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fix reentrancy invariant #39

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merged 12 commits into from
Apr 24, 2024
Merged

fix reentrancy invariant #39

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4098f92
normative: handle reentrancy invariant
guybedford Apr 2, 2024
07b34ab
fixups
guybedford Apr 2, 2024
8826194
simplify
guybedford Apr 2, 2024
9ee06d5
readd note
guybedford Apr 2, 2024
35581c7
Update spec.emu
guybedford Apr 2, 2024
e9094d5
fixup evaluating-async handling
guybedford Apr 2, 2024
3de1cd6
fixups
guybedford Apr 2, 2024
0744c50
simplify diff
guybedford Apr 2, 2024
f1512b8
grammar
guybedford Apr 2, 2024
130ddd9
invert assertion to call out evaluating
guybedford Apr 2, 2024
3dd0025
remove evaluating-async stop condition for now
guybedford Apr 4, 2024
d93f0aa
Update spec.emu
guybedford Apr 5, 2024
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36 changes: 21 additions & 15 deletions spec.emu
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Original file line number Diff line number Diff line change
Expand Up @@ -74,7 +74,9 @@ contributors: Nicolò Ribaudo
1. If _P_ is a Symbol, then
1. Return ! OrdinaryGet(_O_, _P_, _Receiver_).
1. <ins>Let _m_ be _O_.[[Module]].</ins>
1. <ins>If _m_ is not a Cyclic Module Record, or both _m_.[[Status]] is ~linked~ and AnyDependencyNeedsAsyncEvaluation(_m_) is *false*, then</ins>
1. <ins>If _m_ is not a Cyclic Module Record, then</ins>
1. <ins>Perform ? EvaluateSync(_m_).</ins>
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EvaluateSync unconditionally calls module.Evaluate(). It will cause the target non Cyclic Module Record to be evaluated every time its namespace object is accessed.

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I would recommend posting this as a new issue as it is not specific to this PR.

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Evaluate() can be called multiple times and it's expected to cache it's result:

Returns a promise for the evaluation of this module and its dependencies, resolving on successful evaluation or if it has already been evaluated successfully, and rejecting for an evaluation error or if it has already been evaluated unsuccessfully.

https://tc39.es/ecma262/multipage/ecmascript-language-scripts-and-modules.html#table-abstract-methods-of-module-records

Dynamic import also calls Evaluate() every time, even if a module is already evaluated.

1. <ins>Otherwise if _m_.[[Status]] is not ~evaluated~ and ! ReadyForSyncExecution(_m_) is *true*, then</ins>
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if ReadyForSyncExecution(m) is false, then what will this AO return? The (possibly) uninitialized binding and lead to TDZ error (for export let)?

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Yes, in the case of it not being ready, the namespace will expose TDZ or undefined for non-TDZ bindings, per the note.

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This is also what happens with cycles without defer:

// entrypoint
import "dep";
export let a = 1;
// dep
import * as ns from "entrypoint";
ns.a; // TDZ error

1. <ins>Perform ? EvaluateSync(_m_).</ins>
1. Let _exports_ be _O_.[[Exports]].
1. If _exports_ does not contain _P_, return *undefined*.
Expand All @@ -93,29 +95,32 @@ contributors: Nicolò Ribaudo
<p>ResolveExport is side-effect free. Each time this operation is called with a specific _exportName_, _resolveSet_ pair as arguments it must return the same result. An implementation might choose to pre-compute or cache the ResolveExport results for the [[Exports]] of each module namespace exotic object.</p>
</emu-note>
<emu-note>
<ins>AnyDependencyNeedsAsyncEvaluation can return *true* when this [[Get]] operation on a namespace coming from a deferred import is triggered during the evaluation of one of its dependencies, either synchronously or asynchronously. In that case, the module cannot be fully evaluated and some of its exports will not be initialized yet.</ins>
<ins>ReadyForSyncExecution can return *false* when this [[Get]] operation on a namespace coming from a deferred import is triggered during the evaluation of one of its dependencies, either synchronously or asynchronously. In that case, the module cannot be fully evaluated and some of its exports will not be initialized yet.</ins>
</emu-note>

<emu-clause id="sec-module-namespace-exotic-objects-get-p-receiver-AnyDependencyNeedsAsyncEvaluation" type="abstract operation">
<emu-clause id="sec-module-namespace-exotic-objects-get-p-receiver-ReadyForSyncExecution" type="abstract operation">
<h1>
<ins>
AnyDependencyNeedsAsyncEvaluation (
_module_: a Module Record,
ReadyForSyncExecution (
_module_: a Cyclic Module Record,
optional _seen_: a List of Module Records,
): a Boolean
</ins>
</h1>
<dl class="header"></dl>
<emu-alg>
1. If _seen_ is not provided, let _seen_ be a new empty List.
1. If _seen_ contains _module_, return *false*.
1. If _seen_ contains _module_, return *true*.
1. Append _module_ to _seen_.
1. If _module_ is not a Cyclic Module Record or _module_.[[Status]] is ~evaluated~, return *false*.
1. If _module_.[[HasTLA]] is *true*, return *true*.
1. If _module_.[[Status]] is ~evaluated~, return *true*.
1. If _module_.[[Status]] is ~evaluating~ or ~evaluating-async~, return *false*.
1. Assert: _module_.[[Status]] is ~linked~.
1. If _module_.[[HasTLA]] is *true*, return *false*.
1. For each ModuleRequest Record _required_ of _module_.[[RequestedModules]], do
1. Let _requiredModule_ be GetImportedModule(_module_, _required_.[[Specifer]]).
1. If AnyDependencyNeedsAsyncEvaluation(_requiredModule_, _seen_) is *true*, return *true*.
1. Return *false*.
1. If ! ReadyForSyncExecution(_requiredModule_, _seen_) is *false*, then
1. Return *false*.
1. Return *true*.
</emu-alg>
</emu-clause>
</emu-clause>
Expand Down Expand Up @@ -514,7 +519,7 @@ contributors: Nicolò Ribaudo
a List of <del>Strings</del><ins>ModuleRequest Records</ins>
</td>
<td>
A List of all the |ModuleSpecifier| strings used by the module represented by this record to request the importation of a module, <ins>alongside with their maximum specified import phase (~defer~ or ~evaluation~)</ins>. The List is in source text occurrence order.
A List of all the |ModuleSpecifier| strings used by the module represented by this record to request the importation of a module, <ins>along with their maximum specified import phase (~defer~ or ~evaluation~)</ins>. The List is in source text occurrence order.
</td>
</tr>
<tr>
Expand Down Expand Up @@ -874,7 +879,8 @@ contributors: Nicolò Ribaudo
</dl>

<emu-alg>
1. Assert: This call to Evaluate is not happening at the same time as another call to Evaluate within the surrounding agent.
1. <del>Assert: This call to Evaluate is not happening at the same time as another call to Evaluate within the surrounding agent.</del>.
1. <ins>Assert: None of _module_ or any of its recursive dependencies have [[Status]] set to ~evaluating~ or a status earlier than ~linked~.</ins>
1. Assert: _module_.[[Status]] is one of ~linked~, ~evaluating-async~, or ~evaluated~.
1. If _module_.[[Status]] is either ~evaluating-async~ or ~evaluated~, set _module_ to _module_.[[CycleRoot]].
1. If _module_.[[TopLevelCapability]] is not ~empty~, then
Expand Down Expand Up @@ -996,7 +1002,7 @@ contributors: Nicolò Ribaudo
</h1>
<dl class="header">
<dt>description</dt>
<dd>It synchronously evaluates _module_, which must not have asynchronous dependencies.</dd>
<dd>It synchronously evaluates _module_ provided it is ready for synchronous execution.</dd>
</dl>

<emu-alg>
Expand All @@ -1009,7 +1015,7 @@ contributors: Nicolò Ribaudo
</emu-alg>
</emu-clause>

<emu-clause id="sec-InnerAsyncSubgraphsEvaluation" type="abstract operation">
<emu-clause id="sec-GatherAsynchronousTransitiveDependencies" type="abstract operation">
<h1>
<ins>
GatherAsynchronousTransitiveDependencies (
Expand All @@ -1021,7 +1027,7 @@ contributors: Nicolò Ribaudo
</h1>
<dl class="header">
<dt>description</dt>
<dd></dd>
<dd>Collects the direct post-order list of asynchronous unexecuted transitive dependencies, stopping the depth-first search for a branch when an async dependency is found.</dd>
</dl>

<emu-alg>
Expand Down