Improve `makecontainerpkg`

* Parse `pkgname` from `PKGBUILD` via sourcing to cope with variables
* Allow overriding the container name to be able to re-use an existing
  container
* Be verbose when installing packages during the image creation

devel/container/base-devel/Dockerfile

@@ -8,7 +8,7 @@ RUN mkdir -p /startdir /build && \
     pacman-key --recv-keys B9E36A7275FC61B464B67907E06FE8F53CDC6A4C && \
     pacman-key --finger    B9E36A7275FC61B464B67907E06FE8F53CDC6A4C && \
     pacman-key --lsign-key B9E36A7275FC61B464B67907E06FE8F53CDC6A4C && \
-    pacman -Syu --noconfirm --needed base-devel pacman-contrib ccache && \
+    pacman -Syu --verbose --noconfirm --needed base-devel pacman-contrib ccache && \
     pacman -Scc --noconfirm && \
     paccache -r -k0 && \
     rm -rf /usr/share/man/* /tmp/* /var/tmp/*

devel/container/makecontainerpkg

@@ -2,9 +2,18 @@
 set -e
 
 # make basic arguments for cre
-pkgname=$(grep -oP '(?<=pkgname=).+(?=$)' PKGBUILD | tr '+' 'p')
-uuid=$(cat /proc/sys/kernel/random/uuid)
-name=makechrootpkg-$pkgname-$uuid
+if [[ $CONTAINER ]]; then
+    name=$CONTAINER
+else
+    if [[ $PKGNAME ]]; then
+        pkgname=$PKGNAME
+    else
+        source PKGBUILD
+        pkgname=$(echo "$pkgname" | tr '+' 'p')
+    fi
+    uuid=$(cat /proc/sys/kernel/random/uuid)
+    name=makechrootpkg-$pkgname-$uuid
+fi
 cre_args=(--name "$name" --workdir "/startdir" -v "$PWD":/startdir -it)
 
 # parse arguments
@@ -33,8 +42,10 @@ fi
 
 # invoke containerized build
 ec=0 cre=${CRE:-docker}
-"$cre" container create "${cre_args[@]}" "${CRE_IMAGE:-archlinux-base-devel}"
-"$cre" container start "$name"
+if ! [[ $CONTAINER ]]; then
+    "$cre" container create "${cre_args[@]}" "${CRE_IMAGE:-archlinux-base-devel}"
+    "$cre" container start "$name"
+fi
 "$cre" container exec "$name" bash \
     -c "$script_sync $script $script_args" || ec=$?
 
@@ -46,6 +57,8 @@ ec=0 cre=${CRE:-docker}
 [[ $ec != 0 ]] && [[ $DEBUG ]] && echo \
     "You may investigate the failure via:
     $cre exec -it '$name' bash
-    $cre mount '$name'"
+    $cre mount '$name'
+You may retry the build using the same container again via:
+    CONTAINER='$name' DEBUG='$DEBUG' $0 $@"
 
 exit $ec