Upgrading clang on CI

[Hossein Nourikhah]

Hello,

The baseline for LibreOffice C++ source code is now C++20. But, the 
clang 12 installed on CI machines is quite old, and lacks some important 
C++20 features. 
("/home/tdf/lode/opt_private/clang-llvmorg-12.0.1/bin/clang" is visible 
in the build logs)

C++ ranges library is one example:
https://en.cppreference.com/w/cpp/ranges/reverse_view

This is a related CI failure because of lacking C++ ranges library 
support:
https://ci.libreoffice.org/job/gerrit_master_ml/35822/

More details about C++20 support from different compilers can be seen 
here:

C++20 library features
https://en.cppreference.com/w/cpp/compiler_support#C.2B.2B20_library_features

Looking into the details of clang releases, I think clang versions until 
and including 17 are no longer supported.
https://llvm.org/docs/HowToReleaseLLVM.html

The current stable release is 19, an the preview release is 20.
https://releases.llvm.org/

I am not sure about 18, but it is the version available in many Linux 
distributions, and it seems to build LibreOffice from sources smoothly.

Ubuntu LTS: 20.04, 24.04, 22.04 (via llvm apt repository), RHEL 8 and 9 
(via Clang and LLVM Toolset) and many other distributions:
https://packages.ubuntu.com/search?searchon=contents&keywords=clang&mode=exactfilename&suite=focal-updates&arch=any
https://packages.ubuntu.com/search?searchon=contents&keywords=clang&mode=exactfilename&suite=noble-updates&arch=any

Is it possible upgrade clang on CI machines to version 18 (or possibly, 
19)?

Regards,
Hossein

-- 
Hossein Nourikhah, Ph.D., Developer Community Architect
Tel: +49 30 5557992-65 | Email: hossein at libreoffice.org
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