Error on nodes which should not have type predicates.

src/compiler/checker.ts

@@ -11563,11 +11563,14 @@ namespace ts {
             return -1;
         }
 
-        function checkTypePredicate(node: TypePredicateNode) {
+        function checkTypePredicate(node: TypePredicateNode): void {
             const parent = getTypePredicateParent(node);
             if (!parent) {
+                // The parent must not be valid.
+                error(node.parent, Diagnostics.A_type_predicate_is_only_allowed_in_return_type_position_for_functions_and_methods);
                 return;
             }
+
             const typePredicate = getSignatureFromDeclaration(parent).typePredicate;
             if (!typePredicate) {
                 return;

src/compiler/diagnosticMessages.json

@@ -723,6 +723,10 @@
         "category": "Error",
         "code": 1227
     },
+    "A type predicate is only allowed in return type position for functions and methods.": {
+        "category": "Error",
+        "code": 1228
+    },
     "A type predicate cannot reference a rest parameter.": {
         "category": "Error",
         "code": 1229