Add support for 'unique symbol' type

Author: guillaumebrunerie

common/corpus/types.txt

@@ -272,6 +272,40 @@ let x: new < T1, T2 > ( p1, p2 ) => R;
         (type_identifier))))))
 
 
+=======================================
+Symbol types
+=======================================
+
+const symFoo: unique symbol = Symbol("foo");
+const symBar: symbol = Symbol.for("bar");
+
+---
+
+(program
+  (lexical_declaration
+    (variable_declarator
+      (identifier)
+      (type_annotation
+        (predefined_type))
+      (call_expression
+        (identifier)
+        (arguments
+          (string
+            (string_fragment))))))
+  (lexical_declaration
+    (variable_declarator
+      (identifier)
+      (type_annotation
+        (predefined_type))
+      (call_expression
+        (member_expression
+          (identifier)
+          (property_identifier))
+        (arguments
+          (string
+            (string_fragment)))))))
+
+
 =======================================
 Type annotations in parenthesized expressions
 =======================================

common/define-grammar.js

@@ -834,6 +834,7 @@ module.exports = function defineGrammar(dialect) {
         'boolean',
         'string',
         'symbol',
+        alias(seq('unique', 'symbol'), 'unique symbol'),
         'void',
         'unknown',
         'string',