filter-branch: subdirectory filter needs --full-history

When two branches are merged that modify a subdirectory (possibly in
different intermediate steps) such that both end up identical, then
rev-list chooses only one branch. But when we filter history, we want to
keep both branches. Therefore, we must use --full-history.

Signed-off-by: Johannes Sixt <johannes.sixt@telecom.at>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-filter-branch.sh

@@ -323,7 +323,7 @@ case "$filter_subdir" in
 	;;
 *)
 	git-rev-list --reverse --topo-order --default HEAD \
-		--parents "$@" -- "$filter_subdir"
+		--parents --full-history "$@" -- "$filter_subdir"
 esac > ../revs
 commits=$(cat ../revs | wc -l | tr -d " ")
 

t/t7003-filter-branch.sh

@@ -78,4 +78,25 @@ test_expect_success 'subdirectory filter result looks okay' '
 	! git show sub:subdir
 '
 
+test_expect_success 'setup and filter history that requires --full-history' '
+	git checkout master &&
+	mkdir subdir &&
+	echo A > subdir/new &&
+	git add subdir/new &&
+	test_tick &&
+	git commit -m "subdir on master" subdir/new &&
+	git rm a &&
+	test_tick &&
+	git commit -m "again subdir on master" &&
+	git merge branch &&
+	git-filter-branch --subdirectory-filter subdir sub-master
+'
+
+test_expect_success 'subdirectory filter result looks okay' '
+	test 3 = $(git-rev-list -1 --parents sub-master | wc -w) &&
+	git show sub-master^:new &&
+	git show sub-master^2:new &&
+	! git show sub:subdir
+'
+
 test_done