ES6: Spread Element (for function argument)

[markelog]

Syntax:

To be written.

Spec:

https://people.mozilla.org/~jorendorff/es6-draft.html#sec-array-initializer

Relevant AST interfaces (from https://github.com/estree/estree):

interface SpreadElement <: Node {
    type: "SpreadElement";
    argument: Expression;
}

extend interface CallExpression {
    arguments: [ Expression | SpreadElement ];
}

Early Errors:

The following early errors should be detected: (to be written)

Related Tasks:

• Error message

[michaelficarra]

Spread is not just allowed in function argument position, but also as an array initialiser element.

[...a]

[markelog]

As i see it, spread operator is not supported for the function calls. Arrays and fd are.

[markelog]

So for the expression a(...b) correct AST should look like that -

{
  "type": "Program",
  "body": [
    {
      "type": "ExpressionStatement",
      "expression": {
        "type": "CallExpression",
        "callee": {
          "type": "Identifier",
          "name": "a"
        },
        "arguments": [
          {
            "argument": {
              "name": "b",
              "type": "Identifier",
            },
            "type": "SpreadElement",
          }
        ]
      }
    }
  ]
}

@mikesherov, @ariya ?

[markelog]

Does cherry-picking these commits is sufficient?

/cc @Benvie

[markelog]

@mikesherov @ariya could one of you confirm my proposal?

[ariya]

@markelog Probably not. Much has changed since and master has diverged much vs the old harmony branch.

[ariya]

Apparently spread element for array initializer has been done by @ikarienator as part of #1045. Thus, let's scope this only for function argument.