Merge pull request #1080 from svaarala/object-__proto__-toobject

Fix Object.prototype.__proto__ coercion

RELEASES.rst

@@ -1958,6 +1958,10 @@ Planned
   ES6 and other engines; "\078" is now accepted and is the same as
   "\u00078", "\8" and "\9" are accepted as literal "8" and "9"  (GH-1057)
 
+* Fix Object.prototype.__proto__ handling to use ToObject() coercion rather
+  than requiring an object; this matches ES6 requirements and allows e.g.
+  the expression (123).__proto__ to work (GH-1080)
+
 * Fix String.fromCharCode() behavior for non-BMP characters when standard
   behavior is enabled (DUK_USE_NONSTD_STRING_FROMCHARCODE_32BIT disabled):
   use ToUint16() + CESU-8 rather than ToUint32() + CESU-8 which produces

src-input/duk_bi_object.c

@@ -379,11 +379,12 @@ DUK_INTERNAL duk_ret_t duk_bi_object_getprototype_shared(duk_context *ctx) {
 	duk_tval *tv;
 
 	if (duk_get_current_magic(ctx) == 0) {
+		DUK_ASSERT_TOP(ctx, 0);
+		duk_push_this_coercible_to_object(ctx);
 		tv = DUK_HTHREAD_THIS_PTR(thr);
-	} else {
+	}
 	DUK_ASSERT(duk_get_top(ctx) >= 1);
 	tv = DUK_GET_TVAL_POSIDX(ctx, 0);
-	}
 
 	switch (DUK_TVAL_GET_TAG(tv)) {
 	case DUK_TAG_BUFFER:

tests/ecmascript/test-bi-object-proto-__proto__.js

@@ -27,6 +27,9 @@ boolean undefined undefined
 number undefined undefined
 string undefined undefined
 object 123 321
+true
+TypeError
+TypeError
 ===*/
 
 function test() {
@@ -120,7 +123,30 @@ function test() {
         print('no setter');
     }
 
-    // TODO: coercion order tests (side effect / error message if multiple errors)
+    // The __proto__ getter uses ToObject() coercion for its argument so that
+    // e.g. (123).__proto__ is allowed.  This differs from Object.getPrototypeOf()
+    // in ES5.  However, ES6 updates Object.getPrototypeOf() to use ToObject()
+    // coercion too.  Null and undefined are rejected as base values.
+
+    try {
+        print((123).__proto__ === Number.prototype);
+    } catch (e) {
+        print(e.stack || e);
+    }
+
+    try {
+        print(null.__proto__ === Number.prototype);
+    } catch (e) {
+        print(e.name);
+    }
+
+    try {
+        print((void 0).__proto__ === Number.prototype);
+    } catch (e) {
+        print(e.name);
+    }
+
+    // XXX: coercion order tests (side effect / error message if multiple errors)
 }
 
 try {