vfs: disable `git update-git-for-windows`

If a user runs git update-git-for-windows, then they will upgrade to a
version that does not support microsoft/vfsforgit or microsoft/scalar.

Therefore, let's prevent this.

This addresses https://github.com/microsoft/git/issues/241

builtin.h

@@ -236,6 +236,7 @@ int cmd_tag(int argc, const char **argv, const char *prefix);
 int cmd_tar_tree(int argc, const char **argv, const char *prefix);
 int cmd_unpack_file(int argc, const char **argv, const char *prefix);
 int cmd_unpack_objects(int argc, const char **argv, const char *prefix);
+int cmd_update(int argc, const char **argv, const char *prefix);
 int cmd_update_index(int argc, const char **argv, const char *prefix);
 int cmd_update_ref(int argc, const char **argv, const char *prefix);
 int cmd_update_server_info(int argc, const char **argv, const char *prefix);

git.c

@@ -657,6 +657,8 @@ static struct cmd_struct commands[] = {
 	{ "tag", cmd_tag, RUN_SETUP | DELAY_PAGER_CONFIG },
 	{ "unpack-file", cmd_unpack_file, RUN_SETUP | NO_PARSEOPT },
 	{ "unpack-objects", cmd_unpack_objects, RUN_SETUP | NO_PARSEOPT },
+	{ "update", cmd_update },
+	{ "update-git-for-windows", cmd_update },
 	{ "update-index", cmd_update_index, RUN_SETUP },
 	{ "update-ref", cmd_update_ref, RUN_SETUP },
 	{ "update-server-info", cmd_update_server_info, RUN_SETUP },

help.c

@@ -794,3 +794,19 @@ NORETURN void help_unknown_ref(const char *ref, const char *cmd,
 	string_list_clear(&suggested_refs, 0);
 	exit(1);
 }
+
+int cmd_update(int argc, const char **argv, const char *prefix)
+{
+	const char * const usage[] = {
+		N_("git update-git-for-windows [<options>]\n"
+		   "\t(not supported in this build of Git for Windows)"),
+		NULL
+	};
+	struct option options[] = {
+		OPT_END()
+	};
+
+	argc = parse_options(argc, argv, prefix, options, usage, 0);
+
+	die(_("git %s is not supported in VFSforGit"), argv[0]);
+}

t/t0402-block-command-on-gvfs.sh

@@ -36,4 +36,11 @@ test_expect_success 'test gc --auto succeeds when disabled via config' '
 	git gc --auto
 '
 
+test_expect_success 'update-git-for-windows disabled' '
+	test_must_fail git update 2>out &&
+	test_i18ngrep VFS out &&
+	test_must_fail git update-git-for-windows 2>out &&
+	test_i18ngrep VFS out
+'
+
 test_done