def arduino_library_src_dirs(aux_libraries)
      # Pull in all possible places that headers could live, according to the spec:
      # https://github.com/arduino/Arduino/wiki/Arduino-IDE-1.5:-Library-specification
      # TODO: be smart and implement library spec (library.properties, etc)?
      subdirs = ["", "src", "utility"]
      all_aux_include_dirs_nested = aux_libraries.map do |libdir|
        subdirs.map { |subdir| Pathname.new(@arduino_lib_dir) + libdir + subdir }
      end
      all_aux_include_dirs_nested.flatten.select(&:exist?).select(&:directory?)
    end
def arduino_library_src_dirs(aux_libraries)
      # Pull in all possible places that headers could live, according to the spec:
      # https://github.com/arduino/Arduino/wiki/Arduino-IDE-1.5:-Library-specification
      # TODO: be smart and implement library spec (library.properties, etc)?
      subdirs = ["", "src", "utility"]
      all_aux_include_dirs_nested = aux_libraries.map do |libdir|
        subdirs.map { |subdir| Pathname.new(@arduino_lib_dir) + libdir + subdir }
      end
      all_aux_include_dirs_nested.flatten.select(&:exist?).select(&:directory?)
    end
Arduino library directories containing sources
 @return [Array<Pathname>]