Excerpts from Simon Peyton-Jones's message of Mon Mar 11 16:04:31 -0700 2013:
Aha. It is indeed true that
ghc -fdefer-type-errors -w
does not suppress the warnings that arise from the type errors; indeed there is no current way to do so. How to do that?
To be kosher there should really be a flag to switch off those warnings alone, perhaps -fno-warn-type-errors
So then -fwarn-type-errors is on by default, but is only relevant when -fdefer-type-errors is on. Once -fdefer-type-errors is on, -fno-warn-type-errors and -fwarn-type-errors suppress or enable the warnings. -w would then include -fno-warn-type-errors.
Is that a design everyone would like? If so, woudl someone like to open a ticket, implement it, update the documentation, and send a patch?
SGTM. Edward