Positional args with keywords not working in native methods

[dhalbert]

Native method implementations that use mp_arg_parse_all() should be able to accept positional args that are labeled with keywords, but they are not.

Here is an example showing the issue with busio.SPI.
Constructor signature:

busio.SPI(clock: microcontroller.Pin, MOSI: Optional[microcontroller.Pin] = None, MISO: Optional[microcontroller.Pin] = None)

Method signature:

write(self, buffer: _typing.ReadableBuffer, *, start: int = 0, end: Optional[int] = None) → None

I would expect to be able to use or omit the clock, MOSI, and MISO keywords when passing args to the constructor.
I would also expect to be able to omit or include the buffer keyword when calling write().

>> import board,busio
>>> spi = busio.SPI(board.SCK, board.MOSI)    # no keywords
>>> spi.deinit()
>>> spi = busio.SPI(clock=board.SCK, MOSI=board.MOSI)    # keywords supplied
>>> spi.try_lock()
True

>>> spi.write(b'abc')    # no keyword
>>> spi.write(buffer=b'abc')   # keyword should be allowed
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: function missing 1 required positional arguments

We inherited some arg-parsing restrictions from MicroPython, but I don't remember that this is one of them, and it doesn't seem to be documented. Maybe I'm forgetting something.

Generalization of #5405.

[jepler]

busio_spi_write_obj is defined as follows:

MP_DEFINE_CONST_FUN_OBJ_KW(busio_spi_write_obj, 2, busio_spi_write);

I think that the 2 (n_args_min) means that 2 positional (non-keyword) arguments are required, according to mp_arg_check_num_sig. Since all the arguments besides self can be given as kwargs, it should be 1 instead.

[dhalbert]

I think that the 2 (n_args_min) means that 2 positional (non-keyword) arguments are required, according to mp_arg_check_num_sig. Since all the arguments besides self can be given as kwargs, it should be 1 instead.

That makes sense. I think various of us misinterpreted n_args and n_args_min to mean all the args, not just the positional args. The names would be better as n_pos_args_min, but the other naming is pervasive. I'll vet these values everywhere.