Debugging the demangler?

[ea]

How would I go about debugging the demangler?
Currently facing an issue where I'm looking at a macOS binary. Function names are properly demangled, but no types are being created as I would expect from "Extract Types From Mangled Names". Is this limited to binaries produced by other compilers ?
Alternatively, where do I look to see what's going wrong?
This can be tested on any suitable macOS dylib. CoreText for example:

Thanks!

[plafosse]

This seems like a bug. I'm converting this to an issue.