no-unused-vars option to allow unused vars in object destructuring with rest property

I’d like an option for the no-unused-vars rule that would allow unused variables that are created as part of an object destructuring pattern that also includes an experimental rest property.

Use case: experimental object rest properties offer a convenient way to shallow clone an object while omitting certain properties. For example,

let foo = { a: 1, b: 2, extra: { other: 'stuff' }};

// I want a shallow clone of `foo` that omits `extra`
let { extra, ...bar } = foo; // error-- `extra` is unused

return bar; // { a: 1, b: 2 }

This can be done now by naming the unused variables with a pattern (instead of using the shorthand) and configuring no-unused-vars with varsIgnorePattern. It’s less convenient and it adds noise, though.

let { extra: ignored, ...bar } = foo;

Rest/spread properties are still a stage 2 proposal, so it might be premature to add an option to a core rule. I figured I’d open for discussion anyways 😃

[bryanrsmith]

I’ve written a (hopefully temporary) plugin for this at https://github.com/bryanrsmith/eslint-plugin-no-unused-vars-rest. It basically just monkey patches the option into the existing core rule.

I’d be happy to submit a PR to eslint-plugin-babel if everyone would prefer that. It’s a little odd, though, because it doesn’t require babel-eslint. Espree’s experimentalObjectRestSpread option covers it. What do you folks think?

[not-an-aardvark]

With array destructuring, you can use this as a workaround:

const [ , ...tail] = someArray;

This isn’t possible with object destructuring.