filter-branch: also don't fail in map() if a commit cannot be mapped

The map() function can be used by filters to map a commit id to its
rewritten id. Such a mapping may not exist, in which case the identity
mapping is used (the commit is returned unchanged).

In the rewrite loop, this mapping is also needed, but was done
explicitly in the same way. Use the map() function instead.

Signed-off-by: Johannes Sixt <johannes.sixt@telecom.at>
Acked-by: Johannes Schindelin <Johannes.Schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-filter-branch.sh

@@ -184,7 +184,8 @@ USAGE="git-filter-branch [-d TEMPDIR] [FILTERS] DESTBRANCH [REV-RANGE]"
 
 map()
 {
-	[ -r "$workdir/../map/$1" ] || return 1
+	# if it was not rewritten, take the original
+	test -r "$workdir/../map/$1" || echo "$1"
 	cat "$workdir/../map/$1"
 }
 
@@ -347,14 +348,9 @@ while read commit; do
 
 	parentstr=
 	for parent in $(get_parents $commit); do
-		if [ -r "../map/$parent" ]; then
-			for reparent in $(cat "../map/$parent"); do
-				parentstr="$parentstr -p $reparent"
-			done
-		else
-			# if it was not rewritten, take the original
-			parentstr="$parentstr -p $parent"
-		fi
+		for reparent in $(map "$parent"); do
+			parentstr="$parentstr -p $reparent"
+		done
 	done
 	if [ "$filter_parent" ]; then
 		parentstr="$(echo "$parentstr" | eval "$filter_parent")"