WIP: Check for unconstrained superclass kind vars
Commit message
Check for unconstrained superclass kind vars
See Note [Unquantifiable kind variables] in TcTyClsDecls.
The actual fix for this is relatively short. Getting a good
error message printed takes much more code!
test cases: typecheck/should_compile/T17562
typecheck/should_fail/T17562b
Closes #17562.
Tag #17562 (closed).