diffpkg: prefer to search inside the pool dir if available

On certain packaging machines where the pacman cache gets updated very
infrequently, the behavior of diffpkg may not function correctly as old
packages were to be downloaded as diff target. In such cases we look for
a pool directory first and search via a glob for an available pool
package sorted by version.

The pool search glob has three glob segments each disallowing the dash
delimiter to split across pkgrel, pkgver and arch. This will return the
correct package from the pool without considering overly eager wildcards
that potentially match different pkgnames.

The default pool search directory is /srv/ftp/pool

contrib/completion/zsh/_devtools.in

@@ -52,6 +52,7 @@ _diffpkg_args=(
 	'(-y --side-by-side)'{-y,--side-by-side}'[Output in two columns]'
 	'--color=[Color output]:when:($_colors[*])'
 	'(-W --width=)'{-W,--width=}'[Output at most NUM print columns]:num:(auto columns)'
+	'(-P --pool=)'{-P,--pool=}'[pool directory]:dir:_files -/'
 	'(-v --verbose)'{-v,--verbose}'[Provide more detailed/unfiltered output]'
 	'(-h --help)'{-h,--help}'[Display usage]'
 	'*:packages:_devtools_completions_all_packages'

doc/man/diffpkg.1.asciidoc

@@ -21,7 +21,7 @@ When given one package, use it to diff against the locally built one.
 When given two packages, diff both packages against each other.
 
 In either case, a package name will be converted to a filename from the
-cache, and diffpkg will proceed as though this filename was initially
+cache or pool, and diffpkg will proceed as though this filename was initially
 specified.
 
 Options
@@ -30,6 +30,10 @@ Options
 *-M, --makepkg-config*::
 	Set an alternate makepkg configuration file
 
+
+*-P, --pool*='DIR'::
+	Search diff target in pool dir (default `'/srv/ftp/pool'`)
+
 *-v, --verbose*::
 	Provide more detailed/unfiltered output
 

src/diffpkg.in

@@ -24,6 +24,7 @@ usage() {
 
 		OPTIONS
 		    -M, --makepkg-config Set an alternate makepkg configuration file
+		    -P, --pool=DIR       Search diff target in pool dir (default '/srv/ftp/pool')
 		    -v, --verbose        Provide more detailed/unfiltered output
 		    -h, --help           Show this help text
 
@@ -44,6 +45,8 @@ _EOF_
 }
 
 MAKEPKG_CONF=/etc/makepkg.conf
+POOLDIR=/srv/ftp/pool
+
 VERBOSE=0
 TARLIST=0
 DIFFOSCOPE=0
@@ -63,6 +66,7 @@ while (( $# )); do
 			exit 0
 			;;
 		-M|--makepkg-config)
+			(( $# <= 1 )) && die "missing argument for %s" "$1"
 			MAKEPKG_CONF="$2"
 			shift 2
 			;;
@@ -112,6 +116,15 @@ while (( $# )); do
 			DIFFWIDTH="$1"
 			shift
 			;;
+		-P|--pool)
+			(( $# <= 1 )) && die "missing argument for %s" "$1"
+			POOLDIR="$2"
+			shift 2
+			;;
+		--pool=*)
+			POOLDIR="${1#*=}"
+			shift
+			;;
 		--)
 			shift
 			break
@@ -248,8 +261,19 @@ fetch_pkg() {
 			pkg=$1 ;;
 	esac
 
-	[[ -n $pkgurl ]] || pkgurl=$(pacman -Spdd --print-format '%l' --noconfirm "$pkg") ||
-		die "Couldn't download previous package for %s." "$pkg"
+	if [[ -z ${pkgurl} ]]; then
+		# Try to find latest package in pool dir
+		if [[ -d ${POOLDIR} ]]; then
+			shopt -s extglob nullglob
+			pkgurl=$(printf "%s\n" "${POOLDIR}"/*/"${_pkgname}"-!(*-*)-!(*-*)-!(*-*).pkg.tar!(*.sig)|sort -Vr|head -1)
+			shopt -u extglob nullglob
+		fi
+		# Search via pacman database if no pool file exists
+		if [[ ! -f ${pkgurl} ]]; then
+			pkgurl=$(pacman -Spdd --print-format '%l' --noconfirm "$pkg") ||
+				die "Couldn't download previous package for %s." "$pkg"
+		fi
+	fi
 
 	pkg=${pkgurl##*/}
 	pkgdest=$(mktemp -t -d "${pkg}-XXXXXX")/${pkg}