[ErrorProne] Fix UnnecessaryMethodReference Check Findings

[stankiewicz]

This PR enables Error Prone's UnnecessaryMethodReference check and addresses the resulting violations across the codebase.

Changes Included:

• Configuration: Removed UnnecessaryMethodReference from the disabledChecks list in BeamModulePlugin.groovy to enforce the rule explicitly.
• Java Harness: Addressed violations in CombineRunners where output::accept was passed unnecessarily—simplified directly to output.
• Java Core Tests: Fixed violations in TextIOWriteTest by substituting unnecessary method references on variables (e.g., Functions.toStringFunction()::apply to Functions.toStringFunction()).
  All tests in the impacted modules pass locally. Formatted files via Spotless.

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[gemini-code-assist]

Summary of Changes

Hello, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request focuses on improving code quality and consistency by enabling the Error Prone UnnecessaryMethodReference check across the codebase. It resolves instances where method references were used redundantly, leading to cleaner and more idiomatic Java code. The changes ensure that the codebase adheres to stricter static analysis rules, promoting better maintainability and readability without altering functionality.

Highlights

• Error Prone Check Enabled: The UnnecessaryMethodReference check has been enabled in Error Prone by removing it from the disabled checks list in BeamModulePlugin.groovy.
• Java Harness Code Refactored: Violations in CombineRunners were addressed by simplifying output::accept to output, removing unnecessary method references.
• Java Core Tests Updated: Unnecessary method references like Functions.toStringFunction()::apply were simplified to Functions.toStringFunction() in TextIOWriteTest.

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Changelog

• buildSrc/src/main/groovy/org/apache/beam/gradle/BeamModulePlugin.groovy
  • Removed "UnnecessaryMethodReference" from the list of disabled Error Prone checks, effectively enabling the rule.
• sdks/java/core/src/test/java/org/apache/beam/sdk/io/TextIOWriteTest.java
  • Simplified method references within filter and map operations by removing the redundant ::apply suffix.
  • Updated Predicates.compose(...)::apply to Predicates.compose(...).
  • Updated Functions.toStringFunction()::apply to Functions.toStringFunction().
• sdks/java/harness/src/main/java/org/apache/beam/fn/harness/CombineRunners.java
  • Replaced output::accept with output in the processElement method.
  • Replaced output::accept with output in the finishBundle method.

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[stankiewicz]

/gemini review

[gemini-code-assist]

Code Review

This pull request correctly enables the UnnecessaryMethodReference Error Prone check and fixes the resulting violations across the codebase. The changes simplify method references to lambdas where applicable, improving code conciseness. I have one suggestion in TextIOWriteTest.java to further simplify some stream processing logic, which would improve readability and efficiency.

[gemini-code-assist]

This stream processing logic can be simplified. The intermediate collection to a list, getting a spliterator, and then creating a new stream via StreamSupport.stream is unnecessary and less efficient than chaining the stream operations directly. This simplification can be applied to the logic for bElements and cElements as well.

            elements.stream()
                .filter(
                    Predicates.compose(new StartsWith("a"), new ExtractWriteDestination()))
                .map(Functions.toStringFunction())
                .collect(Collectors.toList()),

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R: @ahmedabu98 for label java.
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