Warn if RUBYGEMS_GEMDEPS env. variable is setrubygems-gemdeps-warn

Closes #3656.

2 files changed, 23 insertions, 0 deletions

diff --git a/lib/bundler/cli.rb b/lib/bundler/cli.rb
index 921cd1e68b..138ce5d7b5 100644
--- a/lib/bundler/cli.rb
+++ b/lib/bundler/cli.rb
@@ -29,6 +29,13 @@ module Bundler
       self.options ||= {}
       Bundler.ui = UI::Shell.new(options)
       Bundler.ui.level = "debug" if options["verbose"]
+
+      if ENV["RUBYGEMS_GEMDEPS"] && !ENV["RUBYGEMS_GEMDEPS"].empty?
+        Bundler.ui.warn(
+          "The RUBYGEMS_GEMDEPS environment variable is set. This enables RubyGems' " \
+          "experimental Gemfile mode, which may conflict with Bundler and cause unexpected errors. " \
+          "To remove this warning, unset RUBYGEMS_GEMDEPS.", :wrap => true)
+      end
     end
 
     check_unknown_options!(:except => [:config, :exec])
diff --git a/spec/bundler/cli_spec.rb b/spec/bundler/cli_spec.rb
index 1d5ee7b072..a2f87e45fa 100644
--- a/spec/bundler/cli_spec.rb
+++ b/spec/bundler/cli_spec.rb
@@ -37,4 +37,20 @@ describe "bundle executable" do
       should_be_installed "rack 1.0.0"
     end
   end
+
+  context "when ENV['RUBYGEMS_GEMDEPS'] is set" do
+    it "displays a warning" do
+      gemfile bundled_app("Gemfile"), <<-G
+        source "file://#{gem_repo1}"
+        gem 'rack'
+      G
+
+      bundle :install, :env => { "RUBYGEMS_GEMDEPS" => "foo" }
+      expect(out).to include("RUBYGEMS_GEMDEPS")
+      expect(out).to include("conflict with Bundler")
+
+      bundle :install, :env => { "RUBYGEMS_GEMDEPS" => "" }
+      expect(out).not_to include("RUBYGEMS_GEMDEPS")
+    end
+  end
 end