ES6 feature: Destructuring: Tracking Issue

[ariya]

12.14.5 Destructuring Assignment

They are used in the left hand side of an assignment expression when = is the assignment operator, or at the LeftHandSideExpression position of a for-in or a for-of loop.

Referred to by:

• 12.14.1 Static Semantics: Early Errors
• 13.6.4.1 Static Semantics: Early Errors

Syntax:

AssignmentPattern[Yield] :
  ObjectAssignmentPattern[?Yield]
  ArrayAssignmentPattern[?Yield]

ObjectAssignmentPattern[Yield] :
  { }
  { AssignmentPropertyList[?Yield] }
  { AssignmentPropertyList[?Yield] , }

ArrayAssignmentPattern[Yield] :
  [ Elisionopt AssignmentRestElement[?Yield]opt ]
  [ AssignmentElementList[?Yield] ]
  [ AssignmentElementList[?Yield] , Elisionopt AssignmentRestElement[?Yield]opt ]

AssignmentPropertyList[Yield] :
  AssignmentProperty[?Yield]
  AssignmentPropertyList[?Yield] , AssignmentProperty[?Yield]

AssignmentElementList[Yield] :
  AssignmentElisionElement[?Yield]
  AssignmentElementList[?Yield] , AssignmentElisionElement[?Yield]

AssignmentElisionElement[Yield] :
  Elisionopt AssignmentElement[?Yield]

AssignmentProperty[Yield] :
  IdentifierReference[?Yield] Initializer[In,?Yield]opt
  PropertyName : AssignmentElement[?Yield]

AssignmentElement[Yield] :
  DestructuringAssignmentTarget[?Yield] Initializer[In,?Yield]opt

AssignmentRestElement[Yield] :
  ... DestructuringAssignmentTarget[?Yield]

DestructuringAssignmentTarget[Yield] :
  LeftHandSideExpression[?Yield]

Spec:

Destructuring Assignment: https://people.mozilla.org/~jorendorff/es6-draft.html#sec-destructuring-assignment

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

Early Errors:

AssignmentProperty : IdentifierReference Initializeropt

• It is a Syntax Error if IsValidSimpleAssignmentTarget of IdentifierReference is false.

DestructuringAssignmentTarget : LeftHandSideExpression

• It is a Syntax Error if LeftHandSideExpression is either an ObjectLiteral or an ArrayLiteral and if the lexical token sequence matched by LeftHandSideExpression cannot be parsed with no tokens left over using AssignmentPattern as the goal symbol.
• It is a Syntax Error if LeftHandSideExpression is neither an ObjectLiteral nor an ArrayLiteral and IsValidSimpleAssignmentTarget(LeftHandSideExpression) is false.

13.2.3 Destructuring Binding Patterns

BindingPatterns are used in LexicalBindings, VariableDeclarations, ForBindings and CatchParameters. BindingElement is also used in FormalParameters. A BindingElement is either a BindingPattern or a BindingIdentifier, optionally followed by a Initializer.

Syntax

BindingPattern[Yield,GeneratorParameter] :
  ObjectBindingPattern[?Yield,?GeneratorParameter]
  ArrayBindingPattern[?Yield,?GeneratorParameter]

ObjectBindingPattern[Yield,GeneratorParameter] :
  { }
  { BindingPropertyList[?Yield,?GeneratorParameter] }
  { BindingPropertyList[?Yield,?GeneratorParameter] , }

ArrayBindingPattern[Yield,GeneratorParameter] :
  [ Elisionopt BindingRestElement[?Yield, ?GeneratorParameter]opt ]
  [ BindingElementList[?Yield, ?GeneratorParameter] ]
  [ BindingElementList[?Yield, ?GeneratorParameter] , Elisionopt BindingRestElement[?Yield, ?GeneratorParameter]opt ]

BindingPropertyList[Yield,GeneratorParameter] :
  BindingProperty[?Yield, ?GeneratorParameter]
  BindingPropertyList[?Yield, ?GeneratorParameter] , BindingProperty[?Yield, ?GeneratorParameter]

BindingElementList[Yield,GeneratorParameter] :
  BindingElisionElement[?Yield, ?GeneratorParameter]
  BindingElementList[?Yield, ?GeneratorParameter] , BindingElisionElement[?Yield, ?GeneratorParameter]

BindingElisionElement[Yield,GeneratorParameter] :
  Elisionopt BindingElement[?Yield, ?GeneratorParameter]

BindingProperty[Yield,GeneratorParameter] :
  SingleNameBinding[?Yield, ?GeneratorParameter]
  PropertyName[?Yield, ?GeneratorParameter] : BindingElement[?Yield, ?GeneratorParameter]

BindingElement[Yield,GeneratorParameter] :
  SingleNameBinding[?Yield, ?GeneratorParameter]
  [+GeneratorParameter] BindingPattern[?Yield,GeneratorParameter] Initializer[In]opt
  [~GeneratorParameter] BindingPattern[?Yield] Initializer[In, ?Yield]opt

SingleNameBinding [Yield, GeneratorParameter] :
  [+GeneratorParameter] BindingIdentifier[Yield] Initializer[In]opt
  [~GeneratorParameter] BindingIdentifier[?Yield] Initializer[In, ?Yield]opt

BindingRestElement[Yield, GeneratorParameter] :
  [+GeneratorParameter] ... BindingIdentifier[Yield]
  [~GeneratorParameter] ... BindingIdentifier[?Yield]

Spec

Destructuring Binding Patterns: https://people.mozilla.org/~jorendorff/es6-draft.html#sec-destructuring-binding-patterns

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

SpiderMonkey AST

interface ObjectPattern <: Pattern {
    type: "ObjectPattern";
    properties: [ { key: Literal | Identifier, value: Pattern } ];
}

interface ArrayPattern <: Pattern {
    type: "ArrayPattern";
    elements: [ Pattern | null ];
}

Shift AST

typedef (ObjectBinding or ArrayBinding or BindingIdentifier or MemberExpression) Binding;


interface BindingWithDefault : Node {
  attribute (ObjectBinding or ArrayBinding or BindingIdentifier) binding;
  attribute Expression init;
};

interface BindingIdentifier : Node {
  attribute Identifier identifier;
};

interface ArrayBinding : Node {
  attribute (Binding or BindingWithDefault)?[] elements;
  attribute BindingIdentifier? restElement;
};

interface ObjectBinding : Node {
  attribute BindingProperty[] properties;
};

interface BindingProperty : Node { };

interface BindingPropertyIdentifier : BindingProperty {
  attribute BindingIdentifier identifier;
  attribute Expression? init;
};

interface BindingPropertyProperty : BindingProperty {
  attribute PropertyName name;
  attribute (Binding or BindingWithDefault) binding;
};


interface PropertyName : Node { };

interface ComputedPropertyName : PropertyName {
  attribute Expression value;
};

interface StaticPropertyName : PropertyName {
  attribute string value;
};

Related Tasks:

• Destructuring default Destructuring Defaults #1028 (previous issue 565)
• Previous issue 489
• Step 1