credential-cache: new option to ignore sighup

Introduce new option "credentialCache.ignoreSIGHUP" which stops
git-credential-cache--daemon from quitting on SIGHUP.  This is useful
when "git push" is started from Emacs, because all child
processes (including the daemon) will receive a SIGHUP when "git push"
exits.

Signed-off-by: Noam Postavsky <npostavs@users.sourceforge.net>
Signed-off-by: Jeff King <peff@peff.net>

Documentation/config.txt

@@ -1122,6 +1122,9 @@ credential.<url>.*::
 	example.com. See linkgit:gitcredentials[7] for details on how URLs are
 	matched.
 
+credentialCache.ignoreSIGHUP::
+	Tell git-credential-cache--daemon to ignore SIGHUP, instead of quitting.
+
 include::diff-config.txt[]
 
 difftool.<tool>.path::

credential-cache--daemon.c

@@ -244,6 +244,7 @@ static void check_socket_directory(const char *path)
 int main(int argc, const char **argv)
 {
 	const char *socket_path;
+	int ignore_sighup = 0;
 	static const char *usage[] = {
 		"git-credential-cache--daemon [opts] <socket_path>",
 		NULL
@@ -255,6 +256,8 @@ int main(int argc, const char **argv)
 		OPT_END()
 	};
 
+	git_config_get_bool("credentialcache.ignoresighup", &ignore_sighup);
+
 	argc = parse_options(argc, argv, NULL, options, usage, 0);
 	socket_path = argv[0];
 
@@ -263,6 +266,10 @@ int main(int argc, const char **argv)
 
 	check_socket_directory(socket_path);
 	register_tempfile(&socket_file, socket_path);
+
+	if (ignore_sighup)
+		signal(SIGHUP, SIG_IGN);
+
 	serve_cache(socket_path, debug);
 	delete_tempfile(&socket_file);