fix: Properly merge namespaces

src/Uno.XamlMerge.Task/BatchMergeXaml.cs

@@ -123,19 +123,21 @@ class BatchMerger
                 {
                     try
                     {
-                        mergedDictionary.MergeContent(
+                        mergedDictionary.Prepare(
                             content: File.ReadAllText(page),
                             filePath: Path.GetFullPath(page)
                                 .Replace(projectBasePath, "")
                                 .TrimStart(Path.DirectorySeparatorChar));
                     }
                     catch (Exception)
                     {
-                        owner.LogError($"Exception found when merging page {page}!");
+                        owner.LogError($"Exception found when merging namespaces for page {page}!");
                         throw;
                     }
                 }
 
+                mergedDictionary.MergeContent();
+
                 mergedDictionary.FinalizeXaml();
 
                 Directory.CreateDirectory(Path.GetDirectoryName(mergedXamlFile));

src/Uno.XamlMerge.Task/MergedDictionary.cs

@@ -36,11 +36,8 @@ public override string ToString()
             return Utils.UnEscapeAmpersand(sw.ToString());
         }
 
-        public void MergeContent(String content, string filePath)
+        public void Prepare(String content, string filePath)
         {
-            var comment = owningDocument.CreateComment($"origin: {filePath}");
-            nodeList.Add(comment);
-
             content = Utils.EscapeAmpersand(content);
 
             var document = new XmlDocument();
@@ -56,13 +53,59 @@ public void MergeContent(String content, string filePath)
             {
                 AddNamespace(entry.Key, entry.Value);
             }
-            foreach (XmlNode node in document.ChildNodes)
+
+            documents.Add((document, xmlnsReplacementDictionary, filePath));
+        }
+
+        public void MergeContent()
+        {
+            foreach (var (document, xmlnsReplacementDictionary, filePath) in documents)
             {
-                if (node.Name == "ResourceDictionary")
+                var comment = owningDocument.CreateComment($"origin: {filePath}");
+                nodeList.Add(comment);
+
+                foreach (XmlNode node in document.ChildNodes)
                 {
-                    foreach (XmlNode xmlNode in node.ChildNodes)
+                    if (node.Name == "ResourceDictionary")
                     {
-                        AddNode(xmlNode, xmlnsReplacementDictionary);
+                        foreach (XmlNode xmlNode in node.ChildNodes)
+                        {
+                            if (xmlNode is XmlElement xmlElement)
+                            {
+                                var xmlNodeCloned = (XmlElement)xmlNode.CloneNode(true);
+                                xmlNodeCloned.RemoveAllAttributes();
+
+                                foreach (XmlAttribute xmlAttribute in xmlElement.Attributes)
+                                {
+                                    if (xmlAttribute.Name.Contains(":"))
+                                    {
+                                        var split = xmlAttribute.Name.Split(':');
+                                        var prefix = split[0];
+                                        var nsName = split[1];
+                                        if (knownNamespaces.TryGetValue(prefix, out var nsUri))
+                                        {
+                                            xmlNodeCloned.SetAttribute(nsName, knownNamespaces[prefix], xmlAttribute.Value);
+                                        }
+                                        else
+                                        {
+                                            xmlNodeCloned.SetAttribute(xmlAttribute.Name, xmlAttribute.Value);
+                                        }
+                                    }
+                                    else
+                                    {
+                                        xmlNodeCloned.SetAttribute(xmlAttribute.Name, xmlAttribute.Value);
+                                    }
+
+                                }
+
+                                AddNode(xmlNodeCloned, xmlnsReplacementDictionary);
+                            }
+                            else
+                            {
+                                AddNode(xmlNode, xmlnsReplacementDictionary);
+                            }
+
+                        }
                     }
                 }
             }
@@ -525,6 +568,7 @@ private static XmlNode FindNode(XmlDocument document, string name)
         private XmlElement xmlElement;
         private XmlDocument owningDocument;
         private List<XmlNode> nodeList;
+        private List<(XmlDocument, Dictionary<string, string>, string)> documents = new();
 
         // We'll want to remove nodes from the node list if a child dictionary has the same node,
         // but if we just removed the nodes then the values in nodeKeyToNodeListIndexDictionary would be wrong.

src/Uno.XamlMerge.Tests/Scenarios/When_Different_Namespace_Should_Be_Merged/expected.xml

@@ -1,8 +1,8 @@
 <ResourceDictionary xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" xmlns:wasm="http://uno.ui/wasm#using:NS1;NS2" xmlns:android="http://uno.ui/android#using:AndroidNS" xmlns:ios="http://uno.ui/ios#using:iosNS" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation">
   <!--origin: When_Different_Namespace_Should_Be_Merged\Input_Dictionary_1.xml-->
   <MyElement1 android:MyProp="P1" />
-  <MyElement2 ios:MyProp="P2" xmlns:ios="http://uno.ui/ios" />
+  <MyElement2 ios:MyProp="P2" />
   <!--origin: When_Different_Namespace_Should_Be_Merged\Input_Dictionary_2.xml-->
-  <MyElement3 android:MyProp="P3" xmlns:android="http://uno.ui/android" />
+  <MyElement3 android:MyProp="P3" />
   <MyElement4 ios:MyProp="P4" />
 </ResourceDictionary>