credential: load default config

Make `git credential fill` honour the core.askPass variable.

Signed-off-by: Thomas Koutcher <thomas.koutcher@online.fr>
[jk: added test]
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/credential.c

@@ -1,6 +1,7 @@
 #include "git-compat-util.h"
 #include "credential.h"
 #include "builtin.h"
+#include "config.h"
 
 static const char usage_msg[] =
 	"git credential [fill|approve|reject]";
@@ -10,6 +11,8 @@ int cmd_credential(int argc, const char **argv, const char *prefix)
 	const char *op;
 	struct credential c = CREDENTIAL_INIT;
 
+	git_config(git_default_config, NULL);
+
 	if (argc != 2 || !strcmp(argv[1], "-h"))
 		usage(usage_msg);
 	op = argv[1];

t/t0300-credentials.sh

@@ -265,6 +265,32 @@ test_expect_success 'internal getpass does not ask for known username' '
 	EOF
 '
 
+test_expect_success 'git-credential respects core.askPass' '
+	write_script alternate-askpass <<-\EOF &&
+	echo >&2 "alternate askpass invoked"
+	echo alternate-value
+	EOF
+	test_config core.askpass "$PWD/alternate-askpass" &&
+	(
+		# unset GIT_ASKPASS set by lib-credential.sh which would
+		# override our config, but do so in a subshell so that we do
+		# not interfere with other tests
+		sane_unset GIT_ASKPASS &&
+		check fill <<-\EOF
+		protocol=http
+		host=example.com
+		--
+		protocol=http
+		host=example.com
+		username=alternate-value
+		password=alternate-value
+		--
+		alternate askpass invoked
+		alternate askpass invoked
+		EOF
+	)
+'
+
 HELPER="!f() {
 		cat >/dev/null
 		echo username=foo