Refactor: Handler instances self param

[thekid]

This pull request refactors the API to pass the value the method is invoked on as first argument to handlers' methods instead of filling in $this with it. This way, we're able to overcome the limitation of not being able to modify the value in PHP >= 5.6.0 (making the array_pop example work once again) and gets rid of segmentation faults when PHP relies on $this being an object.

Old

class ArrayHandler {
    public function pop() {
        return array_pop($this);
    }
}
$array= [1, 2, 3];
var_dump($array->pop()); // 3
var_dump($array);        // [1, 2, 3]

New

class ArrayHandler {
    public function pop(&$self) {
        return array_pop($self);
    }
}
$array= [1, 2, 3];
var_dump($array->pop()); // 3
var_dump($array);        // [1, 2]

[thekid]

Unfortunately, I can't find a working alternative for num_additional_args for PHP versions < 5.6.0. If I search for the ZEND_FCALL opcode and modify it like this:

 /* Find the fcall opcode, its extended_value holds the number of arguments */
{
    zend_op *execute_op = execute_data->opline;
    while (ZEND_DO_FCALL_BY_NAME != execute_op->opcode) {
        execute_op++;
    }
    execute_op->extended_value++;
}

It seems to work alright but then gives me a segfault after calling into the handler the second time around. The test "basic-repeated.phpt" added in thekid/scalar_objects@0add4c9730bf5a212d3612db2a35358d8be87605 shows this.

An option to solve this could be to remove PHP 5.4 and 5.5 support.

[nikic]

This doesn't really solve the issue with the by-ref modification - it is independent of how the method is called / the value passed. The issue is that in 5.6 it is no longer possible (as far as I could determine) to do a zval_ptr_ptr fetch on the object of a method call. We can fetch it for an IS_CV operand, but not for IS_VAR. The reason is that FETCH_DIM_R no longer does an AI_SET_PTR.

Just doing a SET_ISREF_P doesn't solve this - if the zval was shared this will make it a reference for everybody, not just this particular usage.

Moving to an argument does resolve the numerous issues that can arise from $this not being an object - however it isn't compatible with PHP<5.6 (and I'd say inherently so). I don't think it's really viable to only support PHP 5.6 (which isn't even released) here.

[nikic]

For PHP <5.6 we could go through an extra indirection: Instead of calling the method directly, we call an internal dummy function which then calls the actual method with an extra parameter.

This is similar to what PHP does for __callStatic, for example.

[nikic]

I've recently updated the ext to use a calling convention with an extra param. I ended up going with a VIA_HANDLER indirection function for all versions, because otherwise arginfo checks won't be correct (also there's a very unlikely, but possible, issue when the call happens exactly at a VM stack page boundary).

I've dropped support for by-reference fetching of the "object" for all versions. It turns out this didn't fully work even in PHP 5.4 and 5.5, see https://github.com/nikic/scalar_objects/issues/13#issuecomment-52553553.