fails to build with gcc-13

[drew-parsons]

Debian reports that basix 0.6.0 is failing to build with gcc-13, https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1037650
mainly affecting finite-element.cpp, finite-element.h, precompute.h
A failing build log can be found at https://tests.reproducible-builds.org/debian/rb-pkg/unstable/amd64/fenics-basix.html
e.g.

[ 75%] Building CXX object CMakeFiles/basix.dir/basix/e-regge.cpp.o
/usr/bin/c++ -Dbasix_EXPORTS -I/build/1st/fenics-basix-0.6.0/obj-x86_64-linux-gnu -I/build/1st/fenics-basix-0.6.0/cpp -g -O2 -ffile-prefix-map=/build/1st/fenics-basix-0.6.0=. -fstack-protector-strong -Wformat -Werror=format-security -Wdate-time -D_FORTIFY_SOURCE=2 -std=c++20 -fPIC -MD -MT CMakeFiles/basix.dir/basix/e-regge.cpp.o -MF CMakeFiles/basix.dir/basix/e-regge.cpp.o.d -o CMakeFiles/basix.dir/basix/e-regge.cpp.o -c /build/1st/fenics-basix-0.6.0/cpp/basix/e-regge.cpp
In file included from /build/1st/fenics-basix-0.6.0/cpp/basix/interpolation.cpp:6:
/build/1st/fenics-basix-0.6.0/cpp/basix/finite-element.h:786:42: error: 'int32_t' is not a member of 'std'; did you mean 'int32_t'?
  786 |   void permute_dofs(const std::span<std::int32_t>& dofs,
      |                                          ^~~~~~~

There was a gcc-13 issue with dolfinx, which is apparently resolved by FEniCS/dolfinx#2646 , using int instead of int32_t. But basix is still using std::int32_t.

The GNU gcc-13 guide indicates <cstdint> should now be included to get std::int32_t. Currently finite-element.h is not including it explicitly. #664 included <concept> and <utility> but not <cstdint>, and it's not obvious that it would give a successful build with gcc-13.

Is it possible to say which patch in the main branch might have fixed basix builds with gcc-13?

[garth-wells]

Fixed in #691.