Add optional types to function/method declarations

src/ast/ast.h

Index: src/ast/ast.h
diff --git a/src/ast/ast.h b/src/ast/ast.h
index 374d250447ca919075f72dbc38a6bdff81e7413d..c3c2d887597c8b0f42f22113e9c0639db85e2d4a 100644
--- a/src/ast/ast.h
+++ b/src/ast/ast.h
@@ -2936,6 +2936,14 @@ class EmptyParentheses final : public Expression {
 // Nodes for the optional type system.
 namespace typesystem {
 
+enum TypeFlags {
+  kNormalTypes = 0,
+  kDisallowTypeParameters = 1 << 0,
+  kDisallowTypeAnnotation = 1 << 1,
+  kAllowSignature = 1 << 2,
+  kConstructorTypes = kDisallowTypeParameters | kDisallowTypeAnnotation
+};
+
 class FormalParameter;