utils/gems: extract from utils.

Also, don’t use any non-standard Ruby functionality to avoid needing any `requires.

Library/Homebrew/utils.rb

@@ -3,6 +3,7 @@ require "utils/analytics"
 require "utils/curl"
 require "utils/fork"
 require "utils/formatter"
+require "utils/gems"
 require "utils/git"
 require "utils/github"
 require "utils/inreplace"
@@ -201,68 +202,6 @@ module Homebrew
     _system(cmd, *args, **options)
   end
 
-  def setup_gem_environment!
-    # Match where our bundler gems are.
-    ENV["GEM_HOME"] = "#{ENV["HOMEBREW_LIBRARY"]}/Homebrew/vendor/bundle/ruby/#{RbConfig::CONFIG["ruby_version"]}"
-    ENV["GEM_PATH"] = ENV["GEM_HOME"]
-
-    # 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
-  end
-
-  # TODO: version can be removed when compat/download_strategy is deleted in 2.0
-  def install_gem!(name, version = nil)
-    setup_gem_environment!
-
-    return unless Gem::Specification.find_all_by_name(name, version).empty?
-
-    ohai "Installing or updating '#{name}' gem"
-    install_args = %W[--no-document #{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
-
-  def install_gem_setup_path!(name, executable: name)
-    install_gem!(name)
-
-    return if which(executable)
-
-    odie <<~EOS
-      The '#{name}' gem is installed but couldn't find '#{executable}' in the PATH:
-      #{ENV["PATH"]}
-    EOS
-  end
-
-  def install_bundler!
-    install_gem_setup_path! "bundler", executable: "bundle"
-  end
-
-  def install_bundler_gems!
-    install_bundler!
-    ENV["BUNDLE_GEMFILE"] = "#{HOMEBREW_LIBRARY_PATH}/test/Gemfile"
-    system "bundle", "install" unless quiet_system("bundle", "check")
-    setup_gem_environment!
-  end
-
   # rubocop:disable Style/GlobalVars
   def inject_dump_stats!(the_module, pattern)
     @injected_dump_stat_modules ||= {}

Library/Homebrew/utils/gems.rb

@@ -0,0 +1,79 @@
+# Never `require` anything in this file (except English). It needs to be able to
+# work as the first item in `brew.rb` so we can load gems with Bundler when
+# needed before anything else is loaded (e.g. `json`).
+
+require "English"
+
+module Homebrew
+  module_function
+
+  def ruby_bindir
+    "#{RbConfig::CONFIG["prefix"]}/bin"
+  end
+
+  def setup_gem_environment!
+    # Match where our bundler gems are.
+    ENV["GEM_HOME"] = "#{ENV["HOMEBREW_LIBRARY"]}/Homebrew/vendor/bundle/ruby/#{RbConfig::CONFIG["ruby_version"]}"
+    ENV["GEM_PATH"] = ENV["GEM_HOME"]
+
+    # Make RubyGems notice environment changes.
+    Gem.clear_paths
+    Gem::Specification.reset
+
+    # Add necessary Ruby and Gem binary directories to PATH.
+    paths = ENV["PATH"].split(":")
+    paths.unshift(ruby_bindir) unless paths.include?(ruby_bindir)
+    paths.unshift(Gem.bindir) unless paths.include?(Gem.bindir)
+    ENV["PATH"] = paths.compact.join(":")
+  end
+
+  def install_gem!(name, version = nil)
+    setup_gem_environment!
+    return unless Gem::Specification.find_all_by_name(name, version).empty?
+
+    # Shell out to `gem` to avoid RubyGems requires e.g. loading JSON.
+    puts "==> Installing '#{name}' gem"
+    install_args = %W[--no-document #{name}]
+    install_args << "--version" << version if version
+    return if system "#{ruby_bindir}/gem", "install", *install_args
+
+    $stderr.puts "Error: failed to install the '#{name}' gem."
+    exit 1
+  end
+
+  def install_gem_setup_path!(name, executable: name)
+    install_gem!(name)
+    return if ENV["PATH"].split(":").any? do |path|
+      File.executable?("#{path}/#{executable}")
+    end
+
+    $stderr.puts <<~EOS
+      Error: the '#{name}' gem is installed but couldn't find '#{executable}' in the PATH:
+      #{ENV["PATH"]}
+    EOS
+    exit 1
+  end
+
+  def install_bundler!
+    install_gem_setup_path! "bundler", executable: "bundle"
+  end
+
+  def install_bundler_gems!
+    install_bundler!
+
+    ENV["BUNDLE_GEMFILE"] = "#{ENV["HOMEBREW_LIBRARY"]}/Homebrew/test/Gemfile"
+    @bundle_installed ||= begin
+      bundle_check_output = `#{Gem.bindir}/bundle check`
+      bundle_check_failed = !$CHILD_STATUS.exitstatus.zero?
+
+      # for some reason sometimes the exit code lies so check the output too.
+      if bundle_check_failed || bundle_check_output.include?("Install missing gems")
+        system "#{Gem.bindir}/bundle", "install"
+      else
+        true
+      end
+    end
+
+    setup_gem_environment!
+  end
+end