Comment 0 for bug 1320080

Charm configuration in config.yaml allows integer, boolean and string datatypes. Some charms require more complex data structures for their configuration, for example a list of (database_name, user_name, access_type) tuples or charm-helper's install_sources and install_keys lists.

One current work around, used by charm-helpers, is to use the 'string' type and allow the user to embed a fragment of yaml. This works, but requires the yaml fragment to be quoted as a string and does not have basic validation.

Other more common work arounds are comma separated lists, space separated lists, base64 and other arbitrary, inconsistent and ad-hoc methods.

It would be lovely if 'yaml' could be specified as a config item datatype, allowing an arbitrary yaml data structure to be embedded as configuration. This would bring consistency, and reduce bugs in charms custom serialization routines.