FULL PRODUCT VERSION :
java version "1.8.0_66"
Java(TM) SE Runtime Environment (build 1.8.0_66-b17)
Java HotSpot(TM) 64-Bit Server VM (build 25.66-b17, mixed mode)

ADDITIONAL OS VERSION INFORMATION :
Darwin eno.local 15.2.0 Darwin Kernel Version 15.2.0: Fri Nov 13 19:56:56 PST 2015; root:xnu-3248.20.55~2/RELEASE_X86_64 x86_64


A DESCRIPTION OF THE PROBLEM :
Type inference fails for a generic method with Function.identity() provided as argument twice. Does not fail when lambda 'x -> x' is substituted for identity() instead.

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
$ javac GenericsTest.java

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
Expected source file to compile without errors.
ACTUAL -
Compilation fails.

ERROR MESSAGES/STACK TRACES THAT OCCUR :
Error:(17, 58) java: method toSortedMap in class com.pexlabs.util.GenericsTest cannot be applied to given types;
  required: java.util.function.Function<? super T,? extends K>,java.util.function.Function<? super T,? extends V>
  found: java.util.function.Function<java.lang.Object,java.lang.Object>,java.util.function.Function<java.lang.Object,java.lang.Object>
  reason: inferred type does not conform to upper bound(s)
    inferred: java.lang.Object
    upper bound(s): K,java.lang.Comparable<? super K>,java.lang.Object

REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
package x;

import java.util.Map;
import java.util.function.Function;
import java.util.stream.Collector;

public class GenericsTest {
    public static <T, K extends Comparable<? super K>, V>
    Collector<T, ?, Map<K, V>> toSortedMap(
            Function<? super T, ? extends K> keyMapper,
            Function<? super T, ? extends V> valueMapper) {
        return null;
    }

    public static void foo() {
        // *** Following statement does not compile ***
        Collector<Integer, ?, Map<Integer, Integer>> a = toSortedMap(Function.identity(), Function.identity());

        // However this statement compiles just fine
        Collector<Integer, ?, Map<Integer, Integer>> b = toSortedMap(i -> i, i -> i);
    }
}
---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
Use lambda 'x -> x' instead of Function.identity()