Add ParentElement interface

Author: twpayne

.golangci.yml

@@ -126,6 +126,10 @@ linters-settings:
     - fieldalignment
     - shadow
     enable-all: true
+  ireturn:
+    allow:
+    - error
+    - github.com/twpayne/go-kml/v3.ParentElement
   misspell:
     locale: US
   stylecheck:

internal/generate/output.go.tmpl

@@ -58,7 +58,12 @@ func {{ $name }}(children ...Element) *{{ $elementTypeName }} {
 	}
 }
 
-// Append appends children to e.
+// Add adds children to e and returns e as a ParentElement.
+func (e *{{ $elementTypeName }}) Add(children ...Element) ParentElement {
+	return e.Append(children...)
+}
+
+// Append appends children to e and returns e.
 func (e *{{ $elementTypeName }}) Append(children ...Element) *{{ $elementTypeName }} {
 	e.Children = append(e.Children, children...)
 	return e

kml.go

@@ -38,6 +38,12 @@ type Element interface {
 	xml.Marshaler
 }
 
+// A ParentElement is a KML element with children.
+type ParentElement interface {
+	Element
+	Add(children ...Element) ParentElement
+}
+
 // A TopLevelElement is a top level KML element.
 type TopLevelElement interface {
 	Element

kml22gx.gen.go

@@ -152,6 +152,17 @@ func GxSimpleArrayField(name, _type string, children ...Element) *GxSimpleArrayF
 	}
 }
 
+// Add adds children to e and returns e as a ParentElement.
+func (e *GxSimpleArrayFieldElement) Add(children ...Element) ParentElement {
+	return e.Append(children...)
+}
+
+// Append appends children to e and returns e.
+func (e *GxSimpleArrayFieldElement) Append(children ...Element) *GxSimpleArrayFieldElement {
+	e.Children = append(e.Children, children...)
+	return e
+}
+
 // MarshalXML implements encoding/xml.Marshaler.MarshalXML.
 func (e *GxSimpleArrayFieldElement) MarshalXML(encoder *xml.Encoder, _ xml.StartElement) error {
 	startElement := xml.StartElement{

kml22gx.go

@@ -164,6 +164,11 @@ func TestSimpleElements(t *testing.T) {
 			element:  kml.OverlayXY(kml.Vec2{X: 0, Y: 0, XUnits: kml.UnitsFraction, YUnits: kml.UnitsFraction}),
 			expected: `<overlayXY x="0" y="0" xunits="fraction" yunits="fraction"></overlayXY>`,
 		},
+		{
+			name:     "Snippet",
+			element:  kml.Snippet("snippet").WithMaxLines(1),
+			expected: `<Snippet maxLines="1">snippet</Snippet>`,
+		},
 		{
 			name:     "value_charData",
 			element:  kml.Value(xml.CharData("<>")),
@@ -289,10 +294,10 @@ func TestSimpleElements(t *testing.T) {
 	}
 }
 
-func TestCompoundElements(t *testing.T) {
+func TestParentElements(t *testing.T) {
 	for _, tc := range []struct {
 		name     string
-		element  kml.Element
+		element  kml.ParentElement
 		expected string
 	}{
 		{
@@ -397,11 +402,6 @@ func TestCompoundElements(t *testing.T) {
 				`</gx:SimpleArrayField>` +
 				`</Schema>`,
 		},
-		{
-			name:     "Snippet",
-			element:  kml.Snippet("snippet").WithMaxLines(1),
-			expected: `<Snippet maxLines="1">snippet</Snippet>`,
-		},
 		{
 			name: "gx:Wait",
 			element: kml.GxWait(