docs: def version_calc(dist, attr, value):
  	"""
  	Handler for parameter to setup(use_vcs_version=value)
  	attr should be 'use_vcs_version' (also allows use_hg_version for
  		compatibility).
  	bool(value) should be true to invoke this plugin.
  	value may optionally be a dict and supply options to the plugin.
  	"""
  	expected_attrs = 'use_hg_version', 'use_vcs_version'
  	if not value or attr not in expected_attrs:
  		return
  	options = value if isinstance(value, dict) else {}
  	dist.metadata.version = calculate_version(options)
  	patch_egg_info()