GH-12371: "internal error" in ReflectionParameter::getDefaultValue on Variable-length argument list

[nielsdos]

When you query if these are optional, they return true, but when you query the default value you get an exception. From the documentation of getDefaultValue() [1] we see that:

If the parameter is not optional a ReflectionException will be thrown.

So that seems to imply it should work with variadics.

The root cause is that we're only checking ZEND_RECV_INIT, and returning NULL in get_default_from_recv() when encountering ZEND_RECV_VARIADIC. Fix it by adding an is_variadic boolean that we can check. We'll also have to change zend_get_default_from_internal_arg_info() to fix the support for internal arguments.

[divinity76]

instead of

	if (!recv || recv->opcode != ZEND_RECV_INIT) {
		*is_variadic = recv && recv->opcode == ZEND_RECV_VARIADIC;
		return NULL;
	}

wouldn't it be better to just

	if (!recv || recv->opcode != ZEND_RECV_INIT) {
		if(recv && recv->opcode == ZEND_RECV_VARIADIC){
			return (whatever RT_CONSTANT(...) would return here when the default is an empty array);
                }
		return NULL;
	}

? then we wouldn't need the extra by-ref argument and no new logic for calling get_default_from_recv~
(* not sure exactly how to implement it, but shouldn't be too hard to figure out if we decide it's worthwhile~)

[iluuu1994]

I think this change makes sense and simplifies things, although I wonder whether that makes isDefaultValueAvailable() useless. Or are there still cases where isOptional returns something other than isDefaultValueAvailable? Nowadays default values are implicitly removed if the parameter is followed by a non-optional parameter (https://3v4l.org/CCXWB). Because of the existence of isDefaultValueAvailable(), I'm also not sure whether this is a bug-fix or an enhancement of the API.

[nielsdos]

I think this change makes sense and simplifies things, although I wonder whether that makes isDefaultValueAvailable() useless. Or are there still cases where isOptional returns something other than isDefaultValueAvailable?

I'm not sure. The expected semantics w.r.t. variadics are not defined in the manual.
If we we define the default value of an argument as "the value you write after the equals sign", then variadics don't have a default value but are still optional. That would however be contradictory with the manual: "If the parameter is not optional a ReflectionException will be thrown.".

I'm also not sure whether this is a bug-fix or an enhancement of the API.

In that case, it may be best to put this into master.