RFE: [tmt lint] add a warning class to handle "warn: Empty environment file"

[bgoncalv]

In our repo we have a lot of tests that when running tmt lint shows warn: Empty environment file

It would be nice if we could force tmt lint to report failure in this cases, afaik it is not handled as a warning class.

My suggestion would be running a command like below would force the lint to report failure.

tmt lint --outcome-only fail --enforce-check Cxxx .

[psss]

For this specific case, when environment-file is pointing to an empty file, I would say we should even give a failure by default. Could be a good first issue, here's an example plan check:

tmt/tmt/base.py

Lines 2027 to 2039 in 22731b9

	def lint_unknown_keys(self) -> LinterReturn:
	""" P001: all keys are known """
	invalid_keys = self._lint_keys(
	list(self.step_names(enabled_only=False)) + self._extra_l2_keys)
	if invalid_keys:
	for key in invalid_keys:
	yield LinterOutcome.FAIL, f'unknown key "{key}" is used'
	return
	yield LinterOutcome.PASS, 'correct keys are used'

[happz]

FTR, can be done for environment-file keys in a plan only, it wouldn't catch the runtime (run --environment @empty.yaml). But should be a nice and easy check.