Do the second part of #2806: Disallow unlifted types in ~ patterns

diff --git a/compiler/typecheck/TcPat.lhs b/compiler/typecheck/TcPat.lhs
index 23e6bbf..bef5ec7 100644 (file)
--- a/compiler/typecheck/TcPat.lhs
+++ b/compiler/typecheck/TcPat.lhs
@@ -367,6 +367,10 @@ tc_pat pstate lpat@(LazyPat pat) pat_ty thing_inside
        -- Check no existentials
        ; unless (null pat_tvs) $ lazyPatErr lpat pat_tvs
 
+       -- Check there are no unlifted types under the lazy pattern
+       ; when (any (isUnLiftedType . idType) $ collectPatBinders pat') $
+               lazyUnliftedPatErr lpat
+
        -- Check that the pattern has a lifted type
        ; pat_tv <- newBoxyTyVar liftedTypeKind
        ; boxyUnify pat_ty (mkTyVarTy pat_tv)
@@ -1039,6 +1043,12 @@ lazyPatErr _ tvs
     hang (ptext (sLit "A lazy (~) pattern cannot match existential or GADT data constructors"))
        2 (vcat (map pprSkolTvBinding tvs))
 
+lazyUnliftedPatErr :: OutputableBndr name => Pat name -> TcM ()
+lazyUnliftedPatErr pat
+  = failWithTc $
+    hang (ptext (sLit "A lazy (~) pattern cannot contain unlifted types"))
+       2 (ppr pat)
+
 nonRigidMatch :: PatCtxt -> DataCon -> SDoc
 nonRigidMatch ctxt con
   =  hang (ptext (sLit "GADT pattern match in non-rigid context for") <+> quotes (ppr con))