Rest operator in function argument declaration throws "Parsing error Invalid left-hand side in formals list"

[jaapz]

When I run eslint on code like this:

{
    initialize({someVar, otherVar, ...options}) {
        // ... do some stuff with options ...
    }
}

I get the error: "Parsing error: Invalid left-hand side in formals list".

This was already reported on eslint, but there it was mentioned that this should be reported on espree, and I cannot find any issue on this project about this so I created this one.

I have experimentalObjectSpread: true in my .eslintrc.

[nzakas]

What version are you using?

[ilyavolodin]

The flag name is actually experimentalObjectRestSpread, not experimentalObjectSpread. So maybe that's the issue?

[jaapz]

@ilyavolodin I actually typo'd in the issue here, I've got the correct flag name in my .eslintrc.
@nzakas espree@2.2.5 which apparently comes with eslint@1.10.3.

[nzakas]

Okay, this might be fixed in 3.0.0. Can you check the master branch of ESLint to see if you're still having the problem?

[jaapz]

When I install the master branch of eslint using npm install eslint/eslint#master, the error seems to be replaced by a different one:

Parsing error: 'import' and 'export' may appear only with 'sourceType: module'

Which is reported on the first import of the file.

I have no idea why this is, and I can't find any documentation on sourceType: module.

I'm not sure this actually fixes the problem though, as eslint seems to crap out directly after seeing a Parsing error. So it might be that the error still persists, but eslint just doesn't get to the line with the spread operator.

[nzakas]

2.0.0 has different options, see http://eslint.org/docs/2.0.0/user-guide/migrating-to-2.0.0#language-options.

I'd also suggest using --no-eslintrc for a sanity check as some rules are different.

[jaapz]

Ok, I followed the guide and moved my config to the 2.0.0 options.
These are the results:

jaapz at tommy in <REDACTED> (master●) (.env)
$ eslint <REDACTED>/page.js
<REDACTED>/page.js
  42:56  error  Parsing error: Unexpected token ..

✖ 1 problem (1 error, 0 warnings)


jaapz at tommy in <REDACTED> (master●) (.env)
$ eslint <REDACTED>/page.js --no-eslintrc

<REDACTED>/page.js
  1:1  error  Parsing error: The keyword 'import' is reserved

✖ 1 problem (1 error, 0 warnings)

So the problem exists, but it's a different error message now, it still points to the ...options though.

When running with --no-eslintrc the ES6 config isn't loaded so it doesn't understand the import statement.

[nzakas]

OK thanks, I'll take a look.

[nzakas]

I've tried this a couple of times and I'm unable to reproduce. I added your exact code as a test and it parses fine: #244

Is it possible you have a typo in your config file? For ESLint 2.0.0, you'd need a config that looks like this:

{
    "parserOptions": {
        "ecmaVersion": 6,
        "ecmaFeatures": {
            "experimentalObjectRestSpread": true
        }
    }
}

[jaapz]

Thanks, I'm not sure if I have the correct config then for eslint 2.0.0. I'll check later when I get back to my laptop.

[nzakas]

This was definitely broken in Espree 2.x. In Espree 3.x, it was also broken, but was fixed in #249.