javac fails (without -XDdev returns error code '4', with -XDdev prints the exception below) processing this source code:
-----
/*
 * @test /nodynamiccopyright/
 * @bug 8016640
 * @summary compiler hangs if the generics arity of a base class is wrong
 * @compile/fail/ref=T8016640.out -XDrawDiagnostics -XDdev T8016640.java
 */
class T8016640 {
    static class Foo<X,Y> { }
    static class BadFoo<T> extends Foo<T> { }
    static class SubBadFoo<T> extends BadFoo<T> { }
}
-----

$ javac -XDdev T8016640.java
T8016640.java:9: error: wrong number of type arguments; required 2
    static class BadFoo<T> extends Foo<T> { }
                                      ^
An exception has occurred in the compiler (1.8.0-ea). Please file a bug at the Java Developer Connection (http://java.sun.com/webapps/bugreport) after checking the Bug Parade for duplicates. Include your program and the following diagnostic in your report. Thank you.
java.lang.NullPointerException
        at com.sun.tools.javac.comp.Check.checkCompatibleConcretes(Check.java:1750)
        at com.sun.tools.javac.comp.Check.checkCompatibleSupertypes(Check.java:2335)
        at com.sun.tools.javac.comp.Attr.attribClassBody(Attr.java:4304)
        at com.sun.tools.javac.comp.Attr.attribClass(Attr.java:4242)
        at com.sun.tools.javac.comp.Attr.attribClass(Attr.java:4177)
        at com.sun.tools.javac.comp.Attr.visitClassDef(Attr.java:871)
        at com.sun.tools.javac.tree.JCTree$JCClassDecl.accept(JCTree.java:687)
        at com.sun.tools.javac.comp.Attr.attribTree(Attr.java:581)
        at com.sun.tools.javac.comp.Attr.attribStat(Attr.java:650)
        at com.sun.tools.javac.comp.Attr.attribClassBody(Attr.java:4334)
        at com.sun.tools.javac.comp.Attr.attribClass(Attr.java:4242)
        at com.sun.tools.javac.comp.Attr.attribClass(Attr.java:4177)
        at com.sun.tools.javac.comp.Attr.attrib(Attr.java:4151)
        at com.sun.tools.javac.main.JavaCompiler.attribute(JavaCompiler.java:1224)
        at com.sun.tools.javac.main.JavaCompiler.compile2(JavaCompiler.java:877)
        at com.sun.tools.javac.main.JavaCompiler.compile(JavaCompiler.java:836)
        at com.sun.tools.javac.main.Main.compile(Main.java:518)
        at com.sun.tools.javac.main.Main.compile(Main.java:376)
        at com.sun.tools.javac.main.Main.compile(Main.java:365)
        at com.sun.tools.javac.main.Main.compile(Main.java:356)
        at com.sun.tools.javac.Main.compile(Main.java:77)
        at com.sun.tools.javac.Main.main(Main.java:62)

This is with:
$ jdk1.8.0/bin/javac -fullversion
javac full version "1.8.0-ea-b100"