merge(3p/git): Merge git subtree at v2.29.2

This also bumps the stable nixpkgs to 20.09 as of 2020-11-21, because
there is some breakage in the git build related to the netrc
credentials helper which someone has taken care of in nixpkgs.

The stable channel is not used for anything other than git, so this
should be fine.

Change-Id: I3575a19dab09e1e9556cf8231d717de9890484fb

third_party/git/t/t4254-am-corrupt.sh

@@ -3,6 +3,37 @@
 test_description='git am with corrupt input'
 . ./test-lib.sh
 
+make_mbox_with_nul () {
+	space=' '
+	q_nul_in_subject=
+	q_nul_in_body=
+	while test $# -ne 0
+	do
+		case "$1" in
+		subject) q_nul_in_subject='=00' ;;
+		body)    q_nul_in_body='=00' ;;
+		esac &&
+		shift
+	done &&
+	cat <<-EOF
+	From ec7364544f690c560304f5a5de9428ea3b978b26 Mon Sep 17 00:00:00 2001
+	From: A U Thor <author@example.com>
+	Date: Sun, 19 Apr 2020 13:42:07 +0700
+	Subject: [PATCH] =?ISO-8859-1?q?=C4=CB${q_nul_in_subject}=D1=CF=D6?=
+	MIME-Version: 1.0
+	Content-Type: text/plain; charset=ISO-8859-1
+	Content-Transfer-Encoding: quoted-printable
+
+	abc${q_nul_in_body}def
+	---
+	diff --git a/afile b/afile
+	new file mode 100644
+	index 0000000000..e69de29bb2
+	--$space
+	2.26.1
+	EOF
+}
+
 test_expect_success setup '
 	# Note the missing "+++" line:
 	cat >bad-patch.diff <<-\EOF &&
@@ -25,13 +56,27 @@ test_expect_success setup '
 #   fatal: unable to write file '(null)' mode 100644: Bad address
 # Also, it had the unwanted side-effect of deleting f.
 test_expect_success 'try to apply corrupted patch' '
-	test_must_fail git -c advice.amWorkDir=false am bad-patch.diff 2>actual
-'
-
-test_expect_success 'compare diagnostic; ensure file is still here' '
+	test_when_finished "git am --abort" &&
+	test_must_fail git -c advice.amWorkDir=false am bad-patch.diff 2>actual &&
 	echo "error: git diff header lacks filename information (line 4)" >expected &&
 	test_path_is_file f &&
 	test_i18ncmp expected actual
 '
 
+test_expect_success "NUL in commit message's body" '
+	test_when_finished "git am --abort" &&
+	make_mbox_with_nul body >body.patch &&
+	test_must_fail git am body.patch 2>err &&
+	grep "a NUL byte in commit log message not allowed" err
+'
+
+test_expect_success "NUL in commit message's header" "
+	test_when_finished 'git am --abort' &&
+	make_mbox_with_nul subject >subject.patch &&
+	test_must_fail git mailinfo msg patch <subject.patch 2>err &&
+	grep \"a NUL byte in 'Subject' is not allowed\" err &&
+	test_must_fail git am subject.patch 2>err &&
+	grep \"a NUL byte in 'Subject' is not allowed\" err
+"
+
 test_done