diff options
Diffstat (limited to 'compiler/GHC/Tc/TyCl/Build.hs')
| -rw-r--r-- | compiler/GHC/Tc/TyCl/Build.hs | 20 |
1 files changed, 14 insertions, 6 deletions
diff --git a/compiler/GHC/Tc/TyCl/Build.hs b/compiler/GHC/Tc/TyCl/Build.hs index e7d423f2e1..f02a5467ed 100644 --- a/compiler/GHC/Tc/TyCl/Build.hs +++ b/compiler/GHC/Tc/TyCl/Build.hs @@ -18,7 +18,7 @@ module GHC.Tc.TyCl.Build ( import GHC.Prelude import GHC.Iface.Env -import GHC.Builtin.Types( isCTupleTyConName, unboxedUnitTy ) +import GHC.Builtin.Types import GHC.Tc.Utils.TcType import GHC.Tc.Utils.Monad @@ -65,11 +65,12 @@ mkNewTyConRhs tycon_name tycon con tvs = tyConTyVars tycon roles = tyConRoles tycon res_kind = tyConResKind tycon - con_arg_ty = case dataConRepArgTys con of - [arg_ty] -> scaledThing arg_ty - tys -> pprPanic "mkNewTyConRhs" (ppr con <+> ppr tys) - rhs_ty = substTyWith (dataConUnivTyVars con) - (mkTyVarTys tvs) con_arg_ty + rhs_ty + -- Only try if the newtype is actually valid (see "otherwise" below). + | [Scaled _ arg_ty] <- dataConRepArgTys con + , null $ dataConExTyCoVars con + = substTyWith (dataConUnivTyVars con) + (mkTyVarTys tvs) arg_ty -- Instantiate the newtype's RHS with the -- type variables from the tycon -- NB: a newtype DataCon has a type that must look like @@ -78,6 +79,13 @@ mkNewTyConRhs tycon_name tycon con -- the newtype arising from class Foo a => Bar a where {} -- has a single argument (Foo a) that is a *type class*, so -- dataConInstOrigArgTys returns []. + | otherwise + -- If the newtype is invalid (e.g. doesn't have a single argument), + -- we fake up a type here. The newtype will get rejected once we're + -- outside the knot-tied loop, in GHC.Tc.TyCl.checkNewDataCon. + -- See the various test cases in T23308. + = unitTy -- Might be ill-kinded, but checkNewDataCon should reject this + -- whole declaration soon enough, before that causes any problems. -- Eta-reduce the newtype -- See Note [Newtype eta] in GHC.Core.TyCon |