Merge pull request #1135 from svaarala/fix-bound-function-prototype

Fix bound function internal prototype handling to match ES6

RELEASES.rst

@@ -1996,6 +1996,10 @@ Planned
   for a target function with name "foo", bound function name is "bound foo"
   (GH-1113)
 
+* Change bound function internal prototype handling to match ES6 requirements;
+  bound function internal prototype is copied from the target function
+  instead of always being Function.prototype (GH-1135)
+
 * Add a fastint check for duk_put_number_list() values (GH-1086)
 
 * Remove an unintended fastint downgrade check for unary minus executor

doc/release-notes-v2-0.rst

@@ -1058,6 +1058,10 @@ Other incompatible changes
   "enumerate" trap has been obsoleted.  Key enumerability is also now checked
   when "ownKeys" trap is used in Object.keys() and for-in.
 
+* Bound function internal prototype is copied from the target function to match
+  ES6 requirements; in ES5 (and Duktape 1.x) bound function internal prototype
+  is always set to Function.prototype.
+
 Known issues
 ============
 

src-input/duk_bi_function.c

@@ -302,6 +302,7 @@ DUK_INTERNAL duk_ret_t duk_bi_function_prototype_call(duk_context *ctx) {
  * merges argument lists etc here.
  */
 DUK_INTERNAL duk_ret_t duk_bi_function_prototype_bind(duk_context *ctx) {
+	duk_hthread *thr = (duk_hthread *) ctx;
 	duk_hobject *h_bound;
 	duk_hobject *h_target;
 	duk_idx_t nargs;
@@ -349,8 +350,15 @@ DUK_INTERNAL duk_ret_t duk_bi_function_prototype_bind(duk_context *ctx) {
 
 	/* [ thisArg arg1 ... argN func boundFunc ] */
 
-	/* bound function 'length' property is interesting */
 	h_target = duk_get_hobject(ctx, -2);
+
+	/* internal prototype must be copied from the target */
+	if (h_target != NULL) {
+		/* For lightfuncs Function.prototype is used and is already in place. */
+		DUK_HOBJECT_SET_PROTOTYPE_UPDREF(thr, h_bound, DUK_HOBJECT_GET_PROTOTYPE(thr->heap, h_target));
+	}
+
+	/* bound function 'length' property is interesting */
 	if (h_target == NULL ||  /* lightfunc */
 	    DUK_HOBJECT_GET_CLASS_NUMBER(h_target) == DUK_HOBJECT_CLASS_FUNCTION) {
 		/* For lightfuncs, simply read the virtual property. */

tests/ecmascript/test-dev-bound-func-prototype.js

@@ -0,0 +1,39 @@
+/*
+ *  Bound function internal prototype is copied from the target in ES6.
+ *  In ES5 it is always Function.prototype.  Test for ES6 behavior.
+ */
+
+/*===
+bar
+bar
+true
+quux
+bar
+false
+===*/
+
+function test() {
+    var F = function foo() {};
+    var proto = { foo: 'bar' };
+    Object.setPrototypeOf(F, proto);
+
+    // Create a bound function; its prototype is copied from the current
+    // prototype of the target.
+    var G = Function.prototype.bind.call(F);
+    print(F.foo);
+    print(G.foo);
+    print(Object.getPrototypeOf(G) === proto);
+
+    // Alter target's internal prototype; doesn't affect the bound function.
+    proto = { foo: 'quux' };
+    Object.setPrototypeOf(F, proto);
+    print(F.foo);
+    print(G.foo);
+    print(Object.getPrototypeOf(G) === proto);
+}
+
+try {
+    test();
+} catch (e) {
+    print(e.stack || e);
+}