fix: add supervision strategy support for expand and extrapolate#3185
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fix: add supervision strategy support for expand and extrapolate#3185He-Pin wants to merge 2 commits into
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Motivation: The expand operator evaluated user-provided expansion logic without consulting SupervisionStrategy, so exceptions failed the stream unconditionally. This also affected extrapolate because it is implemented on top of Expand. Modification: Add supervision handling in Expand for exceptions from the expander function and from iterator evaluation paths (hasNext/next). Stop fails the stage, Resume drops the failed element and continues, and Restart resets extrapolation state before continuing. Update Scala/Java API docs (Flow/Source/SubFlow/SubSource) and operator docs to reflect supervision behavior. Expand docs now explicitly describe Resume vs Restart state semantics. Add directional tests in FlowExpandSpec and FlowExtrapolateSpec for Stop/default Stop/Resume/Restart and iterator-evaluation failures. Result: expand and extrapolate now honor ActorAttributes.SupervisionStrategy for user-function failures, with deterministic regression coverage for exceptional iterator paths. Tests: - sbt "stream-tests/Test/testOnly org.apache.pekko.stream.scaladsl.FlowExpandSpec org.apache.pekko.stream.scaladsl.FlowExtrapolateSpec" -- 23/23 passed - sbt "stream/mimaReportBinaryIssues" -- clean - sbt "docs/paradox" -- passed References: Refs apache#3110
…mantics Motivation: Review of the expand/extrapolate supervision support identified two consistency and documentation gaps. Modification: - Change `private lazy val decider` to `private def decider` in Expand to match the established pattern in Map, Filter, Collect and other fusing operators. - Collapse the Resume and Restart branches in `handleIteratorFailure` since a corrupt iterator must be discarded regardless of the supervision decision, and add a comment explaining why. - Clarify in expand.md that iterator evaluation failures necessarily discard extrapolation state under Resume, while expander-function failures preserve it. Result: Expand's supervision handling is consistent with neighbouring operators and its docs disambiguate the two failure sites. Tests: - sbt "stream-tests/Test/testOnly org.apache.pekko.stream.scaladsl.FlowExpandSpec org.apache.pekko.stream.scaladsl.FlowExtrapolateSpec" (23/23 passed) References: Refs apache#3110
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Motivation
Issue #3110 tracks stream operators that should honor
SupervisionStrategyfor user functions.expandcalled the user-provided expansion logic without supervision, so exceptions failed the stream unconditionally. Sinceextrapolateis implemented viaExpand, the same gap applied there too.Modification
Expandfor:hasNext/next)Stop: fail stageResume: drop failed element and continueRestart: drop failed element, reset current extrapolation state, continueFlow,Source,SubFlow,SubSource) to describe supervision behavior and clarify Resume vs Restart forexpand.expand.mdextrapolate.mdFlowExpandSpec: Stop/default Stop/Resume/Restart + iterator-evaluation failure pathsFlowExtrapolateSpec: Stop/Resume/Restart for extrapolator failures during iterator evaluationResult
expandandextrapolatenow honorActorAttributes.SupervisionStrategyfor user-function failures with explicit regression coverage for exceptional iterator paths.which is now Apache licensed
Tests
sbt "stream-tests/Test/testOnly org.apache.pekko.stream.scaladsl.FlowExpandSpec org.apache.pekko.stream.scaladsl.FlowExtrapolateSpec"(23/23 passed)sbt "stream/mimaReportBinaryIssues"(clean)sbt "docs/paradox"(passed)References
Refs #3110