Avoid crash when converting dict with circular reference

[dbaston]

Fixes #73

[martinRenou]

Neat thanks!

Weird the CI is not picking it up

[martinRenou]

Damn with their new UI the button to approve workflow for new contributors is buried deep behind tabs and buttons

[martinRenou]

Thanks a lot! I just have a small concern, otherwise I think it looks good

[martinRenou]

Neat! Thanks 🚀

[slayoo]

@dbaston, thank you for this fix!
We've bumped pybind11_json version to 0.2.15 and enabled a unit test that features a circular dict. Intriguingly, the behavior, from Python perspective, differs depending on the platform. On Apple Silicon (ARM64) macos-14, we get:

libc++abi: terminating due to uncaught exception of type std::runtime_error: Circular reference detected
Fatal Python error: Aborted

Current thread 0x00000001f6bc0f40 (most recent call first):
  File "/Users/runner/work/PyPartMC/PyPartMC/tests/test_aero_mode.py", line 304 in test_fixed_segfault_case_on_circular_reference
test_aero_mode.py::TestAeroMode::test_fixed_segfault_case_on_circular_reference 

on all other platforms, we get Python's TypeError indicating inconsistent function argument if the argument is a JSON containing a circular reference:

>       ppmc.AeroMode(aero_data, fishy_ctor_arg)
E       TypeError: __init__(): incompatible constructor arguments. The following argument types are supported:
E           1. _PyPartMC.AeroMode(arg0: _PyPartMC.AeroData, arg1: json)
E       
E       Invoked with: <_PyPartMC.AeroData object at 0x7ceea3fe04b0>, {'test_mode': {'mass_frac': [{'H2O': [1]}, [...]], 'diam_type': 'geometric', 'mode_type': 'log_normal', 'num_conc': 100.0, 'geom_mean_diam': 2e-06, 'log10_geom_std_dev': 0.2041199826559248}}

Any hints on why this behavior differs? Thanks

[dbaston]

Any hints on why this behavior differs?

I'm not sure. It looks like the pybind11_json tests are running successfully on ARM64. You could try running the pybind11_json tests in your own CI to see if the problem appears there. You could also try provoking an exception that does not involve this PR, by trying to convert an unsupported type to JSON, and seeing if it is successfully caught.