Exponentiation operator (estools#407)

* Fixed exponentiation operator precedence

* Fixed and added test cases for LHS expression of exponentiation operator

* fix exponentiation PR

Co-authored-by: Michael Ficarra <github@michael.ficarra.me>

Author: sanex3339

escodegen.js

@@ -95,14 +95,15 @@
         BitwiseSHIFT: 10,
         Additive: 11,
         Multiplicative: 12,
-        Await: 13,
-        Unary: 13,
-        Postfix: 14,
-        Call: 15,
-        New: 16,
-        TaggedTemplate: 17,
-        Member: 18,
-        Primary: 19
+        Exponentiation: 13,
+        Await: 14,
+        Unary: 14,
+        Postfix: 15,
+        Call: 16,
+        New: 17,
+        TaggedTemplate: 18,
+        Member: 19,
+        Primary: 20
     };
 
     BinaryPrecedence = {
@@ -130,7 +131,8 @@
         '-': Precedence.Additive,
         '*': Precedence.Multiplicative,
         '%': Precedence.Multiplicative,
-        '/': Precedence.Multiplicative
+        '/': Precedence.Multiplicative,
+        '**': Precedence.Exponentiation
     };
 
     //Flags
@@ -1831,14 +1833,16 @@
         },
 
         BinaryExpression: function (expr, precedence, flags) {
-            var result, currentPrecedence, fragment, leftSource;
+            var result, leftPrecedence, rightPrecedence, currentPrecedence, fragment, leftSource;
             currentPrecedence = BinaryPrecedence[expr.operator];
+            leftPrecedence = expr.operator === '**' ? Precedence.Postfix : currentPrecedence + 1;
+            rightPrecedence = expr.operator === '**' ? currentPrecedence : currentPrecedence + 1;
 
             if (currentPrecedence < precedence) {
                 flags |= F_ALLOW_IN;
             }
 
-            fragment = this.generateExpression(expr.left, currentPrecedence, flags);
+            fragment = this.generateExpression(expr.left, leftPrecedence, flags);
 
             leftSource = fragment.toString();
 
@@ -1848,7 +1852,7 @@
                 result = join(fragment, expr.operator);
             }
 
-            fragment = this.generateExpression(expr.right, currentPrecedence + 1, flags);
+            fragment = this.generateExpression(expr.right, rightPrecedence, flags);
 
             if (expr.operator === '/' && fragment.toString().charAt(0) === '/' ||
             expr.operator.slice(-1) === '<' && fragment.toString().slice(0, 3) === '!--') {

test/compare-acorn-es7.js

@@ -0,0 +1,92 @@
+/*
+  Copyright (C) 2012-2013 Yusuke Suzuki <utatane.tea@gmail.com>
+
+  Redistribution and use in source and binary forms, with or without
+  modification, are permitted provided that the following conditions are met:
+
+    * Redistributions of source code must retain the above copyright
+      notice, this list of conditions and the following disclaimer.
+    * 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 THE COPYRIGHT HOLDERS AND 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 <COPYRIGHT HOLDER> 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.
+*/
+
+'use strict';
+
+var fs = require('fs'),
+    acorn = require('acorn'),
+    escodegen = require('./loader'),
+    chai = require('chai'),
+    expect = chai.expect;
+
+function test(code, expected) {
+    var tree, actual, options, StringObject;
+
+    // alias, so that JSLint does not complain.
+    StringObject = String;
+
+    options = {
+        ranges: true,
+        locations: false,
+        ecmaVersion: 7
+    };
+
+    tree = acorn.parse(code, options);
+
+    // for UNIX text comment
+    actual = escodegen.generate(tree).replace(/[\n\r]$/, '') + '\n';
+    expect(actual).to.be.equal(expected);
+}
+
+function testMin(code, expected) {
+    var tree, actual, options, StringObject;
+
+    // alias, so that JSLint does not complain.
+    StringObject = String;
+
+    options = {
+        ranges: true,
+        locations: false,
+        ecmaVersion: 7
+    };
+
+    tree = acorn.parse(code, options);
+
+    // for UNIX text comment
+    actual = escodegen.generate(tree, {
+        format: escodegen.FORMAT_MINIFY,
+        raw: false
+    }).replace(/[\n\r]$/, '') + '\n';
+    expect(actual).to.be.equal(expected);
+}
+
+describe('compare acorn es7 test', function () {
+    fs.readdirSync(__dirname + '/compare-acorn-es7').sort().forEach(function(file) {
+        var code, expected, exp, min;
+        if (/\.js$/.test(file) && !/expected\.js$/.test(file) && !/expected\.min\.js$/.test(file)) {
+            it(file, function () {
+                exp = file.replace(/\.js$/, '.expected.js');
+                min = file.replace(/\.js$/, '.expected.min.js');
+                code = fs.readFileSync(__dirname + '/compare-acorn-es7/' + file, 'utf-8');
+                expected = fs.readFileSync(__dirname + '/compare-acorn-es7/' + exp, 'utf-8');
+                test(code, expected);
+                if (fs.existsSync(__dirname + '/compare-acorn-es7/' + min)) {
+                    expected = fs.readFileSync(__dirname + '/compare-acorn-es7/' + min, 'utf-8');
+                    testMin(code, expected);
+                }
+            });
+        }
+    });
+});
+/* vim: set sw=4 ts=4 et tw=80 : */

test/compare-acorn-es7/exponentiation-precedence.expected.js

@@ -0,0 +1,9 @@
+x ** y * z;
+x ** (y * z);
+(x * y) ** z;
+x * y ** z;
+x ** y ** z;
+(x ** y) ** z;
+(-1) ** 0;
+a++ ** b;
+0 ** -1;

test/compare-acorn-es7/exponentiation-precedence.js

@@ -0,0 +1,12 @@
+(x ** y) * z;
+x ** (y * z);
+
+(x * y) ** z;
+x * (y ** z);
+
+x ** (y ** z);
+(x ** y) ** z;
+
+(-1) ** 0;
+a++ ** b;
+0 ** (-1);