[PATCH/RFC] filter-branch: support skipping of commits more easily

[Johannes Schindelin <Johannes.Schindelin@gmx.de>]

When commit-filter echoes just "skip", just skip that commit by mapping 
its object name to the same (possibly rewritten) object name(s) its 
parent(s) are mapped to.

IOW, given A-B-C, if commit-filter says "skip" upon B, the rewritten 
branch will look like this: A'-C'.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
---

	Of course, if you think of "patchsets", this behaviour might
	be unexpected, since the children will still contain everything
	which was changed in the skipped revisions, and not changed in
	_them_.

 git-filter-branch.sh |   15 ++++++++++++---
 1 files changed, 12 insertions(+), 3 deletions(-)

diff --git a/git-filter-branch.sh b/git-filter-branch.sh
index 9d61b7f..e6ed7b9 100755
--- a/git-filter-branch.sh
+++ b/git-filter-branch.sh
@@ -102,6 +102,9 @@
 #	multiple commit ids; in that case, all of them will be used
 #	as parents instead of the original commit in further commits.
 #
+#	For the common case, that this commit should be skipped, just
+#	output a single "skip".
+#
 # --tag-name-filter COMMAND:: The filter for rewriting tag names.
 #	If this filter is passed, it will be called for every tag ref
 #	that points to a rewritten object (or to a tag object which
@@ -321,7 +324,7 @@ test $commits -eq 0 && die "Found nothing to rewrite"
 i=0
 while read commit; do
 	i=$(($i+1))
-	printf "$commit ($i/$commits) "
+	printf "\rRewriting commits... ($i/$commits)"
 
 	git-read-tree -i -m $commit
 
@@ -358,8 +361,14 @@ while read commit; do
 
 	sed -e '1,/^$/d' <../commit | \
 		eval "$filter_msg" | \
-		sh -c "$filter_commit" git-commit-tree $(git-write-tree) $parentstr | \
-		tee ../map/$commit
+		sh -c "$filter_commit" \
+			git-commit-tree $(git-write-tree) $parentstr \
+		> ../map/$commit
+
+	test skip = "$(cat ../map/$commit)" &&
+		for parent in $(get_parents $commit); do
+			map "$parent"
+		done > ../map/$commit
 done <../revs
 
 src_head=$(tail -n 1 ../revs)
-- 
1.5.2.1.2689.gaf768-dirty