Add the new handler static method check_precondition which if False
will cause the handler to not be used even if explicitly specified. This
allows for checking for required files or other required extra things
that handlers may require.
Includes a helper decorator
@preconditions.requires_files(files) for handlers that require files to
be present in the extras dir.
More preconditions will probably come later like requiring a library or a binary in path, etc.
Add the new handler static method check_precondition which if False will cause the handler to not be used even if explicitly specified. This allows for checking for required files or other required extra things that handlers may require.
Includes a helper decorator @preconditions.requires_files(files) for handlers that require files to be present in the extras dir.
More preconditions will probably come later like requiring a library or a binary in path, etc.