public boolean isTypeuseOnly(String annotation) {
      synchronized (whetherTypeuseOnly) {
        // don't want to run computation inside computeIfAbsent lambda
        @Nullable Boolean is = whetherTypeuseOnly.get(annotation);
        if (is == null) {
          is = determineIfUnambiguousTypeuse(annotation);
          whetherTypeuseOnly.put(annotation, is);
        }
        return is;
      }
    }
Check if {@code qualifiedName} is known to current environment (annotation processor).
Retrieve (by canonical name) {@link TypeElement} from APT environment.
value-processor/src/org/immutables/value/processor/meta/Proto.java