feat: support push to go slices

Add support for direct use of push to go slices without converting to
array using .slice().

Fixes #357

Also:
* Add classGoSlice and use it, to make it clear the type when debugging.

consts.go

@@ -4,6 +4,7 @@ const (
 	// Common classes.
 	classString   = "String"
 	classGoArray  = "GoArray"
+	classGoSlice  = "GoSlice"
 	classNumber   = "Number"
 	classDate     = "Date"
 	classArray    = "Array"

issue_test.go

@@ -942,3 +942,23 @@ func Test_issue383(t *testing.T) {
 	`)
 	require.NoError(t, err)
 }
+
+func Test_issue357(t *testing.T) {
+	vm := New()
+	arr := []string{"wow", "hey"}
+	err := vm.Set("arr", arr)
+	require.NoError(t, err)
+
+	val, err := vm.Run(`
+		arr.push('another', 'more');
+		arr;
+	`)
+	require.NoError(t, err)
+	iface, err := val.Export()
+	require.NoError(t, err)
+
+	slice, ok := iface.([]string)
+	require.True(t, ok)
+
+	require.Equal(t, []string{"wow", "hey", "another", "more"}, slice)
+}

runtime.go

@@ -431,7 +431,8 @@ func (self *_runtime) convertCallParameter(v Value, t reflect.Type) (reflect.Val
 
 				tt := t.Elem()
 
-				if o.class == classArray {
+				switch o.class {
+				case classArray:
 					for i := int64(0); i < l; i++ {
 						p, ok := o.property[strconv.FormatInt(i, 10)]
 						if !ok {
@@ -450,7 +451,7 @@ func (self *_runtime) convertCallParameter(v Value, t reflect.Type) (reflect.Val
 
 						s.Index(int(i)).Set(ev)
 					}
-				} else if o.class == classGoArray {
+				case classGoArray, classGoSlice:
 					var gslice bool
 					switch o.value.(type) {
 					case *_goSliceObject:

type_array.go

@@ -13,7 +13,16 @@ func (runtime *_runtime) newArrayObject(length uint32) *_object {
 }
 
 func isArray(object *_object) bool {
-	return object != nil && (object.class == classArray || object.class == classGoArray)
+	if object == nil {
+		return false
+	}
+
+	switch object.class {
+	case classArray, classGoArray, classGoSlice:
+		return true
+	default:
+		return false
+	}
 }
 
 func objectLength(object *_object) uint32 {
@@ -25,7 +34,7 @@ func objectLength(object *_object) uint32 {
 		return object.get(propertyLength).value.(uint32)
 	case classString:
 		return uint32(object.get(propertyLength).value.(int))
-	case classGoArray:
+	case classGoArray, classGoSlice:
 		return uint32(object.get(propertyLength).value.(int))
 	}
 	return 0

type_go_slice.go

@@ -7,7 +7,7 @@ import (
 
 func (runtime *_runtime) newGoSliceObject(value reflect.Value) *_object {
 	self := runtime.newObject()
-	self.class = classGoArray // TODO GoSlice?
+	self.class = classGoSlice
 	self.objectClass = _classGoSlice
 	self.value = _newGoSliceObject(value)
 	return self
@@ -31,15 +31,43 @@ func (self _goSliceObject) getValue(index int64) (reflect.Value, bool) {
 	return reflect.Value{}, false
 }
 
-func (self _goSliceObject) setValue(index int64, value Value) bool {
-	indexValue, exists := self.getValue(index)
-	if !exists {
-		return false
+func (self *_goSliceObject) setLength(value Value) {
+	want, err := value.ToInteger()
+	if err != nil {
+		panic(err)
 	}
+
+	wantInt := int(want)
+	switch {
+	case wantInt == self.value.Len():
+		// No change needed.
+	case wantInt < self.value.Cap():
+		// Fits in current capacity.
+		self.value.SetLen(wantInt)
+	default:
+		// Needs expanding.
+		newSlice := reflect.MakeSlice(self.value.Type(), wantInt, wantInt)
+		reflect.Copy(newSlice, self.value)
+		self.value = newSlice
+	}
+}
+
+func (self *_goSliceObject) setValue(index int64, value Value) bool {
 	reflectValue, err := value.toReflectValue(self.value.Type().Elem().Kind())
 	if err != nil {
 		panic(err)
 	}
+
+	indexValue, exists := self.getValue(index)
+	if !exists {
+		if int64(self.value.Len()) == index {
+			// Trying to append e.g. slice.push(...), allow it.
+			self.value = reflect.Append(self.value, reflectValue)
+			return true
+		}
+		return false
+	}
+
 	indexValue.Set(reflectValue)
 	return true
 }
@@ -49,7 +77,7 @@ func goSliceGetOwnProperty(self *_object, name string) *_property {
 	if name == propertyLength {
 		return &_property{
 			value: toValue(self.value.(*_goSliceObject).value.Len()),
-			mode:  0,
+			mode:  0110,
 		}
 	}
 
@@ -93,7 +121,8 @@ func goSliceEnumerate(self *_object, all bool, each func(string) bool) {
 
 func goSliceDefineOwnProperty(self *_object, name string, descriptor _property, throw bool) bool {
 	if name == propertyLength {
-		return self.runtime.typeErrorResult(throw)
+		self.value.(*_goSliceObject).setLength(descriptor.value.(Value))
+		return true
 	} else if index := stringToArrayIndex(name); index >= 0 {
 		if self.value.(*_goSliceObject).setValue(index, descriptor.value.(Value)) {
 			return true