git-add -u paths... now works from subdirectory

git-add -u also takes the path limiters, but unlike the
command without the -u option, the code forgot that it
could be invoked from a subdirectory, and did not correctly
handle the prefix.

Signed-off-by: Salikh Zakirov <salikh@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin-add.c

diff --git a/builtin-add.c b/builtin-add.c
index a5fae7c..07e3ddf 100644
--- a/builtin-add.c
+++ b/builtin-add.c
@@ -123,12 +123,12 @@
 	}
 }
 
-static void update(int verbose, const char **files)
+static void update(int verbose, const char *prefix, const char **files)
 {
 	struct rev_info rev;
-	init_revisions(&rev, "");
+	init_revisions(&rev, prefix);
 	setup_revisions(0, NULL, &rev, NULL);
-	rev.prune_data = get_pathspec(rev.prefix, files);
+	rev.prune_data = get_pathspec(prefix, files);
 	rev.diffopt.output_format = DIFF_FORMAT_CALLBACK;
 	rev.diffopt.format_callback = update_callback;
 	rev.diffopt.format_callback_data = &verbose;
@@ -209,7 +209,7 @@
 	}
 
 	if (take_worktree_changes) {
-		update(verbose, argv + i);
+		update(verbose, prefix, argv + i);
 		goto finish;
 	}
 

t/t2200-add-update.sh

diff --git a/t/t2200-add-update.sh b/t/t2200-add-update.sh
index 4c7c6af..58cd7f3 100755
--- a/t/t2200-add-update.sh
+++ b/t/t2200-add-update.sh
@@ -62,4 +62,18 @@
 
 '
 
+test_expect_success 'update from a subdirectory' '
+	(
+		cd dir1 &&
+		echo more >sub2 &&
+		git add -u sub2
+	)
+'
+
+test_expect_success 'change gets noticed' '
+
+	test "$(git diff-files --name-status dir1)" = ""
+
+'
+
 test_done