[PATCH v4] git: treat "-C <treat>" as a no-op when <path> is empty

[Karthik Nayak <karthik.188@gmail.com>]

'git -C ""' unhelpfully dies with error "Cannot change to ''",
whereas the shell treats `cd ""' as a no-op. Taking the shell's
behavior as a precedent, teach git to treat `-C ""' as a no-op, as
well.

Test to check the no-op behaviour of "-C <path>" when <path> is
empty, written by Junio C Hamano.

Helped-by: Junio C Hamano <gitster@pobox.com>
Helped-by: Eric Sunchine <sunshine@sunshineco.com>
Signed-off-by: Karthik Nayak <karthik.188@gmail.com>
---
 git.c            | 10 ++++++----
 t/t0056-git-C.sh | 10 ++++++++++
 2 files changed, 16 insertions(+), 4 deletions(-)

diff --git a/git.c b/git.c
index 8c7ee9c..b062e0e 100644
--- a/git.c
+++ b/git.c
@@ -204,10 +204,12 @@ static int handle_options(const char ***argv, int *argc, int *envchanged)
 				fprintf(stderr, "No directory given for -C.\n" );
 				usage(git_usage_string);
 			}
-			if (chdir((*argv)[1]))
-				die_errno("Cannot change to '%s'", (*argv)[1]);
-			if (envchanged)
-				*envchanged = 1;
+			if (*(*argv)[1]) {
+				if (chdir((*argv)[1]))
+					die_errno("Cannot change to '%s'", (*argv)[1]);
+				if (envchanged)
+					*envchanged = 1;
+			}
 			(*argv)++;
 			(*argc)--;
 		} else {
diff --git a/t/t0056-git-C.sh b/t/t0056-git-C.sh
index 99c0377..2630e75 100755
--- a/t/t0056-git-C.sh
+++ b/t/t0056-git-C.sh
@@ -14,6 +14,16 @@ test_expect_success '"git -C <path>" runs git from the directory <path>' '
 	test_cmp expected actual
 '
 
+test_expect_success '"git -C <path>" with an empty <path> is a no-op' '
+	(
+		mkdir -p dir1/subdir &&
+		cd dir1/subdir &&
+		git -C "" rev-parse --show-prefix >actual &&
+		echo subdir/ >expect &&
+		test_cmp expect actual
+	)
+'
+
 test_expect_success 'Multiple -C options: "-C dir1 -C dir2" is equivalent to "-C dir1/dir2"' '
 	test_create_repo dir1/dir2 &&
 	echo 1 >dir1/dir2/b.txt &&
-- 
2.3.1.167.g7f4ba4b.dirty