Merge pull request #1177 from svaarala/builtin-function-length-configurable

Make built-in function .length and .name configurable

RELEASES.rst

@@ -2088,7 +2088,7 @@ Planned
 
 * Make function instance .name and .length properties configurable (but
   non-writable and non-enumerable) to match ES6 requirements; also change
-  .fileName to follow the same attribute convention (GH-1153)
+  .fileName to follow the same attribute convention (GH-1153, GH-1177)
 
 * Make Error instance .fileName and .lineNumber properties configurable
   but non-writable and non-enumerable to match function instance property

extras/console/duk_console.c

@@ -100,8 +100,9 @@ static duk_ret_t duk__console_dir(duk_context *ctx) {
 
 static void duk__console_reg_vararg_func(duk_context *ctx, duk_c_function func, const char *name) {
 	duk_push_c_function(ctx, func, DUK_VARARGS);
+	duk_push_string(ctx, "name");
 	duk_push_string(ctx, name);
-	duk_put_prop_string(ctx, -2, "name");  /* Improve stacktraces by displaying function name */
+	duk_def_prop(ctx, -3, DUK_DEFPROP_HAVE_VALUE | DUK_DEFPROP_FORCE);  /* Improve stacktraces by displaying function name */
 	duk_put_prop_string(ctx, -2, name);
 }
 

extras/logging/duk_logging.c

@@ -334,8 +334,9 @@ void duk_logging_init(duk_context *ctx, duk_uint_t flags) {
 
 	/* [ ... func Duktape.Logger Duktape.Logger.prototype ] */
 
+	duk_push_string(ctx, "name");
 	duk_push_string(ctx, "Logger");
-	duk_put_prop_string(ctx, -3, "name");
+	duk_def_prop(ctx, -4, DUK_DEFPROP_HAVE_VALUE | DUK_DEFPROP_FORCE);
 
 	duk_dup_top(ctx);
 	duk_put_prop_string(ctx, -2, "constructor");

src-input/duk_hthread_builtins.c

@@ -264,17 +264,12 @@ DUK_INTERNAL void duk_hthread_create_builtin_objects(duk_hthread *thr) {
 
 			/* XXX: function properties */
 
-			/* Built-in 'name' is not writable by default.  Function '.name'
-			 * is writable to allow user code to set a '.name' on a native
-			 * function.
-			 */
 			duk__push_stridx_or_string(ctx, bd);
 #if defined(DUK_USE_FUNC_NAME_PROPERTY)
 			duk_xdef_prop_stridx_short(ctx,
 			                           -2,
 			                           DUK_STRIDX_NAME,
-			                           (i == DUK_BIDX_FUNCTION_PROTOTYPE) ?
-			                               DUK_PROPDESC_FLAGS_W : DUK_PROPDESC_FLAGS_NONE);
+			                           DUK_PROPDESC_FLAGS_C);
 #else
 			duk_pop(ctx);  /* Not very ideal but good enough for now. */
 #endif
@@ -310,17 +305,14 @@ DUK_INTERNAL void duk_hthread_create_builtin_objects(duk_hthread *thr) {
 		}
 
 		if (len >= 0) {
-			/*
-			 *  For top-level objects, 'length' property has the following
-			 *  default attributes: non-writable, non-enumerable, non-configurable
-			 *  (E5 Section 15).
-			 *
-			 *  However, 'length' property for Array.prototype has attributes
-			 *  expected of an Array instance which are different: writable,
-			 *  non-enumerable, non-configurable (E5 Section 15.4.5.2).
+			/* In ES2015+ built-in function object .length property
+			 * has property attributes C (configurable only):
+			 * http://www.ecma-international.org/ecma-262/7.0/#sec-ecmascript-standard-built-in-objects
 			 *
-			 *  Because Array .length is virtual, it's not encoded in the init
-			 *  data separately.
+			 * Array.prototype remains an Array instance in ES2015+
+			 * and its length has attributes W (writable only).
+			 * Because .length is now virtual for duk_harray, it is
+			 * not encoded explicitly in init data.
 			 */
 
 			DUK_ASSERT(class_num != DUK_HOBJECT_CLASS_ARRAY);  /* .length is virtual */
@@ -328,7 +320,7 @@ DUK_INTERNAL void duk_hthread_create_builtin_objects(duk_hthread *thr) {
 			duk_xdef_prop_stridx_short(ctx,
 			                           -2,
 			                           DUK_STRIDX_LENGTH,
-			                           DUK_PROPDESC_FLAGS_NONE);  /* XXX */
+			                           DUK_PROPDESC_FLAGS_C);
 		}
 
 		/* enable exotic behaviors last */
@@ -608,10 +600,10 @@ DUK_INTERNAL void duk_hthread_create_builtin_objects(duk_hthread *thr) {
 			/* [ (builtin objects) name func ] */
 
 			duk_push_int(ctx, c_length);
-			duk_xdef_prop_stridx_short(ctx, -2, DUK_STRIDX_LENGTH, DUK_PROPDESC_FLAGS_NONE);  /* XXX */
+			duk_xdef_prop_stridx_short(ctx, -2, DUK_STRIDX_LENGTH, DUK_PROPDESC_FLAGS_C);
 
 			duk_dup_m2(ctx);
-			duk_xdef_prop_stridx_short(ctx, -2, DUK_STRIDX_NAME, DUK_PROPDESC_FLAGS_NONE);
+			duk_xdef_prop_stridx_short(ctx, -2, DUK_STRIDX_NAME, DUK_PROPDESC_FLAGS_C);
 
 			/* XXX: other properties of function instances; 'arguments', 'caller'. */
 

tests/api/test-bug-set-cfunc-name.c

@@ -13,13 +13,16 @@
  *  while simultaneously allowing a Function instance's 'name' property
  *  to be set - but Ecmascript cannot express such an access control
  *  policy.
+ *
+ *  Duktape 2.x follows ES6 where .name is again non-writable, but is
+ *  configurable.  So duk_def_prop() can be used to set the name.
  */
 
 /*===
 *** test_1 (duk_safe_call)
-writable: true
+writable: false
 enumerable: false
-configurable: false
+configurable: true
 MyFunc.name: my_func_name
 final top: 0
 ==> rc=0, result='undefined'
@@ -41,8 +44,9 @@ static duk_ret_t test_1(duk_context *ctx, void *udata) {
 		"print('configurable:', pd.configurable);\n");
 
 	duk_push_c_function(ctx, my_func, 0);
+	duk_push_string(ctx, "name");
 	duk_push_string(ctx, "my_func_name");
-	duk_put_prop_string(ctx, -2, "name");
+	duk_def_prop(ctx, -3, DUK_DEFPROP_HAVE_VALUE);
 	duk_put_global_string(ctx, "MyFunc");
 
 	duk_eval_string_noresult(ctx,

tests/api/test-def-prop.c

@@ -243,8 +243,9 @@ static duk_ret_t my_setter(duk_context *ctx) {
 
 static void push_getter(duk_context *ctx) {
 	duk_push_c_function(ctx, my_getter, 0 /*nargs*/);
+	duk_push_string(ctx, "name");
 	duk_push_string(ctx, "getter");
-	duk_put_prop_string(ctx, -2, "name");
+	duk_def_prop(ctx, -3, DUK_DEFPROP_HAVE_VALUE);
 }
 
 static void push_getter_lightfunc(duk_context *ctx) {
@@ -253,8 +254,9 @@ static void push_getter_lightfunc(duk_context *ctx) {
 
 static void push_setter(duk_context *ctx) {
 	duk_push_c_function(ctx, my_setter, 1 /*nargs*/);
+	duk_push_string(ctx, "name");
 	duk_push_string(ctx, "setter");
-	duk_put_prop_string(ctx, -2, "name");
+	duk_def_prop(ctx, -3, DUK_DEFPROP_HAVE_VALUE);
 }
 
 static void push_setter_lightfunc(duk_context *ctx) {

tests/api/test-dev-cfunc-name.c

@@ -3,6 +3,9 @@
  *  You can set it yourself in Duktape 1.1 to get nicer tracebacks.
  *  In Duktape 1.0 Function.prototype.name is not writable so you can't
  *  do this.
+ *
+ *  In Duktape 2.x .name is non-writable but configurable to match ES6
+ *  requirements; duk_def_prop() can be used to set it.
  */
 
 /*===
@@ -51,8 +54,9 @@ static duk_ret_t test_with_name(duk_context *ctx, void *udata) {
 	(void) udata;
 
 	duk_get_global_string(ctx, "MyFunc");
+	duk_push_string(ctx, "name");
 	duk_push_string(ctx, "my_func");
-	duk_put_prop_string(ctx, -2, "name");
+	duk_def_prop(ctx, -3, DUK_DEFPROP_HAVE_VALUE);
 	duk_pop(ctx);
 
 	duk_eval_string_noresult(ctx,

tests/api/test-inspect-callstack-entry.c

@@ -80,8 +80,9 @@ static duk_ret_t test_basic(duk_context *ctx, void *udata) {
 		"    print('exited func');\n"
 		"})");
 	duk_push_c_function(ctx, my_func, 0 /*nargs*/);
+	duk_push_string(ctx, "name");
 	duk_push_string(ctx, "my_func");
-	duk_put_prop_string(ctx, -2, "name");
+	duk_def_prop(ctx, -3, DUK_DEFPROP_HAVE_VALUE);
 	duk_call(ctx, 1);
 	duk_pop(ctx);
 

tests/ecmascript/test-bi-duktape.js

@@ -26,43 +26,43 @@ Duktape.dec function wc
 Duktape.compact function wc
 Duktape.env string wc
 Duktape.modLoaded object wc
-Duktape.Pointer.name string none
-Duktape.Pointer.length number none
+Duktape.Pointer.name string c
+Duktape.Pointer.length number c
 Duktape.Pointer.prototype object none
 Duktape.Pointer.prototype.constructor function wc
 Duktape.Pointer.prototype.toString function wc
 Duktape.Pointer.prototype.valueOf function wc
-Duktape.Pointer.prototype.toString.length number none
-Duktape.Pointer.prototype.toString.name string none
-Duktape.Pointer.prototype.valueOf.length number none
-Duktape.Pointer.prototype.valueOf.name string none
-Duktape.Thread.name string none
-Duktape.Thread.length number none
+Duktape.Pointer.prototype.toString.length number c
+Duktape.Pointer.prototype.toString.name string c
+Duktape.Pointer.prototype.valueOf.length number c
+Duktape.Pointer.prototype.valueOf.name string c
+Duktape.Thread.name string c
+Duktape.Thread.length number c
 Duktape.Thread.prototype object none
 Duktape.Thread.yield function wc
 Duktape.Thread.resume function wc
 Duktape.Thread.current function wc
 Duktape.Thread.prototype.constructor function wc
-Duktape.Thread.yield.length number none
-Duktape.Thread.yield.name string none
-Duktape.Thread.resume.length number none
-Duktape.Thread.resume.name string none
-Duktape.Thread.current.length number none
-Duktape.Thread.current.name string none
-Duktape.info.length number none
-Duktape.info.name string none
-Duktape.act.length number none
-Duktape.act.name string none
-Duktape.gc.length number none
-Duktape.gc.name string none
-Duktape.fin.length number none
-Duktape.fin.name string none
-Duktape.enc.length number none
-Duktape.enc.name string none
-Duktape.dec.length number none
-Duktape.dec.name string none
-Duktape.compact.length number none
-Duktape.compact.name string none
+Duktape.Thread.yield.length number c
+Duktape.Thread.yield.name string c
+Duktape.Thread.resume.length number c
+Duktape.Thread.resume.name string c
+Duktape.Thread.current.length number c
+Duktape.Thread.current.name string c
+Duktape.info.length number c
+Duktape.info.name string c
+Duktape.act.length number c
+Duktape.act.name string c
+Duktape.gc.length number c
+Duktape.gc.name string c
+Duktape.fin.length number c
+Duktape.fin.name string c
+Duktape.enc.length number c
+Duktape.enc.name string c
+Duktape.dec.length number c
+Duktape.dec.name string c
+Duktape.compact.length number c
+Duktape.compact.name string c
 ===*/
 
 function propsTest() {

tests/ecmascript/test-bi-error-instance-custom.js

@@ -40,12 +40,16 @@ all properties (including non-enumerable and inherited)
 "isPrototypeOf"
 "propertyIsEnumerable"
 ---
+function function false true
+function function false true
+function function false true
 ===*/
 
 function test() {
     var err;
     var k;
     var obj;
+    var pd;
 
     err = new Error('my message');
 
@@ -77,6 +81,14 @@ function test() {
         obj = Object.getPrototypeOf(obj);
     }
     print('---');
+
+    // Check a few Duktape 2.x property attributes.
+    pd = Object.getOwnPropertyDescriptor(Error.prototype, 'fileName');
+    print(typeof pd.get, typeof pd.set, pd.enumerable, pd.configurable);
+    pd = Object.getOwnPropertyDescriptor(Error.prototype, 'lineNumber');
+    print(typeof pd.get, typeof pd.set, pd.enumerable, pd.configurable);
+    pd = Object.getOwnPropertyDescriptor(Error.prototype, 'stack');
+    print(typeof pd.get, typeof pd.set, pd.enumerable, pd.configurable);
 }
 
 try {

tests/ecmascript/test-bi-function-constructor.js

@@ -7,6 +7,7 @@ constructor
 true true
 false false false
 true 1
+false false true
 no args
 no args
 one arg foo
@@ -31,7 +32,7 @@ function functionConstructorTest() {
     print(pd.writable, pd.enumerable, pd.configurable);
     print('length' in Function, Function.length);
     pd = Object.getOwnPropertyDescriptor(Function, 'length');
-//    print(pd.writable, pd.enumerable, pd.configurable);
+    print(pd.writable, pd.enumerable, pd.configurable);
 
     /* Test Function() called both as a function and as a constructor. */
 

tests/ecmascript/test-bi-function-instance.js

@@ -14,6 +14,12 @@ true 3
 false false true
 true test
 false false true
+""
+true true
+""
+true true
+"forcedName2"
+true true
 ===*/
 
 function functionInstanceTest() {
@@ -36,6 +42,23 @@ function functionInstanceTest() {
     print('name' in f, f.name);
     pd = Object.getOwnPropertyDescriptor(f, 'name');
     print(pd.writable, pd.enumerable, pd.configurable);
+
+    // Anonymous functions don't have an 'own' .name property but inherit
+    // an empty string name from Function.prototype.  The property .name in
+    // Function.prototype is not writable, but it is configurable, so that
+    // Object.defineProperty() can be used to add a name later on.
+
+    // XXX: not yet implemented, expect string for having a .name.
+
+    var anon = (1, 2, 3, function () {});
+    print(JSON.stringify(anon.name));  // inherited
+    print('name' in anon, anon.hasOwnProperty('name'));
+    anon.name = 'forcedName';  // ineffective, not configurable
+    print(JSON.stringify(anon.name));
+    print('name' in anon, anon.hasOwnProperty('name'));
+    Object.defineProperty(anon, 'name', { value: 'forcedName2' });
+    print(JSON.stringify(anon.name));
+    print('name' in anon, anon.hasOwnProperty('name'));
 }
 
 try {

tests/ecmascript/test-bi-function-prototype.js

@@ -10,10 +10,12 @@ true
 true 0
 true true
 undefined undefined
+string "" false false true
 ===*/
 
 function functionPrototypeTest() {
     var ret;
+    var pd;
 
     print(Object.prototype.toString.call(Function.prototype));
     print(Object.getPrototypeOf(Function.prototype) === Object.prototype);
@@ -23,6 +25,12 @@ function functionPrototypeTest() {
 
     ret = Function.prototype('foo', 'bar');
     print(typeof ret, ret);
+
+    // ES6 added '.name'.  Function.prototype provides an empty default name.
+    // It is not writable, but it is configurable so that Object.defineProperty()
+    // can be used to set the name of an anonymous function.
+    pd = Object.getOwnPropertyDescriptor(Function.prototype, 'name');
+    print(typeof pd.value, JSON.stringify(pd.value), pd.writable, pd.enumerable, pd.configurable);
 }
 
 try {

tests/ecmascript/test-bi-properties.js

@@ -99,7 +99,7 @@ var obj_data = [
         proto: 'Function.prototype',
         class: 'Function',
         props: [
-            { key: 'length', attrs: '', value: 1 },
+            { key: 'length', attrs: 'c', value: 1 },
             { key: 'prototype', attrs: '' },
             { key: 'getPrototypeOf', attrs: 'wc' },
             { key: 'getOwnPropertyDescriptor', attrs: 'wc' },
@@ -141,9 +141,8 @@ var obj_data = [
         proto: 'Function.prototype',
         class: 'Function',
         props: [
-            { key: 'length', attrs: '', value: 1 },
-            { key: 'prototype', 'attrs': '' },
-            { key: 'length', 'attrs': '' },
+            { key: 'length', attrs: 'c', value: 1 },
+            { key: 'prototype', 'attrs': '' }
         ],
         noprops: [
         ],
@@ -154,7 +153,7 @@ var obj_data = [
         proto: 'Object.prototype',
         class: 'Function',  // E5 Section 15.3.4
         props: [
-            { key: 'length', 'attrs': '', value: 0 },  // E5 Section 15.3.4
+            { key: 'length', 'attrs': 'c', value: 0 },
             { key: 'constructor', 'attrs': 'wc' },
             { key: 'toString', 'attrs': 'wc' },
             { key: 'apply', 'attrs': 'wc' },
@@ -170,7 +169,7 @@ var obj_data = [
         proto: 'Function.prototype',
         class: 'Function',
         props: [
-            { key: 'length', attrs: '', value: 1 },
+            { key: 'length', attrs: 'c', value: 1 },
             { key: 'prototype', 'attrs': '' },
             { key: 'isArray', 'attrs': 'wc' },
         ],
@@ -217,7 +216,7 @@ var obj_data = [
         proto: 'Function.prototype',
         class: 'Function',
         props: [
-            { key: 'length', attrs: '', value: 1 },
+            { key: 'length', attrs: 'c', value: 1 },
             { key: 'prototype', 'attrs': '' },
             { key: 'fromCharCode', 'attrs': 'wc' },
         ],
@@ -262,7 +261,7 @@ var obj_data = [
         proto: 'Function.prototype',
         class: 'Function',
         props: [
-            { key: 'length', attrs: '', value: 1 },
+            { key: 'length', attrs: 'c', value: 1 },
             { key: 'prototype', 'attrs': '' },
         ],
         noprops: [
@@ -288,7 +287,7 @@ var obj_data = [
         proto: 'Function.prototype',
         class: 'Function',
         props: [
-            { key: 'length', attrs: '', value: 1 },
+            { key: 'length', attrs: 'c', value: 1 },
             { key: 'prototype', 'attrs': '' },
             { key: 'MAX_VALUE', 'attrs': '' },
             { key: 'MIN_VALUE', 'attrs': '' },
@@ -360,7 +359,7 @@ var obj_data = [
         proto: 'Function.prototype',
         class: 'Function',
         props: [
-            { key: 'length', attrs: '', value: 7 },  // E5 Section 15.9.4
+            { key: 'length', attrs: 'c', value: 7 },  // E5 Section 15.9.4
             { key: 'prototype', 'attrs': '' },
             { key: 'parse', 'attrs': 'wc' },
             { key: 'UTC', 'attrs': 'wc' },
@@ -429,7 +428,7 @@ var obj_data = [
         proto: 'Function.prototype',
         class: 'Function',
         props: [
-            { key: 'length', attrs: '', value: 2 },  // E5 Section 15.10.5
+            { key: 'length', attrs: 'c', value: 2 },  // E5 Section 15.10.5
             { key: 'prototype', 'attrs': '' },
         ],
         noprops: [
@@ -456,7 +455,7 @@ var obj_data = [
         proto: 'Function.prototype',
         class: 'Function',
         props: [
-            { key: 'length', 'attrs': '', value: 1 },
+            { key: 'length', 'attrs': 'c', value: 1 },
             { key: 'prototype', 'attrs': '' },
         ],
         noprops: [
@@ -483,7 +482,7 @@ var obj_data = [
         proto: 'Error',
         class: 'Function',
         props: [
-            { key: 'length', 'attrs': '', value: 1 },
+            { key: 'length', 'attrs': 'c', value: 1 },
             { key: 'prototype', 'attrs': '' },
         ],
         noprops: [
@@ -509,7 +508,7 @@ var obj_data = [
         proto: 'Error',
         class: 'Function',
         props: [
-            { key: 'length', 'attrs': '', value: 1 },
+            { key: 'length', 'attrs': 'c', value: 1 },
             { key: 'prototype', 'attrs': '' },
         ],
         noprops: [
@@ -535,7 +534,7 @@ var obj_data = [
         proto: 'Error',
         class: 'Function',
         props: [
-            { key: 'length', 'attrs': '', value: 1 },
+            { key: 'length', 'attrs': 'c', value: 1 },
             { key: 'prototype', 'attrs': '' },
         ],
         noprops: [
@@ -561,7 +560,7 @@ var obj_data = [
         proto: 'Error',
         class: 'Function',
         props: [
-            { key: 'length', 'attrs': '', value: 1 },
+            { key: 'length', 'attrs': 'c', value: 1 },
             { key: 'prototype', 'attrs': '' },
         ],
         noprops: [
@@ -587,7 +586,7 @@ var obj_data = [
         proto: 'Error',
         class: 'Function',
         props: [
-            { key: 'length', 'attrs': '', value: 1 },
+            { key: 'length', 'attrs': 'c', value: 1 },
             { key: 'prototype', 'attrs': '' },
         ],
         noprops: [
@@ -613,7 +612,7 @@ var obj_data = [
         proto: 'Error',
         class: 'Function',
         props: [
-            { key: 'length', 'attrs': '', value: 1 },
+            { key: 'length', 'attrs': 'c', value: 1 },
             { key: 'prototype', 'attrs': '' },
         ],
         noprops: [
@@ -841,7 +840,7 @@ NOPROPERTY: "length"
 OBJECT: "Object" !sealed !frozen extensible
 PROTOTYPE: "Function.prototype"
 CLASS: Function
-PROPERTY: "length" !writable !enumerable !configurable
+PROPERTY: "length" !writable !enumerable configurable
 PROPERTY: "prototype" !writable !enumerable !configurable
 PROPERTY: "getPrototypeOf" writable !enumerable configurable
 PROPERTY: "getOwnPropertyDescriptor" writable !enumerable configurable
@@ -871,14 +870,13 @@ NOPROPERTY: "length"
 OBJECT: "Function" !sealed !frozen extensible
 PROTOTYPE: "Function.prototype"
 CLASS: Function
-PROPERTY: "length" !writable !enumerable !configurable
+PROPERTY: "length" !writable !enumerable configurable
 PROPERTY: "prototype" !writable !enumerable !configurable
-PROPERTY: "length" !writable !enumerable !configurable
 
 OBJECT: "Function.prototype" !sealed !frozen extensible
 PROTOTYPE: "Object.prototype"
 CLASS: Function
-PROPERTY: "length" !writable !enumerable !configurable
+PROPERTY: "length" !writable !enumerable configurable
 PROPERTY: "constructor" writable !enumerable configurable
 PROPERTY: "toString" writable !enumerable configurable
 PROPERTY: "apply" writable !enumerable configurable
@@ -888,7 +886,7 @@ PROPERTY: "bind" writable !enumerable configurable
 OBJECT: "Array" !sealed !frozen extensible
 PROTOTYPE: "Function.prototype"
 CLASS: Function
-PROPERTY: "length" !writable !enumerable !configurable
+PROPERTY: "length" !writable !enumerable configurable
 PROPERTY: "prototype" !writable !enumerable !configurable
 PROPERTY: "isArray" writable !enumerable configurable
 
@@ -922,7 +920,7 @@ PROPERTY: "reduceRight" writable !enumerable configurable
 OBJECT: "String" !sealed !frozen extensible
 PROTOTYPE: "Function.prototype"
 CLASS: Function
-PROPERTY: "length" !writable !enumerable !configurable
+PROPERTY: "length" !writable !enumerable configurable
 PROPERTY: "prototype" !writable !enumerable !configurable
 PROPERTY: "fromCharCode" writable !enumerable configurable
 
@@ -954,7 +952,7 @@ PROPERTY: "trim" writable !enumerable configurable
 OBJECT: "Boolean" !sealed !frozen extensible
 PROTOTYPE: "Function.prototype"
 CLASS: Function
-PROPERTY: "length" !writable !enumerable !configurable
+PROPERTY: "length" !writable !enumerable configurable
 PROPERTY: "prototype" !writable !enumerable !configurable
 
 OBJECT: "Boolean.prototype" !sealed !frozen extensible
@@ -968,7 +966,7 @@ NOPROPERTY: "length"
 OBJECT: "Number" !sealed !frozen extensible
 PROTOTYPE: "Function.prototype"
 CLASS: Function
-PROPERTY: "length" !writable !enumerable !configurable
+PROPERTY: "length" !writable !enumerable configurable
 PROPERTY: "prototype" !writable !enumerable !configurable
 PROPERTY: "MAX_VALUE" !writable !enumerable !configurable
 PROPERTY: "MIN_VALUE" !writable !enumerable !configurable
@@ -1022,7 +1020,7 @@ NOPROPERTY: "length"
 OBJECT: "Date" !sealed !frozen extensible
 PROTOTYPE: "Function.prototype"
 CLASS: Function
-PROPERTY: "length" !writable !enumerable !configurable
+PROPERTY: "length" !writable !enumerable configurable
 PROPERTY: "prototype" !writable !enumerable !configurable
 PROPERTY: "parse" writable !enumerable configurable
 PROPERTY: "UTC" writable !enumerable configurable
@@ -1079,7 +1077,7 @@ NOPROPERTY: "length"
 OBJECT: "RegExp" !sealed !frozen extensible
 PROTOTYPE: "Function.prototype"
 CLASS: Function
-PROPERTY: "length" !writable !enumerable !configurable
+PROPERTY: "length" !writable !enumerable configurable
 PROPERTY: "prototype" !writable !enumerable !configurable
 
 OBJECT: "RegExp.prototype" !sealed !frozen extensible
@@ -1094,7 +1092,7 @@ NOPROPERTY: "length"
 OBJECT: "Error" !sealed !frozen extensible
 PROTOTYPE: "Function.prototype"
 CLASS: Function
-PROPERTY: "length" !writable !enumerable !configurable
+PROPERTY: "length" !writable !enumerable configurable
 PROPERTY: "prototype" !writable !enumerable !configurable
 
 OBJECT: "Error.prototype" !sealed !frozen extensible
@@ -1109,7 +1107,7 @@ NOPROPERTY: "length"
 OBJECT: "EvalError" !sealed !frozen extensible
 PROTOTYPE: "Error"
 CLASS: Function
-PROPERTY: "length" !writable !enumerable !configurable
+PROPERTY: "length" !writable !enumerable configurable
 PROPERTY: "prototype" !writable !enumerable !configurable
 
 OBJECT: "EvalError.prototype" !sealed !frozen extensible
@@ -1123,7 +1121,7 @@ NOPROPERTY: "length"
 OBJECT: "RangeError" !sealed !frozen extensible
 PROTOTYPE: "Error"
 CLASS: Function
-PROPERTY: "length" !writable !enumerable !configurable
+PROPERTY: "length" !writable !enumerable configurable
 PROPERTY: "prototype" !writable !enumerable !configurable
 
 OBJECT: "RangeError.prototype" !sealed !frozen extensible
@@ -1137,7 +1135,7 @@ NOPROPERTY: "length"
 OBJECT: "ReferenceError" !sealed !frozen extensible
 PROTOTYPE: "Error"
 CLASS: Function
-PROPERTY: "length" !writable !enumerable !configurable
+PROPERTY: "length" !writable !enumerable configurable
 PROPERTY: "prototype" !writable !enumerable !configurable
 
 OBJECT: "ReferenceError.prototype" !sealed !frozen extensible
@@ -1151,7 +1149,7 @@ NOPROPERTY: "length"
 OBJECT: "SyntaxError" !sealed !frozen extensible
 PROTOTYPE: "Error"
 CLASS: Function
-PROPERTY: "length" !writable !enumerable !configurable
+PROPERTY: "length" !writable !enumerable configurable
 PROPERTY: "prototype" !writable !enumerable !configurable
 
 OBJECT: "SyntaxError.prototype" !sealed !frozen extensible
@@ -1165,7 +1163,7 @@ NOPROPERTY: "length"
 OBJECT: "TypeError" !sealed !frozen extensible
 PROTOTYPE: "Error"
 CLASS: Function
-PROPERTY: "length" !writable !enumerable !configurable
+PROPERTY: "length" !writable !enumerable configurable
 PROPERTY: "prototype" !writable !enumerable !configurable
 
 OBJECT: "TypeError.prototype" !sealed !frozen extensible
@@ -1179,7 +1177,7 @@ NOPROPERTY: "length"
 OBJECT: "URIError" !sealed !frozen extensible
 PROTOTYPE: "Error"
 CLASS: Function
-PROPERTY: "length" !writable !enumerable !configurable
+PROPERTY: "length" !writable !enumerable configurable
 PROPERTY: "prototype" !writable !enumerable !configurable
 
 OBJECT: "URIError.prototype" !sealed !frozen extensible

tests/ecmascript/test-dev-es6-builtin-func-props.js

@@ -0,0 +1,55 @@
+/*
+ *  Some ES6 built-in .length and .name spot checks
+ */
+
+/*===
+function
+.name string cos false false true
+.length number 1 false false true
+function
+.name string stringify false false true
+.length number 3 false false true
+function
+.name string hasOwnProperty false false true
+.length number 1 false false true
+function
+.name none
+.length none
+===*/
+
+function test() {
+    var pd;
+
+    function dump(f) {
+        print(typeof f);
+        var pd = Object.getOwnPropertyDescriptor(f, 'name');
+        if (pd) {
+            print('.name', typeof pd.value, pd.value, pd.writable, pd.enumerable, pd.configurable);
+        } else {
+            print('.name', 'none');
+        }
+        var pd = Object.getOwnPropertyDescriptor(f, 'length');
+        if (pd) {
+            print('.length', typeof pd.value, pd.value, pd.writable, pd.enumerable, pd.configurable);
+        } else {
+            print('.length', 'none');
+        }
+    }
+
+    // In ES6 function .name and .length are non-writable, non-enumerable,
+    // but configurable.  This also applies to built-ins.  Spot check a few.
+
+    dump(Math.cos);
+    dump(JSON.stringify);
+    dump(Object.prototype.hasOwnProperty);
+
+    // Currently missing .name and .length: https://github.com/svaarala/duktape/issues/1187
+    pd = Object.getOwnPropertyDescriptor(RegExp.prototype, 'source');  // getter in ES6
+    dump(pd.get);
+}
+
+try {
+    test();
+} catch (e) {
+    print(e.stack || e);
+}

tools/genbuiltins.py

@@ -391,8 +391,8 @@ def metadata_normalize_shorthand(meta):
         obj['class'] = 'Function'
         obj['callable'] = True
         obj['constructable'] = val.get('constructable', False)
-        props.append({ 'key': 'length', 'value': val['length'], 'attributes': '' })
-        props.append({ 'key': 'name', 'value': funprop['key'], 'attributes': '' })
+        props.append({ 'key': 'length', 'value': val['length'], 'attributes': 'c' })  # Configurable in ES6
+        props.append({ 'key': 'name', 'value': funprop['key'], 'attributes': 'c' })   # Configurable in ES6
         return obj
 
     def addAccessor(funprop, magic, nargs, length, name, native_func):
@@ -409,8 +409,8 @@ def metadata_normalize_shorthand(meta):
         obj['constructable'] = False
         # Shorthand accessors are minimal and have no .length or .name
         # right now.  Use longhand if these matter.
-        #props.append({ 'key': 'length', 'value': length, 'attributes': '' })
-        #props.append({ 'key': 'name', 'value': name, 'attributes': '' })
+        #props.append({ 'key': 'length', 'value': length, 'attributes': 'c' })
+        #props.append({ 'key': 'name', 'value': name, 'attributes': 'c' })
         return obj
 
     def decodeGetterShorthand(key, funprop):