”There's nothing lost by putting the sig in a companion file and leaving it to your editor/IDE to provide a popup”It requires every (1) editor and IDE on the planet to add code for doing that, which means every (1) programming language on the planet needs a library for parsing such companion files, for the benefit of ??????
Except for historical corner cases such as original java with its repeated type annotations that make code with types tedious to read, I wouldn’t know what that benefit would be.
(1) that ‘every’ is a bit of hyperbole, but essentially true.
