pkg-config fails to find python3

[aleb (Alex Băluț)]

I have port:python36 but pkg-config fails to find it:

$ find /opt/custom | grep \\.pc$ | grep -i python
/opt/custom/Library/Frameworks/Python.framework/Versions/2.7/lib/pkgconfig/python-2.7.pc
/opt/custom/Library/Frameworks/Python.framework/Versions/2.7/lib/pkgconfig/python.pc
/opt/custom/Library/Frameworks/Python.framework/Versions/2.7/lib/pkgconfig/python2.pc
/opt/custom/Library/Frameworks/Python.framework/Versions/3.6/lib/pkgconfig/python-3.6.pc
/opt/custom/Library/Frameworks/Python.framework/Versions/3.6/lib/pkgconfig/python-3.6m.pc
/opt/custom/Library/Frameworks/Python.framework/Versions/3.6/lib/pkgconfig/python3.pc

$ which python3
/opt/custom/bin/python3

$ /opt/custom/bin/pkg-config --list-all | grep python
.. crickets ..

[aleb (Alex Băluț)]

This happens even though I ran

sudo port select --set python3 python36

[kencu (Ken)]

/opt/custom/Library/Frameworks/Python.framework/Versions/3.6/lib/pkgconfig

is not a default search directory for pkg-config files.

[jmroot (Joshua Root)]

Putting python3.pc in the default pkgconfig search path is bad for ReproducibleBuilds. Fine to link python-2.7.pc, python-3.6.pc and so on.

[raimue (Rainer Müller)]

For those that stumble over this ticket while doing builds outside of MacPorts, the workaround is to set PKG_CONFIG_PATH manually:

$ pkg-config --print-provides python3
Package python3 was not found in the pkg-config search path.
Perhaps you should add the directory containing `python3.pc'
to the PKG_CONFIG_PATH environment variable
No package 'python3' found
$ export PKG_CONFIG_PATH=/opt/local/Library/Frameworks/Python.framework/Versions/3.6/lib/pkgconfig
$ pkg-config --print-provides python3
python3 = 3.6

I agree that we do not want to use python3.pc when building a port. However, python3.pc could be managed by python_select. We also already have symlinks for the python3 and python3-config binaries. If a build system uses pkg-config ... python3, it would be the same as using python3-config. We will always have to handle these cases, most probably with patches.

[kencu (Ken)]

So do we "fix" this by symlinking the properly-versioned *.pc files into the default search path, or just close it as "wontfix"?

[ryandesign (Ryan Carsten Schmidt)]

If port select is already symlinking *-config scripts, then it should also symlink *.pc files.

[aleb (Alex Băluț)]

I noticed this problem while creating a Portfile. Maybe this info should be added in the howto for creating a new Portfile. Or in a "Python for Portfile authors" page if there is one? (see ​https://docs.brew.sh/Python-for-Formula-Authors)