docs: def download_all_dependencies(self, requirements_filename, directory):
          # type: (str, str) -> None
          """Download all dependencies as sdist or wheel."""
          arguments = ['-r', requirements_filename, '--dest', directory]
          rc, out, err = self._execute('download', arguments)
          # When downloading all dependencies we expect to get an rc of 0 back
          # since we are casting a wide net here letting pip have options about
          # what to download. If a package is not found it is likely because it
          # does not exist and was mispelled. In this case we raise an error with
          # the package name. Otherwise a nonzero rc results in a generic
          # download error where we pass along the stderr.
          if rc != 0:
              if err is None:
                  err = b'Unknown error'
              error = err.decode()
              match = re.search(("Could not find a version that satisfies the "
                                 "requirement (.+?) "), error)
              if match:
                  package_name = match.group(1)
                  raise NoSuchPackageError(str(package_name))
              raise PackageDownloadError(error)
          stdout = out.decode()
          matches = re.finditer(self._LINK_IS_DIR_PATTERN, stdout)
          for match in matches:
              wheel_package_path = str(match.group(1))
              # Looks odd we do not check on the error status of building the
              # wheel here. We can assume this is a valid package path since
              # we already passed the pip download stage. This stage would have
              # thrown a PackageDownloadError if any of the listed packages were
              # not valid.
              # If it fails the actual build step, it will have the same behavior
              # as any other package we fail to build a valid wheel for, and
              # complain at deployment time.
              self.build_wheel(wheel_package_path, directory)