1 files changed, 127 insertions, 0 deletions
diff --git a/spec/bundler/support/rubygems_version_manager.rb b/spec/bundler/support/rubygems_version_manager.rb
new file mode 100644
index 0000000000..31f7cc4b08
--- /dev/null
+++ b/spec/bundler/support/rubygems_version_manager.rb
@@ -0,0 +1,127 @@
+# frozen_string_literal: true
+
+require "pathname"
+require_relative "helpers"
+require_relative "path"
+
+class RubygemsVersionManager
+  include Spec::Helpers
+  include Spec::Path
+
+  def initialize(env_version)
+    @env_version = env_version
+  end
+
+  def switch
+    return if use_system?
+
+    unrequire_rubygems_if_needed
+
+    switch_local_copy_if_needed
+
+    prepare_environment
+  end
+
+private
+
+  def use_system?
+    @env_version.nil?
+  end
+
+  def unrequire_rubygems_if_needed
+    return unless rubygems_unrequire_needed?
+
+    require "rbconfig"
+
+    ruby = File.join(RbConfig::CONFIG["bindir"], RbConfig::CONFIG["ruby_install_name"])
+    ruby << RbConfig::CONFIG["EXEEXT"]
+
+    cmd = [ruby, $0, *ARGV].compact
+    cmd[1, 0] = "--disable-gems"
+
+    exec(ENV, *cmd)
+  end
+
+  def switch_local_copy_if_needed
+    return unless local_copy_switch_needed?
+
+    Dir.chdir(local_copy_path) do
+      sys_exec!("git remote update")
+      sys_exec!("git checkout #{target_tag_version} --quiet")
+    end
+  end
+
+  def prepare_environment
+    $:.unshift File.expand_path("lib", local_copy_path)
+  end
+
+  def rubygems_unrequire_needed?
+    defined?(Gem) && Gem::VERSION != target_gem_version
+  end
+
+  def local_copy_switch_needed?
+    !env_version_is_path? && target_gem_version != local_copy_version
+  end
+
+  def target_gem_version
+    @target_gem_version ||= resolve_target_gem_version
+  end
+
+  def target_tag_version
+    @target_tag_version ||= resolve_target_tag_version
+  end
+
+  def local_copy_version
+    gemspec_contents = File.read(local_copy_path.join("lib/rubygems.rb"))
+    version_regexp = /VERSION = ["'](.*)["']/
+
+    version_regexp.match(gemspec_contents)[1]
+  end
+
+  def local_copy_path
+    @local_copy_path ||= resolve_local_copy_path
+  end
+
+  def resolve_local_copy_path
+    return expanded_env_version if env_version_is_path?
+
+    rubygems_path = root.join("tmp/rubygems")
+
+    unless rubygems_path.directory?
+      rubygems_path.parent.mkpath
+      sys_exec!("git clone https://github.com/rubygems/rubygems.git #{rubygems_path}")
+    end
+
+    rubygems_path
+  end
+
+  def env_version_is_path?
+    expanded_env_version.directory?
+  end
+
+  def expanded_env_version
+    @expanded_env_version ||= Pathname.new(@env_version).expand_path(root)
+  end
+
+  def resolve_target_tag_version
+    return "v#{@env_version}" if @env_version.match(/^\d/)
+
+    return "master" if @env_version == master_gem_version
+
+    @env_version
+  end
+
+  def resolve_target_gem_version
+    return local_copy_version if env_version_is_path?
+
+    return @env_version[1..-1] if @env_version.match(/^v/)
+
+    return master_gem_version if @env_version == "master"
+
+    @env_version
+  end
+
+  def master_gem_version
+    "3.1.0.pre1"
+  end
+end