java Annotation Processor only scans the .java files specified by the javac compiler

Question

I wrote an annotation processor (to copy some java sources in my compiling directory). I was surprised to see that only the files specified on the javac command line are processed by my annotation processor. I'm obviously missing something.

Here is a minimal example:

sandbox.Aproc:

(...)
@SupportedSourceVersion(SourceVersion.RELEASE_8)
public class AProc extends AbstractProcessor{   
    @Override
    public Set<String> getSupportedAnnotationTypes() {
        return Arrays.asList( Include.class ).stream().
            map(C->C.getName()).
            collect(Collectors.toSet())
            ;
        }
    
    private void copySource(final javax.lang.model.element.Element element)
        {
        if(element==null || element.getKind()!=ElementKind.CLASS) return;
        final String thisDir = System.getProperty("user.dir");
        System.err.println("##Visit " + element);
        (...)
        }
    
    @Override
    public boolean process(final Set<? extends TypeElement> annotations,
        final RoundEnvironment roundEnv
        ) {             
        roundEnv.getElementsAnnotatedWith(Include.class).stream().
            filter(E->E.getKind()==ElementKind.CLASS).
            filter(E-> E.getAnnotation(Include.class) !=null).
            forEach(E->{                    
                copySource(E);
                });
        
        return true;
       }
    }

sandbox/Test.java This class uses Test2 so I expect this Test2 will also be visited by the processor.

package sandbox;
@Include
public class Test {
Test2 get() { return new Test2();}
}

sandbox/Test2.java

package sandbox;
@Include
public class Test2 {
}

sandbox/Include.java

(...)
package sandbox;
@Retention(RUNTIME)
@Target({ ElementType.TYPE })
public @interface Include
    {
    }

The annotation processor is packaged in a jar with sandbox.AProc in TMP/META-INF/services/javax.annotation.processing.Processor

When I compile with both Test.java and Test2.java they both appear in the processor logs.

$ javac -cp .:annot.jar  -d TMP sandbox/Test.java sandbox/Test2.java
##Visit sandbox.Test
##Visit sandbox.Test2

but if I only compile sandbox/Test.java, Test2 is compiled but ignored by the processor.

$ javac -cp .:annot.jar  -d TMP sandbox/Test.java 
##Visit sandbox.Test
warning: Implicitly compiled files were not subject to annotation processing.
  Use -proc:none to disable annotation processing or -implicit to specify a policy for implicit compilation.
1 warning

(I'm not sure about the warning, using -implicit:class hide the problem).

How can I tell the processor to visit all the classes without specifying them on the javac command line ?