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Add "afterburner-tests"; enhanced Afterburner-for-classpath tests (#347)
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‎afterburner-tests/README.md‎

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# jackson-module-afterburner-tests
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Classpath-mode integration tests for `jackson-module-afterburner`. **This module is
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test-only and is never published.**
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## Why this module exists
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Afterburner's most valuable optimizations come from bytecode injection:
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`PropertyMutatorCollector`, `PropertyAccessorCollector`, and `CreatorOptimizer`
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generate custom mutator / accessor / instantiator classes in the *target bean's
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package* and install them on the bean's `ClassLoader`. This only works when the
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target package is not sealed.
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In Jackson 3.x every module descriptor — including afterburner's own test module
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— is a named JPMS module, and the JVM automatically seals every package inside a
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named module. As a result, every POJO defined inside `tools.jackson.module.afterburner`
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test sources fails the `MyClassLoader.canAddClassInPackageOf` check, and afterburner
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silently falls back to plain reflection. That means **none** of afterburner's
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injection paths are exercised by the in-tree afterburner test suite — the optimized
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code path is effectively dead weight in CI even though the tests appear to pass.
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This module closes that gap. It lives alongside the afterburner module but
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deliberately:
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- has **no `module-info.java`** in either main or test sources,
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- is configured (`useModulePath=false`) to run its tests on the classpath,
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- and therefore loads its test POJOs into the **unnamed module**, whose packages
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are not sealed.
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Afterburner's injection pipeline runs on those POJOs normally, and the tests here
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verify via reflection on databind internals that each property was actually
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replaced with an `OptimizedSettableBeanProperty` / `OptimizedBeanPropertyWriter`
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and each default-creator POJO got an `OptimizedValueInstantiator`.
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## Do not add a `module-info.java` here
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Adding a module descriptor would put these test POJOs back into a named module,
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re-seal their packages, and silently turn this whole module into dead weight —
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same as the in-tree afterburner tests.
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If a future cleanup pass wants to "unify" the project layout by making every
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module JPMS-consistent, this one is the exception. Read this file before doing
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that.
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## Do not publish this module
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Several parent-POM plugin bindings are unbound or skipped in `pom.xml` so that
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`mvn install` on this module produces no jar, no SBOM, no Gradle module metadata,
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and no OSGi bundle. The module exists purely to run tests. If you rename an
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execution override in `pom.xml`, re-verify with:
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```
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./mvnw help:effective-pom -pl afterburner-tests
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```
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A typo in an execution id turns into silent dead config and leaves stale
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artifacts in `target/` rather than a build error.
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## What is covered
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- `PropertyMutatorCollector` — int, long, boolean, and reference-type
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specializations for both public-field and setter-method access
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(`MutatorSpecializationsTest`).
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- `PropertyAccessorCollector` — writer replacement on the serializer side
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(`SerializerInjectionTest`).
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- `CreatorOptimizer` — default-constructor and static-factory positive cases,
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plus property-based `@JsonCreator` negative case (`CreatorOptimizerTest`).
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- `MyClassLoader.defineClass` — transitively exercised by all of the above.
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## What is *not* covered
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- Private-class guard (`_classLoader != null && isPrivate(beanClass)`).
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- `setUseValueClassLoader(false)` toggle.
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- Concurrent deserializer construction.
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- Fallback path when afterburner correctly refuses to optimize (e.g. a bean
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whose package really is sealed — the in-tree afterburner tests inadvertently
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cover this).
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- GraalVM native-image disable path in `AfterburnerModule.setupModule`.
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## Known findings from this module
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### Afterburner parent-classloader caching silently broken on Java 9+ (#348)
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While writing `GeneratedClassCachingTest`, we discovered that Afterburner's
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parent-classloader cache — the mechanism that's supposed to make two
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independent `ObjectMapper` instances share a single generated mutator class
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per POJO — does not work on Java 9+ unless the JVM is launched with
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`--add-opens java.base/java.lang=ALL-UNNAMED`. `MyClassLoader` reflects into
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`ClassLoader#findLoadedClass` and `ClassLoader#defineClass`, both protected
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members of `java.lang.ClassLoader`; on modern JDKs the reflective access
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throws `InaccessibleObjectException`, which Afterburner catches silently and
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falls back to defining each generated class in a fresh throwaway loader.
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That's why this module's `pom.xml` sets
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`--add-opens java.base/java.lang=ALL-UNNAMED` on the surefire `argLine`.
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Without it, `testSameBeanAcrossMappersReusesSameMutatorClass` fails with two
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distinct `Class<?>` instances carrying identical fully-qualified names — the
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exact fingerprint of the leak. This is **not a test-environment quirk**; it
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affects every real Afterburner user on Java 9+. See issue #348 for the fix
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plan.
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## References
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- PR #347: rationale for the module's structure and initial coverage
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- Issue #348: afterburner classloader caching regression (surfaced here)

‎afterburner-tests/pom.xml‎

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<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
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<modelVersion>4.0.0</modelVersion>
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<parent>
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<groupId>tools.jackson.module</groupId>
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<artifactId>jackson-modules-base</artifactId>
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<version>3.2.0-SNAPSHOT</version>
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</parent>
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<artifactId>jackson-module-afterburner-tests</artifactId>
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<name>Jackson module: Afterburner integration tests</name>
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<packaging>jar</packaging>
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<description>Classpath-mode integration tests for jackson-module-afterburner. This module
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intentionally has no module-info.java so that its test POJOs live in the unnamed module, where
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their packages are not sealed-by-module. That lets Afterburner exercise its bytecode injection
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paths (PropertyMutatorCollector, CreatorOptimizer, PropertyAccessorCollector) — paths that are
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gated off when the target bean sits in a named JPMS module. This module is test-only and is
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never published.</description>
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<dependencies>
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<dependency>
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<groupId>tools.jackson.module</groupId>
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<artifactId>jackson-module-afterburner</artifactId>
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<version>${project.version}</version>
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</dependency>
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</dependencies>
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<build>
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<plugins>
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<!-- This module is test-only and must never produce a publishable artifact.
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Packaging stays `jar` so the compile + test lifecycle runs normally,
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but every artifact-producing / artifact-publishing plugin inherited
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from the parent chain is unbound here.
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Verified via `mvn help:effective-pom -pl afterburner-tests`: every
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execution listed below appears in the merged model at phase=none or
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with skip=true. If you rename an execution here, re-verify with that
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command — a typo turns into silent dead config and stale artifacts
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in target/ rather than a build error. -->
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<plugin>
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<groupId>org.apache.maven.plugins</groupId>
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<artifactId>maven-jar-plugin</artifactId>
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<executions>
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<execution>
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<id>default-jar</id>
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<phase>none</phase>
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</execution>
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</executions>
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</plugin>
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<plugin>
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<groupId>org.apache.maven.plugins</groupId>
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<artifactId>maven-install-plugin</artifactId>
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<configuration>
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<skip>true</skip>
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</configuration>
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</plugin>
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<plugin>
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<groupId>org.apache.maven.plugins</groupId>
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<artifactId>maven-deploy-plugin</artifactId>
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<configuration>
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<skip>true</skip>
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</configuration>
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</plugin>
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<!-- Felix bundle plugin: the parent POM binds two explicit executions
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(`bundle-manifest` and `default-install`) so we override both by id. -->
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<plugin>
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<groupId>org.apache.felix</groupId>
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<artifactId>maven-bundle-plugin</artifactId>
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<executions>
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<execution>
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<id>bundle-manifest</id>
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<phase>none</phase>
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</execution>
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<execution>
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<id>default-install</id>
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<phase>none</phase>
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</execution>
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</executions>
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</plugin>
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<!-- CycloneDX SBOM plugin has a plugin-level `skip` flag, which disables
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it independently of execution id merging. More robust than binding a
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phase-override to an unnamed parent execution. -->
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<plugin>
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<groupId>org.cyclonedx</groupId>
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<artifactId>cyclonedx-maven-plugin</artifactId>
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<configuration>
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<skip>true</skip>
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</configuration>
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</plugin>
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<!-- Gradle module metadata plugin has no `skip` parameter, so we unbind
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the parent's unnamed execution via id-based merge. Maven treats
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`default` as the id for unnamed executions when merging child POM
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overrides. Verified in the effective POM. -->
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<plugin>
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<groupId>org.gradlex</groupId>
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<artifactId>gradle-module-metadata-maven-plugin</artifactId>
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<executions>
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<execution>
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<id>default</id>
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<phase>none</phase>
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</execution>
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</executions>
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</plugin>
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<!-- Jacoco report analyzes 0 classes in this module (no main sources) and
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only produces log noise. Unbind the `report` execution. Leave
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`prepare-agent` alone: it is silent and sets the surefire agent which
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is harmless even when no main classes exist. -->
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<plugin>
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<groupId>org.jacoco</groupId>
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<artifactId>jacoco-maven-plugin</artifactId>
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<executions>
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<execution>
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<id>report</id>
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<phase>none</phase>
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</execution>
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</executions>
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</plugin>
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<!-- Force surefire to classpath mode: this module has no module-info.java,
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so tests must run on the classpath (unnamed module) to keep test POJO
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packages unsealed.
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The add-opens flag below is required by Afterburner itself, not by
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the tests. Afterburner's MyClassLoader reflectively invokes
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ClassLoader#findLoadedClass and ClassLoader#defineClass on the bean's
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parent classloader so that generated mutator classes are cached on
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that parent and reused across mappers. Both methods live in
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java.base/java.lang and on Java 17+ are only reachable when the
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module is opened to the unnamed module. Without this flag,
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Afterburner silently falls back to defining each generated class in
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a fresh throwaway MyClassLoader, which leaks classloaders under load
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(and which GeneratedClassCachingTest catches as a regression).
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Note: reflection into databind internals from the tests themselves
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works without opens because this module runs on the classpath, where
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setAccessible(true) from the unnamed module is unrestricted.
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Note 2: surefire's argLine is additive when jacoco's prepare-agent
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already set a value, so we reference @{argLine} to preserve the
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jacoco agent config. -->
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<plugin>
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<groupId>org.apache.maven.plugins</groupId>
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<artifactId>maven-surefire-plugin</artifactId>
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<configuration>
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<useModulePath>false</useModulePath>
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<argLine>@{argLine} --add-opens java.base/java.lang=ALL-UNNAMED</argLine>
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</configuration>
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</plugin>
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</plugins>
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</build>
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</project>

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