Bug#972394: likely cause: Python.h not found because of version mismatch 3.8 vs 3.9

[Stephen Sinclair]

On Wed, Oct 21, 2020 at 10:39 AM Adrian Bunk <bunk at debian.org> wrote:
>
> Control: retitle -1 siconos FTBFS with more than one supported python3 version
>
> On Mon, Oct 19, 2020 at 11:38:42PM +0200, Markus Koschany wrote:
> >
> > I built siconos in a clean chroot environment. The recent rebuild of
> > siconos also shows build failures
> >
> > https://buildd.debian.org/status/package.php?p=siconos
> >
> > I don't think it's specific to my environment.
>
> You need something like python3-dev -> python3-all-dev in the build
> dependencies.

I can confirm that making this change allows the package to build.
However, some Python-related tests in autopkgtest fail when trying to
import the Siconos python modules, so something still needs to be
fixed.  I will investigate.
As for this change, however, is it the correct one to make?  Or should
I wait for more information in #972551?

> The next problem is what it builds - it then builds for the highest
> version only, not for the default version.

Can I ask how you determined this?  It is not surprising that
something could be wrong, as the CMake configuration is very
complicated in this package.
However, the configure step includes the line,

-DPYTHON_EXECUTABLE=$(shell which python3)"

which should specify the path to the default Python interpreter.  Is
there a better way to determine this path?

> This bug could be solved by either adjusting the build dependencies
> and the build to build for all supported python3 versions, or by fixing
> whatever in the build system does not use the default version.

I would prefer the latter as the package is already quite complicated
and does not play well with multiple pythons.

regards,
Steve