brew/Library/Homebrew/build_environment.rb

class BuildEnvironment
  def initialize(*settings)
    @settings = Set.new(*settings)
  end

  def merge(*args)
    @settings.merge(*args)
    self
  end

  def <<(o)
    @settings << o
    self
  end

  def std?
    @settings.include? :std
  end

  def userpaths?
    @settings.include? :userpaths
  end

  module DSL
    def env(*settings)
      @env ||= BuildEnvironment.new
      @env.merge(settings)
    end
  end
end

module Homebrew
  module_function

  def build_env_keys(env)
    %w[
      CC CXX LD OBJC OBJCXX
      HOMEBREW_CC HOMEBREW_CXX
      CFLAGS CXXFLAGS CPPFLAGS LDFLAGS SDKROOT MAKEFLAGS
      CMAKE_PREFIX_PATH CMAKE_INCLUDE_PATH CMAKE_LIBRARY_PATH CMAKE_FRAMEWORK_PATH
      MACOSX_DEPLOYMENT_TARGET PKG_CONFIG_PATH PKG_CONFIG_LIBDIR
      HOMEBREW_DEBUG HOMEBREW_MAKE_JOBS HOMEBREW_VERBOSE
      HOMEBREW_SVN HOMEBREW_GIT
      HOMEBREW_SDKROOT HOMEBREW_BUILD_FROM_SOURCE
      MAKE GIT CPP
      ACLOCAL_PATH PATH CPATH
      LD_LIBRARY_PATH LD_RUN_PATH LD_PRELOAD LIBRARY_PATH
    ].select { |key| env.key?(key) }
  end

  def dump_build_env(env, f = $stdout)
    keys = build_env_keys(env)
    keys -= %w[CC CXX OBJC OBJCXX] if env["CC"] == env["HOMEBREW_CC"]

    keys.each do |key|
      value = env[key]
      s = "#{key}: #{value}"
      case key
      when "CC", "CXX", "LD"
        s << " => #{Pathname.new(value).realpath}" if File.symlink?(value)
      end
      f.puts s
    end
  end
end