Merge pull request #1506 from ndmitchell/zliu41/vars-matchgroup

Fix freeVars computation for MatchGroup

src/GHC/Util/FreeVars.hs

@@ -233,7 +233,7 @@ instance AllVars (LocatedA (HsBindLR GhcPs GhcPs)) where
   allVars (L _ (PatSynBind _ PSB{})) = mempty -- Come back to it.
 
 instance AllVars (MatchGroup GhcPs (LocatedA (HsExpr GhcPs))) where
-  allVars (MG _ _alts@(L _ alts)) = inVars (foldMap (allVars . m_pats) ms) (allVars (map m_grhss ms))
+  allVars (MG _ _alts@(L _ alts)) = foldMap (\m -> inVars (allVars (m_pats m)) (allVars (m_grhss m))) ms
     where ms = map unLoc alts
 
 instance AllVars (LocatedA (Match GhcPs (LocatedA (HsExpr GhcPs)))) where

src/Hint/Lambda.hs

@@ -87,6 +87,7 @@ foo = bar (\x -> case x of [y, z] -> z) -- \[y, z] -> z
 yes = blah (\ x -> case x of A -> a; B -> b) -- \ case A -> a; B -> b
 yes = blah (\ x -> case x of A -> a; B -> b) -- @Note may require `{-# LANGUAGE LambdaCase #-}` adding to the top of the file
 no = blah (\ x -> case x of A -> a x; B -> b x)
+no = blah (\ x -> case x of A -> a x; x -> b x)
 foo = bar (\x -> case x of Y z | z > 0 -> z) -- \case Y z | z > 0 -> z
 yes = blah (\ x -> (y, x)) -- (y,)
 yes = blah (\ x -> (y, x, z+q)) -- (y, , z+q)