./main.go:9:5: cannot use (*rr)(nil) (type *rr) as type Reader in assignment:
*rr does not implement Reader (missing Read method)
What did you see instead?
./main.go:9:16: incompatible type: cannot use (*rr)(nil) (value of type*rr) as Reader value
Others and myself laboured in prior Go cycles to have informative error messages when interfaces weren't satisifed, and we wrote tests to lock this behavior in. We also got feedback from the community about the helpfulness of the prior user experience. I am surprised that this regressed quietly or that the tests perhaps got deleted.