From 10fb9743f55354ceb72e445fed67b16555d879a2 Mon Sep 17 00:00:00 2001
From: Samuel Giddins <segiddins@segiddins.me>
Date: Tue, 13 Jun 2017 15:48:21 -0500
Subject: Add a compatibility guard that prints friendly errors on bundler 2+

---
 lib/bundler.rb                         |  1 +
 lib/bundler/compatibility_guard.rb     | 14 ++++++++++++++
 lib/bundler/inline.rb                  |  1 +
 lib/bundler/shared_helpers.rb          |  1 +
 spec/other/compatibility_guard_spec.rb | 23 +++++++++++++++++++++++
 5 files changed, 40 insertions(+)
 create mode 100644 lib/bundler/compatibility_guard.rb
 create mode 100644 spec/other/compatibility_guard_spec.rb

diff --git a/lib/bundler.rb b/lib/bundler.rb
index 2da2db29c9..a587f1e430 100644
--- a/lib/bundler.rb
+++ b/lib/bundler.rb
@@ -1,4 +1,5 @@
 # frozen_string_literal: true
+require "bundler/compatibility_guard"
 
 require "bundler/vendored_fileutils"
 require "pathname"
diff --git a/lib/bundler/compatibility_guard.rb b/lib/bundler/compatibility_guard.rb
new file mode 100644
index 0000000000..6e40a119d1
--- /dev/null
+++ b/lib/bundler/compatibility_guard.rb
@@ -0,0 +1,14 @@
+# frozen_string_literal: true
+
+require "rubygems"
+require "bundler/version"
+
+if Bundler::VERSION.split(".").first.to_i >= 2
+  if Gem::Version.new(Object::RUBY_VERSION) < Gem::Version.new("2.0.0")
+    abort "Bundler 2 requires Ruby 2+. Either install bundler 1 or update to a supported Ruby version."
+  end
+
+  if Gem::Version.new(Gem::VERSION) < Gem::Version.new("2.0.0")
+    abort "Bundler 2 requires RubyGems 2+. Either install bundler 1 or update to a supported RubyGems version."
+  end
+end
diff --git a/lib/bundler/inline.rb b/lib/bundler/inline.rb
index 8462dd9cc1..f5e3a8c157 100644
--- a/lib/bundler/inline.rb
+++ b/lib/bundler/inline.rb
@@ -1,4 +1,5 @@
 # frozen_string_literal: true
+require "bundler/compatibility_guard"
 
 # Allows for declaring a Gemfile inline in a ruby script, optionally installing
 # any gems that aren't already installed on the user's system.
diff --git a/lib/bundler/shared_helpers.rb b/lib/bundler/shared_helpers.rb
index 5d3956abc1..bc4c1c1d88 100644
--- a/lib/bundler/shared_helpers.rb
+++ b/lib/bundler/shared_helpers.rb
@@ -1,4 +1,5 @@
 # frozen_string_literal: true
+require "bundler/compatibility_guard"
 
 require "pathname"
 require "rubygems"
diff --git a/spec/other/compatibility_guard_spec.rb b/spec/other/compatibility_guard_spec.rb
new file mode 100644
index 0000000000..abe70741a1
--- /dev/null
+++ b/spec/other/compatibility_guard_spec.rb
@@ -0,0 +1,23 @@
+# frozen_string_literal: true
+
+RSpec.describe "bundler compatibility guard" do
+  context "when the bundler version is 2+" do
+    before { simulate_bundler_version "2.0.a" }
+
+    context "when running on Ruby < 2", :ruby => "< 2.a" do
+      it "raises a friendly error" do
+        bundle :version
+        expect(err).to eq("Bundler 2 requires Ruby 2+. Either install bundler 1 or update to a supported Ruby version.")
+      end
+    end
+
+    context "when running on RubyGems < 2" do
+      before { simulate_rubygems_version "1.3.6" }
+
+      it "raises a friendly error" do
+        bundle :version
+        expect(err).to eq("Bundler 2 requires RubyGems 2+. Either install bundler 1 or update to a supported RubyGems version.")
+      end
+    end
+  end
+end
-- 
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