This seems like a good thing to do. Would you mind learning how to make such a patch yourself? It's not particularly difficult and I'm happy to give you pointers.

yeah, I could learn how to do it

Okay, here are the pointers then:

At https://github.com/xdebug/xdebug/blob/master/xdebug.c#L109 you see a list with all of Xdebug's functions. The second argument is NULL instead of the "arginfo" that could be there.

arginfo structs are initialised with ZEND_BEGIN_ARG_INFO, or ZEND_BEGIN_ARG_INFO_EX.

This pull request (https://github.com/mgdm/Mosquitto-PHP/pull/3/files) adds for example ZEND_BEGIN_ARG_INFO structs to Mosquito. But it doesn't take into account the number of optional arguments. For that, you need the more complicated ZEND_BEGIN_ARG_INFO_EX.

The use of the more complicated ZEND_BEGIN_ARG_INFO_EX is seen in this Stack Overflow question: http://stackoverflow.com/questions/14635111/how-to-make-zend-begin-arg-info-ex-control-number-of-arguments-passed-to-a-php -- its answer also has a good overview of what it does (and doesn't).

But the SO question, uses "0, 0, " everywhere, where it really should use a constant for the first argument (as seen in the Mosquito PR's "ZEND_SEND_BY_VAL"), with the possibilities at http://lxr.php.net/xref/PHP-7.1/Zend/zend_compile.h#905; and the second argument is whether it returns a value or a reference (as denoted by the constants at http://lxr.php.net/xref/PHP-7.1/Zend/zend_compile.h#399).

The different items for each argument are defined at http://lxr.php.net/xref/PHP-7.1/Zend/zend_API.h#100 (ZEND_ARG_INFO etc.) With the pass_by_ref argument to this macro being either 0 or 1. (Always 0 in Xebug I think, as there is no pass_by_ref arguments).

Hope that helps :-)

I have assigned you too. Please read the contributing guidelines at https://xdebug.org/contributing.php

Thanks for volunteering :-)

In which branch should I do it ? xdebug_2_5 or master ?

Your call. 2.5 is for bug fixes... The question is whether this is a bug fix or feature. I've tentatively scheduled it for 2.6 (master) though.

For reference, PR is at https://github.com/xdebug/xdebug/pull/303

Thanks a lot Christophe! I have merged this now.