Merge #7296

7296: Improve exec'ing to the proper rubygems version r=deivid-rodriguez a=deivid-rodriguez

### What was the end-user problem that led to this PR?

The problem was that the `with_rubygems` script is hard to work with, because it does complicated ARGV manipulation before exec'ing.

### What was your diagnosis of the problem?

My diagnosis was that we don't need it.

### What is your fix for the problem, implemented in this PR?

My fix is to implement the same thing in a simpler way.

### Why did you choose this fix out of the possible options?

I chose this fix because it simplifies things.

Co-authored-by: David Rodríguez <deivid.rodriguez@riseup.net>
(cherry picked from commit 3260d5994ec33bfaf81162c61d0d20bfff023375)

5 files changed, 137 insertions, 2 deletions

diff --git a/spec/support/helpers.rb b/spec/support/helpers.rb
index b5617d399f..ffcde39df7 100644
--- a/spec/support/helpers.rb
+++ b/spec/support/helpers.rb
@@ -2,6 +2,9 @@
 
 require "open3"
 
+require_relative "command_execution"
+require_relative "the_bundle"
+
 module Spec
   module Helpers
     def reset!
@@ -113,6 +116,7 @@ module Spec
       env["PATH"].gsub!("#{Path.root}/exe", "") if env["PATH"] && system_bundler
 
       requires = options.delete(:requires) || []
+      requires << "support/rubygems"
       requires << "support/hax"
 
       artifice = options.delete(:artifice) do
@@ -146,7 +150,7 @@ module Spec
         end
       end.join
 
-      cmd = "#{sudo} #{Gem.ruby} #{load_path_str} #{requires_str} #{bundle_bin} #{cmd}#{args}"
+      cmd = "#{sudo} #{Gem.ruby} --disable-gems #{load_path_str} #{requires_str} #{bundle_bin} #{cmd}#{args}"
       sys_exec(cmd, env) {|i, o, thr| yield i, o, thr if block_given? }
     end
     bang :bundle
diff --git a/spec/support/path.rb b/spec/support/path.rb
index db28454792..79b55dd42a 100644
--- a/spec/support/path.rb
+++ b/spec/support/path.rb
@@ -22,7 +22,7 @@ module Spec
     end
 
     def gem_bin
-      @gem_bin ||= ruby_core? ? ENV["GEM_COMMAND"] : "#{Gem.ruby} -S gem --backtrace"
+      @gem_bin ||= ruby_core? ? ENV["GEM_COMMAND"] : "#{Gem.ruby} --disable-gems -r#{spec_dir}/support/rubygems -S gem --backtrace"
     end
 
     def spec_dir
diff --git a/spec/support/rubygems.rb b/spec/support/rubygems.rb
new file mode 100644
index 0000000000..e60f9a928e
--- /dev/null
+++ b/spec/support/rubygems.rb
@@ -0,0 +1,7 @@
+# frozen_string_literal: true
+
+require_relative "rubygems_version_manager"
+
+RubygemsVersionManager.new(ENV["RGV"]).switch
+
+require "rubygems"
diff --git a/spec/support/rubygems_ext.rb b/spec/support/rubygems_ext.rb
index 1a9549d2b5..da95837b1b 100644
--- a/spec/support/rubygems_ext.rb
+++ b/spec/support/rubygems_ext.rb
@@ -40,6 +40,7 @@ module Spec
     end
 
     def gem_load(gem_name, bin_container)
+      require_relative "rubygems"
       gem_load_and_activate(gem_name, bin_container)
     end
 
diff --git a/spec/support/rubygems_version_manager.rb b/spec/support/rubygems_version_manager.rb
new file mode 100644
index 0000000000..4be90f7679
--- /dev/null
+++ b/spec/support/rubygems_version_manager.rb
@@ -0,0 +1,123 @@
+# frozen_string_literal: true
+
+require "pathname"
+require_relative "helpers"
+
+class RubygemsVersionManager
+  include Spec::Helpers
+
+  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 = Pathname.new("../../tmp/rubygems").expand_path(__dir__)
+
+    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
+  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 @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