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Normative: Allow initializers in ForInStatement heads (#614)
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@bakkot @bterlson
bakkot authored and bterlson committed Aug 5, 2016
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Expand Up @@ -15384,6 +15384,9 @@ <h2>Syntax</h2>
BindingIdentifier[?Yield]
BindingPattern[?Yield]
</emu-grammar>
<emu-note>
<p>This section is extended by Annex <emu-xref href="#sec-initializers-in-forin-statement-heads"></emu-xref>.</p>
</emu-note>

<!-- es6num="13.7.1" -->
<emu-clause id="sec-iteration-statements-semantics">
Expand Down Expand Up @@ -15848,6 +15851,9 @@ <h1>Static Semantics: ContainsDuplicateLabels</h1>
<emu-alg>
1. Return ContainsDuplicateLabels of |Statement| with argument _labelSet_.
</emu-alg>
<emu-note>
<p>This section is extended by Annex <emu-xref href="#sec-initializers-in-forin-statement-heads"></emu-xref>.</p>
</emu-note>
</emu-clause>

<!-- es6num="13.7.5.4" -->
Expand All @@ -15867,6 +15873,9 @@ <h1>Static Semantics: ContainsUndefinedBreakTarget</h1>
<emu-alg>
1. Return ContainsUndefinedBreakTarget of |Statement| with argument _labelSet_.
</emu-alg>
<emu-note>
<p>This section is extended by Annex <emu-xref href="#sec-initializers-in-forin-statement-heads"></emu-xref>.</p>
</emu-note>
</emu-clause>

<!-- es6num="13.7.5.5" -->
Expand All @@ -15886,6 +15895,9 @@ <h1>Static Semantics: ContainsUndefinedContinueTarget</h1>
<emu-alg>
1. Return ContainsUndefinedContinueTarget of |Statement| with arguments _iterationSet_ and &laquo; &raquo;.
</emu-alg>
<emu-note>
<p>This section is extended by Annex <emu-xref href="#sec-initializers-in-forin-statement-heads"></emu-xref>.</p>
</emu-note>
</emu-clause>

<!-- es6num="13.7.5.6" -->
Expand All @@ -15904,6 +15916,9 @@ <h1>Static Semantics: IsDestructuring</h1>
<emu-alg>
1. Return *true*.
</emu-alg>
<emu-note>
<p>This section is extended by Annex <emu-xref href="#sec-initializers-in-forin-statement-heads"></emu-xref>.</p>
</emu-note>
</emu-clause>

<!-- es6num="13.7.5.7" -->
Expand Down Expand Up @@ -15938,6 +15953,9 @@ <h1>Static Semantics: VarDeclaredNames</h1>
<emu-alg>
1. Return the VarDeclaredNames of |Statement|.
</emu-alg>
<emu-note>
<p>This section is extended by Annex <emu-xref href="#sec-initializers-in-forin-statement-heads"></emu-xref>.</p>
</emu-note>
</emu-clause>

<!-- es6num="13.7.5.8" -->
Expand Down Expand Up @@ -15972,6 +15990,9 @@ <h1>Static Semantics: VarScopedDeclarations</h1>
<emu-alg>
1. Return the VarScopedDeclarations of |Statement|.
</emu-alg>
<emu-note>
<p>This section is extended by Annex <emu-xref href="#sec-initializers-in-forin-statement-heads"></emu-xref>.</p>
</emu-note>
</emu-clause>

<!-- es6num="13.7.5.9" -->
Expand Down Expand Up @@ -16039,6 +16060,9 @@ <h1>Runtime Semantics: LabelledEvaluation</h1>
1. Let _keyResult_ be the result of performing ? ForIn/OfHeadEvaluation(BoundNames of |ForDeclaration|, |AssignmentExpression|, ~iterate~).
1. Return ? ForIn/OfBodyEvaluation(|ForDeclaration|, |Statement|, _keyResult_, ~lexicalBinding~, _labelSet_).
</emu-alg>
<emu-note>
<p>This section is extended by Annex <emu-xref href="#sec-initializers-in-forin-statement-heads"></emu-xref>.</p>
</emu-note>
</emu-clause>

<!-- es6num="13.7.5.12" -->
Expand Down Expand Up @@ -36612,6 +36636,69 @@ <h1>VariableStatements in Catch Blocks</h1>
1. If _thisEnvRec_ is not the Environment Record for a |Catch| clause, let _bindingExists_ be *true*.
</emu-alg>
</emu-annex>

<!-- es6num="B.3.6" -->
<emu-annex id="sec-initializers-in-forin-statement-heads">
<h1>Initializers in ForIn Statement Heads</h1>
<p>The following augments the |IterationStatement| production in <emu-xref href="#sec-iteration-statements"></emu-xref>:</p>
<emu-grammar>
IterationStatement[Yield, Return]:
`for` `(` `var` BindingIdentifier[?Yield] Initializer[~In, ?Yield] `in` Expression[+In, ?Yield] `)` Statement[?Yield, ?Return]
</emu-grammar>
<p>This production only applies when parsing non-strict code.</p>
<p>The static semantics of ContainsDuplicateLabels in <emu-xref href="#sec-for-in-and-for-of-statements-static-semantics-containsduplicatelabels"></emu-xref> are augmented with the following:</p>
<emu-grammar>IterationStatement : `for` `(` `var` BindingIdentifier Initializer `in` Expression `)` Statement</emu-grammar>
<emu-alg>
1. Return ContainsDuplicateLabels of |Statement| with argument _labelSet_.
</emu-alg>
<p>The static semantics of ContainsUndefinedBreakTarget in <emu-xref href="#sec-for-in-and-for-of-statements-static-semantics-containsundefinedbreaktarget"></emu-xref> are augmented with the following:</p>
<emu-grammar>IterationStatement : `for` `(` `var` BindingIdentifier Initializer `in` Expression `)` Statement</emu-grammar>
<emu-alg>
1. Return ContainsUndefinedBreakTarget of |Statement| with argument _labelSet_.
</emu-alg>
<p>The static semantics of ContainsUndefinedContinueTarget in <emu-xref href="#sec-for-in-and-for-of-statements-static-semantics-containsundefinedcontinuetarget"></emu-xref> are augmented with the following:</p>
<emu-grammar>IterationStatement : `for` `(` `var` BindingIdentifier Initializer `in` Expression `)` Statement</emu-grammar>
<emu-alg>
1. Return ContainsUndefinedContinueTarget of |Statement| with arguments _iterationSet_ and &laquo; &raquo;.
</emu-alg>
<p>The static semantics of IsDestructuring in <emu-xref href="#sec-for-in-and-for-of-statements-static-semantics-isdestructuring"></emu-xref> are augmented with the following:</p>
<emu-grammar>
BindingIdentifier :
Identifier
`yield`
</emu-grammar>
<emu-alg>
1. Return *false*.
</emu-alg>
<p>The static semantics of VarDeclaredNames in <emu-xref href="#sec-for-in-and-for-of-statements-static-semantics-vardeclarednames"></emu-xref> are augmented with the following:</p>
<emu-grammar>IterationStatement : `for` `(` `var` BindingIdentifier Initializer `in` Expression `)` Statement</emu-grammar>
<emu-alg>
1. Let _names_ be the BoundNames of |BindingIdentifier|.
1. Append to _names_ the elements of the VarDeclaredNames of |Statement|.
1. Return _names_.
</emu-alg>
<p>The static semantics of VarScopedDeclarations in <emu-xref href="#sec-for-in-and-for-of-statements-static-semantics-varscopeddeclarations"></emu-xref> are augmented with the following:</p>
<emu-grammar>IterationStatement : `for` `(` `var` BindingIdentifier Initializer `in` Expression `)` Statement</emu-grammar>
<emu-alg>
1. Let _declarations_ be a List containing |BindingIdentifier|.
1. Append to _declarations_ the elements of the VarScopedDeclarations of |Statement|.
1. Return _declarations_.
</emu-alg>
<p>The runtime semantics of LabelledEvaluation in <emu-xref href="#sec-for-in-and-for-of-statements-runtime-semantics-labelledevaluation"></emu-xref> are augmented with the following:</p>
<emu-grammar>IterationStatement : `for` `(` `var` BindingIdentifier Initializer `in` Expression `)` Statement</emu-grammar>
<emu-alg>
1. Let _bindingId_ be StringValue of |BindingIdentifier|.
1. Let _lhs_ be ? ResolveBinding(_bindingId_).
1. Let _rhs_ be the result of evaluating |Initializer|.
1. Let _value_ be ? GetValue(_rhs_).
1. If IsAnonymousFunctionDefinition(|Initializer|) is *true*, then
1. Let _hasNameProperty_ be ? HasOwnProperty(_value_, `"name"`).
1. If _hasNameProperty_ is *false*, perform SetFunctionName(_value_, _bindingId_).
1. Perform ? PutValue(_lhs_, _value_).
1. Let _keyResult_ be ? ForIn/OfHeadEvaluation(&laquo; &raquo;, |Expression|, ~enumerate~).
1. Return ? ForIn/OfBodyEvaluation(|BindingIdentifier|, |Statement|, _keyResult_, ~varBinding~, _labelSet_).
</emu-alg>
</emu-annex>
</emu-annex>
</emu-annex>

Expand Down Expand Up @@ -36702,7 +36789,7 @@ <h1>Additions and Changes That Introduce Incompatibilities with Prior Editions</
<p><emu-xref href="#sec-if-statement-runtime-semantics-evaluation"></emu-xref>: In ECMAScript 2015, the normal completion value of an |IfStatement| is never the value ~empty~. If no |Statement| part is evaluated or if the evaluated |Statement| part produces a normal completion whose value is ~empty~, the completion value of the |IfStatement| is *undefined*.</p>
<p><emu-xref href="#sec-iteration-statements"></emu-xref>: In ECMAScript 2015, if the `(` token of a for statement is immediately followed by the token sequence `let [` then the `let` is treated as the start of a |LexicalDeclaration|. In previous editions such a token sequence would be the start of an |Expression|.</p>
<p><emu-xref href="#sec-iteration-statements"></emu-xref>: In ECMAScript 2015, if the ( token of a for-in statement is immediately followed by the token sequence `let [` then the `let` is treated as the start of a |ForDeclaration|. In previous editions such a token sequence would be the start of an |LeftHandSideExpression|.</p>
<p><emu-xref href="#sec-iteration-statements"></emu-xref>: Prior to ECMAScript 2015, an initialization expression could appear as part of the |VariableDeclaration| that precedes the `in` keyword. The value of that expression was always discarded. In ECMAScript 2015, the _ForBinding_ in that same position does not allow the occurrence of such an initializer.</p>
<p><emu-xref href="#sec-iteration-statements"></emu-xref>: Prior to ECMAScript 2015, an initialization expression could appear as part of the |VariableDeclaration| that precedes the `in` keyword. In ECMAScript 2015, the |ForBinding| in that same position does not allow the occurrence of such an initializer. In ECMAScript 2017, such an initializer is permitted only in non-strict code.</p>
<p><emu-xref href="#sec-iteration-statements"></emu-xref>: In ECMAScript 2015, the completion value of an |IterationStatement| is never the value ~empty~. If the |Statement| part of an |IterationStatement| is not evaluated or if the final evaluation of the |Statement| part produces a completion whose value is ~empty~, the completion value of the |IterationStatement| is *undefined*.</p>
<p><emu-xref href="#sec-with-statement-runtime-semantics-evaluation"></emu-xref>: In ECMAScript 2015, the normal completion value of a |WithStatement| is never the value ~empty~. If evaluation of the |Statement| part of a |WithStatement| produces a normal completion whose value is ~empty~, the completion value of the |WithStatement| is *undefined*.</p>
<p><emu-xref href="#sec-switch-statement-runtime-semantics-evaluation"></emu-xref>: In ECMAScript 2015, the completion value of a |SwitchStatement| is never the value ~empty~. If the |CaseBlock| part of a |SwitchStatement| produces a completion whose value is ~empty~, the completion value of the |SwitchStatement| is *undefined*.</p>
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