Why check for -fdefer-type-errors in metaTyVarUpdateOK?
Function checkTypeEq
changes its behavior depending on the presence of -fdefer-type-errors
in an obscure case around heterogeneous equalities; see the code in go_co
. This is undocumented (in the code), and neither Simon nor I can figure out why it's done.
Task: figure this out, and either document or remove this behavior.