I have to write the converter by myself. BindingType::toWireType is not easy, because the emscripten::val cannot be created using a c function. I create a C function wrapper to wrap the std::function ...
To replicate this error, it is necessary to add some debug statements to the expand_derivatives function. In the below MWE, that function is modified from version 6.12.0 only by adding debug printing.
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