cli command basilisp test does not work with Python 3.12.7

[ikappaki]

Hi,

the basilisp test cli command does not work with Basilisp 3.12:
basilisp test: error: the following arguments are required: args

To reproduce

1. With Python 3.12 as the main interpreter, create a new project with Poetry, and basilisp and pytest as dependencies, and shell to it

> poetry new issue-test-312
Created package issue_test_312 in issue-test-312
> cd issue-test-312
> poetry add basilisp
Using version ^0.3.0 for basilisp
...
> poetry add pytest
Using version ^8.3.3 for pytest
...
> poetry shell
Spawning shell within D:\rissue-test-312\.venv
...
> python --version
Python 3.12.7

2. Run basilisp test the error comes up

> basilisp test
usage: basilisp test [-h] [--generate-auto-inlines [GENERATE_AUTO_INLINES]] [--inline-functions [INLINE_FUNCTIONS]]
                     [--warn-on-arity-mismatch [WARN_ON_ARITY_MISMATCH]]
                     [--warn-on-shadowed-name [WARN_ON_SHADOWED_NAME]] [--warn-on-shadowed-var [WARN_ON_SHADOWED_VAR]]
                     [--warn-on-unused-names [WARN_ON_UNUSED_NAMES]]
                     [--warn-on-non-dynamic-set [WARN_ON_NON_DYNAMIC_SET]]
                     [--use-var-indirection [USE_VAR_INDIRECTION]]
                     [--warn-on-var-indirection [WARN_ON_VAR_INDIRECTION]]
                     [--include-unsafe-path [INCLUDE_UNSAFE_PATH]] [-p INCLUDE_PATH]
                     [--data-readers-entry-points [DATA_READERS_ENTRY_POINTS]] [--disable-ns-cache [DISABLE_NS_CACHE]]
                     [--enable-logger [ENABLE_LOGGER]] [-l LOG_LEVEL]
                     [--emit-generated-python [EMIT_GENERATED_PYTHON]]
basilisp test: error: the following arguments are required: args

The same works fine on Python 3.11

> python --version
Python 3.11.4
> poetry new issue-test-311
Created package issue_test_311 in issue-test-311
> cd .\issue-test-311\
> poetry add basilisp
Creating virtualenv issue-test-311 in D:\issue-test-311\.venv
Using version ^0.3.0 for basilisp
...
> poetry add pytest
Using version ^8.3.3 for pytest
...
> poetry shell
Spawning shell within D:\removeme\bas\issue-test-311\.venv
...
> basilisp test
================================================= test session starts =================================================
platform win32 -- Python 3.11.4, pytest-8.3.3, pluggy-1.5.0
rootdir: D:\issue-test-311
configfile: pyproject.toml
plugins: basilisp-0.3.0
collected 0 items

================================================== warnings summary ===================================================
.venv\Lib\site-packages\_pytest\config\__init__.py:1277
  D:\issue-test-311\.venv\Lib\site-packages\_pytest\config\__init__.py:1277: PytestAssertRewriteWarning: Module already imported so cannot be rewritten: basilisp
    self._mark_plugins_for_rewrite(hook)

-- Docs: https://docs.pytest.org/en/stable/how-to/capture-warnings.html
================================================= 1 warning in 0.03s ==================================================

I had a quick look and it seems possible that the error is caused by the negative argument passed to nargs below? I couldn't find anything about negative values in the argparse nargs section of the python documentation, perhaps that was undocumented behavior that has gone away? Maybe an alternative option would be to use an explicit argument such as --pytest-args to signify the arguments to pytest?

basilisp/cli.py

def _add_test_subcommand(parser: argparse.ArgumentParser) -> None:
    parser.add_argument("args", nargs=-1, help="arguments passed on to Pytest")

Thanks

[chrisrink10]

I am unable to reproduce the same on MacOS at least with Python 3.11.7, 3.12.1, or 3.13.0, but I was able to reproduce with specifically the Python 3.12.7 version you were using. I'm looking into this a bit more to see if there was some regression in that version.

[ikappaki]

I am unable to reproduce the same on MacOS at least with Python 3.11.7, 3.12.1, or 3.13.0, but I was able to reproduce with specifically the Python 3.12.7 version you were using. I'm looking into this a bit more to see if there was some regression in that version.

Good catch! Version 3.12.7 is the latest 3.12 release, so GH Actions picked it up accordingly when I tried to upgrade to 0.3.0 😅. Thanks for looking into this!

[chrisrink10]

Were you able to confirm similar findings? Just wondering how widespread the effects here are.

[ikappaki]

Were you able to confirm similar findings? Just wondering how widespread the effects here are.

Hi @chrisrink10,

The issue is due to the python/cpython#124631 PR. It is part of the v3.12.7 tag, but hasn't made it to the v3.13.0 release (this is why it's currently working in 3.13), However, it is ported to the latest 3.13 branch and main, so it is going to fail there too when these are released.

I've created a min repo out of basilisp.cli to reproduce the issue at https://github.com/ikappaki/issue-cpython-argparse-neg.

Basically I've extracted the relevant cpython/Lib/parsearg.py commits across the different cpython versions, and stored them locally, and reference them from the cli.py file (needs manually commented and uncommented the versions). It can be run with

> python cli.py test
:1 args ['cli.py', 'test']
usage: cli.py test [-h]
cli.py test: error: the following arguments are required: args

the above failure is from the v3.12.7 tag, can be reproduced with any python version.

I can open an issue with cpython, but I couldn't find any documentation what a negative nargs supposed to do. Do you happen to have a pointer somewhere so I can reference the (official) expected behavior in the issue description?

Thanks

[ikappaki]

I've updated the repo to the bare minimum repro:

parser = argparse.ArgumentParser()
parser.add_argument("args", nargs=-1, help="extra arguments")
parsed_args, extra = parser.parse_known_args()
print(f":args {parsed_args} :extra {extra}")

$ python cli.py 2 3
usage: cli.py [-h]
cli.py: error: the following arguments are required: args

I noticed that quite a few repos out there using the nargs=-1 pattern

https://grep.app/search?q=nargs%3D-1&filter[lang][0]=Python

[ikappaki]

I went ahead and raised python/cpython#126708 ...

[chrisrink10]

I went ahead and raised python/cpython#126708 ...

Thanks for checking that out and submitting the ticket.

[chrisrink10]

python/cpython#126708 (comment)

It's possible that this comment points to the provenance of this nargs=-1. Basilisp did use Click a long time ago and it might've been configured like this and never migrated properly.

[chrisrink10]

@ikappaki I just tried the change (to using argparse.REMAINDER) in #1122 and that appears to work in 3.11.7, 3.12.7, and 3.13.0. From what I can find in the CPython repository (python/cpython#118920, python/cpython#124509, etc.), that nargs value isn't without its own issues (and it was indeed removed from the documentation due to those issues) but it seems to at least resolve the immediate issue you reported.

Let me know what you think.