format.attach: allow empty value to disable multi-part messages

When a lower precedence configuration file (e.g. /etc/gitconfig)
defines format.attach in any way, there was no way to disable it in
a more specific configuration file (e.g. $HOME/.gitconfig).

Change the behaviour of setting it to an empty string.  It used to
mean that the result is still a multipart message with only dashes
used as a multi-part separator, but now it resets the setting to
the default (which would be to give an inline patch, unless other
command line options are in effect).

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

1 files changed, 18 insertions, 0 deletions

diff --git a/t/t4014-format-patch.sh b/t/t4014-format-patch.sh
index 012f155e10..f3313b8c58 100755
--- a/t/t4014-format-patch.sh
+++ b/t/t4014-format-patch.sh
@@ -2281,6 +2281,24 @@ test_expect_success 'format-patch --attach cover-letter only is non-multipart' '
 	test_line_count = 1 output
 '
 
+test_expect_success 'format-patch with format.attach' '
+	test_when_finished "rm -fr patches" &&
+	separator=attachment-separator &&
+	test_config format.attach "$separator" &&
+	filename=$(git format-patch -o patches -1) &&
+	grep "^Content-Type: multipart/.*$separator" "$filename"
+'
+
+test_expect_success 'format-patch with format.attach=disabled' '
+	test_when_finished "rm -fr patches" &&
+	separator=attachment-separator &&
+	test_config_global format.attach "$separator" &&
+	test_config format.attach "" &&
+	filename=$(git format-patch -o patches -1) &&
+	# The output should not even declare content type for text/plain.
+	! grep "^Content-Type: multipart/" "$filename"
+'
+
 test_expect_success '-c format.mboxrd format-patch' '
 	sp=" " &&
 	cat >msg <<-INPUT_END &&