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Allow implementation-defined choice of property or accessor #10

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Allow implementation-defined choice of property or accessor #10

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509e889
Allow implementation-defined choice of property or accessor
dminor Oct 2, 2025
f349e12
Make non-enumerable
dminor Oct 3, 2025
a83ae63
Use field in Agent Record to control data/accessor behaviour
dminor Oct 7, 2025
950072c
Use closures for getter and setter
dminor Oct 7, 2025
2ec1e89
Apply review suggestions
dminor Oct 7, 2025
8deb622
Apply further review fixes
dminor Oct 8, 2025
afc3b83
Apply suggestions from TG3 discussion
dminor Oct 9, 2025
aab3b05
Fixup realm access
dminor Oct 15, 2025
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42 changes: 41 additions & 1 deletion spec.emu
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Expand Up @@ -15,6 +15,35 @@ markEffects: true
<p></p>
</emu-intro>

<emu-clause id="sec-agents">
<h1>Agents</h1>

<emu-table id="table-agent-record" caption="Agent Record Fields">
<table>
<thead>
<tr>
<th>Field Name</th>
<th>Value</th>
<th>Meaning</th>
</tr>
</thead>
<tr>
<td>[[UseErrorCaptureStackTraceDataProperty]]</td>
<td>a Boolean</td>
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Nit: since this isn't a yes/no, it's an either/or, we would typically use a 2-state enum for this. Something like [[ErrorCaptureStackTraceStrategy]] with type "~data-property~ or ~accessor~".

<td>Whether to use a data property or an accessor property for the "stack" property installed by Error.captureStackTrace.</td>
</tr>
</table>
</emu-table>

<p>Once the values of [[Signifier]], [[IsLockFree1]], [[IsLockFree2]], and [[UseErrorCaptureStackTraceDataProperty]] have been observed by any agent in the agent cluster they cannot change.</p>
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Suggested change
<p>Once the values of [[Signifier]], [[IsLockFree1]], [[IsLockFree2]], and [[UseErrorCaptureStackTraceDataProperty]] have been observed by any agent in the agent cluster they cannot change.</p>
<p>Once the values of [[Signifier]], [[IsLockFree1]], [[IsLockFree2]], and [[ErrorCaptureStackTraceStrategy]] have been observed by any agent in the agent cluster they cannot change.</p>

Need to update this field name here and below.

</emu-clause>

<emu-clause id="sec-agent-clusters">
<h1>Agent Clusters</h1>

<p>All agents within a cluster must have the same value for the [[UseErrorCaptureStackTraceDataProperty]] field in their respective Agent Records.</p>
</emu-clause>

<emu-clause id="sec-fundamental-objects" number="20">
<h1>Fundamental Objects</h1>

Expand All @@ -34,7 +63,18 @@ markEffects: true
1. NOTE: This can be used to hide implementation details on the stack trace that aren't useful to user.
1. Else,
1. Let _string_ be an implementation-defined string that represents the current stack trace.
1. Perform ? SetterThatIgnoresPrototypeProperties(_error_, OrdinaryObjectCreate(*null*), *"stack"*, _string_).
1. Let _useErrorCaptureStackTraceDataProperty_ be the value of the [[UseErrorCaptureStackTraceDataProperty]] field of the surrounding agent's Agent Record.
1. If _useErrorCaptureStackTraceDataProperty_ is *true*, then
1. Perform ? SetterThatIgnoresPrototypeProperties(_error_, OrdinaryObjectCreate(*null*), *"stack"*, _string_)..
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To bring the two cases closer together it would be nice if both cases go through the same definition primitive. E.g., we could have an implementation specific PropertyDescriptor ([[Get]] vs. [[Value]]) which is then installed in the same way (e.g., OrdinaryDefineOwnProperty) in both cases.

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I'd prefer all of the things that share the behaviour described in SetterThatIgnoresPrototypeProperties go through that AO. It's a very specific exception to how we usually do things in the language and it should both have fully consistent normative requirements and be discoverable. Reusing that AO helps with both goals.

1. Else,
1. If ? IsExtensible( _error_ ) is *false*, throw a *TypeError* exception.
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Formatting nit:

Suggested change
1. If ? IsExtensible( _error_ ) is *false*, throw a *TypeError* exception.
1. If ? IsExtensible(_error_) is *false*, throw a *TypeError* exception.

1. Let getterClosure be a new Abstract Closure with no parameters that captures _string_ and performs the following steps when called:
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@michaelficarra michaelficarra Oct 7, 2025 •
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Suggested change
1. Let getterClosure be a new Abstract Closure with no parameters that captures _string_ and performs the following steps when called:
1. Let _getterClosure_ be a new Abstract Closure with no parameters that captures _string_ and performs the following steps when called:

Similarly for all the bindings below.

1. Return NormalCompletion(_string_).
1. Let getter be CreateBuiltinFunction(getterClosure, 0, "", « »).
1. Let setterClosure be a new Abstract Closure with parameters (_value_) that captures _error_ and performs the following steps when called:
1. Perform ! SetterThatIgnoresPrototypeProperties(_error_, OrdinaryObjectCreate(*null*), *"stack"*, _value_).
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Suggested change
1. Perform ! SetterThatIgnoresPrototypeProperties(_error_, OrdinaryObjectCreate(*null*), *"stack"*, _value_).
1. Perform ? SetterThatIgnoresPrototypeProperties(_error_, OrdinaryObjectCreate(*null*), *"stack"*, _value_).

This AO can fail if the setter is called after the "stack" property is deleted, for example.

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Suggested change
1. Perform ! SetterThatIgnoresPrototypeProperties(_error_, OrdinaryObjectCreate(*null*), *"stack"*, _value_).
1. Perform ! SetterThatIgnoresPrototypeProperties(_error_, *null*, *"stack"*, _value_).

This is just used for a SameValue test against _error_, so you just need to pass anything else.

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You still need to return something here.

Suggested change
1. Perform ! SetterThatIgnoresPrototypeProperties(_error_, OrdinaryObjectCreate(*null*), *"stack"*, _value_).
1. Perform ! SetterThatIgnoresPrototypeProperties(_error_, OrdinaryObjectCreate(*null*), *"stack"*, _value_).
2. Return NormalCompletion(*undefined*).

1. Let setter be CreateBuiltinFunction(setterClosure, 1, "", « »).
1. Perform ! OrdinaryDefineOwnProperty(_error_, *"stack"*, PropertyDescriptor { [[Get]]: getter, [[Set]]: setter, [[Enumerable]]: false, [[Configurable]]: true }).
1. Return *undefined*.
</emu-alg>
</emu-clause>
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