Add support for ** under ecmaVersion 7

This adds support for the exponentiation operator, which is currently
Stage 4 for ES7. The supported operators are ** and **=.

Fixes #381

README.md

@@ -62,7 +62,7 @@ object referring to that same position.
 [estree]: https://github.com/estree/estree
 
 - **ecmaVersion**: Indicates the ECMAScript version to parse. Must be
-  either 3, 5, or 6. This influences support for strict mode, the set
+  either 3, 5, 6, or 7. This influences support for strict mode, the set
   of reserved words, and support for new syntax features. Default is 5.
 
 - **sourceType**: Indicate the mode the code should be parsed in. Can be
@@ -304,7 +304,7 @@ The `bin/acorn` utility can be used to parse a file from the command
 line. It accepts as arguments its input file and the following
 options:
 
-- `--ecma3|--ecma5|--ecma6`: Sets the ECMAScript version to parse. Default is
+- `--ecma3|--ecma5|--ecma6|--ecma7`: Sets the ECMAScript version to parse. Default is
   version 5.
 
 - `--module`: Sets the parsing mode to `"module"`. Is set to `"script"` otherwise.

src/bin/acorn.js

@@ -9,7 +9,7 @@ const options = {}
 
 function help(status) {
   const print = (status == 0) ? console.log : console.error
-  print("usage: " + basename(process.argv[1]) + " [--ecma3|--ecma5|--ecma6]")
+  print("usage: " + basename(process.argv[1]) + " [--ecma3|--ecma5|--ecma6|--ecma7]")
   print("        [--tokenize] [--locations] [---allow-hash-bang] [--compact] [--silent] [--module] [--help] [--] [infile]")
   process.exit(status)
 }
@@ -21,6 +21,7 @@ for (let i = 2; i < process.argv.length; ++i) {
   else if (arg == "--ecma3") options.ecmaVersion = 3
   else if (arg == "--ecma5") options.ecmaVersion = 5
   else if (arg == "--ecma6") options.ecmaVersion = 6
+  else if (arg == "--ecma7") options.ecmaVersion = 7
   else if (arg == "--locations") options.locations = true
   else if (arg == "--allow-hash-bang") options.allowHashBang = true
   else if (arg == "--silent") silent = true

src/expression.js

@@ -17,6 +17,7 @@
 // [opp]: http://en.wikipedia.org/wiki/Operator-precedence_parser
 
 import {types as tt} from "./tokentype"
+import {types as tc} from "./tokencontext"
 import {Parser} from "./state"
 
 const pp = Parser.prototype
@@ -162,12 +163,19 @@ pp.parseExprOp = function(left, leftStartPos, leftStartLoc, minPrec, noIn) {
       let startPos = this.start, startLoc = this.startLoc
       node.right = this.parseExprOp(this.parseMaybeUnary(), startPos, startLoc, prec, noIn)
       this.finishNode(node, (op === tt.logicalOR || op === tt.logicalAND) ? "LogicalExpression" : "BinaryExpression")
+      if (this.options.ecmaVersion >= 7 && op === tt.starstar)
+        this.checkExponentiationOperand(node.left)
       return this.parseExprOp(node, leftStartPos, leftStartLoc, minPrec, noIn)
     }
   }
   return left
 }
 
+pp.checkExponentiationOperand = function(node) {
+  if (node.type === "UnaryExpression" && node.operator !== "++" && node.operator !== "--")
+    this.raiseRecoverable(node.start, "Base operand of ** cannot use a unary expression")
+}
+
 // Parse unary operators, both prefix and postfix.
 
 pp.parseMaybeUnary = function(refDestructuringErrors) {

src/tokenize.js

@@ -228,10 +228,20 @@ pp.readToken_slash = function() { // '/'
   return this.finishOp(tt.slash, 1)
 }
 
-pp.readToken_mult_modulo = function(code) { // '%*'
+pp.readToken_mult_modulo_exp = function(code) { // '%*'
   let next = this.input.charCodeAt(this.pos + 1)
-  if (next === 61) return this.finishOp(tt.assign, 2)
-  return this.finishOp(code === 42 ? tt.star : tt.modulo, 1)
+  let size = 1
+  let tokentype = code === 42 ? tt.star : tt.modulo
+
+  // exponentiation operator ** and **=
+  if (this.options.ecmaVersion >= 7 && next === 42) {
+    ++size
+    tokentype = tt.starstar
+    next = this.input.charCodeAt(this.pos + 2)
+  }
+
+  if (next === 61) return this.finishOp(tt.assign, size + 1)
+  return this.finishOp(tokentype, size)
 }
 
 pp.readToken_pipe_amp = function(code) { // '|&'
@@ -343,7 +353,7 @@ pp.getTokenFromCode = function(code) {
     return this.readToken_slash()
 
   case 37: case 42: // '%*'
-    return this.readToken_mult_modulo(code)
+    return this.readToken_mult_modulo_exp(code)
 
   case 124: case 38: // '|&'
     return this.readToken_pipe_amp(code)

src/tokentype.js

@@ -95,7 +95,8 @@ export const types = {
   plusMin: new TokenType("+/-", {beforeExpr: true, binop: 9, prefix: true, startsExpr: true}),
   modulo: binop("%", 10),
   star: binop("*", 10),
-  slash: binop("/", 10)
+  slash: binop("/", 10),
+  starstar: binop("**", 11)
 }
 
 // Map keyword names to token types.

test/run.js

@@ -5,6 +5,7 @@
     driver = require("./driver.js");
     require("./tests.js");
     require("./tests-harmony.js");
+    require("./tests-es7.js");
     require("babel-core/register")
     acorn = require("../src")
     require("../src/loose")