Allow plugins to cause a "command line usage error"

What's the problem this feature will solve?

I am trying to write a pytest plugin that has several command line flags. Some combinations of these flags are "illegal", for example in the sense that they contradict each other. However, I noticed that there seems to be no way to terminate the program with the standard "usage error" output as for example seen from argparse.

Describe the solution you'd like

There should be a method, for example named cmdline_error, for example at the Config class, that causes the usage error message "ERROR: usage: pytest [options] ..." to appear, followed by the termination of the program with the appropriate exit code.

Alternative Solutions

Currently, the way I achieve this is by accessing the error function of the underlying argparse parser via config._parser._getparser().error in the pytest_configure hook. But of course, accessing names starting with underscores is not generally a good idea.

Start by reading the Config class and the pytest_configure hook, then trace how config._parser._getparser().error currently produces argparse-style usage errors. Compare that path with pytest's plugin-facing APIs and define the public behavior requested: standard usage output followed by the appropriate exit code when a plugin reports an invalid flag combination.