Autogenerated install hooks fails to import basic layer

[jacekn]

I have a charm that stopped working on trusty. I'm not sure when it last worked because most of my deployments are on xenial and xenial still works just fine.

Here is the hook error:

./hooks/install 
Traceback (most recent call last):
  File "./hooks/install", line 7, in <module>
    from charms.layer import basic
  File "lib/charms/layer/__init__.py", line 46, in <module>
    patch_options_interface()
  File "lib/charms/layer/__init__.py", line 42, in patch_options_interface
    options.__class__ = OptionsBackwardsCompatibilityHack
TypeError: __class__ assignment: only for heap types

Autogenerated install file looks like this:

#!/usr/bin/env python3

# Load modules from $JUJU_CHARM_DIR/lib
import sys
sys.path.append('lib')

from charms.layer import basic
basic.bootstrap_charm_deps()
basic.init_config_states()


# This will load and run the appropriate @hook and other decorated
# handlers from $JUJU_CHARM_DIR/reactive, $JUJU_CHARM_DIR/hooks/reactive,
# and $JUJU_CHARM_DIR/hooks/relations.
#
# See https://jujucharms.com/docs/stable/authors-charm-building
# for more information on this pattern.
from charms.reactive import main
main()

I'm on juju 2.3.8 if that's important.