python-config breaks when symlinked to another location

[tobik]

BPO	34111
Nosy	@tiran, @iritkatriel
Files	patch-Misc__python-config.sh.in

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2018-07-14.11:21:50.967>
labels = ['3.10', 'type-bug', '3.9', 'build', '3.11']
title = 'python-config breaks when symlinked to another location'
updated_at = <Date 2021-12-09.08:02:36.043>
user = 'https://bugs.python.org/tobik'

bugs.python.org fields:

activity = <Date 2021-12-09.08:02:36.043>
actor = 'christian.heimes'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Build']
creation = <Date 2018-07-14.11:21:50.967>
creator = 'tobik'
dependencies = []
files = ['47690']
hgrepos = []
issue_num = 34111
keywords = []
message_count = 4.0
messages = ['321650', '408055', '408066', '408080']
nosy_count = 3.0
nosy_names = ['christian.heimes', 'tobik', 'iritkatriel']
pr_nums = []
priority = 'normal'
resolution = None
stage = 'needs patch'
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue34111'
versions = ['Python 3.9', 'Python 3.10', 'Python 3.11']

Linked PRs

• gh-78292: Improve python-config build script to respect symbolic link. #156240

[tobik]

When symlinking python3.6-config to another location, it starts
outputting bogus paths. It's convenient to symlink the system
python3.6-config to somewhere else in PATH to make sure the build
of an application with a hardcoded use of python3-config is using
the right Python version. This is something that we would like to
do in FreeBSD Ports instead of having to patch build files.

It works fine with python2.7-config. However when I try a similar
thing with python3.6-config it starts outputting bogus paths. For
example

$ pwd
/home/tobias
$ python2.7-config --includes
-I/usr/local/include/python2.7 -I/usr/local/include/python2.7
$ ln -s /usr/local/bin/python2.7-config python2-config
$ ./python2-config --includes
-I/usr/local/include/python2.7 -I/usr/local/include/python2.7
$ python3.6-config --includes
-I/usr/local/include/python3.6m -I/usr/local/include/python3.6m
$ ln -s /usr/local/bin/python3.6-config python3-config
$ ./python3-config --includes
-I/home/include/python3.6m -I/home/include/python3.6m

It would be nice if this could just work. This was on FreeBSD but
the same problem exists on e.g. Void Linux too.

The problem seems to be that the path to the original script is not
resolved properly when trying to determine the install prefix.
Adding realpath(1) to python-config seems to solve it.

[iritkatriel]

tobik, 3.4/3.5 are no longer maintained. Do you know whether this is impacting current versions (>= 3.9)?

[tobik]

Yes, the bug still exists and all Python versions are affected.

We patch them all in FreeBSD Ports:
https://cgit.freebsd.org/ports/tree/lang/python36/files/patch-Misc__python-config.sh.in
https://cgit.freebsd.org/ports/tree/lang/python37/files/patch-Misc__python-config.sh.in
https://cgit.freebsd.org/ports/tree/lang/python38/files/patch-Misc__python-config.sh.in
https://cgit.freebsd.org/ports/tree/lang/python39/files/patch-Misc__python-config.sh.in
https://cgit.freebsd.org/ports/tree/lang/python310/files/patch-Misc__python-config.sh.in
https://cgit.freebsd.org/ports/tree/lang/python311/files/patch-Misc__python-config.sh.in

[tiran]

Could you open a PR, please? The fix looks trivial.