Introduce Gitlab.next_rails? for dual-booting

Gemfile

 # frozen_string_literal: true
 
+def next?
+  File.basename(__FILE__) == "Gemfile.next"
+end
+
 source 'https://rubygems.org'
 
 if ENV.fetch('BUNDLER_CHECKSUM_VERIFICATION_OPT_IN', 'false') != 'false' # this verification is still experimental
@@ -24,7 +28,12 @@ gem 'bundler-checksum', '~> 0.1.0', path: 'vendor/gems/bundler-checksum', requir
 # https://gitlab.com/gitlab-org/gitlab/-/issues/375713
 #
 # See https://docs.gitlab.com/ee/development/gemfile.html#upgrade-rails for guidelines when upgrading Rails
-gem 'rails', '~> 7.0.8.4' # rubocop:todo Gemfile/MissingFeatureCategory
+
+if next?
+  gem 'rails', '~> 7.1.3.4', feature_category: :shared
+else
+  gem 'rails', '~> 7.0.8.4', feature_category: :shared
+end
 
 gem 'activerecord-gitlab', path: 'gems/activerecord-gitlab' # rubocop:todo Gemfile/MissingFeatureCategory
 

Gemfile.next

+Gemfile
\ No newline at end of file

lib/gitlab.rb

@@ -132,4 +132,16 @@ def self.maintenance_mode?
 
     ::Gitlab::CurrentSettings.maintenance_mode
   end
+
+  # This method will check your environment
+  # (e.g. `ENV['BUNDLE_GEMFILE]`) to determine whether your application is
+  # running with the next set of dependencies or the current set of dependencies.
+  #
+  # @return [Boolean]
+  def self.next_rails?
+    return @next_bundle_gemfile unless @next_bundle_gemfile.nil?
+    return false unless ENV["BUNDLE_GEMFILE"]
+
+    @next_bundle_gemfile = File.exist?(ENV["BUNDLE_GEMFILE"]) && File.basename(ENV["BUNDLE_GEMFILE"]) == "Gemfile.next"
+  end
 end

spec/lib/gitlab_spec.rb

@@ -2,7 +2,7 @@
 
 require 'spec_helper'
 
-RSpec.describe Gitlab do
+RSpec.describe Gitlab, feature_category: :shared do
   %w[root extensions ee? jh?].each do |method_name|
     it "delegates #{method_name} to GitlabEdition" do
       expect(GitlabEdition).to receive(method_name)
@@ -380,4 +380,28 @@
       expect(described_class.maintenance_mode?).to eq(false)
     end
   end
+
+  describe '.next_rails?' do
+    around do |example|
+      example.run
+    ensure
+      described_class.instance_variable_set(:@next_bundle_gemfile, nil)
+    end
+
+    where(:bundle_gemfile, :expected_result) do
+      [
+        [nil, false],
+        ['Gemfile.another', false],
+        ['Gemfile.next', true]
+      ]
+    end
+
+    with_them do
+      it 'returns whether BUNDLE_GEMFILE points to Gemfile.next' do
+        stub_env('BUNDLE_GEMFILE', bundle_gemfile)
+
+        expect(described_class.next_rails?).to eq(expected_result)
+      end
+    end
+  end
 end

vendor/gems/bundler-checksum/lib/bundler_checksum.rb

@@ -83,7 +83,7 @@ def validate_file_checksum(checksum)
 module BundlerChecksum
   class << self
     def checksum_file
-      @checksum_file ||= File.join(File.dirname(Bundler.default_gemfile), 'Gemfile.checksum')
+      @checksum_file ||= "#{Bundler.default_gemfile}.checksum"
     end
 
     def checksums_from_file