Source Generator Performance Improvements:

- Reversed lookup order (Extension second)
- Introduced type cache

```
PERF PROGRESS:
SourceGen - Maui.Controls.Sample (262 XAML files)

1) Unchanged:
- 15640 GetTypeByMetadata calls
- 223s

2) Extensions lookup in XmlTypeXamlExtensions.GetTypeReference() second
- 6232 GetTypeByMetadata calls (~60% reduction)
- 90s                          (~60% reduction)

3) With type cache
- 203 GetTypeByMetadata calls (~97% reduction => ~99% total reduction)
- 6s                          (~93% reduction => ~97% total reduction => 37 times faster!)
```

Author: mgoertz-msft

src/Controls/samples/Controls.Sample/Maui.Controls.Sample.csproj

@@ -51,6 +51,13 @@
     <PackageReference Include="Microsoft.Extensions.DependencyInjection" />
   </ItemGroup>
 
+  <ItemGroup>
+    <ProjectReference
+      Include="..\..\..\Controls\src\Core\Controls.SourceGen.csproj"
+      OutputItemType="Analyzer"
+      ReferenceOutputAssembly="false"/>
+  </ItemGroup>
+
   <ItemGroup>
     <ProjectReference Include="..\..\..\BlazorWebView\samples\MauiRazorClassLibrarySample\MauiRazorClassLibrarySample.csproj" />
   </ItemGroup>

src/Controls/src/SourceGen/CodeBehindGenerator.cs

@@ -1,5 +1,6 @@
 using System;
 using System.Collections.Generic;
+using System.Diagnostics;
 using System.IO;
 using System.Linq;
 using System.Reflection;
@@ -44,20 +45,25 @@ public void Initialize(IncrementalGeneratorInitializationContext initContext)
 			var xmlnsDefinitionsProvider = initContext.CompilationProvider
 				.Select(GetAssemblyAttributes);
 
+			var typeCacheProvider = initContext.CompilationProvider
+				.Select(GetTypeCache);
+
 			var sourceProvider = projectItemProvider
 				.Combine(xmlnsDefinitionsProvider)
+				.Combine(typeCacheProvider)
 				.Combine(initContext.CompilationProvider)
 				.Select(static (t, _) => (t.Left.Left, t.Left.Right, t.Right));
 
 			initContext.RegisterSourceOutput(sourceProvider, static (sourceProductionContext, provider) =>
 			{
-				var (projectItem, caches, compilation) = provider;
+				var ((projectItem, xmlnsCache), typeCache, compilation) = provider;
 				if (projectItem == null)
 					return;
+
 				switch (projectItem.Kind)
 				{
 					case "Xaml":
-						GenerateXamlCodeBehind(projectItem, compilation, sourceProductionContext, caches);
+						GenerateXamlCodeBehind(projectItem, compilation, sourceProductionContext, xmlnsCache, typeCache);
 						break;
 					case "Css":
 						GenerateCssCodeBehind(projectItem, sourceProductionContext);
@@ -137,7 +143,12 @@ static AssemblyCaches GetAssemblyAttributes(Compilation compilation, Cancellatio
 			return new AssemblyCaches(xmlnsDefinitions, internalsVisible);
 		}
 
-		static void GenerateXamlCodeBehind(ProjectItem projItem, Compilation compilation, SourceProductionContext context, AssemblyCaches caches)
+		static IDictionary<XmlType, string> GetTypeCache(Compilation compilation, CancellationToken cancellationToken)
+		{
+			return new Dictionary<XmlType, string>();
+		}
+
+		static void GenerateXamlCodeBehind(ProjectItem projItem, Compilation compilation, SourceProductionContext context, AssemblyCaches caches, IDictionary<XmlType, string> typeCache)
 		{
 			var text = projItem.AdditionalText.GetText(context.CancellationToken);
 			if (text == null)
@@ -149,7 +160,7 @@ static void GenerateXamlCodeBehind(ProjectItem projItem, Compilation compilation
 				return;
 			var uid = Crc64.ComputeHashString($"{compilation.AssemblyName}.{itemName}");
 
-			if (!TryParseXaml(text, uid, compilation, caches, context.CancellationToken, projItem.TargetFramework, out var accessModifier, out var rootType, out var rootClrNamespace, out var generateDefaultCtor, out var addXamlCompilationAttribute, out var hideFromIntellisense, out var XamlResourceIdOnly, out var baseType, out var namedFields, out var parseException))
+			if (!TryParseXaml(text, uid, compilation, caches, typeCache, context.CancellationToken, projItem.TargetFramework, out var accessModifier, out var rootType, out var rootClrNamespace, out var generateDefaultCtor, out var addXamlCompilationAttribute, out var hideFromIntellisense, out var XamlResourceIdOnly, out var baseType, out var namedFields, out var parseException))
 			{
 				if (parseException != null)
 				{
@@ -237,7 +248,7 @@ static void GenerateXamlCodeBehind(ProjectItem projItem, Compilation compilation
 			context.AddSource(hintName, SourceText.From(sb.ToString(), Encoding.UTF8));
 		}
 
-		static bool TryParseXaml(SourceText text, string uid, Compilation compilation, AssemblyCaches caches, CancellationToken cancellationToken, string? targetFramework, out string? accessModifier, out string? rootType, out string? rootClrNamespace, out bool generateDefaultCtor, out bool addXamlCompilationAttribute, out bool hideFromIntellisense, out bool xamlResourceIdOnly, out string? baseType, out IEnumerable<(string, string, string)>? namedFields, out Exception? exception)
+		static bool TryParseXaml(SourceText text, string uid, Compilation compilation, AssemblyCaches caches, IDictionary<XmlType, string> typeCache, CancellationToken cancellationToken, string? targetFramework, out string? accessModifier, out string? rootType, out string? rootClrNamespace, out bool generateDefaultCtor, out bool addXamlCompilationAttribute, out bool hideFromIntellisense, out bool xamlResourceIdOnly, out string? baseType, out IEnumerable<(string, string, string)>? namedFields, out Exception? exception)
 		{
 			cancellationToken.ThrowIfCancellationRequested();
 
@@ -320,9 +331,9 @@ static bool TryParseXaml(SourceText text, string uid, Compilation compilation, A
 				return true;
 			}
 
-			namedFields = GetNamedFields(root, nsmgr, compilation, caches, cancellationToken);
+			namedFields = GetNamedFields(root, nsmgr, compilation, caches, typeCache, cancellationToken);
 			var typeArguments = GetAttributeValue(root, "TypeArguments", XamlParser.X2006Uri, XamlParser.X2009Uri);
-			baseType = GetTypeName(new XmlType(root.NamespaceURI, root.LocalName, typeArguments != null ? TypeArgumentsParser.ParseExpression(typeArguments, nsmgr, null) : null), compilation, caches);
+			baseType = GetTypeName(new XmlType(root.NamespaceURI, root.LocalName, typeArguments != null ? TypeArgumentsParser.ParseExpression(typeArguments, nsmgr, null) : null), compilation, caches, typeCache);
 
 			// x:ClassModifier attribute
 			var classModifier = GetAttributeValue(root, "ClassModifier", XamlParser.X2006Uri, XamlParser.X2009Uri);
@@ -345,7 +356,7 @@ static bool GetXamlCompilationProcessingInstruction(XmlDocument xmlDoc)
 			return true;
 		}
 
-		static IEnumerable<(string name, string type, string accessModifier)> GetNamedFields(XmlNode root, XmlNamespaceManager nsmgr, Compilation compilation, AssemblyCaches caches, CancellationToken cancellationToken)
+		static IEnumerable<(string name, string type, string accessModifier)> GetNamedFields(XmlNode root, XmlNamespaceManager nsmgr, Compilation compilation, AssemblyCaches caches, IDictionary<XmlType, string> typeCache, CancellationToken cancellationToken)
 		{
 			var xPrefix = nsmgr.LookupPrefix(XamlParser.X2006Uri) ?? nsmgr.LookupPrefix(XamlParser.X2009Uri);
 			if (xPrefix == null)
@@ -371,13 +382,17 @@ static bool GetXamlCompilationProcessingInstruction(XmlDocument xmlDoc)
 				var accessModifier = fieldModifier?.ToLowerInvariant().Replace("notpublic", "internal") ?? "private"; //notpublic is WPF for internal
 				if (!new[] { "private", "public", "internal", "protected" }.Contains(accessModifier)) //quick validation
 					accessModifier = "private";
-				yield return (name ?? "", GetTypeName(xmlType, compilation, caches), accessModifier);
+				yield return (name ?? "", GetTypeName(xmlType, compilation, caches, typeCache), accessModifier);
 			}
 		}
 
-		static string GetTypeName(XmlType xmlType, Compilation compilation, AssemblyCaches caches)
+		static string GetTypeName(XmlType xmlType, Compilation compilation, AssemblyCaches caches, IDictionary<XmlType, string> typeCache)
 		{
-			string returnType;
+			if (typeCache.TryGetValue(xmlType, out string returnType))
+			{
+				return returnType;
+			}
+
 			var ns = GetClrNamespace(xmlType.NamespaceUri);
 			if (ns != null)
 				returnType = $"{ns}.{xmlType.Name}";
@@ -388,9 +403,11 @@ static string GetTypeName(XmlType xmlType, Compilation compilation, AssemblyCach
 			}
 
 			if (xmlType.TypeArguments != null)
-				returnType = $"{returnType}<{string.Join(", ", xmlType.TypeArguments.Select(typeArg => GetTypeName(typeArg, compilation, caches)))}>";
+				returnType = $"{returnType}<{string.Join(", ", xmlType.TypeArguments.Select(typeArg => GetTypeName(typeArg, compilation, caches, typeCache)))}>";
 
-			return $"global::{returnType}";
+			returnType = $"global::{returnType}";
+			typeCache[xmlType] = returnType;
+			return returnType;
 		}
 
 		static string? GetClrNamespace(string namespaceuri)

src/Controls/src/SourceGen/Properties/launchSettings.json

@@ -0,0 +1,8 @@
+{
+  "profiles": {
+    "SourceGen - Maui.Controls.Sample": {
+      "commandName": "DebugRoslynComponent",
+      "targetProject": "..\\..\\samples\\Controls.Sample\\Maui.Controls.Sample.csproj"
+    }
+  }
+}

src/Controls/src/Xaml/XamlNode.cs

@@ -53,6 +53,24 @@ public XmlType(string namespaceUri, string name, IList<XmlType> typeArguments)
 		public string NamespaceUri { get; }
 		public string Name { get; }
 		public IList<XmlType> TypeArguments { get; }
+
+		public override bool Equals(object obj)
+		{
+			if (obj is not XmlType other)
+			{
+				return false;
+			}
+
+			return
+				NamespaceUri == other.NamespaceUri &&
+				Name == other.Name &&
+				(TypeArguments == null && other.TypeArguments == null || TypeArguments.SequenceEqual(other.TypeArguments));
+		}
+
+		public override int GetHashCode()
+		{
+			return NamespaceUri.GetHashCode() ^ Name.GetHashCode();
+		}
 	}
 
 	abstract class BaseNode : IXmlLineInfo, INode

src/Controls/src/Xaml/XmlTypeXamlExtensions.cs

@@ -61,9 +61,9 @@ static class XmlTypeXamlExtensions
 			}
 
 			var lookupNames = new List<string>();
+			lookupNames.Add(elementName);
 			if (elementName != "DataTemplate" && !elementName.EndsWith("Extension", StringComparison.Ordinal))
 				lookupNames.Add(elementName + "Extension");
-			lookupNames.Add(elementName);
 
 			for (var i = 0; i < lookupNames.Count; i++)
 			{