Annotation processing by `javac` is enabled by default, including when no annotation processing configuration options are present. Implicit annotation processing by default may be disabled in a future release, possibly as early as JDK 22. To alert `javac` users of this possibility, in JDK 21 `javac` prints a note if implicit annotation processing is being used. The text of the note is:

```
     Annotation processing is enabled because one or more processors were
    found on the class path. A future release of javac may disable
    annotation processing unless at least one processor is specified by
    name (-processor), or a search path is specified (--processor-path,
    --processor-module-path), or annotation processing is enabled
    explicitly (-proc:only, -proc:full).
    Use -Xlint:-options to suppress this message.
    Use -proc:none to disable annotation processing.
```

 Good build hygiene includes explicitly configuring annotation processing. To ease the transition to a different default policy in the future, the new-in-JDK-21 `-proc:full javac` option requests the current default behavior of looking for annotation processors on the class path.