parse-options-cb: implement parse_opt_passthru_argv()

Certain git commands, such as git-pull, are simply wrappers around other
git commands like git-fetch, git-merge and git-rebase. As such, these
wrapper commands will typically need to "pass through" command-line
options of the commands they wrap.

Implement the parse_opt_passthru_argv() parse-options callback, which
will reconstruct all the provided command-line options into an
argv_array, such that it can be passed to another git command. This is
useful for passing command-line options that can be specified multiple
times.

Helped-by: Stefan Beller <sbeller@google.com>
Signed-off-by: Paul Tan <pyokagan@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

parse-options-cb.c

@@ -4,6 +4,7 @@
 #include "commit.h"
 #include "color.h"
 #include "string-list.h"
+#include "argv-array.h"
 
 /*----- some often used options -----*/
 
@@ -183,3 +184,22 @@ int parse_opt_passthru(const struct option *opt, const char *arg, int unset)
 
 	return 0;
 }
+
+/**
+ * For an option opt, recreate the command-line option, appending it to
+ * opt->value which must be a argv_array. This is useful when we need to pass
+ * the command-line option, which can be specified multiple times, to another
+ * command.
+ */
+int parse_opt_passthru_argv(const struct option *opt, const char *arg, int unset)
+{
+	static struct strbuf sb = STRBUF_INIT;
+	struct argv_array *opt_value = opt->value;
+
+	if (recreate_opt(&sb, opt, arg, unset) < 0)
+		return -1;
+
+	argv_array_push(opt_value, sb.buf);
+
+	return 0;
+}