Quoting Richard Guenther <richard.guent...@gmail.com>:
(Btw, why does invoke_plugin_callbacks not return a value, that would make code way more readable than going through the passed by reference appearant return value ...)
Actually, I made it return a value that indicates if a callback took place. But apparently you want it to return the result of the callback itself. For that to make sense, the callbacks themselves would have to return values, and these would have to be somehow accumulated to an overall return value. So, either we'd have to change the interface that all existing plugins use, to give the callbacks a return value, or we'd have to have different variants of register_callback - or one that takes a union - or introduce not quite conformant function casts - to accommodate the different callback function types, and likewise something would have to be done on the invoke_plugin_callbacks side.
