FIX #1729: Don't try to expand syn families with -XLiberalTypeSynonyms

MERGE TO STABLE

diff --git a/compiler/typecheck/TcMType.lhs b/compiler/typecheck/TcMType.lhs
index dc811cb..ebcf5b3 100644 (file)
--- a/compiler/typecheck/TcMType.lhs
+++ b/compiler/typecheck/TcMType.lhs
@@ -1097,7 +1097,7 @@ check_tau_type rank ubx_tup (NoteTy other_note ty)
 check_tau_type rank ubx_tup ty@(TyConApp tc tys)
   | isSynTyCon tc
   = do {       -- Check that the synonym has enough args
-               -- This applies eqaually to open and closed synonyms
+               -- This applies equally to open and closed synonyms
                -- It's OK to have an *over-applied* type synonym
                --      data Tree a b = ...
                --      type Foo a = Tree [a]
@@ -1106,14 +1106,14 @@ check_tau_type rank ubx_tup ty@(TyConApp tc tys)
 
        -- See Note [Liberal type synonyms]
        ; liberal <- doptM Opt_LiberalTypeSynonyms
-       ; if not liberal then
-               -- For H98, do check the type args
+       ; if not liberal || isOpenSynTyCon tc then
+               -- For H98 and synonym families, do check the type args
                mappM_ check_arg_type tys
 
-         else  -- In the liberal case, expand then check
+         else  -- In the liberal case (only for closed syns), expand then check
          case tcView ty of   
             Just ty' -> check_tau_type rank ubx_tup ty' 
-            Nothing -> pprPanic "check_tau_type" (ppr ty)
+            Nothing  -> pprPanic "check_tau_type" (ppr ty)
     }
     
   | isUnboxedTupleTyCon tc