[PATCH v2] t/test-lib: make `test_dir_is_empty` more robust

[William Chargin <wchargin@gmail.com>]

While the `test_dir_is_empty` function appears correct in most normal
use cases, it can fail when filenames contain newlines. This patch
changes the implementation to use `ls -A`, which is specified by POSIX.
The output should be empty exactly if the directory is empty.

The newly added unit test fails before this change and passes after it.

Signed-off-by: William Chargin <wchargin@gmail.com>
---

I originally wrote this patch for the standalone Sharness library, but
that library advises that such patches be sent to the Git mailing list
first.

 t/t0000-basic.sh        | 29 +++++++++++++++++++++++++++++
 t/test-lib-functions.sh |  2 +-
 2 files changed, 30 insertions(+), 1 deletion(-)

diff --git a/t/t0000-basic.sh b/t/t0000-basic.sh
index 34859fe4a..3885b26f9 100755
--- a/t/t0000-basic.sh
+++ b/t/t0000-basic.sh
@@ -821,6 +821,35 @@ test_expect_success 'tests clean up even on failures' "
 	EOF
 "
 
+test_expect_success 'test_dir_is_empty behaves even in pathological cases' "
+	run_sub_test_lib_test \
+		dir-empty 'behavior of test_dir_is_empty' <<-\\EOF &&
+	test_expect_success 'should pass with actually empty directory' '
+		mkdir empty_dir &&
+		test_dir_is_empty empty_dir
+	'
+	test_expect_success 'should fail with a normal filename' '
+		mkdir nonempty_dir &&
+		touch nonempty_dir/some_file &&
+		test_must_fail test_dir_is_empty nonempty_dir
+	'
+	test_expect_success 'should fail with dot-newline-dot filename' '
+		mkdir pathological_dir &&
+		printf \"pathological_dir/.\\\\n.\\\\0\" | xargs -0 touch &&
+		test_must_fail test_dir_is_empty pathological_dir
+	'
+	test_done
+	EOF
+	check_sub_test_lib_test dir-empty <<-\\EOF
+	> ok 1 - should pass with actually empty directory
+	> ok 2 - should fail with a normal filename
+	> ok 3 - should fail with dot-newline-dot filename
+	> # passed all 3 test(s)
+	> 1..3
+	EOF
+"
+
+
 ################################################################
 # Basics of the basics
 
diff --git a/t/test-lib-functions.sh b/t/test-lib-functions.sh
index 2b2181dca..f7ff28ef6 100644
--- a/t/test-lib-functions.sh
+++ b/t/test-lib-functions.sh
@@ -568,7 +568,7 @@ test_path_is_dir () {
 # Check if the directory exists and is empty as expected, barf otherwise.
 test_dir_is_empty () {
 	test_path_is_dir "$1" &&
-	if test -n "$(ls -a1 "$1" | egrep -v '^\.\.?$')"
+	if test "$(ls -A1 "$1" | wc -c)" != 0
 	then
 		echo "Directory '$1' is not empty, it contains:"
 		ls -la "$1"
-- 
2.18.0.548.geb6c14151