Bug#871794: sagemath: FTBFS with python3-dev >= 3.6

[Steve Langasek]

Package: sagemath
Version: 7.6-3
Severity: serious
Tags: patch
Justification: imminent FTBFS
User: ubuntu-devel at lists.ubuntu.com
Usertags: origin-ubuntu artful ubuntu-patch

Hi folks,

The sagemath package failed to build in Ubuntu for the gsl soname
transition, because the python3 3.5->3.6 transition has already been
completed here and debian/pruner has incorrectly hard-coded a check for
python-3.5.pc.

The python3-dev package provides a generic python3.pc, which should be used
here instead.

I've uploaded the attached patch to Ubuntu, which fixes the build failure. 
Unfortunately, since sagemath was removed from artful due to this build
failure, the new version of cysignals has migrated in the meantime which
means we are also affected by bug #870688.  Nevertheless, this patch will
also be needed in Debian, as the python3.6 transition has begun in unstable
and this will be a build failure in Debian imminently.

-- 
Steve Langasek                   Give me a lever long enough and a Free OS
Debian Developer                   to set it on, and I can move the world.
Ubuntu Developer                                    http://www.debian.org/
slangasek at ubuntu.com                                     vorlon at debian.org
-------------- next part --------------
diff -Nru sagemath-7.6/debian/pruner/configure.ac sagemath-7.6/debian/pruner/configure.ac
--- sagemath-7.6/debian/pruner/configure.ac	2017-07-22 15:08:10.000000000 -0700
+++ sagemath-7.6/debian/pruner/configure.ac	2017-08-10 23:42:09.000000000 -0700
@@ -285,7 +285,7 @@
 PKG_CHECK_MODULES(python, python-2.7, [HAS_PYTHON='True'], [HAS_PYTHON='False'])
 AC_SUBST(HAS_PYTHON)
 
-PKG_CHECK_MODULES(python3, python-3.5, [HAS_PYTHON3='True'], [HAS_PYTHON3='False'])
+PKG_CHECK_MODULES(python3, python3, [HAS_PYTHON3='True'], [HAS_PYTHON3='False'])
 AC_SUBST(HAS_PYTHON3)
 
 AC_CHECK_PROG(HAS_R, R, "True", "False")