<type>processor</type> does not pick up annotation processor

[inaldt]

Affected version

4.0.0-beta-4

Bug description

While trying out maven 4 with the latest compiler plugin with my private project, I stumbled on something curious with regards to annotation processing.

Scenario:

• run ./mvnw compile in the root folder of this project
• expected: a class named MyGeneratedClass gets generated
• actual: no code gets generated

Note: said class does get generated if one uses the (now deprecated) AnnotationProcessorPaths element, as commented out in the pom of the clientproject subproject.

[desruisseaux]

The bug does not seem to be in the compiler plugin. Analysis:

• In a debugger, ignore the compilation of the first modules and focus on the last module: clientproject.
• In AbstractCompilerMojo.resolveDependencies(…), there is a call to Maven dependency resolver with a allowedTypes argument containing the following values: CLASSES, MODULES, PROCESSOR_CLASSES, PROCESSOR_MODULES.
• org.apache.maven.impl.DefaultDependencyResolver.resolve(DependencyResolverRequest) returns a list which does not contains the dependency of type processor, despite this type being requested by the compiler plugin.
• The dependency seems to be lost somewhere in org.eclipse.aether.internal.impl.collect.DependencyCollectorDelegate.collectDependencies(RepositorySystemSession, CollectRequest). The CollectRequest argument contains the processor dependency, but the DependencyResult return value does not.
• The problem seems to be in the call to doCollectDependencies(…) or in the lines that follow it.

Debugging is a bit difficult because of multiple dependency classes with objects wrapping other objects for historical reasons (a problem mentioned on the mailing list). Will need to try harder later.