POA for getting this done!

Rider/README.md

@@ -1,4 +1,6 @@
-# RapidXaml for Rider and ReSharper
+# RapidXaml for Rider
 
 [![Rider](https://img.shields.io/jetbrains/plugin/v/RIDER_PLUGIN_ID.svg?label=Rider&colorB=0A7BBB&style=for-the-badge&logo=rider)](https://plugins.jetbrains.com/plugin/RIDER_PLUGIN_ID)
-[![ReSharper](https://img.shields.io/jetbrains/plugin/v/RESHARPER_PLUGIN_ID.svg?label=ReSharper&colorB=0A7BBB&style=for-the-badge&logo=resharper)](https://plugins.jetbrains.com/plugin/RESHARPER_PLUGIN_ID)
+<!--[![ReSharper](https://img.shields.io/jetbrains/plugin/v/RESHARPER_PLUGIN_ID.svg?label=ReSharper&colorB=0A7BBB&style=for-the-badge&logo=resharper)](https://plugins.jetbrains.com/plugin/RESHARPER_PLUGIN_ID)-->
+
+

Rider/src/dotnet/ReSharperPlugin.RapidXaml/IRapidXamlZone.cs

@@ -1,13 +1,14 @@
 using JetBrains.Application.BuildScript.Application.Zones;
 using JetBrains.ReSharper.Feature.Services.Daemon;
-using JetBrains.ReSharper.Psi;
 using JetBrains.ReSharper.Psi.CSharp;
+using JetBrains.ReSharper.Psi.Xaml;
 
-namespace ReSharperPlugin.RapidXaml
+namespace ReSharperPlugin.RapidXaml;
+
+[ZoneDefinition]
+// [ZoneDefinitionConfigurableFeature("Title", "Description", IsInProductSection: false)]
+public interface IRapidXamlZone : IZone,
+    IRequire<ILanguageXamlZone>,
+    IRequire<DaemonZone>
 {
-    [ZoneDefinition]
-    // [ZoneDefinitionConfigurableFeature("Title", "Description", IsInProductSection: false)]
-    public interface IRapidXamlZone : IZone
-    {
-    }
-}
+}

Rider/src/dotnet/ReSharperPlugin.RapidXaml/OutlineZoneMarker.cs

@@ -0,0 +1,8 @@
+using JetBrains.Application.BuildScript.Application.Zones;
+
+namespace ReSharperPlugin.RapidXaml;
+
+[ZoneMarker]
+public class OutlineZoneMarker : IRequire<IRapidXamlZone>
+{
+}

Rider/src/dotnet/ReSharperPlugin.RapidXaml/XamlNamespaceCodeFoldingProcessor.cs

@@ -0,0 +1,111 @@
+using System;
+using System.Collections.Generic;
+using JetBrains.DocumentModel;
+using JetBrains.ReSharper.Daemon.CodeFolding;
+using JetBrains.ReSharper.Psi.Tree;
+using JetBrains.ReSharper.Psi.Xml.Impl;
+using JetBrains.ReSharper.Psi.Xml.Tree;
+
+namespace ReSharperPlugin.RapidXaml;
+
+public sealed class XamlNamespaceCodeFoldingProcessor :
+    XmlTreeVisitor<FoldingHighlightingConsumer, bool>,
+    ICodeFoldingProcessor
+{
+    private readonly Stack<(DocumentOffset offset, string regionText)> _regionStarts =
+        new Stack<(DocumentOffset offset, string regionText)>();
+
+    public bool InteriorShouldBeProcessed(ITreeNode element, FoldingHighlightingConsumer context) => true;
+    public bool IsProcessingFinished(FoldingHighlightingConsumer context) => false;
+
+    public void ProcessBeforeInterior(ITreeNode element, FoldingHighlightingConsumer context)
+    {
+        if (!(element is IXmlTreeNode xamlElement))
+        {
+            return;
+        }
+
+        xamlElement.AcceptVisitor(this, context);
+    }
+
+    public void ProcessAfterInterior(ITreeNode element, FoldingHighlightingConsumer context)
+    {
+    }
+
+    public override bool Visit(IXmlTag tag, FoldingHighlightingConsumer context)
+    {
+        System.Diagnostics.Debug.WriteLine(tag);
+
+        // If is IXamlTypeDeclaration
+        // If has multiple NamespaceAliases
+        // place fold start at the start position of the first
+        // place fold end at the end of the last one
+
+        // TODO: use tag.GetDocumentRange() to review lines that shouldn't be included
+        // ((JetBrains.ReSharper.Psi.Xaml.Impl.Tree.XamlTypeDeclaration) tag).NamespaceAliases.myNodes[1].GetDocumentRange()
+        // TODO: review siblings to check that there's nothing else between aliases
+
+        return base.Visit(tag, context);
+    }
+
+    public override bool Visit(IXmlDocumentNode document, FoldingHighlightingConsumer context)
+    {
+        System.Diagnostics.Debug.WriteLine(document);
+        return base.Visit(document, context);
+    }
+
+    public override bool Visit(IXmlCommentNode xmlComment, FoldingHighlightingConsumer context)
+    {
+        var commentText = xmlComment.CommentText.Trim();
+        if (IsRegionStart(commentText, out var regionText))
+        {
+            _regionStarts.Push((xmlComment.GetDocumentRange().StartOffset, regionText));
+            return true;
+        }
+
+        if (IsRegionEnd(commentText))
+        {
+            if (_regionStarts.Count > 0)
+            {
+                var (regionStartOffset, placeholder) = _regionStarts.Pop();
+                var regionEndRange = xmlComment.GetDocumentRange();
+                var regionRange = regionEndRange.SetStartTo(regionStartOffset);
+                context.AddLowerPriorityFolding("XAML Region Regions Folding", regionRange, regionRange,
+                    placeholder);
+                return true;
+            }
+
+            // endregion without start
+            return false;
+        }
+
+        return false;
+    }
+
+    private const string RegionStartTag = "#region";
+    private const string RegionEndTag = "#endregion";
+
+    private static bool IsRegionEnd(string commentText)
+    {
+        return (commentText.Contains(RegionEndTag));
+    }
+
+    private static bool IsRegionStart(string commentText, out string regionText)
+    {
+        if (commentText.StartsWith(RegionStartTag))
+        {
+            regionText = commentText
+                .Substring(Math.Min(commentText.Length, RegionStartTag.Length + 1))
+                .Trim();
+            if (string.IsNullOrWhiteSpace(regionText))
+            {
+                regionText = "#region";
+            }
+
+            return true;
+        }
+
+        regionText = null;
+        return false;
+    }
+}

Rider/src/dotnet/ReSharperPlugin.RapidXaml/XamlNamespaceCodeFoldingProcessorFactory.cs

@@ -0,0 +1,13 @@
+using JetBrains.Annotations;
+using JetBrains.ReSharper.Daemon.CodeFolding;
+using JetBrains.ReSharper.Psi;
+using JetBrains.ReSharper.Psi.Xaml;
+
+namespace ReSharperPlugin.RapidXaml;
+
+[Language(typeof(XamlLanguage))]
+public sealed class XamlNamespaceCodeFoldingProcessorFactory : ICodeFoldingProcessorFactory
+{
+    [NotNull]
+    public ICodeFoldingProcessor CreateProcessor() => new XamlNamespaceCodeFoldingProcessor();
+}