1 files changed, 42 insertions, 0 deletions
diff --git a/Library/Homebrew/utils.rb b/Library/Homebrew/utils.rb
index 6ae75a4fb..60af39d93 100644
--- a/Library/Homebrew/utils.rb
+++ b/Library/Homebrew/utils.rb
@@ -179,6 +179,48 @@ module Homebrew
     _system(cmd, *args)
   end
 
+  def install_gem_setup_path!(name, version = nil, executable = name)
+    # Respect user's preferences for where gems should be installed.
+    ENV["GEM_HOME"] = ENV["GEM_OLD_HOME"].to_s
+    ENV["GEM_HOME"] = Gem.user_dir if ENV["GEM_HOME"].empty?
+    ENV["GEM_PATH"] = ENV["GEM_OLD_PATH"] unless ENV["GEM_OLD_PATH"].to_s.empty?
+
+    # Make rubygems notice env changes.
+    Gem.clear_paths
+    Gem::Specification.reset
+
+    # Add Gem binary directory and (if missing) Ruby binary directory to PATH.
+    path = PATH.new(ENV["PATH"])
+    path.prepend(RUBY_BIN) if which("ruby") != RUBY_PATH
+    path.prepend(Gem.bindir)
+    ENV["PATH"] = path
+
+    if Gem::Specification.find_all_by_name(name, version).empty?
+      ohai "Installing or updating '#{name}' gem"
+      install_args = %W[--no-ri --no-rdoc #{name}]
+      install_args << "--version" << version if version
+
+      # Do `gem install [...]` without having to spawn a separate process or
+      # having to find the right `gem` binary for the running Ruby interpreter.
+      require "rubygems/commands/install_command"
+      install_cmd = Gem::Commands::InstallCommand.new
+      install_cmd.handle_options(install_args)
+      exit_code = 1 # Should not matter as `install_cmd.execute` always throws.
+      begin
+        install_cmd.execute
+      rescue Gem::SystemExitException => e
+        exit_code = e.exit_code
+      end
+      odie "Failed to install/update the '#{name}' gem." if exit_code.nonzero?
+    end
+
+    return if which(executable)
+    odie <<-EOS.undent
+      The '#{name}' gem is installed but couldn't find '#{executable}' in the PATH:
+      #{ENV["PATH"]}
+    EOS
+  end
+
   def run_bundler_if_needed!
     return unless Pathname.glob("#{HOMEBREW_GEM_HOME}/bin/*").empty?