Test with linux clang-23, and gcc-16 in docker

[ClausKlein]

This is not intended to be merged, only to show the current problems with import std;

see https://gitlab.kitware.com/cmake/cmake/-/work_items/27962

and ClausKlein/fmt-module#5

[coveralls]

coverage: 93.742% (+0.004%) from 93.738% — ClausKlein:feature/test-with-linux-clang-23 into bemanproject:main

[ClausKlein]

my docker file to build clang-23:

# SPDX-License-Identifier: GPL-3.0-or-later
# Copyright © 2025-2026 GSI Helmholtzzentrum fuer Schwerionenforschung GmbH
#                       Matthias Kretz <m.kretz@gsi.de>

FROM ghcr.io/mattkretz/cplusplus-ci/gcc14

ENV DEBIAN_FRONTEND=noninteractive

ENV LLVM_VERSION=23

# NOTE: pipx ensurepath -> appends /root/.local/bin to the PATH environment variable.
ENV PATH="/root/.local/bin:${PATH}"

RUN wget -O - https://apt.llvm.org/llvm-snapshot.gpg.key|apt-key add - && \
    add-apt-repository "deb http://apt.llvm.org/noble/ llvm-toolchain-noble main" && \
    apt-get update && \
    apt-get install -y --no-install-recommends \
    bash bash-completion vim tree less symlinks direnv \
    build-essential curl git wget libssl-dev \
    doxygen graphviz python3-pip python-is-python3 pipx \
    zip ccache \
    clang-${LLVM_VERSION} \
    clang-tidy-${LLVM_VERSION} \
    clang-format-${LLVM_VERSION} \
    libc++-${LLVM_VERSION}-dev \
    libc++abi-${LLVM_VERSION}-dev && \
    apt-get install -y --no-install-recommends libclang-rt-${LLVM_VERSION}-dev && \
    update-alternatives --install /usr/bin/clang clang /usr/bin/clang-${LLVM_VERSION} ${LLVM_VERSION}0 \
                        --slave /usr/bin/clang++ clang++ /usr/bin/clang++-${LLVM_VERSION} && \
    update-alternatives --install /usr/bin/clang-tidy clang-tidy /usr/bin/clang-tidy-${LLVM_VERSION} ${LLVM_VERSION}0 && \
    update-alternatives --install /usr/bin/run-clang-tidy run-clang-tidy /usr/bin/run-clang-tidy-${LLVM_VERSION} ${LLVM_VERSION}0 && \
    update-alternatives --install /usr/bin/clang-format clang-format /usr/bin/clang-format-${LLVM_VERSION} ${LLVM_VERSION}0 && \
    apt-get clean

# QUICKFIX: ajust the broken relative paths inside libc++.modules.json
RUN sed -i \
    's#\.\./share/libc++#/usr/lib/llvm-'${LLVM_VERSION}'/share/libc++#' \
    /lib/x86_64-linux-gnu/libc++.modules.json

RUN pipx install cmake && \
    pipx install --include-deps cmake-format && \
    pipx install codespell && \
    pipx install conan && \
    pipx install gcovr && \
    pipx install gersemi && \
    pipx install ninja && \
    pipx install pre-commit && \
    pipx install uv

WORKDIR /home/builder/workdir

[ClausKlein]

Not sure why it is needed, but it works fine!

line 120 should be message(WARNING ...)