2 files changed, 22 insertions, 0 deletions
diff --git a/compiler/GHC/Tc/Errors/Ppr.hs b/compiler/GHC/Tc/Errors/Ppr.hs
index 10d1c60fb1..02acd47e2e 100644
--- a/compiler/GHC/Tc/Errors/Ppr.hs
+++ b/compiler/GHC/Tc/Errors/Ppr.hs
@@ -277,6 +277,10 @@ instance Diagnostic TcRnMessage where
       -> mkSimpleDecorated $
            hang (text "Bad call to tagToEnum# at type" <+> ppr ty)
               2 (text "Result type must be an enumeration type")
+    TcRnTagToEnumResTyTypeData ty
+      -> mkSimpleDecorated $
+           hang (text "Bad call to tagToEnum# at type" <+> ppr ty)
+              2 (text "Result type cannot be headed by a `type data` type")
     TcRnArrowIfThenElsePredDependsOnResultTy
       -> mkSimpleDecorated $
            text "Predicate type of `ifThenElse' depends on result type"
@@ -1391,6 +1395,8 @@ instance Diagnostic TcRnMessage where
       -> ErrorWithoutFlag
     TcRnTagToEnumResTyNotAnEnum{}
       -> ErrorWithoutFlag
+    TcRnTagToEnumResTyTypeData{}
+      -> ErrorWithoutFlag
     TcRnArrowIfThenElsePredDependsOnResultTy
       -> ErrorWithoutFlag
     TcRnIllegalHsBootFileDecl
@@ -1821,6 +1827,8 @@ instance Diagnostic TcRnMessage where
       -> noHints
     TcRnTagToEnumResTyNotAnEnum{}
       -> noHints
+    TcRnTagToEnumResTyTypeData{}
+      -> noHints
     TcRnArrowIfThenElsePredDependsOnResultTy
       -> noHints
     TcRnIllegalHsBootFileDecl
diff --git a/compiler/GHC/Tc/Errors/Types.hs b/compiler/GHC/Tc/Errors/Types.hs
index e2707b4aa4..0420a4e498 100644
--- a/compiler/GHC/Tc/Errors/Types.hs
+++ b/compiler/GHC/Tc/Errors/Types.hs
@@ -665,6 +665,20 @@ data TcRnMessage where
   -}
   TcRnTagToEnumResTyNotAnEnum :: Type -> TcRnMessage
 
+  {-| TcRnTagToEnumResTyTypeData is an error that occurs when the 'tagToEnum#'
+      function is given a result type that is headed by a @type data@ type, as
+      the data constructors of a @type data@ do not exist at the term level.
+
+      Example(s):
+      type data Letter = A | B | C
+
+      foo :: Letter
+      foo = tagToEnum# 0#
+
+     Test cases: type-data/should_fail/TDTagToEnum.hs
+  -}
+  TcRnTagToEnumResTyTypeData :: Type -> TcRnMessage
+
   {-| TcRnArrowIfThenElsePredDependsOnResultTy is an error that occurs when the
       predicate type of an ifThenElse expression in arrow notation depends on
       the type of the result.