Wouter Deconinck

While you're at it, can you also rebase the branch to pick up more recent CI checks.

> @wdconinc added CMake constraint now. Can I do it like this with `depends_on` or do I need to introduce separate `conflicts`? Yes, perfectly fine. You didn't even need to...

There's an issue with ci that's under investigation. Might be Monday before we can merge this.

The CI error seems to be due to `whizard` compiling with `-std=c++11` even though it (through `hepmc3`?) depends on `root` compiled with C++20. @vvolkl You're a `whizard` user, right?

Whizard issue hopefully resolved by https://github.com/spack/spack/pull/50255.

> @balay sure I can add that! It may be Monday, though. @georgiastuart Did you want to add those new versions? If not, we can merge this and keep it...

Revived and ready for review. This builds fine with the following results on codespaces: ``` root@codespaces-f81189:/workspaces/spack# spack spec [+] [email protected]%[email protected]+r build_system=makefile arch=linux-ubuntu20.04-x86_64_v3 [+] ^[email protected]%[email protected]~gssapi~ldap+libidn2~librtmp~libssh~libssh2+nghttp2 build_system=autotools libs=shared,static tls=openssl arch=linux-ubuntu20.04-x86_64_v3 [+] ^[email protected]%[email protected]...

Interesting new issue: `acts` can now depend on `traccc`, and `traccc` depends on `acts` (PluginJson in io/). Does anyone know how deep the dependency is? (tagging @stephenswat too)

There does not seem to be any actual functionality enabled by the covfie, detray, traccc options, and they appear provided for [forward planning only](https://github.com/acts-project/acts/commit/210b8979078704af25154b594071826f3dbb2a59). There are missing definitions of `_acts_traccc_version`...

@spackbot fix style