RFR: JDK-8193561: Cyclic hierarchy causes a NullPointerException when setting DEFAULT flag

[Jan Lahoda]

Hi,

Consider code like:
---
package p;

interface T8193561 extends p.T8193561.I {

     interface I  extends T8193561 {
         default boolean m() {
             return false;
         }
     }

     default boolean m() {
         return false;
     }

}
---

There is apparently a cycle between the interfaces, and an error will be 
reported correctly for it, but then it will crash in MemberEnter:
---
$ javac -XDdev T8193561.java
T8193561.java:9: error: cyclic inheritance involving T8193561
interface T8193561 extends p.T8193561.I {
^
1 error
An exception has occurred in the compiler (12-internal). Please file a 
bug against the Java compiler via the Java bug reporting page 
(http://bugreport.java.com) after checking the Bug Database 
(http://bugs.java.com) for duplicates. Include your program and the 
following diagnostic in your report. Thank you.
java.lang.NullPointerException
         at 
jdk.compiler/com.sun.tools.javac.comp.MemberEnter.visitMethodDef(MemberEnter.java:186)
[snip]
---

(Note the -XDdev - as there is an error already reported, the exception 
would normally be hidden, but the crash is still observable in certain 
cases, e.g. in tests.)

The offending line is:
             m.enclClass().flags_field |= DEFAULT;

The issue here, IMO, is that when the cycle is detected, the 
class/interface is marked as erroneous, and m.enclClass() won't return 
erroneous owner (will return null instead). Seems that using "m.owner" 
instead of "m.enclClass()" should be sufficient at this place?

Proposed patch: http://cr.openjdk.java.net/~jlahoda/8193561/webrev.00/
Bug: https://bugs.openjdk.java.net/browse/JDK-8193561

How does this look?

Thanks,
     Jan