Add support for records of records of types (#700)

... as standardized in dhall-lang/dhall-lang#300

Fixes #692

Author: Gabriella439

dhall/src/Dhall/TypeCheck.hs

@@ -512,10 +512,7 @@ typeWithA tpa = loop
                                 Left (TypeError ctx e (InvalidFieldType k t))
                 Dhall.Map.traverseWithKey_ process rest
 
-                case c of
-                    Type -> return (Const Type)
-                    Kind -> return (Const Sort)
-                    Sort -> return (Const Sort)
+                return (Const c)
     loop ctx e@(RecordLit kvs   ) = do
         case Dhall.Map.toList kvs of
             []         -> return (Record mempty)

dhall/tests/TypeCheck.hs

@@ -47,9 +47,6 @@ typecheckTests =
         , should
             "allow records of types of mixed kinds"
             "success/recordOfTypes"
-        , should
-            "allow Boehm-Berarducci-encoded records of types of mixed kinds"
-            "success/encodedRecordOfTypes"
         , should
             "allow accessing a type from a record"
             "success/accessType"
@@ -62,6 +59,9 @@ typecheckTests =
         , should
             "allow accessing a constructor from a type stored inside a record"
             "success/simple/mixedFieldAccess"
+        , should
+            "allow a record of a record of types"
+            "success/recordOfRecordOfTypes"
         ]
 
 preludeExamples :: TestTree

dhall/tests/typecheck/success/encodedRecordOfTypesA.dhall

@@ -0,0 +1,3 @@
+let types = { Scopes = < Public : {} | Private : {} >}
+let prelude = { types = types }
+in  prelude.types.Scopes.Public {=}

dhall/tests/typecheck/success/encodedRecordOfTypesB.dhall

@@ -0,0 +1 @@
+< Public : {} | Private : {} >