This is generally related to JDK-8055219, which discussed handling of ErrorType in javax.lang.model.util.Types.

I think it would be valuable for the specification of Types#directSupertypes and TypeElement#getInterfacese to discuss how ErrorType is handled.

Consider an example like:

import java.util.List;
class T implements List<String>, NoSuch {}

Calling Types#directSupertypes on T omits the ErrorType:

directSupertypes(T) = [java.lang.Object, java.util.List<java.lang.String>]

on the other hand, TypeElement#getInterfaces includes the ErrorType:

getInterfaces() = java.util.List<java.lang.String>,NoSuch

I found it surprising that they weren't consistent, but I also don't have concerns wtih the current behaviour, mostly it wasn't clear to me what to expect and I think it would be valuable for the specification to address that the behaviour is.

---

import java.util.Set;
import javax.annotation.processing.AbstractProcessor;
import javax.annotation.processing.RoundEnvironment;
import javax.annotation.processing.SupportedAnnotationTypes;
import javax.lang.model.SourceVersion;
import javax.lang.model.element.TypeElement;
import javax.tools.Diagnostic;

@SupportedAnnotationTypes("*")
public class P extends AbstractProcessor {
  @Override
  public SourceVersion getSupportedSourceVersion() {
    return SourceVersion.latestSupported();
  }

  private boolean first = true;

  @Override
  public boolean process(Set<? extends TypeElement> annotations, RoundEnvironment roundEnv) {
    if (!first) {
      return false;
    }
    first = false;
    TypeElement e = processingEnv.getElementUtils().getTypeElement("T");
    processingEnv
        .getMessager()
        .printMessage(
            Diagnostic.Kind.ERROR,
            String.format("%s.getInterfaces() = %s", e, e.getInterfaces()),
            e);

    processingEnv
        .getMessager()
        .printMessage(
            Diagnostic.Kind.ERROR,
            String.format(
                "directSupertypes(%s) = %s",
                e.asType(), processingEnv.getTypeUtils().directSupertypes(e.asType())),
            e);
    return false;
  }
}