difftool: handle unmerged files in dir-diff modeda/difftool

When files are unmerged they can show up as both unmerged and
modified in the output of `git diff --raw`.  This causes
difftool's dir-diff to create filesystem entries for the same
path twice, which fails when it encounters a duplicate path.

Ensure that each worktree path is only processed once.
Add a test to demonstrate the breakage.

Reported-by: Jan Smets <jan@smets.cx>
Signed-off-by: David Aguilar <davvid@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 23 insertions, 0 deletions

diff --git a/t/t7800-difftool.sh b/t/t7800-difftool.sh
index 4e713f7aa5..6a7207b950 100755
--- a/t/t7800-difftool.sh
+++ b/t/t7800-difftool.sh
@@ -419,6 +419,29 @@ run_dir_diff_test 'difftool --dir-diff when worktree file is missing' '
 	grep file2 output
 '
 
+run_dir_diff_test 'difftool --dir-diff with unmerged files' '
+	test_when_finished git reset --hard &&
+	test_config difftool.echo.cmd "echo ok" &&
+	git checkout -B conflict-a &&
+	git checkout -B conflict-b &&
+	git checkout conflict-a &&
+	echo a >>file &&
+	git add file &&
+	git commit -m conflict-a &&
+	git checkout conflict-b &&
+	echo b >>file &&
+	git add file &&
+	git commit -m conflict-b &&
+	git checkout master &&
+	git merge conflict-a &&
+	test_must_fail git merge conflict-b &&
+	cat >expect <<-EOF &&
+		ok
+	EOF
+	git difftool --dir-diff $symlinks -t echo >actual &&
+	test_cmp expect actual
+'
+
 write_script .git/CHECK_SYMLINKS <<\EOF
 for f in file file2 sub/sub
 do