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Correctly check reserved word for PropertyDefinition: IdentifierReference #11862

merged 3 commits into from Jul 29, 2020


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JLHwung commented Jul 21, 2020

Q                       A
Fixed Issues? Fixes #10411
Patch: Bug Fix? Yes
Tests Added + Pass? Yes
License MIT

For object shorthand property, e.g. ({ arguments }) is allowed because

PropertyDefinition -> IdentifierReference -> Identifier -> IdentifierName but not ReservedWord

and arguments and eval is not ReservedWord

For destructuring patterns, e.g. ({ arguments = 1 }) = {} is allowed (in sloppy mode) because

PropertyDefinition -> CoverInitializedName -> IdentifierReference -> Identifier -> IdentifierName but not ReservedWord

If the fourth argument of this.checkReservedWord is true, it should be applied on BindingIdentifier, where eval and arguments are forbidden. Therefore the fix here is to align the spec and pass false instead.

This PR fixes a downstream issue: angular/angular-cli#17439

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nicolo-ribaudo commented Jul 22, 2020

For destructuring patterns, e.g. ({ arguments = 1 }) = {} is allowed because

I don't think so: the destructuring pattern must match the "AssignmentPattern" production, and: Static Semantics: Early Errors

AssignmentProperty : IdentifierReference Initializer[opt]

  • It is a Syntax Error if AssignmentTargetType of IdentifierReference is not simple.

12.1.3 Static Semantics: AssignmentTargetType

IdentifierReference : Identifier

  1. If this IdentifierReference is contained in strict mode code and StringValue of Identifier is "eval" or "arguments", return invalid.
  2. Return simple.
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JLHwung commented Jul 22, 2020

If this IdentifierReference is contained in strict mode code and StringValue of Identifier is "eval" or "arguments", return invalid.

As for destructuring, we will check the BindingIdentifier ReservedWord in checkLVal later:

this.state.strict &&
// "Global" reserved words have already been checked by parseIdentifier,
// unless they have been found in the id or parameters of a strict-mode
// function in a sloppy context.
? isStrictBindReservedWord(, this.inModule)
: isStrictBindOnlyReservedWord(

Thus the following test case still throws.

"use strict";
const { arguments } = foo();

Since we can not differentiate between CoverInitializedName and AssignmentProperty until we see an = or =>, I think the change here is okay.

hzoo approved these changes Jul 29, 2020
@JLHwung JLHwung merged commit 01d4625 into babel:main Jul 29, 2020
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@JLHwung JLHwung deleted the JLHwung:fix-10411 branch Jul 29, 2020
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