Specify path which we'll load bundler from

Fixes rails#456. See my analysis at
rails#456 (comment)

Previously we were implicitly relying on Bundler setting RUBYLIB so that
we'd be able to find Bundler in the child process.

Bundler 1.11 no longer does that for us, so we need to explicitly do it
ourselves (it was a bug that Bundle.with_clean_env didn't clear it).

Author: jonleighton

CHANGELOG.md

@@ -1,3 +1,7 @@
+## 1.6.3
+
+* Fix problem with using Bundler 1.11 with a custom `BUNDLE_PATH` (#456)
+
 ## 1.6.2
 
 * Fix problems with the implementation of the new "Running via Spring preloader"

lib/spring/application_manager.rb

@@ -101,6 +101,7 @@ def start_child(preload = false)
             "SPRING_PRELOAD"      => preload ? "1" : "0"
           },
           "ruby",
+          "-I", File.expand_path("../..", $LOADED_FEATURES.grep(/bundler\/setup\.rb$/).first),
           "-I", File.expand_path("../..", __FILE__),
           "-e", "require 'spring/application/boot'",
           3 => child_socket

lib/spring/test/acceptance_test.rb

@@ -495,6 +495,19 @@ def exec_name
         expr = "p Kernel.private_instance_methods.include?(:raise)"
         assert_success %(bin/rails runner '#{expr}'), stdout: "true"
       end
+
+      test "custom bundle path" do
+        bundle_path = app.path(".bundle/#{Bundler.ruby_scope}")
+        bundle_path.dirname.mkpath
+
+        FileUtils.cp_r "#{app.gem_home}/", bundle_path.to_s
+
+        app.run! "bundle install --path .bundle --clean --local"
+
+        assert_speedup do
+          2.times { assert_success "bundle exec rails runner ''" }
+        end
+      end
     end
   end
 end