Don't write env.rb from inside an env.rb bundle

lib/bundler/environment.rb

@@ -76,16 +76,12 @@ def locked?
     end
 
     def write_rb_lock
-      if Bundler.env_file.exist? && !Bundler.env_file.writable?
-        Bundler.ui.warn "Cannot write to outdated .bundle/environment.rb to update it"
-      else
-        shared_helpers = File.read(File.expand_path("../shared_helpers.rb", __FILE__))
-        template = File.read(File.expand_path("../templates/environment.erb", __FILE__))
-        erb = ERB.new(template, nil, '-')
-        Bundler.env_file.dirname.mkpath
-        File.open(Bundler.env_file, 'w') do |f|
-          f.puts erb.result(binding)
-        end
+      shared_helpers = File.read(File.expand_path("../shared_helpers.rb", __FILE__))
+      template = File.read(File.expand_path("../templates/environment.erb", __FILE__))
+      erb = ERB.new(template, nil, '-')
+      Bundler.env_file.dirname.mkpath
+      File.open(Bundler.env_file, 'w') do |f|
+        f.puts erb.result(binding)
       end
     end
 

lib/bundler/runtime.rb

@@ -6,7 +6,7 @@ class Runtime < Environment
 
     def initialize(*)
       super
-      write_rb_lock if locked?
+      write_rb_lock if locked? && !defined?(Bundler::ENV_LOADED)
     end
 
     def setup(*groups)

spec/runtime/environment_rb_spec.rb

@@ -261,5 +261,21 @@ def require(*a, &b)
       RUBY
       err.should be_empty
     end
+
+    it "does not write out env.rb if env.rb has already been loaded" do
+      install_gemfile <<-G
+        source "file://#{gem_repo1}"
+        gem "bundler", :path => "#{File.expand_path("..", lib)}"
+        gem "rake"
+      G
+      bundle :lock
+
+      FileUtils.chmod 0444, env_file
+      run <<-RUBY, :lite_runtime => true
+        require 'bundler'
+        Bundler.runtime
+      RUBY
+      env_file.rmtree
+    end
   end
 end