Fix multiple gem files deprecation

lib/bundler/shared_helpers.rb

@@ -157,11 +157,16 @@ def print_major_deprecations!
       multiple_gemfiles = search_up(".") do |dir|
         gemfiles = gemfile_names.select {|gf| File.file? File.expand_path(gf, dir) }
         next if gemfiles.empty?
-        break false if gemfiles.size == 1
+        break gemfiles.size != 1
       end
-      return unless multiple_gemfiles && Bundler.bundler_major_version == 1
-      Bundler::SharedHelpers.major_deprecation 2, \
-        "gems.rb and gems.locked will be preferred to Gemfile and Gemfile.lock."
+      return unless multiple_gemfiles
+      diagnosis = "Multiple gemfiles (gems.rb and Gemfile) detected."
+      advice = if Bundler.feature_flag.prefer_gems_rb?
+        "Make sure you remove Gemfile and Gemfile.lock since bundler is ignoring them in favor of gems.rb and gems.rb.locked."
+      else
+        "The gems.rb and gems.rb.locked files are currently ignored, but they will get used as soon as you delete your Gemfile and Gemfile.lock files."
+      end
+      Bundler.ui.warn [diagnosis, advice].join(" ")
     end
 
     def trap(signal, override = false, &block)

spec/other/major_deprecation_spec.rb

@@ -71,7 +71,7 @@
     end
   end
 
-  context "when bundle is run" do
+  context "when bundle install is run" do
     it "should not warn about gems.rb" do
       create_file "gems.rb", <<-G
         source "file://#{gem_repo1}"
@@ -82,15 +82,32 @@
       expect(warnings).not_to have_major_deprecation
     end
 
-    xit "should print a Gemfile deprecation warning" do
+    it "should print a proper warning when both gems.rb and Gemfile present, and use Gemfile", :bundler => "< 2" do
       create_file "gems.rb"
       install_gemfile! <<-G
         source "file://#{gem_repo1}"
         gem "rack"
       G
+
+      expect(warnings).to include(
+        "Multiple gemfiles (gems.rb and Gemfile) detected. The gems.rb and gems.rb.locked files are currently ignored, but they will get used as soon as you delete your Gemfile and Gemfile.lock files."
+      )
+
       expect(the_bundle).to include_gem "rack 1.0"
+    end
+
+    it "should print a proper warning when both gems.rb and Gemfile present, and use gems.rb", :bundler => "2" do
+      create_file "gems.rb"
+      install_gemfile! <<-G
+        source "file://#{gem_repo1}"
+        gem "rack"
+      G
 
-      expect(warnings).to have_major_deprecation a_string_including("gems.rb and gems.locked will be preferred to Gemfile and Gemfile.lock.")
+      expect(warnings).to include(
+        "Multiple gemfiles (gems.rb and Gemfile) detected. Make sure you remove Gemfile and Gemfile.lock since bundler is ignoring them in favor of gems.rb and gems.rb.locked."
+      )
+
+      expect(the_bundle).not_to include_gem "rack 1.0"
     end
 
     context "with flags" do
@@ -108,7 +125,7 @@
   end
 
   context "when Bundler.setup is run in a ruby script" do
-    it "should print a single deprecation warning" do
+    before do
       create_file "gems.rb"
       install_gemfile! <<-G
         source "file://#{gem_repo1}"
@@ -124,8 +141,18 @@
         Bundler.setup
         Bundler.setup
       RUBY
+    end
+
+    it "should print a single deprecation warning", :bundler => "< 2" do
+      expect(warnings).to include(
+        "Multiple gemfiles (gems.rb and Gemfile) detected. The gems.rb and gems.rb.locked files are currently ignored, but they will get used as soon as you delete your Gemfile and Gemfile.lock files."
+      )
+    end
 
-      expect(warnings).to have_major_deprecation("gems.rb and gems.locked will be preferred to Gemfile and Gemfile.lock.")
+    it "should print a single deprecation warning", :bundler => "2" do
+      expect(warnings).to include(
+        "Multiple gemfiles (gems.rb and Gemfile) detected. Make sure you remove Gemfile and Gemfile.lock since bundler is ignoring them in favor of gems.rb and gems.rb.locked."
+      )
     end
   end