The tracking issue for this feature is: #125704.

This option of the --print flag print the list of expected cfgs.

This is related to the --check-cfg flag which allows specifying arbitrary expected names and values.

This print option works similarly to --print=cfg (modulo check-cfg specifics):

  • check_cfg syntax: output of --print=check-cfg
  • cfg(windows): windows
  • cfg(feature, values("foo", "bar")): feature="foo" and feature="bar"
  • cfg(feature, values(none(), "")): feature and feature=""
  • cfg(feature, values(any())): feature=any()
  • cfg(feature, values()): feature=
  • cfg(any()): any()
  • nothing: any()=any()

To be used like this:

rustc --print=check-cfg -Zunstable-options