Rethrow exceptions from destructors called by the GC in a fiber

[nicolas-grekas]

Found while working on #24117.

Since 8.4, when the GC is triggered inside a fiber, it calls destructors in a dedicated fiber. If one of them throws, the exception isn't rethrown into the frame that triggered the GC: the code after the triggering statement keeps running, and the exception then escapes the enclosing catch block.

class Cycle {
    public $self;
    public function __construct() { $this->self = $this; }
    public function __destruct() { throw new Exception('from __destruct'); }
}

$objects = [];
for ($i = 0; $i < 20000; $i++) { $objects[] = new stdClass(); }

function g() {
    global $objects;
    try {
        $copies = [...$objects];
        new Cycle();
        $copies = null; // fills the GC root buffer
        echo "after assign\n";
    } catch (Exception $e) {
        echo "caught in g()\n";
    }
}

(new Fiber(function () {
    try {
        g();
    } catch (Exception $e) {
        echo "escaped g()\n";
    }
}))->start();

8.3 prints caught in g(), 8.4 and up print after assign then escaped g().

zend_call_function() can't rethrow into that frame from the destructor fiber, so gc_call_destructors_in_fiber() now does it when no exception was pending before the GC run, like zend_fiber_object_destroy() does.

This conflicts with #24117 on the last lines of gc_call_destructors_in_fiber(): the EG(opline_before_exception) restore has to come before the rethrow, which destructors_013.phpt checks.

[arnaud-lb]

Thank you!