python: fix editable installs for modern pip/setuptools

The way editable installs work has changed at some point since Fedora 40
was released. Generally, we should be opting to use pyproject.toml
installs (PEP517/518) - but those are not fully supported until v61 of
setuptools, and CentOS Stream 9 ships v53.

Until that time, we can make use of a transitional feature in
pip/setuptools to use "legacy" editable installs, which is enough to fix
"make check-dev" on modern local workstations for now.

By using the environment variable approach to configure pip, we avoid
any problems for older versions of pip that don't recognize this option,
so it's harmless. The config-settings option first appeared in v23 of
pip. editable_mode was first supported by setuptools in v64.

(I'm not currently precisely aware of when the default behavior of '-e'
switched away from 'compat', but it appears to be a joint effect between
setuptools and pip versions.)

Version information for supported build platforms:

distro              python3  pip     setuptools  sphinx
--------------------------------------------------------
centos_stream_9     3.9.23   21.3.1  53.0.0      3.4.3
ubuntu_22_04        3.10.12  22.0.2  59.6.0      4.3.2

** pyproject.toml installs supported as of here **

freebsd             3.11.13  23.3.2  63.1.0      5.3.0
debian_12           3.11.2   23.0.1  66.1.1      5.3.0
ubuntu_24_04        3.12.3   24.0    68.1.2      7.2.6
centos_stream_10    3.12.11  23.3.2  69.0.3      7.2.6
fedora_41           3.13.5   24.2    69.2.0      7.3.7
alpine_3_19         3.11.13  23.3.1  70.3.0      6.2.1
alpine_3_20         3.12.11  24.0    70.3.0      7.2.6
alpine_3_21         3.12.11  24.3.1  70.3.0      8.1.3
ubuntu_24_10        3.12.7   24.2    74.1.2      7.4.7
fedora_42           3.13.5   24.3.1  74.1.3      8.1.3
ubuntu_25_04        3.13.3   25.0    75.8.0      8.1.3
macports            3.13.5   25.1.1  78.1.1      8.2.3
openbsd             3.12.11  25.1.1  79.0.1      8.2.3
alpine_3_22         3.12.11  25.1.1  80.9.0      8.2.3
homebrew            3.13.5   ---     80.9.0      8.2.3
pkgsrc_current      3.12.11  25.1.1  80.9.0      8.2.3

Signed-off-by: John Snow <jsnow@redhat.com>
Message-ID: <20250715222548.198888-1-jsnow@redhat.com>
Tested-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>

0 files changed, 0 insertions, 0 deletions