Bug in parsing standard ES6 syntax

[getify]

I'm using Node v7.7.1 and Istanbul 0.4.5.

/tmp/foo.js:

function foo({x: y = 1}) {
    return y;
}

foo({ x: 1 });

Trying to run istanbul against that file:

$] istanbul cover /tmp/foo.js

/tmp/foo.js:9
function foo({y=1:y=1}){__cov_HZB7T0SjedjCpEtyBZ5mdA.f['1']++;__cov_HZB7T0SjedjCpEtyBZ5mdA.s['2']++;return y;}__cov_HZB7T0SjedjCpEtyBZ5mdA.s['3']++;foo({x:1});
                 ^
SyntaxError: Unexpected token :
    at createScript (vm.js:53:10)
    at Object.runInThisContext (vm.js:95:10)
    at Module._compile (module.js:543:28)
    at Object.Module._extensions.(anonymous function) [as .js] (/usr/local/lib/node_modules/istanbul/lib/hook.js:107:24)
    at Module.load (module.js:488:32)
    at tryModuleLoad (module.js:447:12)
    at Function.Module._load (module.js:439:3)
    at Function.Module.runMain (module.js:605:10)
    at runFn (/usr/local/lib/node_modules/istanbul/lib/command/common/run-with-cover.js:122:16)
    at /usr/local/lib/node_modules/istanbul/lib/command/common/run-with-cover.js:251:17

The code in /tmp/foo.js is totally valid ES6 syntax, and in fact it parses fine with Esprima.

If I take out the = 1 part in that parameter destructuring, Istanbul parses and tests fine. Using a parameter default is also fine. It's only the default inside the object destructuring that causes this failure.

Looking at the code quoted in the error output, it's transformed the function declaration to:

function foo({y=1:y=1}){ ..

That's clearly invalid. Doesn't seem like this is a bug in Esprima, but rather an Istanbul bug.

[MarkHerhold]

You may want to try version 1.1.0-alpha.1. Code is on the v1 branch.

[getify]

Thanks seems to be working!