What does native_functions.yaml have to do with the TorchScript compiler? What multiple use cases is native_functions.yaml trying to serve? What's up with the JIT schema type system? Why isn't it just Python types? What the heck is the (a!) thingy inside the schema? Why is it important that I actually annotate all of my functions accurately with this information? Why is my seemingly BC change to native_functions.yaml actually breaking people's code? Do I have to understand the entire compiler to understand how to work with these systems?

Further reading.

• native_functions.yaml README https://github.com/pytorch/pytorch/blob/master/aten/src/ATen/native/README.md
• Tracking issue for serializing default arguments https://github.com/pytorch/pytorch/issues/54613
• Test for BC breaking changes in native_functions.yaml https://github.com/pytorch/pytorch/blob/master/test/backward_compatibility/check_backward_compatibility.py