Ability to convert native engine types to JSON and back.

[reduz]

Closes godotengine/godot-proposals#9510

TODO: Unit tests.

[akien-mga]

Pushed an update with some style nitpicks, but also flagging some bugs in the implementation based on a first code review. Diff of my update: akien-mga@d06f058

[akien-mga]

Depends on #85474.

[akien-mga]

Merged, so enabled this code.

[akien-mga]

You seem to have forgotten Color, I added this TODO.

[akien-mga]

Added the missing implementation.

[akien-mga]

Dictionary was there twice with the same code, seems like you forgot to edit it after copying to handle Array.

[akien-mga]

Fixed, Array doesn't use GDTYPE so it doesn't need to be handled here (it's handled below).
I added an error check in case this changes, but we could also just remove this branch.

[AThousandShips]

This looks very interesting, I'll test it out and go through the code this weekend hopefully

[akien-mga]

Did some testing locally with this project, which could be used as a base for further testing and unit tests:
testjson.zip

Some issues I noticed:

• As expected in Add support for all engine types in JSON encoding/decoding godot-proposals#9510 (comment), this doesn't guarantee proper conversion of int and float. Round float values are written without .0 and so Godot reads them as int. This is alleviated for typed properties, but for variants this is still an issue.

• Null objects are serialized as e.g.

"material": {
	"__gdtype": "Object"
},

but the to_native code will currently just throw an error in this case:

ERROR: Condition "!d.has("type")" is true. Returning: Variant()
   at: to_native (./core/io/json.cpp:1167)

It needs better handling of null Objects as a valid format.

• Array logic seems to crash, this in my test project causes a segfault:

@export var _array: Array = [42.0, 10, Vector2.AXIS_X

• If converting an object to JSON and back with objects and scripts allowed, and the script has a class name, converting to native causes an error:

Parser Error: Class "MyNode2D" hides a global script class.

• I'll admit this is arcane QA, but using PackedByteArray as key in a Dictionary doesn't seem to work:

@export var _packed_byte_array: PackedByteArray = PackedByteArray([10, 20, 30, 40])
@export var _dictionary: Dictionary = {_packed_byte_array: 1.0}

Output:

		"_dictionary": {
			"pairs": [
				{
					"key": {
						"values": [],
						"__gdtype": "PackedByteArray"
					},
					"value": 1
				}
			],
			"__gdtype": "Dictionary"
		},

The values are empty.

[reduz]

@akien-mga Ah thanks for the feedback and the fixes, I did not test the code much because I wanted to ask for implementation feedback first, then I was going to do the unit testing to ensure everything works properly.

[aaronp64]

Suggested change

	v.z = values[1];
	v.z = values[2];

[aaronp64]

Should arr be assigned to p_variant here? Same for the other packed array types

[AThousandShips]

Tested and works as expected, at a glance the code looks good too, with some cases pointed out above

[fire]

I support this pr enhancement. What is needed to get this mergable for a future release?

Reduz wrote unit tests, but traditionally that has not been a blocker.

Edited:

Did some thinking, if we know the types of the Variant, we can coherce the float into int and int into floats. The minimal epsilon between floats is small until we use the exponential scientific notation in floats to scale.

[AThousandShips]

I don't necessarily see anything that's needed save for the code errors that need resolving

[fire]

I did some review, the entire Variant section is failing to convert. I'll probably write some unit tests.

[AThousandShips]

I did some review, the entire Variant section is failing to convert

Probably the code errors reviewed above, try fixing those and see if it works then

[akien-mga]

Superseded by #92656.