SCRIPTS: teach git-show-backports how to report upstream commits

When git-show-backports is called with -u, instead of reporting the
commit IDs of the original branch on the left, it will display the
upstream commit IDs when such IDs are known, and will also display
them in the suggested "git cherry-pick" command line. This is useful
when the new branch is more recent than the one being checked and/or
it is desired to get rid of intermediary changes.

scripts/git-show-backports

@@ -28,7 +28,7 @@
 #   show-backports -q -m -r hapee-r2 hapee-r1
 
 
-USAGE="Usage: ${0##*/} [-q] [-m] [-r reference] [-l logexpr] [-s subject] [-b base] branch [...]"
+USAGE="Usage: ${0##*/} [-q] [-m] [-u] [-r reference] [-l logexpr] [-s subject] [-b base] branch [...]"
 BRANCHES=( )
 REF=master
 BASE=
@@ -36,6 +36,7 @@ QUIET=
 LOGEXPR=
 SUBJECT=
 MISSING=
+UPSTREAM=
 
 die() {
 	[ "$#" -eq 0 ] || echo "$*" >&2
@@ -73,7 +74,7 @@ dump_commit_matrix() {
 
 		upstream="none"
 		missing=0
-		line="$(short $ref)"
+		line=""
 		for branch in "${BRANCHES[@]}"; do
 			set -- $(grep -m 1 $ref "$WORK/${branch//\//_}")
 			newhash=$1 ; shift
@@ -116,7 +117,11 @@ dump_commit_matrix() {
 		if [ -z "$MISSING" -o $missing -gt 0 ]; then
 			[ $((count++)) -gt 0 ] || echo $title
 			[ "$QUIET" != "" -o $count -lt 20 ] || count=0
-			echo "$line"
+			if [ -z "$UPSTREAM" -o "$upstream" = "none" -o -z "$upstream" ]; then
+				echo "$(short $ref) $line"
+			else
+				echo "$(short $upstream) $line"
+			fi
 		fi
 	done < "$WORK/${REF//\//_}"
 }
@@ -129,6 +134,7 @@ while [ -n "$1" -a -z "${1##-*}" ]; do
 		-s)        SUBJECT="$2"   ; shift 2 ;;
 		-q)        QUIET=1        ; shift   ;;
 		-m)        MISSING=1      ; shift   ;;
+		-u)        UPSTREAM=1     ; shift   ;;
 		-h|--help) quit "$USAGE" ;;
 		*)         die  "$USAGE" ;;
 	esac