In the following example, javac crashes with a stack overflow when compiling a file that references a class file containing a circular hierarchy.

The class file is not well formed, but it would be nice if the compiler reported an error instead of crashing.

Repro:

=== Gen.java ===
import java.nio.file.Files;
import java.nio.file.Paths;
import org.objectweb.asm.AnnotationVisitor;
import org.objectweb.asm.ClassWriter;
import org.objectweb.asm.FieldVisitor;
import org.objectweb.asm.MethodVisitor;
import org.objectweb.asm.Opcodes;

public class Gen implements Opcodes {

  public static void main(String[] args) throws Exception {
    Files.write(Paths.get("SubInner.class"), dumpSubInner());
    Files.write(Paths.get("Sub.class"), dumpSub());
  }

  public static byte[] dumpSubInner() throws Exception {

    ClassWriter classWriter = new ClassWriter(0);
    FieldVisitor fieldVisitor;
    MethodVisitor methodVisitor;
    AnnotationVisitor annotationVisitor0;

    classWriter.visit(
        V1_8,
        ACC_SUPER,
        "SubInner",
        "<F:Ljava/lang/Object;>Ljava/lang/Object;LSubInner<TF;>;",
        "java/lang/Object",
        new String[] {"SubInner"});

    {
      methodVisitor = classWriter.visitMethod(0, "<init>", "()V", null, null);
      methodVisitor.visitEnd();
    }
    classWriter.visitEnd();

    return classWriter.toByteArray();
  }

  public static byte[] dumpSub() throws Exception {

    ClassWriter classWriter = new ClassWriter(0);
    FieldVisitor fieldVisitor;
    MethodVisitor methodVisitor;
    AnnotationVisitor annotationVisitor0;

    classWriter.visit(
        V1_8,
        ACC_SUPER,
        "Sub",
        "<E:Ljava/lang/Object;>LSuper<TE;>;",
        "Super",
        null);

    {
      methodVisitor = classWriter.visitMethod(0, "<init>", "()V", null, null);
      methodVisitor.visitEnd();
    }
    {
      methodVisitor =
          classWriter.visitMethod(
              ACC_PUBLIC,
              "f",
              "()Ljava/util/Collection;",
              "()Ljava/util/Collection<+LSubInner<TE;>;>;",
              null);
      methodVisitor.visitEnd();
    }
    classWriter.visitEnd();

    return classWriter.toByteArray();
  }
}
=== Lib.java ===
import java.util.Collection;

abstract class Super<V> {
  public abstract Collection<? extends SuperInner<V>> f();
}

interface SuperInner<X> {}
=== Test.java ===
class Test {

  <E> void t(Sub<E> x) {
    x.f();
  }
}
===

```
$ javac -cp asm-7.2.jar:asm-util-7.2.jar Gen.java
$ java -cp asm-7.2.jar:asm-util-7.2.jar:. Gen
$ javac Lib.java
$ javac -fullversion Test.java |& head
javac full version "14-ea+30-1385"


The system is out of resources.
Consult the following stack trace for details.
java.lang.StackOverflowError
at jdk.compiler/com.sun.tools.javac.code.Type.equalsIgnoreMetadata(Type.java:512)
at jdk.compiler/com.sun.tools.javac.code.Types$Subst.visitTypeVar(Types.java:3295)
at jdk.compiler/com.sun.tools.javac.code.Types$Subst.visitTypeVar(Types.java:3271)
at jdk.compiler/com.sun.tools.javac.code.Type$TypeVar.accept(Type.java:1685)

```