userdiff tests: list builtin drivers via test-tool

Change the userdiff test to list the builtin drivers via the
test-tool, using the new for_each_userdiff_driver() API function.

This gets rid of the need to modify this part of the test every time a
new pattern is added, see 2ff6c34612 (userdiff: support Bash,
2020-10-22) and 09dad9256a (userdiff: support Markdown, 2020-05-02)
for two recent examples.

I only need the "list-builtin-drivers "argument here, but let's add
"list-custom-drivers" and "list-drivers" too, just because it's easy.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 46 insertions, 0 deletions

diff --git a/t/helper/test-userdiff.c b/t/helper/test-userdiff.c
new file mode 100644
index 0000000000..f013f8a31e
--- /dev/null
+++ b/t/helper/test-userdiff.c
@@ -0,0 +1,46 @@
+#include "test-tool.h"
+#include "cache.h"
+#include "userdiff.h"
+#include "config.h"
+
+static int driver_cb(struct userdiff_driver *driver,
+		     enum userdiff_driver_type type, void *priv)
+{
+	enum userdiff_driver_type *want_type = priv;
+	if (type & *want_type && driver->funcname.pattern)
+		puts(driver->name);
+	return 0;
+}
+
+static int cmd__userdiff_config(const char *var, const char *value, void *cb)
+{
+	if (userdiff_config(var, value) < 0)
+		return -1;
+	return 0;
+}
+
+int cmd__userdiff(int argc, const char **argv)
+{
+	enum userdiff_driver_type want = 0;
+	if (argc != 2)
+		return 1;
+
+	if (!strcmp(argv[1], "list-drivers"))
+		want = (USERDIFF_DRIVER_TYPE_BUILTIN |
+			USERDIFF_DRIVER_TYPE_CUSTOM);
+	else if (!strcmp(argv[1], "list-builtin-drivers"))
+		want = USERDIFF_DRIVER_TYPE_BUILTIN;
+	else if (!strcmp(argv[1], "list-custom-drivers"))
+		want = USERDIFF_DRIVER_TYPE_CUSTOM;
+	else
+		return error("unknown argument %s", argv[1]);
+
+	if (want & USERDIFF_DRIVER_TYPE_CUSTOM) {
+		setup_git_directory();
+		git_config(cmd__userdiff_config, NULL);
+	}
+
+	for_each_userdiff_driver(driver_cb, &want);
+
+	return 0;
+}