michael@0: /*
michael@0:  * Any copyright is dedicated to the Public Domain.
michael@0:  * http://creativecommons.org/licenses/publicdomain/
michael@0:  */
michael@0: 
michael@0: var count = 0;
michael@0: 
michael@0: function testCaller(obj) {
michael@0:     switch (++count) {
michael@0:       case 1:
michael@0:       case 2:
michael@0:         /*
michael@0:          * The first two times, obj is objA. The first time, we reference
michael@0:          * arguments.callee.caller before obj.go, so the caller getter must
michael@0:          * force the joined function object in the stack frame to cross the
michael@0:          * method read barrier. The second time, obj.go has been cloned and
michael@0:          * it should match the new frame's callee from the get-go.
michael@0:          */
michael@0:         assertEq(obj, objA);
michael@0:         break;
michael@0: 
michael@0:       case 3: {
michael@0:         assertEq(obj, objB);
michael@0: 
michael@0:         /*
michael@0:          * Store another clone of the joined function object before obj.go has
michael@0:          * been read, but after it has been invoked via objB.go(objB).
michael@0:          *
michael@0:          * In this case, arguments.callee.caller must not lie and return what
michael@0:          * is currently stored in objB.go, since that function object (objA.go)
michael@0:          * was cloned earlier, when count was 1, and it is not the function
michael@0:          * object that was truly invoked.
michael@0:          *
michael@0:          * But since the invocation of objB.go(objB) did not clone go, and the
michael@0:          * following assignment overwrote the invoked value, leaving the only
michael@0:          * reference to the joined function object for go in the stack frame's
michael@0:          * callee (argv[-2]) member, the arguments.callee.caller reference must
michael@0:          * clone a function object for the callee, store it as the callee, and
michael@0:          * return it here.
michael@0:          *
michael@0:          * It won't equal obj.go, but (implementation detail) it should have
michael@0:          * the same proto as obj.go
michael@0:          */
michael@0:         obj.go = objA.go;
michael@0: 
michael@0:         let caller = arguments.callee.caller;
michael@0:         let obj_go = obj.go;
michael@0:         return caller != obj_go && caller.__proto__ == obj_go.__proto__;
michael@0:       }
michael@0: 
michael@0:       case 4: {
michael@0:         assertEq(obj, objC);
michael@0: 
michael@0:         let save = obj.go;
michael@0:         delete obj.go;
michael@0:         return arguments.callee.caller == save;
michael@0:       }
michael@0: 
michael@0:       case 5: {
michael@0:         assertEq(obj, objD);
michael@0: 
michael@0:         let read = obj.go;
michael@0:         break;
michael@0:       }
michael@0:     }
michael@0: 
michael@0:     return arguments.callee.caller == obj.go;
michael@0: }
michael@0: 
michael@0: function make() {
michael@0:     return {
michael@0:         go: function(obj) {
michael@0:             return testCaller(obj);
michael@0:         }
michael@0:     };
michael@0: }
michael@0: 
michael@0: var objA = make(),
michael@0:     objB = make(),
michael@0:     objC = make(),
michael@0:     objD = make();
michael@0: 
michael@0: reportCompare(true, objA.go(objA), "1");
michael@0: reportCompare(true, objA.go(objA), "2");
michael@0: reportCompare(true, objB.go(objB), "3");
michael@0: reportCompare(true, objC.go(objC), "4");
michael@0: reportCompare(true, objD.go(objD), "5");