argv-array: return the pushed string from argv_push*()

Such an API change allows us to use an argv_array this way:

    struct argv_array to_free = ARGV_ARRAY_INIT;
    const char *msg;

    if (some condition) {
            msg = "constant string message";
            ... other logic ...
    } else {
            msg = argv_array_pushf(&to_free, "format %s", var);
    }
    ... use "msg" ...
    ... do other things ...
    argv_array_clear(&to_free);

Note that argv_array_pushl() and argv_array_pushv() are used to push
one or more strings with a single call, so we do not return any one
of these strings from these two functions in order to reduce the
chance to misuse the API.

Signed-off-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: Martin Ågren <martin.agren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

argv-array.c

@@ -21,12 +21,13 @@ static void argv_array_push_nodup(struct argv_array *array, const char *value)
 	array->argv[array->argc] = NULL;
 }
 
-void argv_array_push(struct argv_array *array, const char *value)
+const char *argv_array_push(struct argv_array *array, const char *value)
 {
 	argv_array_push_nodup(array, xstrdup(value));
+	return array->argv[array->argc - 1];
 }
 
-void argv_array_pushf(struct argv_array *array, const char *fmt, ...)
+const char *argv_array_pushf(struct argv_array *array, const char *fmt, ...)
 {
 	va_list ap;
 	struct strbuf v = STRBUF_INIT;
@@ -36,6 +37,7 @@ void argv_array_pushf(struct argv_array *array, const char *fmt, ...)
 	va_end(ap);
 
 	argv_array_push_nodup(array, strbuf_detach(&v, NULL));
+	return array->argv[array->argc - 1];
 }
 
 void argv_array_pushl(struct argv_array *array, ...)

argv-array.h

@@ -12,9 +12,9 @@ struct argv_array {
 #define ARGV_ARRAY_INIT { empty_argv, 0, 0 }
 
 void argv_array_init(struct argv_array *);
-void argv_array_push(struct argv_array *, const char *);
+const char *argv_array_push(struct argv_array *, const char *);
 __attribute__((format (printf,2,3)))
-void argv_array_pushf(struct argv_array *, const char *fmt, ...);
+const char *argv_array_pushf(struct argv_array *, const char *fmt, ...);
 LAST_ARG_MUST_BE_NULL
 void argv_array_pushl(struct argv_array *, ...);
 void argv_array_pushv(struct argv_array *, const char **);