Skip AddAnnotationProcessor when processor already in effective POM via ancestor

[mcebanupgrade]

Summary

AddAnnotationProcessor would add a redundant annotation processor entry when an in-reactor parent POM inherits the configuration from a parent outside the reactor. The processor was present in the effective POM (via merged ancestor configs) but not in the in-reactor parent's own XML, causing a duplicate to be written.

Root cause: The scanner only tracked reactor topology — it had no visibility into whether the annotation processor was already inherited from an external ancestor via the effective POM.

Fix:

• In the scanner phase, compare ResolvedPom.getPlugins()/getPluginManagement() (merged effective lists from all ancestors) against Pom.getPlugins()/getPluginManagement() (current POM's own XML only)
• If processor is in effective POM but not in own XML → mark path as alreadyConfiguredInEffectivePomPaths
• In the visitor phase, skip any path in alreadyConfiguredInEffectivePomPaths

Added hasAnnotationProcessor(List<Plugin>) and isMatchingProcessor(JsonNode) helpers for the effective POM check, using Jackson JsonNode traversal of Plugin.getConfiguration() (consistent with how ResolvedPom exposes plugin config).

Test plan

• New EffectivePomCheck.doesNotAddWhenAlreadyInEffectivePomViaAncestor test in AddAnnotationProcessorTest: 3-level hierarchy where grandparent has the processor in pluginManagement, intermediate parent inherits it via effective POM but has no own XML config — intermediate parent must NOT be modified

🤖 Generated with Claude Code

[mcebanupgrade]

The CI failure in rewrite-gradle:test > RemoveRedundantDependencyVersionsTest.unmanagedDependency() is unrelated to this PR.

Evidence:

1. This PR only modifies two files, both in rewrite-maven:
   • rewrite-maven/src/main/java/org/openrewrite/maven/AddAnnotationProcessor.java
   • rewrite-maven/src/test/java/org/openrewrite/maven/AddAnnotationProcessorTest.java
2. The failing test is in rewrite-gradle:test — a separate module with no dependency on rewrite-maven
3. The failure is a Kotlin stdlib version mismatch (2.2.0 vs 1.9.0 expected) in a Gradle tooling API test that resolves Spring Boot platform dependencies — nothing to do with Maven annotation processor configuration
4. All recent CI runs on main were green

This appears to be a pre-existing flaky test. Could a maintainer re-run the CI?

[mcebanupgrade]

Local test results: All 23 AddAnnotationProcessorTest tests pass locally (installed Java 8 toolchain to run rewrite-maven:test):

AddAnnotationProcessorTest$EffectivePomCheck:          1 test,  0 failures
AddAnnotationProcessorTest$SeparatedAggregatorAndParent: 5 tests, 0 failures
AddAnnotationProcessorTest$CombinedAggregatorAndParent:  8 tests, 0 failures
AddAnnotationProcessorTest$SingleModuleProject:          5 tests, 0 failures
AddAnnotationProcessorTest (top-level):                  4 tests, 0 failures

CI flakiness confirmation: The second CI run failed with a completely different error — GradleConnectionException: Could not fetch model of type 'OpenRewriteModelProxy' using connection to Gradle distribution 'https://services.gradle.org/distributions/gradle-8.6-bin.zip' (a network failure downloading Gradle 8.6 in rewrite-gradle-tooling-model:model:test). Different test, different module, different root cause — confirming these are pre-existing flaky infrastructure tests.

[timtebeek]

Thanks for the fix & validation @mcebanupgrade ! Any reason your PR is still marked as draft? Can it be reviewed and merged?

[mcebanupgrade]

Hi @timtebeek !
I was having some issues with CI last night and had to put it on pause. The tests seem to pass after a couple of retries 🤷
I was able to confirm locally that this fix indeed fixes the issue I was having, so the PR is ready for review now!