Kafka API-checker plugins

This is a separate Gradle build (composite-included from the root settings.gradle via pluginManagement { includeBuild 'api-checker' }) that produces the KIP-1265 API checkers. Living outside Kafka's main build keeps the Maven runtime dependencies off the main-build classpath and lets each published artifact carry only the classes its consumers need.

End-user documentation (Gradle/Maven snippets, @SuppressKafkaInternalApiUsage, audience-inheritance rules) lives at docs/apis/internal-api-checker.md. The notes below cover building, testing, and publishing the plugins themselves.

Build

./gradlew :api-checker:core:build :api-checker:gradle-plugins:build :api-checker:maven-plugin:build

Test

./gradlew :api-checker:core:test :api-checker:gradle-plugins:test :api-checker:maven-plugin:test

• :core:test — unit tests for the scanner, validators, and reporter, plus the shared testFixtures (AsmClassFactory, TempJarBuilder) they and the plugin tests use.
• :gradle-plugins:test — includes a Gradle TestKit end-to-end test that applies the org.apache.kafka.internal-api-checker plugin to a synthetic consumer project.
• :maven-plugin:test — hosts PluginXmlParityTest, which locks the generated plugin.xml Mojo descriptor against the fields on KafkaInternalApiCheckerMojo so adding a parameter without exposing it (or vice versa) fails locally.

Publish

Each subproject's publish task stages to the URL passed via -PmavenUrl (with -PmavenUsername / -PmavenPassword for credentials). The version is read from the repo-root gradle.properties, so release.py's existing updateVersion call sets it automatically. -PkafkaPluginsVersion=… overrides for one-off out-of-band publishes.

# Stage to ASF Nexus alongside the rest of an AK release
./gradlew :api-checker:core:publish \
         :api-checker:gradle-plugins:publish \
         :api-checker:maven-plugin:publish \
  -PmavenUrl=$ASF_NEXUS_STAGING_URL \
  -PmavenUsername=$NEXUS_USER \
  -PmavenPassword=$NEXUS_PASS

# Local smoke-test
./gradlew :api-checker:core:publishToMavenLocal \
         :api-checker:gradle-plugins:publishToMavenLocal \
         :api-checker:maven-plugin:publishToMavenLocal

The five published coordinates:

• org.apache.kafka:kafka-api-checker-core:$KAFKA_VERSION — shared scanner library.
• org.apache.kafka:kafka-internal-api-checker-gradle-plugin:$KAFKA_VERSION — Gradle plugin implementation jar (consumed by the marker poms).
• org.apache.kafka.internal-api-checker:org.apache.kafka.internal-api-checker.gradle.plugin:$KAFKA_VERSION — marker pom for plugins { id 'org.apache.kafka.internal-api-checker' }.
• org.apache.kafka.public-api-checker:org.apache.kafka.public-api-checker.gradle.plugin:$KAFKA_VERSION — marker pom for the producer-side checker. (Kafka-internal use, but published from the same module for consistency.)
• org.apache.kafka:kafka-internal-api-checker-maven-plugin:$KAFKA_VERSION — Maven plugin (packaging maven-plugin).

Layout

api-checker/
├── settings.gradle           # declares the three subprojects
├── build.gradle              # group / version / signing / common publishing config
├── core/
│   ├── build.gradle          # ASM dep; published as kafka-api-checker-core
│   └── src/
│       ├── main/java/.../apicheck/                # scanner, validators, reporter
│       ├── test/java/.../apicheck/                # unit tests
│       └── testFixtures/java/.../apicheck/        # AsmClassFactory, TempJarBuilder
│                                                  # — re-used by :gradle-plugins' tests
├── gradle-plugins/
│   ├── build.gradle          # java-gradle-plugin; depends on :core
│   └── src/{main,test}/java/.../gradle/           # Plugin/Task/Extension × 2
└── maven-plugin/
    ├── build.gradle          # Maven deps; templates plugin.xml at processResources
    └── src/
        ├── main/
        │   ├── java/.../maven/KafkaInternalApiCheckerMojo.java
        │   └── resources/META-INF/maven/plugin.xml
        └── test/java/.../maven/PluginXmlParityTest.java   # locks plugin.xml ↔ Mojo fields