Remove a HACK by instead inferring opaque types during expected/formal type checking
I was wondering why I couldn't come up with a test that hits the code path of the argument check checking the types we inferred from the return type... Turns out we reject those attempts early during fudging.
I have absolutely no information for you as to what kind of type inference changes this may incur, but I think we should just land this out of two reasons:
* had I found the other place to use opaque type inference on before I added the hack, we'd be using that today and this PR would never have happened
* if it is possible to hit this path, it requires some god awful recursive RPIT logic that I doubt anyone would have written without actively trying to write obscure code
r? ``@ghost``
许杰友 Jieyou Xu (Joe)
699612fb8a