Sorry for the mistake in the summary seems I could not change it myself but it is for xdebug.collect_params = 5 of course...

Could you please provide a reproducible script? I'm having trouble reproducing this myself.

well I'd believe that this simple script should already raise an issue:

<?php

function testClosureParamSerialization(callable $fn) {
$fn('hello');
}

testClosureParamSerialization(
function($a) {
echo $a;
}
);

I have just tried this with PHP 5.6.23, and I can not reproduce this. I get
a "N;" (base64 encoded); in the trace file. What does the following do for you:

php -n -dzend_extension=xdebug.so -dxdebug.auto_trace=1 -dxdebug.trace_format=0

do? Does that still crash? Can you try a later PHP 5.6.x version?

Hello,

I've been giving a quick try and I've to agree that simple script does not crash. I'm not sure how to reproduce it then as the original use case was very complex (a lot of code involved) and I just trusted the error reported as the root cause.

So I thought this script should do something already but it must be of higher complexity than that.

However is it normal to get a N; base64 encoded? I was somehow expecting the text return in collect_parameter=4 base64 encoded...

I guess it is somehow also related to the non serializability of the closure? Maybe with some more complex use case the test fail to see that one of the parameter include a closure and crash instead of putting N; instead?

I haven't had the time to reproduce this.

Hi, I've tried reproducing this again, but I am still not having success.
I'm afraid I will need a (short) and fully contained reproducible case that
I can run locally to investigate and fix this issue.

Can't reproduce this, and no feedback provided.