FULL PRODUCT VERSION :
java version "1.8.0"
Java(TM) SE Runtime Environment (build 1.8.0-b132)
Java HotSpot(TM) 64-Bit Server VM (build 25.0-b70, mixed mode)


ADDITIONAL OS VERSION INFORMATION :
Linux yolo 3.5.0-45-generic #68-Ubuntu SMP Mon Dec 2 21:58:52 UTC 2013 x86_64 x86_64 x86_64 GNU/Linux

OS X-version: 10.9.2 (Darwin Kernel Version 13.1.0: Thu Jan 16 19:40:37 PST 2014; root:xnu-2422.90.20~2/RELEASE_X86_64 x86_64)

A DESCRIPTION OF THE PROBLEM :
Javac generates an exception when using the FunctionalInterface-annotation for an interface extending two or more generic superinterfaces, where at least one of them is used without explicit type arguments.

ADDITIONAL REGRESSION INFORMATION:
The test case compiled in javac 1.8.0-ea

java version "1.8.0"
Java(TM) SE Runtime Environment (build 1.8.0-b132)
Java HotSpot(TM) 64-Bit Server VM (build 25.0-b70, mixed mode)

javac 1.8.0

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Compile the test case with javac.

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
Compile was expected to pass.
ACTUAL -
Compile failed with a ClassCastException.

ERROR MESSAGES/STACK TRACES THAT OCCUR :
An exception has occurred in the compiler (1.8.0). 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.ClassCastException: com.sun.tools.javac.code.Type$MethodType cannot be cast to com.sun.tools.javac.code.Type$ForAll
        at com.sun.tools.javac.code.Types$DescriptorCache.mergeDescriptors(Types.java:521)
        at com.sun.tools.javac.code.Types$DescriptorCache.findDescriptorInternal(Types.java:433)
        at com.sun.tools.javac.code.Types$DescriptorCache.get(Types.java:394)
        at com.sun.tools.javac.code.Types.findDescriptorSymbol(Types.java:562)
        at com.sun.tools.javac.comp.Check.checkFunctionalInterface(Check.java:3515)
        at com.sun.tools.javac.comp.Attr.attribClass(Attr.java:4219)
        at com.sun.tools.javac.comp.Attr.attribClass(Attr.java:4149)
        at com.sun.tools.javac.comp.Attr.visitClassDef(Attr.java:877)
        at com.sun.tools.javac.tree.JCTree$JCClassDecl.accept(JCTree.java:687)
        at com.sun.tools.javac.comp.Attr.attribTree(Attr.java:596)
        at com.sun.tools.javac.comp.Attr.attribStat(Attr.java:665)
        at com.sun.tools.javac.comp.Attr.attribClassBody(Attr.java:4305)
        at com.sun.tools.javac.comp.Attr.attribClass(Attr.java:4215)
        at com.sun.tools.javac.comp.Attr.attribClass(Attr.java:4149)
        at com.sun.tools.javac.comp.Attr.attrib(Attr.java:4124)
        at com.sun.tools.javac.main.JavaCompiler.attribute(JavaCompiler.java:1251)
        at com.sun.tools.javac.main.JavaCompiler.compile2(JavaCompiler.java:904)
        at com.sun.tools.javac.main.JavaCompiler.compile(JavaCompiler.java:863)
        at com.sun.tools.javac.main.Main.compile(Main.java:523)
        at com.sun.tools.javac.main.Main.compile(Main.java:381)
        at com.sun.tools.javac.main.Main.compile(Main.java:370)
        at com.sun.tools.javac.main.Main.compile(Main.java:361)
        at com.sun.tools.javac.Main.compile(Main.java:56)
        at com.sun.tools.javac.Main.main(Main.java:42)


REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
import java.util.*;
import java.io.Serializable;

class Test {
        interface X<A> { <T extends A> void execute(int a); }
        interface Y<B> { <S extends B> void execute(int a); }

        @FunctionalInterface
        interface Exec<A> extends Y, X<A> { }
}

---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
Use the superinterfaces with explicit type arguments.