feat: move to Dockerfile heredoc

As of Dockerfile format spec 1.4, we can use heredocs instead of escaped line breaks. This is much more readable.

containers/debian/base.Dockerfile

@@ -17,13 +17,13 @@ ENV CLICOLOR_FORCE=1                                                    \
 
 ## Install additional packages. Remove the auto-cleanup functionality
 ## for docker, as we're using the new buildkit cache instead.
-RUN --mount=type=cache,target=/var/cache/apt,sharing=locked             \
-    --mount=type=cache,target=/var/lib/apt/lists,sharing=locked         \
-    rm -f /etc/apt/apt.conf.d/docker-clean                              \
- && ln -fs /usr/share/zoneinfo/America/New_York /etc/localtime          \
- && echo "US/Eastern" > /etc/timezone                                   \
- && apt-get -yqq update                                                 \
- && apt-get -yqq install --no-install-recommends                        \
+RUN --mount=type=cache,target=/var/cache/apt,sharing=locked \
+    --mount=type=cache,target=/var/lib/apt/lists,sharing=locked <<EOF
+rm -f /etc/apt/apt.conf.d/docker-clean
+ln -fs /usr/share/zoneinfo/America/New_York /etc/localtime
+echo "US/Eastern" > /etc/timezone
+apt-get -yqq update
+apt-get -yqq install --no-install-recommends                            \
         bc                                                              \
         bzip2                                                           \
         ca-certificates                                                 \
@@ -54,49 +54,39 @@ RUN --mount=type=cache,target=/var/cache/apt,sharing=locked             \
         unzip                                                           \
         vim-nox                                                         \
         wget                                                            \
- && apt-get -yqq autoremove                                             \
- && localedef -i en_US -f UTF-8 en_US.UTF-8
+apt-get -yqq autoremove
+localedef -i en_US -f UTF-8 en_US.UTF-8
+EOF
 
 # Install updated compilers, with support for multiple base images
 ## Ubuntu: latest gcc from toolchain ppa, latest stable clang
 ## Debian: default gcc with distribution, latest stable clang
-RUN --mount=type=cache,target=/var/cache/apt,sharing=locked             \
-    --mount=type=cache,target=/var/lib/apt/lists,sharing=locked         \
-    . /etc/os-release                                                   \
- && mkdir -p /etc/apt/source.list.d                                     \
- && if [ "${ID}" = "ubuntu" ] ; then                                    \
-      echo "deb http://ppa.launchpad.net/ubuntu-toolchain-r/ppa/ubuntu/ \
-            ${VERSION_CODENAME} main"                                   \
-      > /etc/apt/source.list.d/ubuntu-toolchain.list                    \
-   && if [ "${VERSION_ID}" = "20.04" ] ; then GCC="-10" CLANG="-12" ; fi\
-   && if [ "${VERSION_ID}" = "22.04" ] ; then GCC="-12" CLANG="-14" ; fi\
-   && curl -s https://apt.llvm.org/llvm-snapshot.gpg.key | apt-key add -\
-   && echo "deb http://apt.llvm.org/${VERSION_CODENAME}                 \
-            llvm-toolchain-${VERSION_CODENAME}${CLANG} main"            \
-      > /etc/apt/source.list.d/llvm.list                                \
-   && apt-get -yqq update                                               \
-   && apt-get -yqq install                                              \
-          gcc${GCC} g++${GCC} gfortran${GCC}                            \
-   && apt-get -yqq install                                              \
-          clang${CLANG} clang-tidy${CLANG} clang-format${CLANG}         \
-          iwyu                                                          \
-   && update-alternatives --install /usr/bin/gcc gcc                    \
-                                    /usr/bin/gcc${GCC} 100              \
-   && update-alternatives --install /usr/bin/g++ g++                    \
-                                    /usr/bin/g++${GCC} 100              \
-   && update-alternatives --install /usr/bin/gfortran gfortran          \
-                                    /usr/bin/gfortran${GCC} 100         \
-   && update-alternatives --install /usr/bin/clang clang                \
-                                    /usr/bin/clang${CLANG} 100          \
-   && update-alternatives --install /usr/bin/clang++ clang++            \
-                                    /usr/bin/clang++${CLANG} 100        \
- ; else                                                                 \
-      apt-get -yqq update                                               \
-   && apt-get -yqq install                                              \
-          gcc g++ gfortran                                              \
-          clang clang-tidy clang-format                                 \
-          iwyu                                                          \
- ; fi                                                                   \
- && apt-get -yqq autoremove                                             \
- && gcc --version                                                       \
- && clang --version
+RUN --mount=type=cache,target=/var/cache/apt,sharing=locked \
+    --mount=type=cache,target=/var/lib/apt/lists,sharing=locked <<EOF
+. /etc/os-release
+mkdir -p /etc/apt/source.list.d
+if [ "${ID}" = "ubuntu" ] ; then
+  echo "deb http://ppa.launchpad.net/ubuntu-toolchain-r/ppa/ubuntu/${VERSION_CODENAME} main" > /etc/apt/source.list.d/ubuntu-toolchain.list
+  if [ "${VERSION_ID}" = "20.04" ] ; then GCC="-10" CLANG="-12" ; fi
+  if [ "${VERSION_ID}" = "22.04" ] ; then GCC="-12" CLANG="-14" ; fi
+  curl -s https://apt.llvm.org/llvm-snapshot.gpg.key | apt-key add -
+  echo "deb http://apt.llvm.org/${VERSION_CODENAME} llvm-toolchain-${VERSION_CODENAME}${CLANG} main" > /etc/apt/source.list.d/llvm.list
+  apt-get -yqq update
+  apt-get -yqq install gcc${GCC} g++${GCC} gfortran${GCC}
+  apt-get -yqq install clang${CLANG} clang-tidy${CLANG} clang-format${CLANG}
+  apt-get -yqq install iwyu
+  update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc${GCC} 100
+  update-alternatives --install /usr/bin/g++ g++ /usr/bin/g++${GCC} 100
+  update-alternatives --install /usr/bin/gfortran gfortran /usr/bin/gfortran${GCC} 100
+  update-alternatives --install /usr/bin/clang clang /usr/bin/clang${CLANG} 100
+  update-alternatives --install /usr/bin/clang++ clang++ /usr/bin/clang++${CLANG} 100
+else
+  apt-get -yqq update
+  apt-get -yqq install gcc g++ gfortran
+  apt-get -yqq install clang clang-tidy clang-format
+  apt-get -yqq install iwyu
+fi
+apt-get -yqq autoremove
+gcc --version
+clang --version
+EOF