filter-branch: introduce convenience function "skip_commit"

With this function, a commit filter can leave out unwanted commits
(such as temporary commits).  It does _not_ undo the changeset
corresponding to that commit, but it _skips_ the revision.  IOW
no tree object is changed by this.

If you like to commit early and often, but want to filter out all
intermediate commits, marked by "@@@" in the commit message, you can
now do this with

	git filter-branch --commit-filter '
		if git cat-file commit $GIT_COMMIT | grep '@@@' > /dev/null;
		then
			skip_commit "$@";
		else
			git commit-tree "$@";
		fi' newbranch

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 14 insertions, 0 deletions

diff --git a/git-filter-branch.sh b/git-filter-branch.sh
index 3b041d81e..a4b6577bd 100755
--- a/git-filter-branch.sh
+++ b/git-filter-branch.sh
@@ -23,6 +23,20 @@ map()
 	fi
 }
 
+# if you run 'skip_commit "$@"' in a commit filter, it will print
+# the (mapped) parents, effectively skipping the commit.
+
+skip_commit()
+{
+	shift;
+	while [ -n "$1" ];
+	do
+		shift;
+		map "$1";
+		shift;
+	done;
+}
+
 # override die(): this version puts in an extra line break, so that
 # the progress is still visible