Bug ID: JDK-8073842 Invalid method reference when referencing a method on a wildcard type

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JDK 9
9 b54Fixed

FULL PRODUCT VERSION :
java version "1.8.0_31"
Java(TM) SE Runtime Environment (build 1.8.0_31-b13)
Java HotSpot(TM) 64-Bit Server VM (build 25.31-b07, mixed mode)

ADDITIONAL OS VERSION INFORMATION :
Linux jacek 3.2.0-4-amd64 #1 SMP Debian 3.2.63-2+deb7u2 x86_64 GNU/Linux

A DESCRIPTION OF THE PROBLEM :
Invalid method reference thrown by javac when making a reference to a method on an upper bounded wildcard generic type.

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
1. Create a file named Sample.java containing the attached source code for class Sample
2. Compile: javac Sample.java 


EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
File compiles OK.
ACTUAL -
Compilation error occurs 

ERROR MESSAGES/STACK TRACES THAT OCCUR :
Sample.java:8: error: invalid method reference
    Stream<Runnable> r = s.map(o -> o::work);
                                    ^
  cannot find symbol
    symbol:   method work()
    location: bound of type variable CAP#1
  where CAP#1 is a fresh type-variable:
    CAP#1 extends Sample from capture of ? extends Sample
1 error


REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
import java.util.stream.Stream;
public class Sample {

  void work() { }

  void process(Stream<? extends Sample> s) {
    Stream<Runnable> r = s.map(o -> o::work);
  }
}
---------- END SOURCE ----------

URL: http://hg.openjdk.java.net/jdk9/jdk9/langtools/rev/218d589184d3 User: lana Date: 2015-03-11 02:21:17 +0000
11-03-2015
URL: http://hg.openjdk.java.net/jdk9/dev/langtools/rev/218d589184d3 User: mcimadamore Date: 2015-02-27 18:24:22 +0000
27-02-2015
The problem is that javac is unable to perform method lookup on type-variables sites; in all cases where lookup occurs, javac tries to lift the receiver type to a class type, by repeatedly calling getUpperBound() on the receiver; this is not done for method reference lookup, which results in spurious accessibility issues.
25-02-2015
The input stream contains Sample - meaning that the argument to map() should be something like Function<Simple, Runnable>. The lambda is not pertinent to applicability (as its return expression isn't) but that doesn't constitute an issue, as there's no overloading of Stream.map. So, from invocation type inference, we should be able to establish that the target type of the nested method reference is a Runnable, which should be compatible with the method reference (as work() is a void method). This is a bug.
25-02-2015
Checked this for JDK 8u31 and 8u40 ea b23 and could notice the error: >javac Sample.java Sample.java:7: error: invalid method reference Stream<Runnable> r = s.map(o -> o::work); ^ cannot find symbol symbol: method work() location: bound of type variable CAP#1 where CAP#1 is a fresh type-variable: CAP#1 extends Sample from capture of ? extends Sample 1 error
25-02-2015

Duplicate :	JDK-8133123 - javac: AssertionError: isSubClass T
Duplicate :	JDK-8199123 - AssertionError when compiling reference to abstract class' method, defined in interface, when other non-abstract same-named method exists
Duplicate :	JDK-8158497 - JDK-8133123 and JDK-8157845 not fixed on java 8
Duplicate :	JDK-8157845 - javac: AssertionError: isSubClass T
Duplicate :	JDK-8133239 - Method reference can't see package-access tvar method
Relates :	JDK-8318160 - javac does not reject private method reference with type-variable receiver