[libc++][CI] Updates Docker image.

[Mordante]

Summary

• Updates the image to use Ubuntu Jammy.
• Installs GCC-12 as preparation to migrate to that GCC version.

[jloser]

LGTM % a typo nit.

libcxx/utils/ci/Dockerfile

59

s/LVM/LLVM, please.

[ldionne]

If we can't install LLVM 12 with jammy, we might have to wait until we branch for LLVM 15 (in a couple of months) before we can land this. Once we branch LLVM 15, our latest-2 will become LLVM 13, which should work with jammy.

libcxx/utils/ci/Dockerfile

58

I think this comment should be reworded to something like:

# We also install <latest-2> because we need to support the "latest-1" of the current release branch,
# which is effectively the <latest-2> of the tip-of-trunk LLVM. For example, after branching LLVM 14
# but before branching LLVM 15, we still need to have Clang 12 in this Docker image because the LLVM
# 14 release branch CI uses it. The tip-of-trunk CI will never use Clang 12, though.

64

As explained above, the problem with removing this line as-is is that it's going to break CI on release/14.x.

[Mordante]

libcxx/utils/ci/Dockerfile

59

Good catch, thanks. I'll update it before landing unless there are other review comments.

64

As discussed during the online review Ubuntu Jammy ships clang-12, so I'll use that.

[Mordante]

Addresses review comments.

[ldionne]

LGTM, thanks! Once we land this, let's monitor the bots a bit more closely in case something breaks.

libcxx/utils/ci/Dockerfile

87

Nitpick, but can we switch the order?

libcxx/utils/ci/Dockerfile

 # A pre-built version of this image is maintained on DockerHub as ldionne/libcxx-builder.
 # To update the image, rebuild it and push it to ldionne/libcxx-builder (which
 # will obviously only work if you have permission to do so).
 #
 #   $ docker build -t ldionne/libcxx-builder libcxx/utils/ci
 #   $ docker push ldionne/libcxx-builder
 #
 
-FROM ubuntu:focal
+FROM ubuntu:jammy
 
 # Make sure apt-get doesn't try to prompt for stuff like our time zone, etc.
 ENV DEBIAN_FRONTEND=noninteractive
 
 # This dummy command is meant to be edited from time to time, which causes the
 # CI builders to rebuild their copy of the Docker image. This is not a great
 # solution, however without that, the CI builders will keep the same cached
 # Docker image forever.
RUN apt-get update && apt-get install -y language-pack-en language-pack-fr \
                                          language-pack-zh-hans
 # These two are not enabled by default so generate them
 RUN printf "fr_CA ISO-8859-1\ncs_CZ ISO-8859-2" >> /etc/locale.gen
 RUN mkdir /usr/local/share/i1en/
 RUN printf "fr_CA ISO-8859-1\ncs_CZ ISO-8859-2" >> /usr/local/share/i1en/SUPPORTED
 RUN locale-gen
 
 # Install Clang <latest>, <latest-1> and ToT, which are the ones we support.
 # We also install <latest-2> to allow smooth CI transitions around release points.
+# TODO enable LVM_LATEST_VERSION - 2 after changing to version 15
+# Normally this is enabled but LLVM 12 isn't backported to Jammy.
 ENV LLVM_LATEST_VERSION=14
 RUN apt-get update && apt-get install -y lsb-release wget software-properties-common
 RUN wget https://apt.llvm.org/llvm.sh -O /tmp/llvm.sh
-RUN bash /tmp/llvm.sh $(($LLVM_LATEST_VERSION - 2)) # for CI transitions
+#RUN bash /tmp/llvm.sh $(($LLVM_LATEST_VERSION - 2)) # for CI transitions
 RUN bash /tmp/llvm.sh $(($LLVM_LATEST_VERSION - 1)) # previous release
 RUN bash /tmp/llvm.sh $LLVM_LATEST_VERSION          # latest release
 RUN bash /tmp/llvm.sh $(($LLVM_LATEST_VERSION + 1)) # current ToT
 
 # Make the latest version of Clang the "default" compiler on the system
 # TODO: In the future, all jobs should be using an explicitly-versioned version of Clang instead,
 #       and we can get rid of this entirely.
 RUN ln -fs /usr/bin/clang++-$LLVM_LATEST_VERSION /usr/bin/c++ && [ -e $(readlink /usr/bin/c++) ]
 RUN ln -fs /usr/bin/clang-$LLVM_LATEST_VERSION /usr/bin/cc && [ -e $(readlink /usr/bin/cc) ]
 
 # Install clang-format
 RUN apt-get install -y clang-format-$LLVM_LATEST_VERSION
 RUN ln -s /usr/bin/clang-format-$LLVM_LATEST_VERSION /usr/bin/clang-format && [ -e $(readlink /usr/bin/clang-format) ]
 RUN ln -s /usr/bin/git-clang-format-$LLVM_LATEST_VERSION /usr/bin/git-clang-format && [ -e $(readlink /usr/bin/git-clang-format) ]
 
 # Install clang-tidy
 RUN apt-get install -y clang-tidy-$LLVM_LATEST_VERSION
 RUN ln -s /usr/bin/clang-tidy-$LLVM_LATEST_VERSION /usr/bin/clang-tidy && [ -e $(readlink /usr/bin/clang-tidy) ]
 
-# Install the most recent GCC
-ENV GCC_LATEST_VERSION=11
-RUN add-apt-repository ppa:ubuntu-toolchain-r/test
+# Install the most recent GCC, like clang install the previous version as a transition.
+ENV GCC_LATEST_VERSION=12
 RUN apt-get update && apt install -y gcc-$GCC_LATEST_VERSION g++-$GCC_LATEST_VERSION
+RUN apt-get update && apt install -y gcc-$((GCC_LATEST_VERSION - 1)) g++-$((GCC_LATEST_VERSION - 1))
 
 # Install a recent CMake
 RUN wget https://github.com/Kitware/CMake/releases/download/v3.21.1/cmake-3.21.1-linux-x86_64.sh -O /tmp/install-cmake.sh
 RUN bash /tmp/install-cmake.sh --prefix=/usr --exclude-subdir --skip-license
 RUN rm /tmp/install-cmake.sh
 
 # Change the user to a non-root user, since some of the libc++ tests
 # (e.g. filesystem) require running as non-root. Also setup passwordless sudo.