Start toward moving the dense RUN to a commented script

Author: EliahKagan

etc/docker/customize-test-cross-image.sh

@@ -0,0 +1,112 @@
+#!/bin/bash
+set -euxC
+
+target="$1"
+
+# Arrange for the indirect `tzdata` dependency to be installed and configured
+# without prompting for the time zone. (Passing `-y` is not enough.)
+export DEBIAN_FRONTEND=noninteractive TZ=UTC
+
+# Install tools for setting up APT repositores. Install `apt-utils` before the
+# others, so the installation of `gnupg` can use it for debconf.
+apt-get update
+apt-get install --no-install-recommends -y apt-utils
+apt-get install --no-install-recommends -y apt-transport-https dpkg-dev gnupg
+type dpkg-architecture  # Make sure we really have this.
+
+# Decide what architecture to use for `git`, shared libraries for gitoxide when
+# attempting to build `max`, and shared libraries used by `git` itself.
+apt_suffix=
+if target_arch="$(dpkg-architecture --host-type "$target" --query DEB_HOST_ARCH)"; then
+    dpkg --add-architecture "$target_arch"
+    apt_suffix=":$target_arch"
+fi
+
+# Add the git-core PPA manually. (Faster than installing `add-apt-repository`.)
+release="$(sed -n 's/^VERSION_CODENAME=//p' /etc/os-release)"
+echo "deb https://ppa.launchpadcontent.net/git-core/ppa/ubuntu $release main" \
+    >/etc/apt/sources.list.d/git-core-ubuntu-ppa.list
+apt-key adv --keyserver keyserver.ubuntu.com \
+    --recv-keys F911AB184317630C59970973E363C90F8F1B6217
+apt-get update
+
+# Remove the old `git` and associated packages.
+apt-get purge --autoremove -y git
+
+# Git dependencies. These are for the desired architecture, except `git-man` is
+# the same package for all architectures, and we can't always install `perl` or
+# `liberror-perl` for the desired architecture (at least in s390x).
+# TODO(maint): Resolve these dynamically to support future `cross` base images.
+git_deps=(
+    git-man
+    "libc6$apt_suffix"
+    "libcurl3-gnutls$apt_suffix"
+    "libexpat1$apt_suffix"
+    liberror-perl
+    "libpcre2-8-0$apt_suffix"
+    "zlib1g$apt_suffix"
+    perl
+)
+
+# Other dependencies for running the gitoxide test suite and fixture scripts,
+# and for building and testing gitoxide for feature sets beyond `max-pure`.
+gix_test_deps=(
+    ca-certificates
+    cmake
+    "curl$apt_suffix"
+    jq
+    "libc-dev$apt_suffix"
+    "libssl-dev$apt_suffix"
+    patch
+    pkgconf
+)
+
+# Install everything we need except `git` (and what we already have). We can't
+# necessarily install `git` this way, because it insists on `perl` and
+# `liberror-perl` dependencies of the same architecture as it. These may not be
+# possible to install in a mixed environment, where most packages are a
+# different architecture, and where `perl` is a dependency of other important
+# packages. So we will install everything else first (then manually add `git`).
+apt-get install --no-install-recommends -y \
+    "${git_deps[@]}" "${gix_test_deps[@]}" file
+
+# Add `git` by manually downloading it and installing it with `dpkg`, forcing
+# installation to proceed even if its `perl` and `liberror-perl` dependencies,
+# as declared by `git`, are absent. (We have already installed them, but in a
+# possibly different architecture. `git` can still use them, because its use is
+# to run scripts, rather than to link to a shared library they provide.) It is
+# preferred to let `apt-get download` drop privileges to the `_apt` user during
+# download, so we download it inside `/tmp`. But we create a subdirectory so it
+# is safe to make assumptions about what files globs can expand to, even if
+# `/tmp` is mounted to an outside share temp dir on a multi-user system.
+mkdir /tmp/dl  # Don't use `-p`; if it exists already, we cannot trust it.
+chown _apt /tmp/dl  # Use owner, as the container may not have an `_apt` group.
+(cd /tmp/dl && apt-get download "git$apt_suffix")
+dpkg --ignore-depends="perl$apt_suffix,liberror-perl$apt_suffix" \
+    -i /tmp/dl/git[-_]*.deb
+
+# Show information about the newly installed `git` (and ensure it can run).
+git version --build-options
+git="$(command -v git)"
+file -- "$git"
+
+# Clean up files related to package management that we won't need anymore.
+apt-get clean
+rm -rf /tmp/dl /var/lib/apt/lists/*
+
+# If this is an Android-related image or otherwise has a runner script `cross`
+# uses for Android, then patch the script to add the ability to suppress its
+# customization of `LD_PRELOAD`. This runner script sets `LD_PRELOAD` to the
+# path of `libc++_shared.so` in the vendored Android NDK. But this causes a
+# problem for us because, when a non-Android (i.e. a host-architecture) program
+# is run, `ld.so` shows a message about the "wrong ELF class". Such programs
+# can still run, but when we make an assertion about, parse, or otherwise rely
+# on their output to standard error, we get test failures. (That especially
+# affects fixtures.) This change lets us pass `NO_PRELOAD_CXX=1` to avoid that.
+if test -f /android-runner; then
+    sed -i.orig 's/^export LD_PRELOAD=/test "${NO_PRELOAD_CXX:-0}" != 0 || &/'
+        /android-runner
+fi
+
+# Ensure a nonempty Git `system` scope (for the `installation_config` tests).
+git config --system gitoxide.imaginary.arbitraryVariable arbitraryValue