Thanks for cleaning this up! I would propose to change the error format to something like this:

• No overload variant of "f" of "A" matches argument type "B" if there is a single argument
• No overload variant of "f" of "A" matches argument types "A", "B", "C" otherwise.

(Note that quotes are used by some editor plugins to better highlight types/methods in error messages.)

Yes, that would be better. What do you suggest for the case where the list is empty? (All overloads take at least one argument, but the user called f().) I suggest All overloads of "f" require at least one argument.

Yes this makes sense.

(also error message in tests needs to be updated)

Oops, just pushed a commit fixing the two tests I messed up.