Fix ProfileScorer.getChildren() to expose wrapped scorer in scorer tree

[martin-gaievski]

Description

ProfileScorer.getChildren() currently delegates directly to the wrapped scorer's getChildren(),
which skips the ProfileScorer level in the scorer tree. This makes the wrapped scorer invisible to
any code traversing the scorer hierarchy via the standard Lucene Scorable.getChildren() API.

This change makes ProfileScorer expose the wrapped scorer as a child with the "PROFILED"
relationship label, allowing plugins and custom collectors to discover wrapped scorers through
profiling wrappers using standard tree traversal — without requiring reflection.

Changes

• ProfileScorer.java: Changed getChildren() from return scorer.getChildren() to
  return Collections.singletonList(new ChildScorable(scorer, "PROFILED"))
• ProfileScorerTests.java: Added testGetChildren_exposesWrappedScorerAsChild() to verify
  the new behavior

Related Issues

Resolves #20548

PR #20549 added getWrappedScorer() — a public method on ProfileScorer that returns the wrapped scorer. This was intended to let neural-search unwrap ProfileScorer to find HybridQueryScorer.

When implementing the neural-search side, we discovered that getWrappedScorer() alone doesn't solve the problem because ProfileScorer is a package-private final class. Even though getWrappedScorer() is a public method, Java's access control system blocks Method.invoke() from external modules (plugins) on methods of non-public classes. The plugin code gets:

IllegalAccessException: class LeafCollector cannot access a member of class 
org.opensearch.search.profile.query.ProfileScorer with modifiers "public"

This means the neural-search plugin had to use method.setAccessible(true) + @SuppressForbidden to call getWrappedScorer() via reflection — defeating the purpose of having a clean public API.

Check List

• Functionality includes testing.
• API changes companion pull request created, if applicable.
• Public documentation issue/PR created, if applicable.

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[coderabbitai]

📝 Walkthrough

Walkthrough

This PR modifies ProfileScorer to expose the wrapped scorer as a child through the getChildren() method, which now returns a singleton list containing a ChildScorable with "PROFILED" relationship instead of delegating to the wrapped scorer's children. Includes corresponding test coverage and changelog documentation.

Changes

Cohort / File(s)	Summary
ProfileScorer Implementation server/src/main/java/org/opensearch/search/profile/query/ProfileScorer.java	Added java.util.Collections import. Modified getChildren() to return a singleton list wrapping the scorer in a ChildScorable with "PROFILED" relationship, exposing the wrapped scorer for plugin access instead of delegating to the wrapped scorer's children.
Test Coverage server/src/test/java/org/opensearch/search/profile/query/ProfileScorerTests.java	Added testGetChildren_exposesWrappedScorerAsChild() test method verifying that getChildren() returns exactly one child (the wrapped scorer) with PROFILED relationship. Updated imports to include java.util.Collection.
Documentation CHANGELOG.md	Added Fixed entry under Unreleased 3.x describing that ProfileScorer.getChildren() now exposes the wrapped scorer for plugin compatibility.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~22 minutes

Possibly related PRs

• opensearch-project/OpenSearch#20549: Implements an alternative approach (getWrappedScorer() accessor method) to expose the wrapped scorer in ProfileScorer for the same plugin compatibility use case.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and concisely describes the main change: fixing ProfileScorer.getChildren() to expose the wrapped scorer in the scorer tree.
Linked Issues check	✅ Passed	The PR implementation aligns with issue #20548's objective of exposing the wrapped scorer, though via getChildren() rather than a dedicated getWrappedScorer() method.
Out of Scope Changes check	✅ Passed	All changes are directly scoped to the linked issue: ProfileScorer.getChildren() modification, import addition, and corresponding test coverage.
Description check	✅ Passed	The PR description is comprehensive and well-structured, covering problem statement, solution, changes, related issues, and checklist items as required by the template.

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✨ Finishing touches

• 📝 Generate docstrings

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment

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[github-actions]

❌ Gradle check result for 6fddaa4: FAILURE

Please examine the workflow log, locate, and copy-paste the failure(s) below, then iterate to green. Is the failure a flaky test unrelated to your change?

[martin-gaievski]

Looks like rarely failing test, not related to this change, passes in my local environment

Task :server:test

REPRODUCE WITH: ./gradlew ':server:test' --tests 'org.opensearch.index.shard.IndexShardTests.testRestoreSearchOnlyShardFromStoreOnNewNode' -Dtests.seed=B3BDACD5418087E4 -Dtests.security.manager=true -Dtests.jvm.argline="-XX:TieredStopAtLevel=1 -XX:ReservedCodeCacheSize=64m" -Dtests.locale=ha-NE -Dtests.timezone=Asia/Makassar -Druntime.java=25

IndexShardTests > testRestoreSearchOnlyShardFromStoreOnNewNode FAILED
    [index][[index][0]] IndexShardRecoveryException[Failed to recover from gateway]; nested: CorruptIndexException[misplaced codec footer (file truncated?): length=0 but footerLength==16 (resource=metadata__9223372036854775805__9223372036854775804__9223372036854775802__9223372036854775805__-1039764442__9223370265996427162__2)];
        at __randomizedtesting.SeedInfo.seed([B3BDACD5418087E4:7369770EE6AE81DC]:0)
        at app//org.opensearch.index.shard.StoreRecovery.internalRecoverFromStoreForSearchReplica(StoreRecovery.java:815)
        at app//org.opensearch.index.shard.StoreRecovery.lambda$recoverFromStore$0(StoreRecovery.java:127)
        at app//org.opensearch.core.action.ActionListener.completeWith(ActionListener.java:344)
        at app//org.opensearch.index.shard.StoreRecovery.recoverFromStore(StoreRecovery.java:124)
        at app//org.opensearch.index.shard.IndexShard.recoverFromStore(IndexShard.java:3198)
        at app//org.opensearch.index.shard.IndexShardTestCase.recoverFromStore(IndexShardTestCase.java:1479)
        at app//org.opensearch.index.shard.IndexShardTestCase.recoverShardFromStore(IndexShardTestCase.java:1085)
        at app//org.opensearch.index.shard.IndexShardTests.testRestoreSearchOnlyShardFromStoreOnNewNode(IndexShardTests.java:3092)

        Caused by:
        org.apache.lucene.index.CorruptIndexException: misplaced codec footer (file truncated?): length=0 but footerLength==16 (resource=metadata__9223372036854775805__9223372036854775804__9223372036854775802__9223372036854775805__-1039764442__9223370265996427162__2)
            at app//org.apache.lucene.codecs.CodecUtil.checksumEntireFile(CodecUtil.java:616)
            at app//org.opensearch.common.io.VersionedCodecStreamWrapper.readStream(VersionedCodecStreamWrapper.java:63)
            at app//org.opensearch.index.store.RemoteSegmentStoreDirectory.readMetadataFile(RemoteSegmentStoreDirectory.java:282)
            at app//org.opensearch.index.store.RemoteSegmentStoreDirectory.readLatestMetadataFile(RemoteSegmentStoreDirectory.java:271)
            at app//org.opensearch.index.store.RemoteSegmentStoreDirectory.init(RemoteSegmentStoreDirectory.java:178)
            at app//org.opensearch.index.shard.IndexShard.syncSegmentsFromRemoteSegmentStore(IndexShard.java:5497)
            at app//org.opensearch.index.shard.IndexShard.syncSegmentsFromRemoteSegmentStore(IndexShard.java:5480)
            at app//org.opensearch.index.shard.IndexShard.innerOpenEngineAndTranslog(IndexShard.java:2871)
            at app//org.opensearch.index.shard.IndexShard.openEngineAndSkipTranslogRecovery(IndexShard.java:2838)
            at app//org.opensearch.index.shard.IndexShard.openEngineAndSkipTranslogRecoveryFromSnapshot(IndexShard.java:2832)
            at app//org.opensearch.index.shard.StoreRecovery.completeRecovery(StoreRecovery.java:843)
            at app//org.opensearch.index.shard.StoreRecovery.internalRecoverFromStoreForSearchReplica(StoreRecovery.java:813)
            ... 7 more

> Task :plugins:mapper-murmur3:bundlePlugin

[github-actions]

❌ Gradle check result for 6fddaa4: FAILURE

Please examine the workflow log, locate, and copy-paste the failure(s) below, then iterate to green. Is the failure a flaky test unrelated to your change?