@Override
    public boolean process(Set<? extends TypeElement> annotations, RoundEnvironment roundEnv) {
      if (first) {
        TypeSpec.Builder type = TypeSpec.classBuilder("G");
        GeneratedAnnotationSpecs.generatedAnnotationSpec(
                processingEnv.getElementUtils(),
                processingEnv.getSourceVersion(),
                TestProcessor.class)
            .ifPresent(type::addAnnotation);
        JavaFile javaFile = JavaFile.builder("", type.build()).build();
        try {
          javaFile.writeTo(processingEnv.getFiler());
        } catch (IOException e) {
          throw new UncheckedIOException(e);
        }
        first = false;
      }
      return false;
    }
A toy annotation processor for testing. Matches on all annotations, and unconditionally
generates a source that uses {@code @Generated}.
common/src/test/java/com/google/auto/common/GeneratedAnnotationsTest.java