Config check subcommand

[nielsdrost]

While doing the tutorial, one error encountered was an invalid config file. This leads to all sorts of parser and "data not found" errors. Perhaps we could add a sub command specifically to check the configuration for validity (#125), and perhaps check if all the paths exist.

Once we have an importable config object (#785) this should not be hard to implement.

[valeriupredoi]

good idea @nielsdrost 🍺

[schlunma]

We now have a working configuration validator (see this comment). However, this only checks the validity of the options, not the values (i.e., no paths are checked).

I propose we close this, feel free to re-open if necessary 👍

[zklaus]

I think this is still a bit open. @schlunma, do you know the PR in which this was added? In any case, I think adding the checking of paths as suggested by @nielsdrost would be very nice and useful.

[schlunma]

I think in #1300, the validation happens here:

ESMValCore/esmvalcore/_config/_config.py

Lines 179 to 183 in e9daad3

	with warnings.catch_warnings():
	# ignore experimental API warning
	warnings.simplefilter("ignore")
	from esmvalcore.experimental.config._config_object import Session
	Session.from_config_user(cfg)

I'm not 100% convinced of this check for existence. Maybe a warning is okay, but definitely not an error. If I'm using a configuration file written by someone else and they remove the path to CORDEX, I don't want my recipe to fail even though I'm not using any CORDEX data.

[schlunma]

I guess this can easily be added here:

ESMValCore/esmvalcore/experimental/config/_config_validators.py

Lines 121 to 130 in e9daad3

	def validate_path(value, allow_none=False):
	"""Return a `Path` object."""
	if (value is None) and allow_none:
	return value
	try:
	path = Path(value).expanduser().absolute()
	except TypeError as err:
	raise ValidationError(f"Expected a path, but got {value}") from err
	else:
	return path

[schlunma]

I just realized that we have a already show a warning if a root path does not exist:

ESMValCore/esmvalcore/_data_finder.py

Lines 394 to 396 in 2d3df9d

	logger.warning(
	"'%s' rootpaths '%s' set in config-user.yml do not exist",
	key, ', '.join(nonexistent))