filter-branch: nearest-ancestor rewriting outside subdir filter

Since a0e4639 (filter-branch: fix ref rewriting with
--subdirectory-filter, 2008-08-12) git-filter-branch has done
nearest-ancestor rewriting when using a --subdirectory-filter.

However, that rewriting strategy is also a useful building block in
other tasks.  For example, if you want to split out a subset of files
from your history, you would typically call

  git filter-branch -- <refs> -- <files>

But this fails for all refs that do not point directly to a commit
that affects <files>, because their referenced commit will not be
rewritten and the ref remains untouched.

The code was already there for the --subdirectory-filter case, so just
introduce an option that enables it independently.

Signed-off-by: Thomas Rast <trast@student.ethz.ch>
Signed-off-by: Johannes Sixt <j6t@kdbg.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/Documentation/git-filter-branch.txt b/Documentation/git-filter-branch.txt
index 2b40babb6ba1c5eb99ae2cc7748854f5e4dcd864..394a77a35f2019f5c86f9e90e94b88cf56da04ae 100644 (file)
--- a/Documentation/git-filter-branch.txt
+++ b/Documentation/git-filter-branch.txt
@@ -159,7 +159,18 @@ to other tags will be rewritten to point to the underlying commit.
 --subdirectory-filter <directory>::
        Only look at the history which touches the given subdirectory.
        The result will contain that directory (and only that) as its
-       project root.
+       project root.  Implies --remap-to-ancestor.
+
+--remap-to-ancestor::
+       Rewrite refs to the nearest rewritten ancestor instead of
+       ignoring them.
++
+Normally, positive refs on the command line are only changed if the
+commit they point to was rewritten.  However, you can limit the extent
+of this rewriting by using linkgit:rev-list[1] arguments, e.g., path
+limiters.  Refs pointing to such excluded commits would then normally
+be ignored.  With this option, they are instead rewritten to point at
+the nearest ancestor that was not excluded.
 
 --prune-empty::
        Some kind of filters will generate empty commits, that left the tree

diff --git a/git-filter-branch.sh b/git-filter-branch.sh
index ed3db7d6e5785cfb2ea0fa504bca0d00541ce058..6b8b6a4f26a60c325a2c76e1d5b0e747b9d1d99b 100755 (executable)
--- a/git-filter-branch.sh
+++ b/git-filter-branch.sh
@@ -125,6 +125,7 @@ filter_subdir=
 orig_namespace=refs/original/
 force=
 prune_empty=
+remap_to_ancestor=
 while :
 do
        case "$1" in
@@ -137,6 +138,11 @@ do
                force=t
                continue
                ;;
+       --remap-to-ancestor)
+               shift
+               remap_to_ancestor=t
+               continue
+               ;;
        --prune-empty)
                shift
                prune_empty=t
@@ -182,6 +188,7 @@ do
                ;;
        --subdirectory-filter)
                filter_subdir="$OPTARG"
+               remap_to_ancestor=t
                ;;
        --original)
                orig_namespace=$(expr "$OPTARG/" : '\(.*[^/]\)/*$')/
@@ -354,12 +361,13 @@ while read commit parents; do
                        die "could not write rewritten commit"
 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 unique nearest
-# ancestor that survived the pruning.
+# If we are filtering for paths, as in the 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.
+# Ancestor remapping fixes this by mapping these heads to the unique
+# nearest ancestor that survived the pruning.
 
-if test "$filter_subdir"
+if test "$remap_to_ancestor" = t
 then
        while read ref
        do

diff --git a/t/t7003-filter-branch.sh b/t/t7003-filter-branch.sh
index 329c851685b1c663ee88d45a5d21d452a293fa8e..9503875e97e09ad94283e63ae298551453e5787a 100755 (executable)
--- a/t/t7003-filter-branch.sh
+++ b/t/t7003-filter-branch.sh
@@ -288,4 +288,22 @@ test_expect_success 'Prune empty commits' '
        test_cmp expect actual
 '
 
+test_expect_success '--remap-to-ancestor with filename filters' '
+       git checkout master &&
+       git reset --hard A &&
+       test_commit add-foo foo 1 &&
+       git branch moved-foo &&
+       test_commit add-bar bar a &&
+       git branch invariant &&
+       orig_invariant=$(git rev-parse invariant) &&
+       git branch moved-bar &&
+       test_commit change-foo foo 2 &&
+       git filter-branch -f --remap-to-ancestor \
+               moved-foo moved-bar A..master \
+               -- -- foo &&
+       test $(git rev-parse moved-foo) = $(git rev-parse moved-bar) &&
+       test $(git rev-parse moved-foo) = $(git rev-parse master^) &&
+       test $orig_invariant = $(git rev-parse invariant)
+'
+
 test_done