Harden Attr against typed nil wrappers

node.go

@@ -4,6 +4,7 @@ import (
 	"html"
 	"iter"
 	"maps"
+	"reflect"
 	"slices"
 	"strconv"
 )
@@ -98,24 +99,42 @@ func El(tag string, children ...Node) Node {
 // It recursively traverses through wrappers like If, Unless, Entitled, Each,
 // EachSeq, Switch, Layout, and Responsive when present.
 func Attr(n Node, key, value string) Node {
-	if n == nil {
-		return n
+	if isNilNode(n) {
+		return nil
 	}
 
 	switch t := n.(type) {
 	case *elNode:
+		if t == nil {
+			return nil
+		}
 		t.attrs[key] = value
 	case *ifNode:
+		if t == nil {
+			return nil
+		}
 		Attr(t.node, key, value)
 	case *unlessNode:
+		if t == nil {
+			return nil
+		}
 		Attr(t.node, key, value)
 	case *entitledNode:
+		if t == nil {
+			return nil
+		}
 		Attr(t.node, key, value)
 	case *switchNode:
+		if t == nil {
+			return nil
+		}
 		for _, child := range t.cases {
 			Attr(child, key, value)
 		}
 	case *Layout:
+		if t == nil {
+			return nil
+		}
 		if t.slots != nil {
 			for slot, children := range t.slots {
 				for i := range children {
@@ -134,6 +153,20 @@ func Attr(n Node, key, value string) Node {
 	return n
 }
 
+func isNilNode(n Node) bool {
+	if n == nil {
+		return true
+	}
+
+	v := reflect.ValueOf(n)
+	switch v.Kind() {
+	case reflect.Chan, reflect.Func, reflect.Interface, reflect.Map, reflect.Pointer, reflect.Slice:
+		return v.IsNil()
+	default:
+		return false
+	}
+}
+
 // AriaLabel sets an aria-label attribute on an element node.
 // Usage example: AriaLabel(El("button", Text("save")), "Save changes")
 func AriaLabel(n Node, label string) Node {

node_test.go

@@ -456,6 +456,29 @@ func TestAttr_NonElement_Ugly(t *testing.T) {
 	}
 }
 
+func TestAttr_TypedNilWrappers_Ugly(t *testing.T) {
+	tests := []struct {
+		name string
+		node Node
+	}{
+		{name: "layout", node: (*Layout)(nil)},
+		{name: "responsive", node: (*Responsive)(nil)},
+		{name: "if", node: (*ifNode)(nil)},
+		{name: "unless", node: (*unlessNode)(nil)},
+		{name: "entitled", node: (*entitledNode)(nil)},
+		{name: "switch", node: (*switchNode)(nil)},
+		{name: "each", node: (*eachNode[string])(nil)},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := Attr(tt.node, "data-test", "x"); got != nil {
+				t.Fatalf("Attr on typed nil %s should return nil, got %#v", tt.name, got)
+			}
+		})
+	}
+}
+
 func TestUnlessNode_True_Good(t *testing.T) {
 	ctx := NewContext()
 	node := Unless(func(*Context) bool { return true }, Raw("hidden"))