`nargs=argparse.REMAINDER` can break config file option parsing

[stxue1]

Example:

import configargparse

parser = configargparse.ArgParser()
parser.add_argument("--config", is_config_file_arg=True, default="config.cfg")
parser.add_argument('--config_file_option', nargs="*", default=None) # also happens with action="append" and any of its derivatives
parser.add_argument("remainder_option", nargs=argparse.REMAINDER, default=None)
args = ["test"]
options = parser.parse_args(args)

With config.cfg:

config_file_option=Option from config file

remainder_option should be ["test"], but it swallows the config file and becomes ["test", "--config_file_option=Option from config file"], which results in all config file options not being set.

I believe it is due to these lines:

ConfigArgParse/configargparse.py

Lines 948 to 955 in ee77f44

	if (action and action.nargs or
	isinstance(action, argparse._AppendAction)):
	nargs = True
	if nargs:
	args = args + config_args
	else:
	args = config_args + args

It looks like if there is any other argument with nargs or action="append", then it will put all config options after the remainder option instead of before.

Changing it to args = config_args + args fixes this, but will probably break #144.

[mihaic]

Upstream removed the documentation for argparse.REMAINDER because of the issues it causes, so it is unlikely this issue will be fixed.
python/cpython#18661