break label out of a switch in an async generator throws TypeError reading 'done' #9199

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1. proggeramlug

   added

   bugConfirmed defect or regressionConfirmed defect or regression

   on Aug 30, 2026
2. proggeramlug commented on Sep 4, 2026

   

   proggeramlug

   on Sep 4, 2026

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   Taking this. I'll reproduce against current main (which already carries #9189), work out why the labeled break leaves the async-generator state machine without a well-formed iterator result, add a gap regression, and open a PR.
3. proggeramlug commented on Sep 4, 2026

   

   proggeramlug

   on Sep 4, 2026

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   Re-measured against current main (28c292517, which carries #9189). Two things changed since this was filed, and the second is why the issue should stay open.

   This issue's own repro now passes. The one-level shape — break loop from a switch inside a single labeled for…of — prints y1,d3, matching node. #9189 covered it after all, despite the note here that it was out of scope.

   The defect it describes is still live, one level deeper, with the identical error. The switch turns out to be a red herring; the trigger is a labeled break/continue that targets an outer loop from inside a nested loop, after a yield. Three isolated programs, each on its own:

   // p6 — break an outer label from the inner loop
   async function* p6() { O: for (const x of [1,2]) { I: for (const y of [0,1]) { yield "p6"+x+y; break O; } } }
   // node: p610      perry: TypeError: Cannot read properties of undefined (reading 'done')
   
   // p5 — continue an outer label from the inner loop
   async function* p5() { O: for (const x of [1,2]) { I: for (const y of [0,1]) { yield "p5"+x+y; continue O; } } }
   // node: p510,p520     perry: NO OUTPUT AT ALL — the `for await` never yields and never settles
   
   // pD — this issue's shape with the switch deleted
   async function* d() { outer: for (const x of [1,2]) { inner: for (const y of [0,1]) {
     if (x+y === 3) break outer; if (x+y === 1) { yield "D"+x+y; continue inner; } } } }
   // node: D10      perry: TypeError: Cannot read properties of undefined (reading 'done')

   p6's error is character-for-character the one reported here, so this is the same defect, not a new one.

   What still works, which brackets it tightly:

   shape	result
   labeled continue on the same loop, after a yield	OK
   labeled continue of the inner label from the inner loop	OK
   unlabeled continue after a yield	OK
   labeled continue over a while	OK
   labeled break/continue in a sync generator, same shape	OK
   break outer from a switch in the inner loop, when nothing yields in the inner loop	OK
   break/continue of an OUTER label from a nested loop, after a yield	broken

   So the surviving hole is specifically the cross-loop target: one linearized loop's label resolved from inside another linearized loop, where the inner loop has a suspension point. continue and break fail differently (silent drop vs. malformed iterator result), which suggests the target resumption state is wrong rather than absent.

   Also worth noting for whoever picks this up: the sibling async function hang mentioned at the bottom of this issue does not reproduce — asyncfn-break-label returns f1,f3, matching node.

   I'm working on this now; probes are on the build host under /root/cc9575/ts/iso_p5.ts, iso_p6.ts, iso_pD.ts.
4. proggeramlug

   closed this as completedin 70e411don Sep 4, 2026
5. pull

   added a commit that references this issue on Sep 4, 2026

   fix(transform): unwind a labeled escape out of nested loops

   ...

   This issue will close once commit 70e411d is merged into the 'main' branch.

   70e411d