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Editorial: Eliminate monkey-patching from "VariableStatements in Catc…
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…h Blocks"
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@jmdyck
jmdyck committed Oct 31, 2022
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Showing 1 changed file with 12 additions and 33 deletions.
45 changes: 12 additions & 33 deletions spec.html
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Expand Up @@ -22909,12 +22909,9 @@ <h1>Static Semantics: Early Errors</h1>
It is a Syntax Error if any element of the BoundNames of |CatchParameter| also occurs in the LexicallyDeclaredNames of |Block|.
</li>
<li>
It is a Syntax Error if any element of the BoundNames of |CatchParameter| also occurs in the VarDeclaredNames of |Block|.
It is a Syntax Error if any element of the BoundNames of |CatchParameter| also occurs in the VarDeclaredNames of |Block|<ins normative-optional>, unless the host supports <emu-xref href="#sec-variablestatements-in-catch-blocks" title></emu-xref> and |CatchParameter| is <emu-grammar>CatchParameter : BindingIdentifier</emu-grammar></ins>.
</li>
</ul>
<emu-note>
<p>An alternative static semantics for this production is given in <emu-xref href="#sec-variablestatements-in-catch-blocks"></emu-xref>.</p>
</emu-note>
</emu-clause>

<emu-clause id="sec-runtime-semantics-catchclauseevaluation" type="sdo">
Expand Down Expand Up @@ -28829,8 +28826,10 @@ <h1>
1. NOTE: The environment of with statements cannot contain any lexical declaration so it doesn't need to be checked for var/let hoisting conflicts.
1. For each element _name_ of _varNames_, do
1. If ! _thisEnv_.HasBinding(_name_) is *true*, then
1. [id="step-evaldeclarationinstantiation-throw-duplicate-binding"] Throw a *SyntaxError* exception.
1. NOTE: Annex <emu-xref href="#sec-variablestatements-in-catch-blocks"></emu-xref> defines alternate semantics for the above step.
1. [id="step-evaldeclarationinstantiation-throw-duplicate-binding"] If <ins normative-optional>the host supports <emu-xref href="#sec-variablestatements-in-catch-blocks" title></emu-xref></ins>, then
1. If _thisEnv_ is not the Environment Record for a |Catch| clause, throw a *SyntaxError* exception.
1. Else,
1. Throw a *SyntaxError* exception.
1. NOTE: A direct eval will not hoist var declaration over a like-named lexical declaration.
1. Set _thisEnv_ to _thisEnv_.[[OuterEnv]].
1. Let _privateIdentifiers_ be a new empty List.
Expand Down Expand Up @@ -28874,7 +28873,10 @@ <h1>
1. Repeat, while _thisEnv_ is not the same as _varEnv_,
1. If _thisEnv_ is not an Object Environment Record, then
1. If ! _thisEnv_.HasBinding(_F_) is *true*, then
1. [id="step-evaldeclarationinstantiation-web-compat-bindingexists"] Let _bindingExists_ be *true*.
1. [id="step-evaldeclarationinstantiation-web-compat-bindingexists"] If <ins normative-optional>the host supports <emu-xref href="#sec-variablestatements-in-catch-blocks" title></emu-xref></ins>, then
1. If _thisEnv_ is not the Environment Record for a |Catch| clause, let _bindingExists_ be *true*.
1. Else,
1. Let _bindingExists_ be *true*.
1. Set _thisEnv_ to _thisEnv_.[[OuterEnv]].
1. If _bindingExists_ is *false* and _varEnv_ is a Global Environment Record, then
1. If _varEnv_.HasLexicalDeclaration(_F_) is *false*, then
Expand Down Expand Up @@ -28932,9 +28934,6 @@ <h1>
1. Perform ! _varEnv_.InitializeBinding(_vn_, *undefined*).
1. Return ~unused~.
</emu-alg>
<emu-note>
<p>An alternative version of this algorithm is described in <emu-xref href="#sec-variablestatements-in-catch-blocks"></emu-xref>.</p>
</emu-note>
</emu-clause>
</emu-clause>

Expand Down Expand Up @@ -48257,31 +48256,11 @@ <h1>FunctionDeclarations in IfStatement Statement Clauses</h1>

<emu-annex id="sec-variablestatements-in-catch-blocks">
<h1>VariableStatements in Catch Blocks</h1>
<p>The content of subclause <emu-xref href="#sec-try-statement-static-semantics-early-errors"></emu-xref> is replaced with the following:</p>
<emu-grammar>Catch : `catch` `(` CatchParameter `)` Block</emu-grammar>
<ul>
<li>
It is a Syntax Error if BoundNames of |CatchParameter| contains any duplicate elements.
</li>
<li>
It is a Syntax Error if any element of the BoundNames of |CatchParameter| also occurs in the LexicallyDeclaredNames of |Block|.
</li>
<li>
It is a Syntax Error if any element of the BoundNames of |CatchParameter| also occurs in the VarDeclaredNames of |Block| unless |CatchParameter| is <emu-grammar>CatchParameter : BindingIdentifier</emu-grammar>.
</li>
</ul>
<p>In this feature, the |Block| of a |Catch| clause may contain `var` declarations that bind a name that is also bound by the |CatchParameter|. This is accomplished by modifying an early error rule for <emu-grammar>Catch : `catch` `(` CatchParameter `)` Block</emu-grammar> in <emu-xref href="#sec-try-statement-static-semantics-early-errors"></emu-xref>.</p>
<emu-note>
<p>The |Block| of a |Catch| clause may contain `var` declarations that bind a name that is also bound by the |CatchParameter|. At runtime, such bindings are instantiated in the VariableDeclarationEnvironment. They do not shadow the same-named bindings introduced by the |CatchParameter| and hence the |Initializer| for such `var` declarations will assign to the corresponding catch parameter rather than the `var` binding.</p>
<p>At runtime, such bindings are instantiated in the VariableDeclarationEnvironment. They do not shadow the same-named bindings introduced by the |CatchParameter| and hence the |Initializer| for such `var` declarations will assign to the corresponding catch parameter rather than the `var` binding.</p>
</emu-note>
<p>This modified behaviour also applies to `var` and `function` declarations introduced by direct eval calls contained within the |Block| of a |Catch| clause. This change is accomplished by modifying the algorithm of <emu-xref href="#sec-evaldeclarationinstantiation"></emu-xref> as follows:</p>
<p>Step <emu-xref href="#step-evaldeclarationinstantiation-throw-duplicate-binding"></emu-xref> is replaced by:</p>
<emu-alg replaces-step="step-evaldeclarationinstantiation-throw-duplicate-binding">
1. If _thisEnv_ is not the Environment Record for a |Catch| clause, throw a *SyntaxError* exception.
</emu-alg>
<p>Step <emu-xref href="#step-evaldeclarationinstantiation-web-compat-bindingexists"></emu-xref> is replaced by:</p>
<emu-alg replaces-step="step-evaldeclarationinstantiation-web-compat-bindingexists">
1. If _thisEnv_ is not the Environment Record for a |Catch| clause, let _bindingExists_ be *true*.
</emu-alg>
<p>This modified behaviour also applies to `var` and `function` declarations introduced by direct eval calls contained within the |Block| of a |Catch| clause. This change is accomplished by modifying steps <emu-xref href="#step-evaldeclarationinstantiation-throw-duplicate-binding"></emu-xref> and <emu-xref href="#step-evaldeclarationinstantiation-web-compat-bindingexists"></emu-xref> in EvalDeclarationInstantiation.</p>
</emu-annex>

<emu-annex id="sec-initializers-in-forin-statement-heads">
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