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 check that the output of `ls -a` has at
most two lines (for `.` and `..`), which should be better behaved.

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

Signed-off-by: William Chargin <wchar...@gmail.com>
---
This patch depends on "t: factor out FUNNYNAMES as shared lazy prereq"
(2018-08-06), available from `wc/make-funnynames-shared-lazy-prereq`.
The code will work on master, but the test will not run due to a missing
prereq.

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        | 31 +++++++++++++++++++++++++++++++
 t/test-lib-functions.sh |  2 +-
 2 files changed, 32 insertions(+), 1 deletion(-)

diff --git a/t/t0000-basic.sh b/t/t0000-basic.sh
index 34859fe4a..60134d7ab 100755
--- a/t/t0000-basic.sh
+++ b/t/t0000-basic.sh
@@ -821,6 +821,37 @@ test_expect_success 'tests clean up even on failures' "
        EOF
 "
 
+test_expect_success FUNNYNAMES \
+       '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 &&
+               touch \"pathological_dir/.
+       .\" &&
+               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..f0241992b 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 -l)" -gt 2
        then
                echo "Directory '$1' is not empty, it contains:"
                ls -la "$1"
-- 
2.18.0.548.g101af7bd4

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