bugfix imliedDisables; don't drop ext on the floor (#1656)

Author: shayne-fletcher

hlint.cabal

@@ -90,7 +90,7 @@ library
       build-depends:
           ghc-lib-parser == 9.12.*
     build-depends:
-        ghc-lib-parser-ex >= 9.12.0.0 && < 9.13.0
+        ghc-lib-parser-ex >= 9.12 && < 9.13
 
     if flag(gpl)
         build-depends: hscolour >= 1.21

src/GHC/All.hs

@@ -174,7 +174,7 @@ impliedEnables ext = case Data.List.lookup ext extensionImplications of
 impliedDisables :: Extension -> [Extension]
 impliedDisables ext = case Data.List.lookup ext extensionImplications  of
   Just exts -> ext : snd exts
-  Nothing -> []
+  Nothing -> [ext]
 
 -- | Parse a Haskell module. Applies the C pre processor, and uses
 -- best-guess fixity resolution if there are ambiguities.  The