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Normative: Eliminate extra environment for eval in parameter initializers #1046

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Jan 2, 2020
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Normative: Eliminate extra environment for eval in parameter initializers #1046

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43 changes: 11 additions & 32 deletions spec.html
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Original file line number Diff line number Diff line change
Expand Up @@ -8620,8 +8620,6 @@ <h1>FunctionDeclarationInstantiation ( _func_, _argumentsList_ )</h1>
-->
<emu-alg>
1. Let _calleeContext_ be the running execution context.
1. Let _env_ be the LexicalEnvironment of _calleeContext_.
1. Let _envRec_ be _env_'s EnvironmentRecord.
1. Let _code_ be _func_.[[ECMAScriptCode]].
1. Let _strict_ be _func_.[[Strict]].
1. Let _formals_ be _func_.[[FormalParameters]].
Expand Down Expand Up @@ -8651,6 +8649,15 @@ <h1>FunctionDeclarationInstantiation ( _func_, _argumentsList_ )</h1>
1. Else if _hasParameterExpressions_ is *false*, then
1. If *"arguments"* is an element of _functionNames_ or if *"arguments"* is an element of _lexicalNames_, then
1. Set _argumentsObjectNeeded_ to *false*.
1. If _strict_ is *true* or if _hasParameterExpressions_ is *false*, then
1. NOTE: Only a single lexical environment is needed for the parameters and top-level vars.
1. Let _env_ be the LexicalEnvironment of _calleeContext_.
1. Let _envRec_ be _env_'s EnvironmentRecord.
1. Else,
1. NOTE: A separate Environment Record is needed to ensure that bindings created by direct eval calls in the formal parameter list are outside the environment where parameters are declared.
1. Let _calleeEnv_ be the LexicalEnvironment of _calleeContext_.
1. Let _env_ be NewDeclarativeEnvironment(_calleeEnv_).
1. Let _envRec_ be _env_'s EnvironmentRecord.
1. For each String _paramName_ in _parameterNames_, do
1. Let _alreadyDeclared_ be _envRec_.HasBinding(_paramName_).
1. NOTE: Early errors ensure that duplicate parameter names can only occur in non-strict functions that do not have parameter default values or rest parameters.
Expand Down Expand Up @@ -19560,40 +19567,12 @@ <h1>Runtime Semantics: IteratorBindingInitialization</h1>
</emu-alg>
<emu-grammar>FormalParameter : BindingElement</emu-grammar>
<emu-alg>
1. If ContainsExpression of |BindingElement| is *false*, return the result of performing IteratorBindingInitialization for |BindingElement| using _iteratorRecord_ and _environment_ as the arguments.
1. Let _currentContext_ be the running execution context.
1. Let _originalEnv_ be the VariableEnvironment of _currentContext_.
1. Assert: The VariableEnvironment and LexicalEnvironment of _currentContext_ are the same.
1. Assert: If _environment_ is not *undefined*, then _environment_ and _originalEnv_ are the same.
1. Let _paramVarEnv_ be NewDeclarativeEnvironment(_originalEnv_).
1. Set the VariableEnvironment of _currentContext_ to _paramVarEnv_.
1. Set the LexicalEnvironment of _currentContext_ to _paramVarEnv_.
1. Let _result_ be IteratorBindingInitialization of |BindingElement| with arguments _iteratorRecord_ and _environment_.
1. Set the VariableEnvironment of _currentContext_ to _originalEnv_.
1. Set the LexicalEnvironment of _currentContext_ to _originalEnv_.
1. Return _result_.
1. Return the result of performing IteratorBindingInitialization for |BindingElement| with arguments _iteratorRecord_ and _environment_.
</emu-alg>
<emu-note>
<p>The new Environment Record created in step 6 is only used if the |BindingElement| contains a direct eval.</p>
</emu-note>
<emu-grammar>FunctionRestParameter : BindingRestElement</emu-grammar>
<emu-alg>
1. If ContainsExpression of |BindingRestElement| is *false*, return the result of performing IteratorBindingInitialization for |BindingRestElement| using _iteratorRecord_ and _environment_ as the arguments.
1. Let _currentContext_ be the running execution context.
1. Let _originalEnv_ be the VariableEnvironment of _currentContext_.
1. Assert: The VariableEnvironment and LexicalEnvironment of _currentContext_ are the same.
1. Assert: If _environment_ is not *undefined*, then _environment_ and _originalEnv_ are the same.
1. Let _paramVarEnv_ be NewDeclarativeEnvironment(_originalEnv_).
1. Set the VariableEnvironment of _currentContext_ to _paramVarEnv_.
1. Set the LexicalEnvironment of _currentContext_ to _paramVarEnv_.
1. Let _result_ be IteratorBindingInitialization of |BindingRestElement| with arguments _iteratorRecord_ and _environment_.
1. Set the VariableEnvironment of _currentContext_ to _originalEnv_.
1. Set the LexicalEnvironment of _currentContext_ to _originalEnv_.
1. Return _result_.
1. Return the result of performing IteratorBindingInitialization for |BindingRestElement| with arguments _iteratorRecord_ and _environment_.
</emu-alg>
<emu-note>
<p>The new Environment Record created in step 6 is only used if the |BindingRestElement| contains a direct eval.</p>
</emu-note>
</emu-clause>

<emu-clause id="sec-function-definitions-runtime-semantics-instantiatefunctionobject">
Expand Down