[5.0RC1] utils.minversion("astropy", "5.0") doesn't work (and seems unneeded?)

[olebole]

Description

When building the Debian package, the tests are run on the built but not installed package. In this case, I get the following error:

cd '/build/astropy-5.0~rc1/.pybuild/cpython3_3.9/build'; python3.9 -m pytest 
[…]
astropy/utils/introspection.py:157: in minversion
    module_version = metadata.version(module_name)
/usr/lib/python3.9/importlib/metadata.py:551: in version
    return distribution(distribution_name).version
/usr/lib/python3.9/importlib/metadata.py:524: in distribution
    return Distribution.from_name(distribution_name)
/usr/lib/python3.9/importlib/metadata.py:187: in from_name
    raise PackageNotFoundError(name)
E   importlib.metadata.PackageNotFoundError: astropy

During handling of the above exception, another exception occurred:
/usr/lib/python3.9/importlib/__init__.py:127: in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
<frozen importlib._bootstrap>:1030: in _gcd_import
    ???
<frozen importlib._bootstrap>:1007: in _find_and_load
    ???
<frozen importlib._bootstrap>:972: in _find_and_load_unlocked
    ???
<frozen importlib._bootstrap>:228: in _call_with_frames_removed
    ???
<frozen importlib._bootstrap>:1030: in _gcd_import
    ???
<frozen importlib._bootstrap>:1007: in _find_and_load
    ???
<frozen importlib._bootstrap>:986: in _find_and_load_unlocked
    ???
<frozen importlib._bootstrap>:680: in _load_unlocked
    ???
<frozen importlib._bootstrap_external>:850: in exec_module
    ???
<frozen importlib._bootstrap>:228: in _call_with_frames_removed
    ???
astropy/cosmology/tests/__init__.py:7: in <module>
    import mypackage
astropy/cosmology/tests/mypackage/__init__.py:1: in <module>
    from . import cosmology, io
astropy/cosmology/tests/mypackage/io/__init__.py:20: in <module>
    ASTROPY_GE_5 = minversion("astropy", "5.0")
astropy/utils/decorators.py:547: in wrapper
    return function(*args, **kwargs)
astropy/utils/introspection.py:164: in minversion
    module_version = metadata.version(dist_names[module_name][0])
E   KeyError: 'astropy'

Aside from the error itself, I am wondering why we need to check for the version here at all?

Expected behavior

Tests should pass; I would expect this even on a non-installed Astropy.

Actual behavior

See above

Steps to Reproduce

1. Build the package with python3 setup.py build
2. cd to the build dir; python3.9 -m pytest

System Details

Python 3.9.7, pytest-6.2.5, py-1.10.0, pluggy-0.13.0

Platform: Linux-5.14.0-2-amd64-x86_64-with-glibc2.32

Full Python Version:
3.9.7 (default, Sep 24 2021, 09:43:00)
[GCC 10.3.0]

encodings: sys: utf-8, locale: UTF-8, filesystem: utf-8
byteorder: little
float info: dig: 15, mant_dig: 15

Package versions:
Numpy: 1.19.5
Scipy: 1.7.1
Matplotlib: 3.3.4
h5py: not available
Pandas: not available
PyERFA: 2.0.0
Cython: 0.29.24
Scikit-image: not available
asdf: not available
pyarrow: not available

Using Astropy options: remote_data: none.

Matplotlib: 3.3.4
Freetype: 2.11.0
ARCH_ON_CI: undefined
IS_CRON: undefined

rootdir: /build/astropy-5.0~rc1, configfile: setup.cfg
plugins: astropy-header-0.1.2, hypothesis-5.43.3, arraydiff-0.3, mpl-0.11, filter-subpackage-0.1.1, cov-3.0.0, doctestplus-0.11.0, remotedata-0.3.2, mock-3.6.1, openfiles-0.5.0

[pllim]

Yeah, minversion was refactored in #11714 so its behavior is different now. Maybe @saimn can advise?

[pllim]

I am putting a v5.0 milestone here in case this will block actual release. Please remove it if that is not the case. Thanks!

[saimn]

I don't understand why this is needed in the cosmology tests, @nstarman ?
If we need to keep it, we could use instead import astropy; minversion(astropy, ....) since minversion would then use the __version__ attribute.

[nstarman]

All this comes from https://docs.astropy.org/en/latest/cosmology/dev.html#astropy-cosmology-for-developers
where I walk through how the maintainer of another cosmology package (e.g. cosmolopy) can register their file formats with Astropy I/O and more importantly the ability to convert cosmology objects between the their package and Astropy.
3rd party packages would need to check Astropy's minimum version, if it's even installed.

[astrofrog]

@pllim just to confirm, this is definitely a release blocker as it is causing issues with Debian packaging

[nstarman]

I'll push a fix that does

try:
    import astropy
    from astropy.utils.introspection import minversion
except ImportError:
    ASTROPY_GE_5 = False
else:
    ASTROPY_GE_5 = minversion(astropy, "5.0")

It used to do

try:
    from astropy.utils.introspection import minversion
except ImportError:
    ASTROPY_GE_5 = False
else:
    ASTROPY_GE_5 = minversion("astropy", "5.0")

[olebole]

Thanks to @nstarman for the quick fix!