Compilation issues with gcc 14.1.1, C++20, ROOT v6.30.06

[wiechula]

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Description

After updating from gcc 13.2.1 to gcc 14.1.1 I get several compile errors starting with e.g.

While building module 'Core':
While building module 'std' imported from input_line_1:1:
In file included from <module-includes>:10:
In file included from /usr/include/c++/14.1.1/chrono:49:
In file included from /usr/include/c++/14.1.1/bits/shared_ptr.h:53:
In file included from /usr/include/c++/14.1.1/bits/shared_ptr_base.h:66:
/usr/include/c++/14.1.1/bits/align.h:93:21: error: call to 'has_single_bit' is ambiguous
      static_assert(std::has_single_bit(_Align));
                    ^~~~~~~~~~~~~~~~~~~
/usr/include/c++/14.1.1/bit:439:5: note: candidate function [with _Tp = unsigned long]
    has_single_bit(_Tp __x) noexcept
    ^

The full log is install.txt

Reproducer

git clone https://github.com/root-project/root.git
cd root/
git checkout v6-30-06
mkdir build install
cd build
cmake -DCMAKE_INSTALL_PREFIX=../install -DCMAKE_CXX_STANDARD=20 ../
cmake --build . --target install -j 12 &> install.txt

ROOT version

v6-30-06

Installation method

from source

Operating system

Linux (arch linux)

Additional context

No response

[guitargeek]

You're using ArchLinux, where ROOT 6.30.06 is part of the official system packages: https://archlinux.org/packages/extra/x86_64/root/

If you look at the linked packages sources and do exactly as in the PKGBUILD, your build will succeed: https://gitlab.archlinux.org/archlinux/packaging/packages/root

I think getting the right settings.cmake is important. Maybe for your particular problem, the cxxmodules=OFF part of it is the solution?

[guitargeek]

Ah, now that I tried it: I see that it doesn't work, also with the official config!

So you have two easy options until someone fixes this issue:

1. Build the 6.32 release candidate branch, where it works just fine https://github.com/root-project/root/tree/v6-32-00-patches

2. Install and use GCC 13 with -DCMAKE_C_COMPILER=/usr/bin/gcc-13 -DCMAKE_CXX_COMPILER=/usr/bin/g++-13

[wiechula]

Dear @guitargeek , thanks a lot for your fast feedback! Indeed, v6-32-00-patches builds fine. I'm building root as part of the ALICE software stack with custom build options. Using pre-packaged versions will not work.

[guitargeek]

Hi! I didn't get from your answer if the workaround of using 6.32 or an older compiler is unblocking your work. Can you please clarify? That will help to assess the priority of this issue. Thanks!

[wiechula]

After adjusting some parts of our software to modifications made in v6.32 I manage to compile the full stack. So for me this is fine for the moment. Thanks again for you support!