There are two situations where these dependencies need to be used: - in the Builder when it decides if the `venv` directory needs to be primed - in charm_builder when dependencies are actually handled (hashed, installed, etc.) I created a helper to collect all the dependencies, used from those two places. Located it in the charmlibs module for convenience (initially I thought putting it in `charmcraft/utils` but hit a circular import). Alternatively, these dependencies could have been collected where other dependencies are defined or dynamically included: in the CharmPluginProperties class. This will make "pydeps" management much more similar to standard python packages or requirements files, but there are several drawbacks of this path: - a new `charm_libs_deps` or similar key would have need to be included, even if that key should not be exposed to the user as a real config key - an extra validator would need to be added to collect all PYDEPS values, which would be called *twice* (when config is validated, and when the plugin is actually run), so there is no drawback in calling the collection twice in the current model - furthermore, that validator would have been executed (and all PYDEPS collected) when the config is validated *for any command* (e.g. `charmcraft names`) Also, I include here these needed changes in the charm libraries: - included PYDEPS in the parsing of a library internals - added a `root` parameter to the `get_libs_from_tree` function; notably, this function relied on being on the project's root directory, which is suspicious, so I opened #1002 to ensure everything is fine (or fix it) - moved the `emit` usage out of `get_libs_from_tree` as it is now used also from the charm_builder.py, called from the plugin, as a standard subprocess that does not use the Craft CLI infrastructure.