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PyPI sdist missing C++ source — cannot build native libraries from source

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Assessment

Difficulty
4/5
Estimated time
3-5 days
Newbie friendliness
58/100
Issue type
Bug
Clarity
Mostly clear
Activity status
Active
Tech stack
cmake, cpp, python
Domain
build-system

Research direction

Start with setup.py, MANIFEST.in, CMakeLists.txt, and the PEP 517 build configuration, then reproduce the failure with pip install --no-binary coremltools from the sdist. Verify that the sdist contains the listed C++ source directories, that installation builds the native libraries, and that the provided model-conversion command no longer raises BlobWriter not loaded.

Written by the indexing model from the issue text.

Description

bug

🐞Describing the bug

The PyPI source distribution (sdist) does not include the C++ source directories needed to build the native libraries (libmilstoragepython, libmodelpackage, kmeans1d/_core). Building from the sdist produces a wheel without these libraries, so model conversion crashes at runtime.

The Git repository contains everything needed — CMakeLists.txt, deps/, mlmodel/, cmake/, modelpackage/, milstoragepython/ — but these are excluded from the sdist tarball. The setup.py packages the resulting .so files via package_data, but since the CMake build never runs during pip install, they don't exist.

Stack Trace

WARNING: No module named 'coremltools.libmilstoragepython'
WARNING: No module named 'coremltools.libcoremlpython'

RuntimeError: BlobWriter not loaded

To Reproduce

pip install coremltools --no-binary coremltools
python -c "
import coremltools as ct
import torch

model = torch.nn.Linear(10, 5)
traced = torch.jit.trace(model, torch.randn(1, 10))
ct.convert(traced) # RuntimeError: BlobWriter not loaded
"

System environment (please complete the following information):

  • coremltools version: 8.3 and 9.0 (likely all versions)
  • OS (e.g. MacOS version or Linux type): Linux x86_64 (RHEL 9), but affects any platform when building from sdist
  • Any other relevant version information (e.g. PyTorch or TensorFlow version): Python 3.12, PyTorch 2.6.0

Additional context

Building from the Git repository with CMake works perfectly — all three native libraries compile and model conversion succeeds. The published wheels on PyPI (both macOS and manylinux) include the native libraries and work fine — the issue is only with the sdist.

The fix would be to include the C++ source directories in MANIFEST.in (or equivalent) and wire the CMake build into the PEP 517 build backend so pip install from the sdist produces a working package.

Dominant language
Python
Stars
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Forks
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Avg merge
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Merged PRs (30d)
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First steps

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  4. Open a pull request that references the issue number.

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