6 files changed, 64 insertions, 25 deletions
diff --git a/Library/Homebrew/brew.rb b/Library/Homebrew/brew.rb
index e19819cf5..6dab50f29 100644
--- a/Library/Homebrew/brew.rb
+++ b/Library/Homebrew/brew.rb
@@ -8,13 +8,13 @@ std_trap = trap("INT") { exit! 130 } # no backtrace thanks
 RUBY_TWO = RUBY_VERSION.split(".").first.to_i >= 2
 raise "Homebrew must be run under Ruby 2!" unless RUBY_TWO
 
-require "pathname"
-HOMEBREW_LIBRARY_PATH = Pathname.new(__FILE__).realpath.parent
-$:.unshift(HOMEBREW_LIBRARY_PATH)
+homebrew_library_path = File.dirname(File.realpath(__FILE__))
+$:.unshift(homebrew_library_path)
+
+require_relative "#{homebrew_library_path}/vendor/bundler/setup"
 
-load_path_before_bundler = $:.dup
-require_relative "#{HOMEBREW_LIBRARY_PATH}/vendor/bundler/setup"
-ENV["HOMEBREW_GEMS_LOAD_PATH"] = ($: - load_path_before_bundler).join(":")
+require "pathname"
+HOMEBREW_LIBRARY_PATH = Pathname.new(homebrew_library_path)
 
 require "global"
 require "tap"
@@ -25,6 +25,8 @@ if ARGV == %w[--version] || ARGV == %w[-v]
   exit 0
 end
 
+HOMEBREW_GEM_HOME = HOMEBREW_LIBRARY_PATH/"vendor/#{RUBY_ENGINE}/#{RUBY_VERSION}"
+
 def require?(path)
   require path
 rescue LoadError => e
@@ -58,21 +60,18 @@ begin
   path.append(Pathname.glob(Tap::TAP_DIRECTORY/"*/*/cmd"))
 
   # Add RubyGems.
-  HOMEBREW_GEM_HOME = HOMEBREW_LIBRARY_PATH/"vendor/#{RUBY_ENGINE}/#{RUBY_VERSION}"
+  ENV["GEM_HOME"] = ENV["GEM_PATH"] = HOMEBREW_GEM_HOME
   path.append(HOMEBREW_GEM_HOME/"bin")
 
+  # Make RubyGems notice environment changes.
+  Gem.clear_paths
+  Gem::Specification.reset
+
   # Add SCM wrappers.
   path.append(HOMEBREW_SHIMS_PATH/"scm")
 
   ENV["PATH"] = path
 
-  # Setup RubyGems environment.
-  ENV["GEM_HOME"] = ENV["GEM_PATH"] = HOMEBREW_GEM_HOME
-  # Make RubyGems notice environment changes.
-  Gem.clear_paths
-  Gem::Specification.reset
-  Homebrew.run_bundler_if_needed! unless HOMEBREW_GEM_HOME.exist?
-
   if cmd
     internal_cmd = require? HOMEBREW_LIBRARY_PATH.join("cmd", cmd)
 
diff --git a/Library/Homebrew/brew.sh b/Library/Homebrew/brew.sh
index 6f4453f28..02ce5e1c1 100644
--- a/Library/Homebrew/brew.sh
+++ b/Library/Homebrew/brew.sh
@@ -69,6 +69,10 @@ then
   odie "Cowardly refusing to continue at this prefix: $HOMEBREW_PREFIX"
 fi
 
+# Save value to use for installing gems
+export GEM_OLD_HOME="$GEM_HOME"
+export GEM_OLD_PATH="$GEM_PATH"
+
 # Users may have these set, pointing the system Ruby
 # at non-system gem paths
 unset GEM_HOME
diff --git a/Library/Homebrew/config.rb b/Library/Homebrew/config.rb
index ef07434de..38d7c8043 100644
--- a/Library/Homebrew/config.rb
+++ b/Library/Homebrew/config.rb
@@ -46,8 +46,5 @@ unless defined? HOMEBREW_LIBRARY_PATH
   HOMEBREW_LIBRARY_PATH = Pathname.new(__FILE__).realpath.parent
 end
 
-# Load path to vendored gems used by Homebrew
-HOMEBREW_GEMS_LOAD_PATH = ENV["HOMEBREW_GEMS_LOAD_PATH"]
-
 # Load path used by standalone scripts to access the Homebrew code base
-HOMEBREW_LOAD_PATH = [HOMEBREW_LIBRARY_PATH, *HOMEBREW_GEMS_LOAD_PATH].join(":")
+HOMEBREW_LOAD_PATH = HOMEBREW_LIBRARY_PATH
diff --git a/Library/Homebrew/os/mac/mach.rb b/Library/Homebrew/os/mac/mach.rb
index 416183f68..71f501fe9 100644
--- a/Library/Homebrew/os/mac/mach.rb
+++ b/Library/Homebrew/os/mac/mach.rb
@@ -1,11 +1,10 @@
+require "macho"
 require "os/mac/architecture_list"
 
 module MachOShim
   # @private
   def macho
     @macho ||= begin
-      require "macho"
-
       MachO.open(to_s)
     end
   end
@@ -13,8 +12,6 @@ module MachOShim
   # @private
   def mach_data
     @mach_data ||= begin
-      require "macho"
-
       machos = []
       mach_data = []
 
diff --git a/Library/Homebrew/test/support/lib/config.rb b/Library/Homebrew/test/support/lib/config.rb
index 41f4cbe33..fb5c210fe 100644
--- a/Library/Homebrew/test/support/lib/config.rb
+++ b/Library/Homebrew/test/support/lib/config.rb
@@ -14,9 +14,9 @@ TEST_TMPDIR = ENV.fetch("HOMEBREW_TEST_TMPDIR") do |k|
 end
 
 # Paths pointing into the Homebrew code base that persist across test runs
-HOMEBREW_LIBRARY_PATH   = Pathname.new(File.expand_path("../../../..", __FILE__))
-HOMEBREW_SHIMS_PATH     = HOMEBREW_LIBRARY_PATH.parent+"Homebrew/shims"
-HOMEBREW_LOAD_PATH      = [File.expand_path("..", __FILE__), HOMEBREW_LIBRARY_PATH, ENV["HOMEBREW_GEMS_LOAD_PATH"]].join(":")
+HOMEBREW_LIBRARY_PATH  = Pathname.new(File.expand_path("../../../..", __FILE__))
+HOMEBREW_SHIMS_PATH    = HOMEBREW_LIBRARY_PATH.parent+"Homebrew/shims"
+HOMEBREW_LOAD_PATH     = [File.expand_path("..", __FILE__), HOMEBREW_LIBRARY_PATH].join(":")
 
 # Paths redirected to a temporary directory and wiped at the end of the test run
 HOMEBREW_PREFIX        = Pathname.new(TEST_TMPDIR).join("prefix")
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?