Auto merge of #5901 - bundler:seg-bundler-2-tasks, r=indirect

Add tasks to make running in 2.0 mode easier

### What was the end-user problem that led to this PR?

The problem was it was too difficult to run Bundler in 2.0 mode.

### What was your diagnosis of the problem?

My diagnosis was we needed a way to install a dev version of 2.0, and also to run commands as bundler 2.

### What is your fix for the problem, implemented in this PR?

My fix adds a `bin/bundle2` bin stub that runs bundler as 2.0.0.dev, and a `bundle_2:install` rake task that will install `bundler-2.0.0.dev`

2 files changed, 18 insertions, 0 deletions

diff --git a/bin/bundle2 b/bin/bundle2
new file mode 100755
index 0000000000..e8ab8c33c9
--- /dev/null
+++ b/bin/bundle2
@@ -0,0 +1,8 @@
+#!/usr/bin/env ruby
+# frozen_string_literal: true
+
+module Bundler
+  VERSION = "2.0.0.dev".freeze
+end
+
+load File.expand_path("../bundle", __FILE__)
diff --git a/task/bundler_2.rake b/task/bundler_2.rake
new file mode 100644
index 0000000000..b76b63d85f
--- /dev/null
+++ b/task/bundler_2.rake
@@ -0,0 +1,10 @@
+# frozen_string_literal: true
+
+namespace :bundler_2 do
+  task :install do
+    ENV["BUNDLER_SPEC_SUB_VERSION"] = "2.0.0.dev"
+    Rake::Task["spec:travis:sub_version"].invoke
+    Rake::Task["install"].invoke
+    sh("git", "checkout", "--", "lib/bundler/version.rb")
+  end
+end