[codeconsole]

BroadcastChannel.asPublisher() now ends a subscriber that arrives after the broadcast closed the same way as one that was attached before the close. After close() it receives onComplete, so for await (x in broadcast.asPublisher()) ends without values and await broadcast.asPublisher() returns null. Before, both threw ChannelClosedException. After close(failure) it receives failure itself, not a ChannelClosedException wrapping it. This matches SubmissionPublisher, Agent.changes() and for await over a closed AsyncChannel, and makes the result independent of whether the consumer subscribed before or after the producer closed. BroadcastChannel.subscribe() still throws ChannelClosedException once the broadcast is closed. The async channels guide says so.

BroadcastChannel shipped in 6.0.0, so this changes behavior there; it is a candidate for master only.

Tests

BroadcastChannelAsPublisherTest (marked // GROOVY-12571): a subscriber and a for await that arrive after close() and after close(failure); they fail without the change.

The groovy.concurrent tests pass (271), as do the Checkstyle and CodeNarc gates.

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❌ Build and test / lts (17, macos-latest)

🏷️ Commit: 43ec544
▶️ Tests: 99364 executed
⚪️ Checks: 26/26 completed

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[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 73.6788%. Comparing base (5b077f9) to head (43ec544).
⚠️ Report is 4 commits behind head on master.

Additional details and impacted files

@@                Coverage Diff                 @@
##               master      #3105        +/-   ##
==================================================
+ Coverage     73.6711%   73.6788%   +0.0077%     
- Complexity      42584      42590         +6     
==================================================
  Files            1678       1678                
  Lines          146907     146916         +9     
  Branches        27790      27793         +3     
==================================================
+ Hits           108228     108246        +18     
+ Misses          28528      28519         -9     
  Partials        10151      10151                

Files with missing lines	Coverage Δ
.../main/java/groovy/concurrent/BroadcastChannel.java	78.2946% <100.0000%> (+4.4850%)	⬆️

... and 15 files with indirect coverage changes

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[daniellansun]

GROOVY-12571 behavior change is coherent with Reactive Streams: a late asPublisher() subscriber after close should see the same terminal signal as an in-flight one — onComplete for normal close, onError(cause) for close(failure) — not ChannelClosedException.

Implementation matches closedNow(): normal close has null cause → onComplete; failed close wraps the failure as CCE cause → onError(cause). Docs and tests (subscriberArrivingAfterANormalCloseCompletes / …FailedCloseReceivesTheFailure, including for await / await) are good. Direct subscribe() still throws CCE — correctly left alone.

CI: lts (17, macos-latest) 60m Gradle timeout — please re-run; then APPROVE. Codecov clean.

Compat: callers that caught ChannelClosedException from late publisher subscribe will now see completion/error instead — call that out on the JIRA if not already.