feat: Introduce Experimental tvm_ffi.dataclasses.c_class

[junrushao]

Depends on #32.

This PR introduces an experimental @c_class decorator that enables Python dataclass-like syntax for exposing C++ objects through TVM FFI. The decorator automatically handles field reflection, inheritance, and constructor generation for FFI-backed classes.

Example

On C++ side, register types using tvm::ffi::reflection::ObjectDef<>:

TVM_FFI_STATIC_INIT_BLOCK() {
    namespace refl = tvm::ffi::reflection;
    refl::ObjectDef<MyClass>()
        .def_static("__init__", [](int64_t v_i64, int32_t v_i32, double v_f64, float v_f32) -> Any {
            return ObjectRef(ffi::make_object<MyClass>(v_i64, v_i32, v_f64, v_f32));
        })
        .def_rw("v_i64", &MyClass::v_i64)
        .def_rw("v_i32", &MyClass::v_i32)
        .def_rw("v_f64", &MyClass::v_f64)
        .def_rw("v_f32", &MyClass::v_f32);
}

Mirror the same structure in Python using dataclass-style annotations:

from tvm_ffi.dataclasses import c_class, field

@c_class("example.MyClass")
class MyClass:
    v_i64: int
    v_i32: int
    v_f64: float = field(default=0.0)
    v_f32: float = field(default_factory=lambda: 1.0)

obj = MyClass(v_i64=4, v_i32=8)
obj.v_f64 = 3.14  # transparently forwards to the underlying C++ object

Future work

Supporting as many dataclass features as possible, including: repr, init, order, etc.

[junrushao]

@tqchen This PR is finally ready for review!

[Copilot]

Pull Request Overview

This PR introduces an experimental c_class decorator that enables Python dataclass-like syntax for exposing C++ objects through TVM FFI. The decorator automatically handles field reflection, inheritance, and constructor generation for FFI-backed classes.

• Adds c_class decorator for creating dataclass-style FFI bindings
• Implements field introspection and default value handling
• Provides inheritance support for FFI classes

Reviewed Changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
python/tvm_ffi/dataclasses/init.py	Package initialization exporting the new dataclass functionality
python/tvm_ffi/dataclasses/c_class.py	Core c_class decorator implementation with field reflection
python/tvm_ffi/dataclasses/field.py	Field specification utilities similar to dataclasses.field
python/tvm_ffi/dataclasses/_utils.py	Utility functions for class construction and method generation
python/tvm_ffi/core.pyi	Type stub updates for the new dataclass_field attribute
python/tvm_ffi/cython/type_info.pxi	Addition of dataclass_field to TypeField class
python/tvm_ffi/testing.py	Example usage with test classes demonstrating inheritance
src/ffi/extra/testing.cc	C++ test classes for validating the FFI dataclass functionality
tests/python/test_dataclasses_c_class.py	Comprehensive tests for the new c_class decorator

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[tqchen]

I think we only need to put experimental at the docstring for dataclasses __init__.py

[junrushao]

It doesn’t hurt :))

[junrushao]

@tqchen Rebased against the latest main. Could you re-review? Thanks!!