Disable RubyGems by default.

This speeds up all Ruby invocations where we don't need RubyGems by
around 10%. Where we do need RubyGems: include it manually.

Library/Homebrew/brew.sh

@@ -327,6 +327,12 @@ then
 
   # Don't allow non-developers to customise Ruby warnings.
   unset HOMEBREW_RUBY_WARNINGS
+
+  # Disable Ruby options we don't need. RubyGems provides a decent speedup.
+  RUBY_DISABLE_OPTIONS="--disable=gems,did_you_mean,rubyopt"
+else
+  # Don't disable did_you_mean for developers as it's useful.
+  RUBY_DISABLE_OPTIONS="--disable=gems,rubyopt"
 fi
 
 if [[ -z "$HOMEBREW_RUBY_WARNINGS" ]]
@@ -480,5 +486,5 @@ else
 
   # Unshift command back into argument list (unless argument list was empty).
   [[ "$HOMEBREW_ARG_COUNT" -gt 0 ]] && set -- "$HOMEBREW_COMMAND" "$@"
-  { update-preinstall "$@"; exec "$HOMEBREW_RUBY_PATH" $HOMEBREW_RUBY_WARNINGS "$HOMEBREW_LIBRARY/Homebrew/brew.rb" "$@"; }
+  { update-preinstall "$@"; exec "$HOMEBREW_RUBY_PATH" $HOMEBREW_RUBY_WARNINGS "$RUBY_DISABLE_OPTIONS" "$HOMEBREW_LIBRARY/Homebrew/brew.rb" "$@"; }
 fi

Library/Homebrew/formula_assertions.rb

@@ -1,5 +1,6 @@
 module Homebrew
   module Assertions
+    require "rubygems"
     require "test/unit/assertions"
     include ::Test::Unit::Assertions
 

Library/Homebrew/shims/super/cc

@@ -1,13 +1,11 @@
 #!/bin/sh
 # Make sure this shim uses the same Ruby interpreter that is used by Homebrew.
-unset RUBYLIB
-unset RUBYOPT
 if [ -z "$HOMEBREW_RUBY_PATH" ]
 then
   echo "${0##*/}: The build tool has reset ENV; --env=std required." >&2
   exit 1
 fi
-exec "$HOMEBREW_RUBY_PATH" -x "$0" "$@"
+exec "$HOMEBREW_RUBY_PATH" --disable=gems,did_you_mean,rubyopt -x "$0" "$@"
 #!/usr/bin/env ruby -W0
 
 require "pathname"

Library/Homebrew/test/support/helper/spec/shared_context/integration_test.rb

@@ -89,6 +89,7 @@ RSpec.shared_context "integration test" do
         "-I", $LOAD_PATH.join(File::PATH_SEPARATOR)
       ]
       if ENV["HOMEBREW_TESTS_COVERAGE"]
+        require "rubygems"
         simplecov_spec = Gem.loaded_specs["simplecov"]
         specs = [simplecov_spec]
         simplecov_spec.runtime_dependencies.each do |dep|

Library/Homebrew/utils/gems.rb

@@ -12,6 +12,7 @@ module Homebrew
   end
 
   def gem_user_bindir
+    require "rubygems"
     "#{Gem.user_dir}/bin".freeze
   end
 
@@ -39,6 +40,7 @@ module Homebrew
     ENV["GEM_PATH"] = ENV["GEM_HOME"]
 
     # Make RubyGems notice environment changes.
+    require "rubygems"
     Gem.clear_paths
     Gem::Specification.reset
 
@@ -76,6 +78,7 @@ module Homebrew
   end
 
   def install_bundler!
+    require "rubygems"
     setup_gem_environment!(gem_home: Gem.user_dir, gem_bindir: gem_user_bindir)
     install_gem_setup_path!("bundler", version: ">=2", executable: "bundle", setup_gem_environment: false)
   end

Library/Homebrew/utils/ruby.sh

@@ -37,7 +37,7 @@ setup-ruby-path() {
 
       if [[ -n "$HOMEBREW_RUBY_PATH" && -z "$HOMEBREW_FORCE_VENDOR_RUBY" ]]
       then
-        ruby_version_new_enough="$("$HOMEBREW_RUBY_PATH" -rrubygems -e "puts Gem::Version.new(RUBY_VERSION.to_s.dup) >= Gem::Version.new('$minimum_ruby_version')")"
+        ruby_version_new_enough="$("$HOMEBREW_RUBY_PATH" --disable=gems -rrubygems -e "puts Gem::Version.new(RUBY_VERSION.to_s.dup) >= Gem::Version.new('$minimum_ruby_version')")"
       fi
 
       if [[ -z "$HOMEBREW_RUBY_PATH" || -n "$HOMEBREW_FORCE_VENDOR_RUBY" || "$ruby_version_new_enough" != "true" ]]