brew/Library/Homebrew/development_tools.rb

# @private
class DevelopmentTools
  class << self
    def locate(tool)
      # Don't call tools (cc, make, strip, etc.) directly!
      # Give the name of the binary you look for as a string to this method
      # in order to get the full path back as a Pathname.
      (@locate ||= {}).fetch(tool) do |key|
        @locate[key] = if File.executable?(path = "/usr/bin/#{tool}")
          Pathname.new path
        # Homebrew GCCs most frequently; much faster to check this before xcrun
        elsif (path = HOMEBREW_PREFIX/"bin/#{tool}").executable?
          path
        end
      end
    end

    def installed?
      which("clang") || which("gcc")
    end

    def default_cc
      cc = DevelopmentTools.locate "cc"
      cc.realpath.basename.to_s rescue nil
    end

    def default_compiler
      case default_cc
      # if GCC 4.2 is installed, e.g. via Tigerbrew, prefer it
      # over the system's GCC 4.0
      when /^gcc-4.0/ then gcc_42_build_version ? :gcc : :gcc_4_0
      when /^gcc/ then :gcc
      when /^llvm/ then :llvm
      else :clang
      end
    end

    def gcc_40_build_version
      @gcc_40_build_version ||=
        if (path = locate("gcc-4.0"))
          `#{path} --version 2>/dev/null`[/build (\d{4,})/, 1].to_i
        end
    end
    alias_method :gcc_4_0_build_version, :gcc_40_build_version

    def gcc_42_build_version
      @gcc_42_build_version ||=
        begin
          gcc = locate("gcc-4.2") || HOMEBREW_PREFIX.join("opt/apple-gcc42/bin/gcc-4.2")
          if gcc.exist? && !gcc.realpath.basename.to_s.start_with?("llvm")
            `#{gcc} --version 2>/dev/null`[/build (\d{4,})/, 1].to_i
          end
        end
    end
    alias_method :gcc_build_version, :gcc_42_build_version

    def llvm_build_version
      @llvm_build_version ||=
        if (path = locate("llvm-gcc")) && !path.realpath.basename.to_s.start_with?("clang")
          `#{path} --version`[/LLVM build (\d{4,})/, 1].to_i
        end
    end

    def clang_version
      @clang_version ||=
        if (path = locate("clang"))
          `#{path} --version`[/(?:clang|LLVM) version (\d\.\d)/, 1]
        end
    end

    def clang_build_version
      @clang_build_version ||=
        if (path = locate("clang"))
          `#{path} --version`[/clang-(\d{2,})/, 1].to_i
        end
    end
  end
end

require "extend/os/development_tools"