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Implement Error.prototype.stack accessor proposal #1536

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Merged
saghul merged 1 commit into from
Jun 21, 2026
Merged

Implement Error.prototype.stack accessor proposal #1536

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84 changes: 73 additions & 11 deletions quickjs.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1863,7 +1863,7 @@ typedef struct JSClassShortDef {
static JSClassShortDef const js_std_class_def[] = {
{ JS_ATOM_Object, NULL, NULL }, /* JS_CLASS_OBJECT */
{ JS_ATOM_Array, js_array_finalizer, js_array_mark }, /* JS_CLASS_ARRAY */
{ JS_ATOM_Error, NULL, NULL }, /* JS_CLASS_ERROR */
{ JS_ATOM_Error, js_object_data_finalizer, js_object_data_mark }, /* JS_CLASS_ERROR */
{ JS_ATOM_Number, js_object_data_finalizer, js_object_data_mark }, /* JS_CLASS_NUMBER */
{ JS_ATOM_String, js_object_data_finalizer, js_object_data_mark }, /* JS_CLASS_STRING */
{ JS_ATOM_Boolean, js_object_data_finalizer, js_object_data_mark }, /* JS_CLASS_BOOLEAN */
Expand Down Expand Up @@ -5829,6 +5829,7 @@ static JSValue JS_NewObjectFromShape(JSContext *ctx, JSShape *sh, JSClassID clas
p->u.array.u.ptr = NULL;
p->u.array.count = 0;
break;
case JS_CLASS_ERROR:
case JS_CLASS_NUMBER:
case JS_CLASS_STRING:
case JS_CLASS_BOOLEAN:
Expand Down Expand Up @@ -7286,6 +7287,7 @@ void JS_ComputeMemoryUsage(JSRuntime *rt, JSMemoryUsage *s)
}
}
break;
case JS_CLASS_ERROR: /* u.object_data */
case JS_CLASS_NUMBER: /* u.object_data */
case JS_CLASS_STRING: /* u.object_data */
case JS_CLASS_BOOLEAN: /* u.object_data */
Expand Down Expand Up @@ -7749,7 +7751,23 @@ static bool can_add_backtrace(JSValueConst obj)
if (JS_VALUE_GET_TAG(obj) != JS_TAG_OBJECT)
return false;
p = JS_VALUE_GET_OBJ(obj);
if (p->class_id != JS_CLASS_ERROR && p->class_id != JS_CLASS_DOM_EXCEPTION)
if (p->class_id != JS_CLASS_DOM_EXCEPTION)
return false;
if (find_own_property1(p, JS_ATOM_stack))
return false;
return true;
}

/* Note: it is important that no exception is returned by this function */
static bool can_store_error_stack(JSValueConst obj)
{
JSObject *p;
if (JS_VALUE_GET_TAG(obj) != JS_TAG_OBJECT)
return false;
p = JS_VALUE_GET_OBJ(obj);
if (p->class_id != JS_CLASS_ERROR)
return false;
if (!JS_IsUndefined(p->u.object_data))
return false;
if (find_own_property1(p, JS_ATOM_stack))
return false;
Expand Down Expand Up @@ -7952,7 +7970,18 @@ static void build_backtrace(JSContext *ctx, JSValueConst error_val,

if (JS_IsUndefined(ctx->error_back_trace))
ctx->error_back_trace = js_dup(stack);
if (has_filter_func || can_add_backtrace(error_obj)) {
if (has_filter_func) {
/* Error.captureStackTrace(target, ...): install an own data property
on the (possibly non-Error) target, shadowing the accessor */
JS_DefinePropertyValue(ctx, error_obj, JS_ATOM_stack, stack,
JS_PROP_WRITABLE | JS_PROP_CONFIGURABLE);
} else if (can_store_error_stack(error_obj)) {
/* genuine Error instance: store as the [[ErrorData]] stack value */
p = JS_VALUE_GET_OBJ(error_obj);
JS_FreeValue(ctx, p->u.object_data);
p->u.object_data = stack;
} else if (can_add_backtrace(error_obj)) {
/* DOMException and the like keep an own "stack" data property */
JS_DefinePropertyValue(ctx, error_obj, JS_ATOM_stack, stack,
JS_PROP_WRITABLE | JS_PROP_CONFIGURABLE);
} else {
Expand Down Expand Up @@ -17536,14 +17565,7 @@ static void print_func_name(JSFunctionBytecode *b);

static bool needs_backtrace(JSValue exc)
{
JSObject *p;

if (JS_VALUE_GET_TAG(exc) != JS_TAG_OBJECT)
return false;
p = JS_VALUE_GET_OBJ(exc);
if (p->class_id != JS_CLASS_ERROR)
return false;
return !find_own_property1(p, JS_ATOM_stack);
return can_store_error_stack(exc) || can_add_backtrace(exc);
}

/* argv[] is modified if (flags & JS_CALL_FLAG_COPY_ARGV) = 0. */
Expand Down Expand Up @@ -42005,10 +42027,50 @@ static JSValue js_error_toString(JSContext *ctx, JSValueConst this_val,
return JS_ConcatString(ctx, name, msg);
}

static JSValue js_error_get_stack(JSContext *ctx, JSValueConst this_val)
{
JSObject *p;

if (JS_VALUE_GET_TAG(this_val) != JS_TAG_OBJECT)
return JS_ThrowTypeErrorNotAnObject(ctx);
p = JS_VALUE_GET_OBJ(this_val);
if (p->class_id != JS_CLASS_ERROR)
return JS_UNDEFINED;
return js_dup(p->u.object_data);
}

static JSValue js_error_set_stack(JSContext *ctx, JSValueConst this_val,
JSValueConst value)
{
int ret, flags;

if (JS_VALUE_GET_TAG(this_val) != JS_TAG_OBJECT)
return JS_ThrowTypeErrorNotAnObject(ctx);
if (!JS_IsString(value))
return JS_ThrowTypeError(ctx, "Error.prototype.stack setter expects a string");
if (js_same_value(ctx, this_val, ctx->class_proto[JS_CLASS_ERROR]))
return JS_ThrowTypeError(ctx, "Error.prototype.stack setter called on the home object");
ret = JS_GetOwnPropertyFlagsInternal(ctx, &flags, JS_VALUE_GET_OBJ(this_val),
JS_ATOM_stack);
if (ret < 0)
return JS_EXCEPTION;
if (ret == 0) {
if (JS_DefinePropertyValue(ctx, this_val, JS_ATOM_stack, js_dup(value),
JS_PROP_C_W_E | JS_PROP_THROW) < 0)
return JS_EXCEPTION;
} else {
if (JS_SetPropertyInternal2(ctx, this_val, JS_ATOM_stack, js_dup(value),
this_val, JS_PROP_THROW) < 0)
return JS_EXCEPTION;
}
return JS_UNDEFINED;
}

static const JSCFunctionListEntry js_error_proto_funcs[] = {
JS_CFUNC_DEF("toString", 0, js_error_toString ),
JS_PROP_STRING_DEF("name", "Error", JS_PROP_WRITABLE | JS_PROP_CONFIGURABLE ),
JS_PROP_STRING_DEF("message", "", JS_PROP_WRITABLE | JS_PROP_CONFIGURABLE ),
JS_CGETSET_DEF("stack", js_error_get_stack, js_error_set_stack ),
};

static JSValue js_error_isError(JSContext *ctx, JSValueConst this_val,
Expand Down
2 changes: 1 addition & 1 deletion test262.conf
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Original file line number Diff line number Diff line change
Expand Up @@ -98,7 +98,7 @@ destructuring-assignment
destructuring-binding
dynamic-import
error-cause
error-stack-accessor=skip
error-stack-accessor
Error.isError
explicit-resource-management
exponentiation
Expand Down
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