Add working ONNX 1.15 recipe

[metalmancode]

Summary

Add an experimental ONNX 1.15.0 recipe with a reproducible, working WebAssembly build.

Closes #216 with a version set that has been built from the recipe, structurally verified, and exercised through a full browser conversion path.

Cross-compilation fixes

• use a host-native protoc 22.3 while compiling the Protobuf runtime for WebAssembly;
• pass the target Python include directories from PYTHONINCLUDE to CMake;
• remove the ELF-only --exclude-libs linker option unsupported by wasm-ld; and
• disable Protobuf thread-safety for the standard single-threaded side-module build.

The host protoc archive is pinned by SHA-256.

Validation

The independently reproduced Pyodide 0.29.4 / Python 3.13 build produced a 1.7 MB wheel and passed:

1. WebAssembly magic and CPython module-export checks;
2. import onnx, onnx.checker, and onnx.helper;
3. browser-local scikit-learn training;
4. conversion with skl2onnx 1.19.1;
5. ONNX validation and serialization; and
6. execution with ONNX Runtime Web 1.22.0.

Public recipe and build provenance:
https://github.com/metalmancode/onnx-pyodide

Live end-to-end proof:
https://metalmancode.github.io/onnx-pyodide/demo/

Verified release and wheel:
https://github.com/metalmancode/onnx-pyodide/releases/tag/v0.1.0

Wheel SHA-256:
2a827f6e2649395743afac49186343ca9221f48a1c67cce300cd019a7f448cd4

Current-repository validation

The recipe now builds successfully with the repository's current Python 3.14 / Pyodide toolchain. A targeted fork CI run built the wheel and passed the recipe's runtime test in Chrome, Firefox, and Node:

https://github.com/metalmancode/pyodide-recipes/actions/runs/29262798470

The runtime test creates a small ONNX graph, validates it through the compiled checker, serializes it, loads it back, and validates the restored model.

Related work: #463 targets ONNX 1.20.0 but currently has a failing build. This pull request intentionally starts from the independently reproduced and current-toolchain-validated 1.15.0 baseline rather than claiming unverified 1.20.0 support.

Provenance

The port and browser proof were created by Gholamreza Rashidi Ardestani (@metalmancode) from the browser-local ONNX export work used in MLDeck.

[ryanking13]

Thanks, but onnx is already building pyodide wheels in their repository and publishing to pypi so this is not needed.

[agriyakhetarpal]

Yes, agreed. Also, they only build for the 2025 ABI and not the 2026 ABI based on https://pypi.org/project/onnx/#files, so perhaps you please request them to do so, @metalmancode? Thanks!

[metalmancode]

Thank you for pointing me to the correct upstream location. I moved the 2026 ABI follow-up to ONNX and opened:

onnx/onnx#8192

The change now successfully builds onnx_weekly-1.23.0.dev20260714-cp312-abi3-pyemscripten_2026_0_wasm32.whl with ONNX's official Pyodide workflow and passes the Python 3.14 Pyodide runtime test. The first run also exposed an Emscripten/Abseil deprecation-pragmas issue, which the pull request addresses while retaining ONNX_WERROR=ON for other warnings.

Thanks again for the guidance.

— Gholamreza Rashidi Ardestani