Bug: JMH APT processor claims all annotations

[Dimitar Dimitrov]

Problem:
------------
When a codebase using JMH also uses other annotation processors (i.e.
Lombok, Dagger 2, etc) The other processors will not get a chance to run if
they are ordered after JMH.


Root cause:
----------------
The JMH BenchmarkProcessor#process() method returns unconditionally true
regardless of whether it processed an annotation or not.

http://hg.openjdk.java.net/code-tools/jmh/file/397891feda1b/jmh-generator-annprocess/src/main/java/org/openjdk/jmh/generators/BenchmarkProcessor.java

According to the Javadoc, if a processor returns true, it will "claim" the
annotation for itself and no other processors will be given a chance to
process it.


Proposed fix:
------------------
I am not deeply familiar with JMH, but for what I know, it has a closed set
of annotations, so line 41 in on BenchmarkProcessor.java to:

     SupportedAnnotationTypes("org.openjdk.jmh.annotations.*")

If JMH allows user-defined annotations things get a bit more complicated.
If the user-defined annotations are known in advance, one can override
Processor#getSupportedAnnotationTypes()

if there is a need to dynamically support user defined annotations, one
needs to inspect the first arg of the process() method and sure that it
returns true only in cases where all annotations are for JMH.

AFinally, a simpler option is for the main processor to always return false
and add a separate processor that doesn't do anything else but claim the
known JMH annotations. That covers most cases, though that may result in
javac warning (-Xlint:processing) with user-defined annotations.

Best regards,
Dimitar