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AGENTS.md — Apache TVM FFI

What is this project?

TVM FFI is an open ABI and FFI (Foreign Function Interface) for machine learning systems. It provides a stable C ABI, C++17 API, Python bindings (via Cython), and Rust bindings. The core abstractions are type-erased values (Any/AnyView), reference-counted objects (Object/ObjectRef), and packed functions (Function).

Repository layout

include/tvm/ffi/    C++ public headers (core API)
src/ffi/            C++ implementation
python/tvm_ffi/     Python package (Cython bindings in cython/)
rust/               Rust crate workspace (tvm-ffi, tvm-ffi-sys, tvm-ffi-macros)
tests/cpp/          GoogleTest C++ tests
tests/python/       pytest Python tests
tests/lint/         Lint scripts (ASF header, file type, version check)
docs/               Sphinx documentation (RST + Markdown)
examples/           Runnable examples
cmake/Utils/        CMake utility modules
3rdparty/           Vendored deps (dlpack, libbacktrace)
addons/             Optional addons (torch_c_dlpack_ext)

Building

All Python commands use uv. The default virtualenv is .venv in the repo root.

Python editable install (primary workflow)

uv pip install --force-reinstall --verbose -e .

C++/Cython changes always require re-running this command. Pure Python changes are reflected immediately.

Update Python stubs

After building (or after C++/Cython reflection changes), regenerate inline type stubs:

uv run tvm-ffi-stubgen python

This updates inline stub blocks (between tvm-ffi-stubgen(begin) / tvm-ffi-stubgen(end) markers) inside .py files with type annotations derived from the C++ reflection registry (field types, method signatures, global function schemas).

C++-only build

cmake . -B build_cpp -DCMAKE_BUILD_TYPE=RelWithDebInfo
cmake --build build_cpp --parallel --config RelWithDebInfo --target tvm_ffi_shared

Prerequisites

  • Python 3.9+, C++17 compiler, CMake 3.26+, Ninja
  • Submodules: git submodule update --init --recursive

Testing

C++ tests

cmake . -B build_test -DTVM_FFI_BUILD_TESTS=ON -DCMAKE_BUILD_TYPE=Debug
cmake --build build_test --clean-first --config Debug --target tvm_ffi_tests
ctest -V -C Debug --test-dir build_test --output-on-failure

Python tests

uv pip install --force-reinstall --verbose --group test -e .
uv run pytest -vvs tests/python

Rust tests

cd rust && cargo test   # requires Python package installed first

Linting

Pre-commit (primary lint workflow)

pre-commit run --all-files     # all hooks
pre-commit run <hook-id> --all-files  # single hook (e.g. ruff-check, clang-format)

Key linters: ruff (Python), clang-format (C++, Google style, 100-col), cython-lint, cmake-format, shfmt/shellcheck, markdownlint-cli2.

clang-tidy (separate from pre-commit)

uv run --no-project --with "clang-tidy==21.1.1" \
  python tests/lint/clang_tidy_precommit.py \
    --build-dir=build-pre-commit \
    --jobs=$(sysctl -n hw.ncpu) \
    ./src/ ./include ./tests

Code conventions

C++

  • Source files: .cc (not .cpp). Headers: .h.
  • Style: Google (via clang-format), 100-col limit, pointer-left (int* ptr).
  • Namespaces: namespace tvm { namespace ffi { ... } } (no C++17 nested form).
  • Header guards: #ifndef TVM_FFI_<PATH>_H_.
  • Object pattern: FooObj (data) + Foo (ref wrapper extending ObjectRef).
    • TVM_FFI_DECLARE_OBJECT_INFO("key", FooObj, ParentObj) in the Obj class.
    • TVM_FFI_DEFINE_OBJECT_REF_METHODS(Foo, ParentRef, FooObj) in the Ref class.
  • Errors: TVM_FFI_THROW(ErrorType) << "message".
  • Doc comments: Doxygen (/*! \brief ... */).
  • Every file needs an Apache 2.0 license header.

Python

  • from __future__ import annotations at the top of every file.
  • Style: ruff (100-col, double quotes, Google docstrings).
  • Register objects: @register_object("type.Key").
  • Register functions: register_global_func("name", fn).

Commit messages

Tag-based style: [FEAT], [FIX], [ERROR], [TEST], [CORE], [EXTRA], etc. Conventional style (feat:, fix:, doc:) is also used. Include PR number.

Key architecture concepts

  • Any/AnyView: Type-erased value containers. AnyView is non-owning, Any owns.
  • Object system: Ref-counted heap objects. ObjectObj holds data, Object is the ref wrapper. Created via make_object<T>(args...).
  • Function: Type-erased callable with packed calling convention (const AnyView* args, int32_t num_args, Any* rv).
  • Global registry: Functions registered by string name, accessible cross-language via register_global_func/get_global_func.
  • Containers: Array<T> (immutable), List<T> (mutable), Map<K,V> (immutable), Dict (mutable), String, Tensor, Shape, Tuple, Variant<T...>.
  • Reflection: ObjectDef<T> builder with def_field/def_method. Exposed to Python as tvm_ffi.dataclasses.c_class.
  • Module system: load_module("path.so") wraps shared libraries, exposing functions via __tvm_ffi_<name> symbol prefix.

CI

Runs on: Linux x86_64 + aarch64, macOS arm64, Windows AMD64. Jobs: lint -> clang-tidy (if C++ changed) -> doc build -> test (C++, Python, Rust).

Further reading

The docs/ directory contains the full Sphinx documentation site, including:

  • docs/concepts/ — design docs (ABI overview, Any, Object/Class, Tensor, Function, etc.)
  • docs/guides/ — usage guides (exporting functions/classes, kernel libraries, C++/Python/Rust)
  • docs/get_started/ — quickstart and stable C ABI
  • docs/dev/ — developer instructions (source build, CI/CD, release process, doc build)
  • docs/packaging/ — Python packaging guide