Rewrite constraints docs to be more helpful

juju/charm/directory.py

 import os
 import stat
 import zipfile
 import tempfile
 
-from juju.charm.base import CharmBase, get_revision, ZIP_SYMLINK_ATTR
+from juju.charm.base import CharmBase, get_revision
 from juju.charm.bundle import CharmBundle
 from juju.charm.config import ConfigOptions
 from juju.charm.errors import InvalidCharmFile
 from juju.charm.metadata import MetaData
 
 
 class CharmDirectory(CharmBase):
     """Directory that holds charm content.
 
     :param path: Path to charm directory
@@ skipping 81 matching lines @@
         link_path = os.path.join(path_dir, link_path)
         if not link_path.startswith(os.path.abspath(self.path)):
             raise InvalidCharmFile(
                 self.metadata.name, path, "Only internal symlinks are allowed")
 
     def _write_symlink(self, zf, link_target, link_path):
         """Package symlinks with appropriate zipfile metadata."""
         info = zipfile.ZipInfo()
         info.filename = link_path
         info.create_system = 3
-        info.external_attr = ZIP_SYMLINK_ATTR
+        # Preserve the pre-existing voodoo mode in a slightly clearer form.
+        info.external_attr = (stat.S_IFLNK | 0755) << 16
         zf.writestr(info, link_target)
 
     def _ignore(self, path):
         if path == "build" or path.startswith("build/"):
             return True
         if path.startswith('.'):
             return True
 
     def as_bundle(self):
         if self._temp_bundle is None:
             prefix = "%s-%d.charm." % (self.metadata.name, self.get_revision())
             temp_file = tempfile.NamedTemporaryFile(prefix=prefix)
             self.make_archive(temp_file.name)
             self._temp_bundle = CharmBundle(temp_file.name)
             # Attach the life time of temp_file to self:
             self._temp_bundle_file = temp_file
         return self._temp_bundle
 
     def as_directory(self):
         return self
 
     def compute_sha256(self):
         """
         Compute sha256, based on the bundle.
         """
         return self.as_bundle().compute_sha256()