RFR: JDK-8242802: javac crashes when checking equals and hashCode in unresolvable anonymous class

[Jan Lahoda]

Hi,

javac may crash with an exception when running with -Xlint:options 
processing code like this:
---
public class InvalidAnonymous {
     private void t() {
         new Undefined() {};
     }
}
---

---
$ javac -XDdev -Xlint:overrides InvalidAnonymous.java
InvalidAnonymous.java:3: error: cannot find symbol
         new Undefined() {};
             ^
   symbol: class Undefined
   location: class InvalidAnonymous
1 error
An exception has occurred in the compiler (15-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, the 
following diagnostic, and the parameters passed to the Java compiler in 
your report. Thank you.
java.lang.NullPointerException
         at 
jdk.compiler/com.sun.tools.javac.comp.Check.checkClassOverrideEqualsAndHash(Check.java:2148)
         at 
jdk.compiler/com.sun.tools.javac.comp.Check.checkClassOverrideEqualsAndHashIfNeeded(Check.java:2138)
---

This is because Types.implementation may return null if there is no 
method implementing the given input method (Object.equals in this case - 
and due to the "Undefined", the anonymous does not have Object as a 
supertype, and hence does not have any implementation of equals).

The proposed fix is to add a null check on the result of 
Types.implementation.

Webrev: http://cr.openjdk.java.net/~jlahoda/8242802/webrev.00/
JBS: https://bugs.openjdk.java.net/browse/JDK-8242802

How does this look?

Thanks,
     Jan