems ‘normally’.

source 'https://rubygems.org'

# Bundle edge Rails instead: gem 'rails', github: 'rails/rails'
gem 'rails', '4.0.0'

# yadda yadda yadda

gem "sinatra", "~> 1.4.3"
gem "sinatra-contrib", "~> 1.4.1"

The problem comes because Bundler is really helpful and requires the gems for you automatically, using the gem name by default. Unfortunately this means that Bundler will end up running require 'sinatra' (and require 'sinatra-contrib') and when used this way Sinatra adds its DSL to the global namespace.

That means that when you run rake, for example, you could see odd error messages like “rake aborted! undefined method ‘task’ for Sinatra::Application:Class”

In my case, sinatra-contrib was intercepting rake’s DSL and obviously failing.

The solution

The solution is to fix the Gemfile to instruct Bundler how to correctly require the sinatra gems.

gem "sinatra", "~> 1.4.3", require: 'sinatra/base'
gem "sinatra-contrib", "~> 1.4.1", require: false

This change results in Sinatra being required correctly for modular app use, and turns off automatic requiring for sinatra-contrib so you can require just the bits you need at the place you need them, since sinatra-contrib is just a set of helpful modules.

It’s not complex or difficult, but the error message (and backtrace) was a little non-obvious.