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[[CycleRoot]] is expected on all evaluated modules, but it's not set on modules that throw synchronously #3582

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@nicolo-ribaudo
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Test case:

// entrypoint.js
await import("./foo.js").catch(() => {});
await import("./foo.js");
// foo.js
throw 1;

When we call module.Evaluate() for the first dynamic import:

  • Step 8 of Evaluate() calls InnerModuleEvaluation(module)
  • Step 13.a of InnerModuleEvaluation does ? module.ExecuteModule()
    • module.ExecuteModule() returns an abrupt completion, so we return early without going to step 16.b.viii (which is the only place in the spec that sets module.[[CycleRoot]])
  • Step 9 of Evaluate sets module.[[Status]] to ~evaluated~ and module.[[EvaluationError]] to the throw completion.

When we call module.Evaluate() for the second dynamic import:

  • Step 3 of Evaluate() does "If module.[[Status]] is either ~evaluating-async~ or ~evaluated~, set module to module.[[CycleRoot]]".
  • [[CycleRoot]] was never set on module, so it's ~empty~.
  • Step for tries to read [[TopLevelCapability]] from it, which doesn't make sense because it's not a module record.

Step-by-step debugger for the first import: https://nicolo-ribaudo.github.io/es-module-evaluation/#s=QQo%3D&c=&a=Cg%3D%3D&f=QQ%3D%3D

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nicolo-ribaudo

nicolo-ribaudo commented on May 5, 2025

@nicolo-ribaudo
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Oh well, this is the same as #2823

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        [[CycleRoot]] is expected on all evaluated modules, but it's not set on modules that throw synchronously · Issue #3582 · tc39/ecma262