RID as default value are empty in extension_api.json

[touilleMan]

Godot version

4.0-rc13

System information

n/a

Issue description

RID as default value are not serialized properly, for instance PhysicsServer2D::joint_make_pin

{
	"name": "joint_make_pin",
        [...]
	"arguments": [
		{
			"name": "joint",
			"type": "RID"
		},
		{
			"name": "anchor",
			"type": "Vector2"
		},
		{
			"name": "body_a",
			"type": "RID"
		},
		{
			"name": "body_b",
			"type": "RID",
			"default_value": ""  # <== ?????
		}
	]
},

This is because Variant::get_construct_string is use for the serialization which doesn't support serialization of RID:

godot/core/extension/extension_api_dump.cpp

Line 528 in 7c7ce7d

d3["default_value"] = default_args[dargidx].get_construct_string();

Variant::get_construct_string doesn't support serialization of RID and default to an empty string:

godot/core/variant/variant_parser.cpp

Lines 1886 to 1887 in 7c7ce7d

	default: {
	}

The main issue

We represent the default value in ClassDB as an instance of RID which doesn't tell us we don't care about this instance (i.e. the default value is in fact "a new instance of RID is going to be created each time you call the function")

I think the easier solution would be to add a workaround in extension_api_dump.cpp (typically adding "RID()" as default_value if the argument type is RID and it has a default value set).

Of course this is not perfect given this way extension_api.json also don't provide the "this default value should be generated before each use". However we can fix this by adding a reusable_default_value boolean flag (that would only be true for RID).

Bonus issue

I'm not sure why Variant::get_construct_string doesn't serialize RID 🤔
It is also the case for Callable and Signal.

It means Dictionary/Array containing RID/Callable/Signal are not properly serialized as they will be displayed as [, , ,]

In the case this behavior is expected, shouldn't we add a warning when trying to serialize RID/Callable/Signal ?

Steps to reproduce

n/a

Minimal reproduction project

No response

[AThousandShips]

Got a PR open for this, due to default serialization indeed