Howdy, I started looking at Trac #12056 (https://ghc.haskell.org/trac/ghc/ticket/12056), but I'm a bit stuck. Indeed, if I run the following command, I get no warnings ghc Main.hs -Wfoo -w -Wunrecognised-warning-flags -Wbar But if I also specify -Wdeprecated-flags, I get warnings again ghc Main.hs -Wfoo -w -Wunrecognised-warning-flags -Wdeprecated-flags -Wbar on the commandline: warning: unrecognised warning flag: -Wfoo on the commandline: warning: unrecognised warning flag: -Wbar Then I found this little function in compiler/main/HscTypes handleFlagWarnings :: DynFlags -> [Located String] -> IO () handleFlagWarnings dflags warns = when (wopt Opt_WarnDeprecatedFlags dflags) $ do -- It would be nicer if warns :: [Located MsgDoc], but that -- has circular import problems. let bag = listToBag [ mkPlainWarnMsg dflags loc (text warn) | L loc warn <- warns ] printOrThrowWarnings dflags bag So I updated it accept Opt_WarnDeprecatedFlags and Opt_WarnUnrecognisedWarningsFlags. Complete patch here: https://phabricator.haskell.org/D3581 Unfortunately when I did that, -Wno-deprecated-flags no longer had an effect so long as -Wunrecognised-warnings-flags ./inplace/bin/ghc-stage2 -Wunrecognised-warning-flags -Wno-deprecated-flags -XOverlappingInstances on the commandline: warning: -XOverlappingInstances is deprecated: instead use per-instance pragmas OVERLAPPING/OVERLAPPABLE/OVERLAPS And now that is where I'm stuck; I can't seem to find a place where I can distinguish between the different warning types. Even WarnReason is set to NoReason because of the usage of mkPlainWarnMsg. So if I could get some guidance on this, I'd be very grateful. Thanks Sean G