makechrootpkg, arch-nspawn: Force-enable local '/repo/' repository

The change in arch-nspawn is subtle:

  This was the source of "infamous" "it fails every other time" bug that
  took me over a year to solve.  <https://labs.parabola.nu/issues/435>

  By having a repository of local packages (rather than simply running
  `pacman -U`), we are inviting pacman to cache them in
  `/var/cache/pacman/pkg`.  Besides being needless disk writes, this
  actually causes a real issue.  If the package gets rebuilt, pacman
  will balk, as the file no longer matches the cached signature.

  So, how do we prevent pacman from caching these local packages?
  Simple: include the directory they are already in in the
  pacman.conf:CacheDir list.  This will prevent pacman from copying
  the files to one of the other cache directories.

2 files changed, 14 insertions, 0 deletions

diff --git a/arch-nspawn.in b/arch-nspawn.in
index 028191b..c448056 100644
--- a/arch-nspawn.in
+++ b/arch-nspawn.in
@@ -105,6 +105,7 @@ elif [[ $(cat "$working_dir/.arch-chroot") != "$CHROOT_VERSION" ]]; then
 fi
 
 build_mount_args
+cache_dirs+=('/repo/')
 copy_hostconf
 
 eval "$(grep -a '^CARCH=' "$working_dir/etc/makepkg.conf")"
diff --git a/makechrootpkg.in b/makechrootpkg.in
index e9859e1..0c21ed5 100644
--- a/makechrootpkg.in
+++ b/makechrootpkg.in
@@ -201,6 +201,19 @@ builduser ALL = NOPASSWD: /usr/bin/pacman
 EOF
 	chmod 440 "$copydir/etc/sudoers.d/builduser-pacman"
 
+	if ! grep -q '^\[repo\]' "$copydir/etc/pacman.conf"; then
+		local line
+		line=$(grep -n '^\[' "$copydir/etc/pacman.conf" |grep -Fv ':[options]'|sed 's/:.*//;1q')
+		local ins='[repo]
+SigLevel = Optional TrustAll
+Server = file:///repo
+'
+		sed -i "${line}i${ins//$'\n'/\\n}" "$copydir/etc/pacman.conf"
+	fi
+	# Avoid having to use `pacman -Sy` to update [repo], as
+	# networking might be disabled inside of the chroot.
+	cp "$copydir/repo/repo.db" "$copydir/var/lib/pacman/sync/repo.db"
+
 	# This is a little gross, but this way the script is recreated every time in the
 	# working copy
 	{