`text_signature` with enum default arguments cannot be processed by Sphinx

We are using Sphinx to generate the documentation for our Python package that we build using pyO3.
With the latest changes to signature and text_signature, we wanted to properly document default values for function and method arguments, including enum arguments.

For example, we added a text signature like text_signature ="(a=MyEnum.Variant1)" where MyEnum is a Rust enum and pyclass. Sphinx (autodoc) is not able to parse these signatures - it crashes with an exception:

<function record_typehints at 0x7f90007ed3a0> for event 'autodoc-process-signature' threw an exception (exception: )

I wasn't able to figure out what exactly goes wrong here. If this is not an issue of PyO3 but Sphinx, feel free to close this issue.
I'd be grateful for help or ideas to resolve this. For now, we removed the defaults in text_signature (signature works fine) but that's not an ideal solution.

I built a small crate that reproduces the error here.

Start with the linked test crate and the interaction between signature, text_signature, and Sphinx's autodoc-process-signature event. Compare how ordinary defaults and enum defaults are handled; done means Sphinx can process the enum default without raising the reported exception.