Allow to get list of non objects (like String, Plane etc.) and its methods from GDScript

[qarmin]

Describe the project you are working on

Currently I'm working on Qarminer - automated tool(or maybe fuzzer is better name) to check every available functions with random parameters.

Describe the problem or limitation you are having in your project

Currently I don't see possibility to get from Godot list of all available classes which don't instance from Object like String, int, GDScript(global scope class) etc. and execute on them not known at compilation time functions.

Describe the feature / enhancement and how it helps to overcome the problem or limitation

1. Get list of functions of non objects like String
   If Godot will provide API to get list of such things, then I will be able to check every single class and its methods.
   This will allow to find some hidden bugs in engine.
   e.g.

ClassDB.get_non_object_methods_list(TYPE_STRING) # Should return method info just like get_methods_list()

2. Instance non object with default values
   Something like this:

ClassDB.instance_non_object(TYPE_VECTOR2)

should do same thing as

Vector2()

This is not so important since it can be easily implemented manually with match/if/else

3. Allow to execute on non object, not known at "compilation" time function
   For object I can use such code

get_random_object().call("show")

This will fail when object is type Timer and work properly when this will be Node2D
I cannot do this with e.g. Vector2

Vector2().call("size")

because they don't implement call function.
This will allow users to use exactly same code across different Godot version, without worrying about breaking changes
e.g.

var text : String = "allow"

if text.has_method("length"): # Godot 20 before breaking change
    print(text.call("length")
else: # Godot 21 after breaking change
    print(text.call("size"))

Example: https://github.com/qarmin/RegressionTestProject/blob/aa250456edea167c9f110cb85a2db2a4ddabbc47/Autoload/Autoload.gd#L27-L30

Describe how your proposal will work, with code, pseudo-code, mock-ups, and/or diagrams

I think that ClassDB.get_class_list() should return all available classes.

If this enhancement will not be used often, can it be worked around with a few lines of script?

I don't think it would be a frequently used feature, but it would make it possible to attach it to CI, where it would automatically respond to API changes.

Manually created project needs constant changes when someone add/remove/modify functions

Is there a reason why this should be core and not an add-on in the asset library?

Yes, this are API changes which must be done in core.

[qarmin]

Looks that Godot already have list of methods in Variant class
https://github.com/godotengine/godot/blob/1d14c22d5f9561d1c4757dc9a40b3e5c5bdb3b63/core/variant/variant_call.cpp#L628-L644