[PATCH] filter-branch: fix ancestor discovery for --subdirectory-filter

[Thomas Rast <trast@student.ethz.ch>]

The previous code failed on any refs that are (pre-rewrite) ancestors
of commits marked for rewriting.  This means that in a situation

   A -- B(topic) -- C(master)

where B is dropped by --subdirectory-filter pruning, the 'topic' is
not moved up to A as intended, but left unrewritten.

Fix this by using a more stupid approach: we let 'rev-list -1' figure
out a nearby ancestor, which handles the pruning automatically.

Signed-off-by: Thomas Rast <trast@student.ethz.ch>
---

I guarded it with a $filter_subdir check to not cause any unintended
harm.  It might be useful in some border cases of rev-list arguments
given to filter-branch too, but I can't figure out a safe way to
handle that.

Either way, this fixes the problem.

- Thomas

 git-filter-branch.sh |   27 +++++++++++----------------
 1 files changed, 11 insertions(+), 16 deletions(-)

diff --git a/git-filter-branch.sh b/git-filter-branch.sh
index a324cf0..7924aa1 100755
--- a/git-filter-branch.sh
+++ b/git-filter-branch.sh
@@ -317,24 +317,19 @@ done <../revs
 
 # In case of a subdirectory filter, it is possible that a specified head
 # is not in the set of rewritten commits, because it was pruned by the
-# revision walker.  Fix it by mapping these heads to the next rewritten
-# ancestor(s), i.e. the boundaries in the set of rewritten commits.
+# revision walker.  Fix it by mapping these heads to a (random!) nearby
+# ancestor that survived the pruning.
 
-# NEEDSWORK: we should sort the unmapped refs topologically first
-while read ref
-do
-	sha1=$(git rev-parse "$ref"^0)
-	test -f "$workdir"/../map/$sha1 && continue
-	# Assign the boundarie(s) in the set of rewritten commits
-	# as the replacement commit(s).
-	# (This would look a bit nicer if --not --stdin worked.)
-	for p in $( (cd "$workdir"/../map; ls | sed "s/^/^/") |
-		git rev-list $ref --boundary --stdin |
-		sed -n "s/^-//p")
+if test "$filter_subdir"
+then
+	while read ref
 	do
-		map $p >> "$workdir"/../map/$sha1
-	done
-done < "$tempdir"/heads
+		sha1=$(git rev-parse "$ref"^0)
+		test -f "$workdir"/../map/$sha1 && continue
+		ancestor=$(git rev-list -1 $ref -- "$filter_subdir")
+		test "$ancestor" && echo $(map $ancestor) >> "$workdir"/../map/$sha1
+	done < "$tempdir"/heads
+fi
 
 # Finally update the refs
 
-- 
1.6.0.rc2.22.g7d28.dirty