bpo-41987: Fix unnecessary evaluation of return type forward declaratons in singledispatch. by mental32 · Pull Request #23216 · python/cpython

@gvanrossum thank you for the review!

I've applied and committed the suggested changes, and will be investigating the regression further when I can.

At the moment I am only comparing diffs of tag 3.8 and tag 3.9 for file /Lib/typing.py since I suspect the regression will be visible there. If I can't eyeball it I'll start bisecting commits from 3.8 to master's head testing for reproducibility.