Support BigInt syntax

This change adds BigInt support which is specified in [1].

[1]: https://github.com/estree/estree/blob/master/es2020.md

escodegen.js

@@ -11,6 +11,7 @@
   Copyright (C) 2012 Joost-Wim Boekesteijn <joost-wim@boekesteijn.nl>
   Copyright (C) 2012 Kris Kowal <kris.kowal@cixar.com>
   Copyright (C) 2012 Arpad Borsos <arpad.borsos@googlemail.com>
+  Copyright (C) 2020 Apple Inc. All rights reserved.
 
   Redistribution and use in source and binary forms, with or without
   modification, are permitted provided that the following conditions are met:
@@ -2348,6 +2349,16 @@
               return '/' + expr.regex.pattern + '/' + expr.regex.flags;
             }
 
+            if (typeof expr.value === 'bigint') {
+                return expr.value.toString() + 'n';
+            }
+
+            // `expr.value` can be null if `expr.bigint` exists. We need to check
+            // `expr.bigint` first.
+            if (expr.bigint) {
+                return expr.bigint + 'n';
+            }
+
             if (expr.value === null) {
                 return 'null';
             }

test/compare-acorn-es2020/bigint.expected.js

@@ -0,0 +1,3 @@
+2000n + 30;
+20000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000n + 30;
+-20000000000000000000000000000n;

test/compare-acorn-es2020/bigint.expected.min.js

@@ -0,0 +1 @@
+2000n+30;20000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000n+30;-20000000000000000000000000000n

test/compare-acorn-es2020/bigint.js

@@ -0,0 +1,28 @@
+/*
+ * Copyright (C) 2020 Apple Inc.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS''
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
+ * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+ * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS
+ * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
+ * THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+2000n + 30;
+20000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000n + 30;
+-20000000000000000000000000000n;