The PyUnicode_FSConverter function has confusing reference semantics, and confusing documentation.

https://docs.python.org/3/c-api/unicode.html#c.PyUnicode_FSConverter says the output argument "must be a PyBytesObject* which must be released when it is no longer used." That seems to suggest one must pass a PyBytesObject to it, and indeed one of the error paths assumes an object was passed (https://github.com/python/cpython/blob/main/Objects/unicodeobject.c#L4116-- 'addr' is called 'result' in the docs). Not passing a valid object would result in trying to DECREF NULL, or garbage. However, the function doesn't actually use the object, and later in the function overwrites the value *without* DECREFing it, so passing a valid object would in fact cause a leak.

I understand the function signature is the way it is so it can be used with PyArg_ParseTuple's O& format, but there are reasons to call it directly (e.g. with METH_O functions), and it would be nice if the semantics were more clear.