diff-no-index: DWIM "diff D F" into "diff D/F F"

"git diff --no-index" was supposed to be a poor-man's approach to
allow using Git diff goodies outside of a Git repository, without
having to patch mainstream diff implementations.

Unlike a POSIX diff that treats "diff D F" (or "diff F D") as a
request to compare D/F and F (or F and D/F) when D is a directory
and F is a file, however, we did not accept such a command line and
instead barfed with "file/directory conflict".

Imitate what POSIX diff does and append the basename of the file
after the name of the directory before comparing.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 22 insertions, 0 deletions

diff --git a/t/t4053-diff-no-index.sh b/t/t4053-diff-no-index.sh
index 2ab3c48734..01eca4c278 100755
--- a/t/t4053-diff-no-index.sh
+++ b/t/t4053-diff-no-index.sh
@@ -55,4 +55,26 @@ test_expect_success 'git diff --no-index executed outside repo gives correct err
 	)
 '
 
+test_expect_success 'diff D F and diff F D' '
+	(
+		cd repo &&
+		echo in-repo >a &&
+		echo non-repo >../non/git/a &&
+		mkdir sub &&
+		echo sub-repo >sub/a &&
+
+		test_must_fail git diff --no-index sub/a ../non/git/a >expect &&
+		test_must_fail git diff --no-index sub/a ../non/git/ >actual &&
+		test_cmp expect actual &&
+
+		test_must_fail git diff --no-index a ../non/git/a >expect &&
+		test_must_fail git diff --no-index a ../non/git/ >actual &&
+		test_cmp expect actual &&
+
+		test_must_fail git diff --no-index ../non/git/a a >expect &&
+		test_must_fail git diff --no-index ../non/git a >actual &&
+		test_cmp expect actual
+	)
+'
+
 test_done