* include -Wcompat and -Wall, but make it "magic" so that -Wcompat never causes a build to fail even when users set -Wall -Werror.
Tbh, I don't like the "magic" part at all. In fact, I currently rely on `-Wcompat -Werror` triggering an error in my builds.
Point is - if -Wall implies -Wcompat that's simply not an option for many companies, who have a huge codebase, turn on -Wall -Werror as a matter of policy yet need the time granted by the 3 release policy to adapt their codebase.
To address the concern more generally is what
https://ghc.haskell.org/trac/ghc/ticket/11219
aims to, but without any magic. Then you'd say
-Wall -Werror -Wno-error=compat
if -Wcompat implied by -Wall.
That sounds good. -Wno-error=compat should work fine.
But we ran out of time for GHC 8.0, so #11219 will have to wait till GHC 8.2.
Then is it reasonable to prevent -Wall -Werror from failing builds because of -Wcompat through some kind of special casing in GHC 8.0, to be generalized via -Wno-error in GHC 8.2?