Other changes after review

src/Avalonia.Build.Tasks/XamlCompilerTaskExecutor.cs

@@ -3,6 +3,7 @@ using System.Collections.Generic;
 using System.IO;
 using System.Linq;
 using Avalonia.Markup.Xaml.XamlIl.CompilerExtensions;
+using Avalonia.Platform;
 using Microsoft.Build.Framework;
 using Mono.Cecil;
 using Mono.Cecil.Cil;
@@ -134,6 +135,10 @@ namespace Avalonia.Build.Tasks
                     engine.LogMessage("Debugging cancelled.", MessageImportance.Normal);
                 }
             }
+            
+            // Some transformers might need to parse "avares://" Uri.
+            AssetLoader.RegisterResUriParsers();
+
             var asm = typeSystem.TargetAssemblyDefinition;
             var avares = new AvaloniaResources(asm, projectDirectory);
             if (avares.Resources.Count(CheckXamlName) == 0)

src/Markup/Avalonia.Markup.Xaml.Loader/CompilerExtensions/GroupTransformers/XamlIncludeGroupTransformer.cs

@@ -45,22 +45,17 @@ internal class AvaloniaXamlIncludeTransformer : IXamlAstGroupTransformer
             return node;
         }
 
-        if (originalAssetPath.StartsWith("avares://"))
-        {
-        }
-        else if (originalAssetPath.StartsWith("/"))
+        if (originalAssetPath.StartsWith("/"))
         {
             var baseUrl = context.CurrentDocument.Uri ?? throw new InvalidOperationException("CurrentDocument URI is null.");
             originalAssetPath = baseUrl.Substring(0, baseUrl.LastIndexOf('/')) + originalAssetPath;
         }
-        else
+        else if (!originalAssetPath.StartsWith("avares://"))
         {
             return context.ParseError(
                 $"Avalonia supports only \"avares://\" sources or relative sources starting with \"/\" on the \"{nodeTypeName}\" node.",
                 node);
         }
-        
-        AssetLoader.RegisterResUriParsers();
 
         originalAssetPath = Uri.UnescapeDataString(new Uri(originalAssetPath).AbsoluteUri);
         var assetPath = originalAssetPath.Replace("avares://", "");