Bug#1096535: dolfinx-mpc: ftbfs with GCC-15

[Drew Parsons]

Source: dolfinx-mpc
Followup-For: Bug #1096535
Control: tags -1 ftbfs
Control: affects -1 src:nanobind

Your build log shows the build used package versions
gcc-15 15-20250213-1
nanobind 2.5.0-1
dolfinx 1:0.9.0-6+b2
python 3.13.2-1

dolfinx 1:0.9.0-6+b2 was built against nanobind 2.4.0-1 and python3
3.13.1-3.

So likely the problem is the mismatch between nanobind 2.4.0 and 2.5.0,
not in gcc-15 itself.

nanobind updates should be treated as library transitions, and if fact
we do have a mechanism for nanobind, but it's in the major version,
currently,

  Depends: python3-nanobind (>= 2.5), python3-nanobind (<< 3)
  
So fenics-dolfinx 1:0.9.0-6+b2 had
 
 python3-dolfinx-real Depends: python3-nanobind (>= 2.4), python3-nanobind (<< 3)

and therefore nanobind 2.5.0 was considered compatible.

Perhaps the nanobind dependency needs to be tightened to apply to the
minor version.

Alternatively perhaps you're right in the first place and the problem
is gcc-15 after all, not nanobind.

fenicsx-dolfinx 1:0.9.0-6 is now built against nanobind 2.5.0.

Can you retry the gcc-15 build? If it still fails the same way then we
can be sure the issue is gcc-15 not nanobind.