<proc>only</proc> does not work as expected

[alerosmile]

Affected version

3.14.1

Bug description

I attempted to create a separate Maven execution for the Log4j annotation processor as described in the Log4j plugin documentation.

When the second execution is bound to the process-classes phase, the plugin outputs
Nothing to compile - all classes are up to date. and the annotation processor does not run.

If I move the execution to the generate-sources phase, the processor runs correctly and generates the expected output. However, the log message says Compiling n source files with javac which is misleading because no source files are actually compiled—only the annotation processor is executed.

It appears that the maven-compiler-plugin does not handle the setting beyond passing it to javac. This makes it difficult to run annotation processors in isolation without triggering confusing or incorrect log messages.

[Manas-Dikshit]

Right now, the Maven Compiler Plugin:
passes only straight to javac, treating it as a compiler option.
However, when it discovers no changes, it internally skips execution.files in Java.
This optimization keeps annotation processing from starting unless actual compilation work is required.

may be