Vision: Library not loaded error when running hello_world example

[carlocab]

🐛 Bug

I am unable to run examples/cpp/hello_world/main.cpp after compilation using torchvision 0.8.2 with libtorch 1.7.1.

I encountered this in a CI run when trying to update libtorch and torchvision on Homebrew: https://github.com/Homebrew/homebrew-core/pull/66688

The test attempts to compile and run the example mentioned above. It produced this error:

==> /usr/bin/clang++ -std=c++14 main.cpp -o test -I/usr/local/opt/libtorch/include -I/usr/local/opt/libtorch/include/torch/csrc/api/include -L/usr/local/opt/libtorch/lib -ltorch -ltorch_cpu -lc10 -L/usr/local/Cellar/torchvision/0.8.2/lib -ltorchvision
==> ./test
dyld: Library not loaded: /usr/local/opt/[email protected]/Frameworks/Python.framework/Versions/3.9/Python
  Referenced from: /usr/local/opt/torchvision/lib/libtorchvision.dylib
  Reason: image not found

Error: torchvision: failed

This was the same test used with previous versions of torchvision in Homebrew CI. I'm trying to reproduce the error locally, but libtorch is taking ages to compile on my woefully underpowered laptop.

To Reproduce

Steps to reproduce the behavior:

1. Build libtorch and torchvision from source using the formulae in this PR: https://github.com/Homebrew/homebrew-core/pull/66688
2. brew test torchvision

CI run logs available here: https://github.com/Homebrew/homebrew-core/pull/66688/checks?check_run_id=1535220352

Expected behavior

No errors.

Environment

• PyTorch / torchvision Version (e.g., 1.0 / 0.4.0): 1.7.1 / 0.8.2
• OS (e.g., Linux): macOS 10.14
• How you installed PyTorch / torchvision (conda, pip, source): brew install --build-from-source
• Build command you used (if compiling from source): pytorch and torchvision were built using cmake. Exact commands can be found below.
  
  
  
  • pytorch: https://github.com/Homebrew/homebrew-core/blob/2b03686b37aacc420d11e9126dfd96f97fc0ab18/Formula/libtorch.rb#L42-L63
  
  
  • torchvision: https://github.com/Homebrew/homebrew-core/blob/2b03686b37aacc420d11e9126dfd96f97fc0ab18/Formula/torchvision.rb#L21-L28
  
  
• Python version: 3.9.0
• CUDA/cuDNN version: N/A
• GPU models and configuration: N/A
• Any other relevant information: None.

Additional context

None.

[carlocab]

Ok, things finally finished compiling. I'm unable to reproduce the error locally. Apologies for cluttering your issue tracker.

[carlocab]

In case anyone was following along, pytorch and torchvision are now at their latest versions on Homebrew. As a bonus, Homebrew torchvision comes with torchvision's C++ front-end.

Thanks for the great work you've put into this project.

[fmassa]

@carlocab thanks for the heads up!

cc @datumbox as a FYI because we are making breaking changes for the C++ frontend of torchvision