Commit a0e46390 authored by Thomas Rast's avatar Thomas Rast Committed by Junio C Hamano

filter-branch: fix ref rewriting with --subdirectory-filter

The previous ancestor discovery 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' was
not moved up to A as intended, but left unrewritten because we asked
about 'git rev-list ^master topic', which does not return anything.

Instead, we use the straightforward

   git rev-list -1 $ref -- $filter_subdir

to find the right ancestor.  To justify this, note that the nearest
ancestor is unique: We use the output of

  git rev-list --parents -- $filter_subdir

to rewrite commits in the first pass, before any ref rewriting.  If B
is a non-merge commit, the only candidate is its parent.  If it is a
merge, there are two cases:

- All sides of the merge bring the same subdirectory contents.  Then
  rev-list already pruned away the merge in favour for just one of its
  parents, so there is only one candidate.

- Some merge sides, or the merge outcome, differ.  Then the merge is
  not pruned and can be rewritten directly.

So it is always safe to use rev-list -1.
Signed-off-by: default avatarThomas Rast <>
Signed-off-by: default avatarJunio C Hamano <>
parent 6e84b712
......@@ -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 the unique nearest
# ancestor that survived the pruning.
# NEEDSWORK: we should sort the unmapped refs topologically first
while read ref
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"
while read ref
map $p >> "$workdir"/../map/$sha1
done < "$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
# Finally update the refs
......@@ -101,7 +101,7 @@ test_expect_success 'filter subdirectory only' '
refs/heads/sub refs/heads/sub-earlier
test_expect_failure 'subdirectory filter result looks okay' '
test_expect_success 'subdirectory filter result looks okay' '
test 2 = $(git rev-list sub | wc -l) &&
git show sub:new &&
test_must_fail git show sub:subdir &&
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