I am not sure how this creates "infinite recursion", but I can reproduce your
output. I will need to investigate this.

No, I thoughtlessly copied the title of the issue, that I also referenced in the title - but too late I remembered to change it.
Sorry about that :)

Just tried reproducing it again in PHP 7.0.6 and XDebug 2.5.0-dev - still an issue.

13:43 $ php -dxdebug.auto_trace=1 -dxdebug.collect_params=3 -r 'class Foo extends IteratorIterator{function construct($items){if(is_array($items)){$items=new ArrayIterator($items);}}function __debugInfo(){return ["count"=>iterator_count($this)];}};$a=new Foo([1,2,3]);var_dump($a);'
PHP Warning: Uncaught LogicException: The object is in an invalid state as the parent constructor was not called in Command line code:1
Stack trace:
#0 [internal function]: IteratorIterator->rewind()
#1 Command line code(1): iterator_count(Object(Foo))
0000002 [internal function]: Foo->debugInfo()
0000003 Command line code(1): var_dump(Object(Foo))
0000004 {main}
thrown in Command line code on line 1
PHP Stack trace:
PHP 1. {main}() Command line code:0
PHP 2. var_dump(class Foo { }) Command line code:1

Warning: Uncaught LogicException: The object is in an invalid state as the parent constructor was not called in Command line code:1
Stack trace:
#0 [internal function]: IteratorIterator->rewind()
#1 Command line code(1): iterator_count(Object(Foo))
0000002 [internal function]: Foo->__debugInfo()
0000003 Command line code(1): var_dump(Object(Foo))
0000004 {main}
thrown in Command line code on line 1

Call Stack:
0.0010 350840 1. {main}() Command line code:0
0.0032 351032 2. var_dump(class Foo { }) Command line code:1

PHP Fatal error: __debuginfo() must return an array in Command line code on line 1
PHP Stack trace:
PHP 1. {main}() Command line code:0
PHP 2. var_dump(class Foo { }) Command line code:1

Fatal error: __debuginfo() must return an array in Command line code on line 1

Call Stack:
0.0010 350840 1. {main}() Command line code:0
0.0032 351032 2. var_dump(class Foo { }) Command line code:1

I can reproduce this issue still with PHP 7.0.13 and Xdebug 2.5.0RC2-dev.

I tried this again, this time without Xdebug loaded (see the -n), and the result is exactly the same:

derick@whisky:~/dev/php/derickr-xdebug $ cat tests/bug01296.phpt
--TEST--
Test for bug 0001296: Using $this in debugInfo() causes issues
--FILE--
<?php
class Foo extends IteratorIterator
{
function construct( $items )
{
if ( is_array( $items ) )
{
$items = new ArrayIterator( $items );
}
}

function __debugInfo()
{
    return [ "count" => iterator_count( $this ) ];
}

}

$a = new Foo( [ 1, 2, 3] );
var_dump( $a );
[GIT: issue1296-debuginfo][PHP: 7.0.13-dev ]
derick@whisky:~/dev/php/derickr-xdebug $ php -n tests/bug01296.phpt
--TEST--
Test for bug 0001296: Using $this in __debugInfo() causes issues
--FILE--

Warning: Uncaught LogicException: The object is in an invalid state as the parent constructor was not called in /home/derick/dev/php/derickr-xdebug/tests/bug01296.phpt:17
Stack trace:
#0 [internal function]: IteratorIterator->rewind()
#1 /home/derick/dev/php/derickr-xdebug/tests/bug01296.phpt(17): iterator_count(Object(Foo))
0000002 [internal function]: Foo->__debugInfo()
0000003 /home/derick/dev/php/derickr-xdebug/tests/bug01296.phpt(22): var_dump(Object(Foo))
0000004 {main}
thrown in /home/derick/dev/php/derickr-xdebug/tests/bug01296.phpt on line 17

Fatal error: __debuginfo() must return an array in /home/derick/dev/php/derickr-xdebug/tests/bug01296.phpt on line 22

So I fail to see why this is an Xdebug issue. Can you clarify please?

Ping?

Closing this as no additional feedback was provided, and the behaviour was the same without Xdebug loaded.