Nullable annotations for projects using XamlX (#15796)

* Nullable annotations for projects using XamlX

* Update .NET SDK

* Update XamlX to latest master

* Use ILRepack tool instead of submodule

* Fix build

---------

Co-authored-by: Max Katz <maxkatz6@outlook.com>

.gitmodules

@@ -4,6 +4,3 @@
 [submodule "src/Markup/Avalonia.Markup.Xaml/XamlIl/xamlil.github"]
 	path = src/Markup/Avalonia.Markup.Xaml.Loader/xamlil.github
 	url = https://github.com/kekekeks/XamlX.git
-[submodule "nukebuild/il-repack"]
-	path = nukebuild/il-repack
-	url = https://github.com/Gillibald/il-repack

global.json

@@ -1,6 +1,6 @@
 {
   "sdk": {
-    "version": "8.0.101",
+    "version": "8.0.204",
     "rollForward": "latestFeature"
   },
   "msbuild-sdks": {

nukebuild/Build.cs

@@ -40,7 +40,8 @@ partial class Build : NukeBuild
     [PackageExecutable("Microsoft.DotNet.GenAPI.Tool", "Microsoft.DotNet.GenAPI.Tool.dll", Framework = "net8.0")]
     Tool ApiGenTool;
 
-
+    [PackageExecutable("dotnet-ilrepack", "ILRepackTool.dll", Framework = "net8.0")]
+    Tool IlRepackTool;
     
     protected override void OnBuildInitialized()
     {
@@ -307,7 +308,8 @@ partial class Build : NukeBuild
         .Executes(() =>
         {
             BuildTasksPatcher.PatchBuildTasksInPackage(Parameters.NugetIntermediateRoot / "Avalonia.Build.Tasks." +
-                                                       Parameters.Version + ".nupkg");
+                                                       Parameters.Version + ".nupkg",
+                                                       IlRepackTool);
             var config = Numerge.MergeConfiguration.LoadFile(RootDirectory / "nukebuild" / "numerge.config");
             EnsureCleanDirectory(Parameters.NugetRoot);
             if(!Numerge.NugetPackageMerger.Merge(Parameters.NugetIntermediateRoot, Parameters.NugetRoot, config,

nukebuild/BuildTasksPatcher.cs

@@ -2,9 +2,9 @@ using System;
 using System.IO;
 using System.IO.Compression;
 using System.Linq;
-using ILRepacking;
 using Mono.Cecil;
 using Mono.Cecil.Cil;
+using Nuke.Common.Tooling;
 
 public class BuildTasksPatcher
 {
@@ -56,7 +56,7 @@ public class BuildTasksPatcher
         return null;
     }
 
-    public static void PatchBuildTasksInPackage(string packagePath)
+    public static void PatchBuildTasksInPackage(string packagePath, Tool ilRepackTool)
     {
         using (var archive = new ZipArchive(File.Open(packagePath, FileMode.Open, FileAccess.ReadWrite),
             ZipArchiveMode.Update))
@@ -70,7 +70,7 @@ public class BuildTasksPatcher
                     Directory.CreateDirectory(tempDir);
                     var temp = Path.Combine(tempDir, entry.Name);
                     var output = temp + ".output";
-                    File.Copy(typeof(Microsoft.Build.Framework.ITask).Assembly.GetModules()[0].FullyQualifiedName,
+                    File.Copy(GetAssemblyPath(typeof(Microsoft.Build.Framework.ITask)),
                         Path.Combine(tempDir, "Microsoft.Build.Framework.dll"));
                     var patched = new MemoryStream();
                     try
@@ -78,22 +78,15 @@ public class BuildTasksPatcher
                         entry.ExtractToFile(temp, true);
                         // Get Original SourceLinkInfo Content
                         var sourceLinkInfoContent = GetSourceLinkInfo(temp);
-                        var repack = new ILRepacking.ILRepack(new RepackOptions()
-                        {
-                            Internalize = true,
-                            InputAssemblies = new[]
-                            {
-                                temp,
-                                typeof(Mono.Cecil.AssemblyDefinition).Assembly.GetModules()[0].FullyQualifiedName,
-                                typeof(Mono.Cecil.Rocks.MethodBodyRocks).Assembly.GetModules()[0].FullyQualifiedName,
-                                typeof(Mono.Cecil.Pdb.PdbReaderProvider).Assembly.GetModules()[0].FullyQualifiedName,
-                                typeof(Mono.Cecil.Mdb.MdbReaderProvider).Assembly.GetModules()[0].FullyQualifiedName,
-                            },
-                            SearchDirectories = Array.Empty<string>(),
-                            DebugInfo = true, // Allowed read debug info
-                            OutputFile = output
-                        });
-                        repack.Repack();
+
+                        var cecilAsm = GetAssemblyPath(typeof(Mono.Cecil.AssemblyDefinition));
+                        var cecilRocksAsm = GetAssemblyPath(typeof(Mono.Cecil.Rocks.MethodBodyRocks));
+                        var cecilPdbAsm = GetAssemblyPath(typeof(Mono.Cecil.Pdb.PdbReaderProvider));
+                        var cecilMdbAsm = GetAssemblyPath(typeof(Mono.Cecil.Mdb.MdbReaderProvider));
+
+                        ilRepackTool.Invoke(
+                            $"/internalize /out:\"{output}\" \"{temp}\" \"{cecilAsm}\" \"{cecilRocksAsm}\" \"{cecilPdbAsm}\" \"{cecilMdbAsm}\"",
+                            tempDir);
 
                         // 'hurr-durr assembly with the same name is already loaded' prevention
                         using (var asm = AssemblyDefinition.ReadAssembly(output,
@@ -161,4 +154,7 @@ public class BuildTasksPatcher
             }
         }
     }
+
+    private static string GetAssemblyPath(Type typeInAssembly)
+        => typeInAssembly.Assembly.GetModules()[0].FullyQualifiedName;
 }

nukebuild/_build.csproj

@@ -20,7 +20,6 @@
     <PackageReference Include="MicroCom.CodeGenerator" Version="0.11.0" />
     <!-- Keep in sync with Avalonia.Build.Tasks -->
     <PackageReference Include="Mono.Cecil" Version="0.11.5" />
-    <PackageReference Include="Microsoft.Debugging.Tools.PdbStr" Version="20230731.1609.0" GeneratePathProperty="true" PrivateAssets="All"/>
     <PackageReference Include="Microsoft.Build.Framework" Version="17.3.2" PrivateAssets="All" />
     <PackageReference Include="xunit.runner.console" Version="2.4.2">
       <PrivateAssets>all</PrivateAssets>
@@ -29,6 +28,7 @@
 
     <PackageDownload Include="Microsoft.DotNet.ApiCompat.Tool" Version="[8.0.200]" />
     <PackageDownload Include="Microsoft.DotNet.GenAPI.Tool" Version="[8.0.300-preview.24115.44]" />
+    <PackageDownload Include="dotnet-ilrepack" Version="[1.0.0]" />
   </ItemGroup>
 
   <ItemGroup>
@@ -38,9 +38,7 @@
     <!-- Common build related files -->
     <Compile Remove="Numerge/**/*.*" />
     <Compile Include="Numerge/Numerge/**/*.cs" Exclude="Numerge/Numerge/obj/**/*.cs" />
-    <EmbeddedResource Include="$(PkgMicrosoft_Debugging_Tools_PdbStr)/content/x86/pdbstr.exe" />
     <EmbeddedResource Include="../build/avalonia.snk" />
-    <Compile Remove="il-repack\ILRepack\Application.cs" />
   </ItemGroup>
 
   <ItemGroup>

nukebuild/il-repack

@@ -1 +0,0 @@
-Subproject commit 892f079ea8cb0c178f0a68f53a7a7eac13acdda9

src/Avalonia.Base/Metadata/NullableAttributes.cs → src/Avalonia.Base/Compatibility/NullableAttributes.cs

@@ -1,63 +1,30 @@
-#pragma warning disable MA0048 // File name must match type name
-#define INTERNAL_NULLABLE_ATTRIBUTES
-
-// https://github.com/dotnet/corefx/blob/48363ac826ccf66fbe31a5dcb1dc2aab9a7dd768/src/Common/src/CoreLib/System/Diagnostics/CodeAnalysis/NullableAttributes.cs
+// https://raw.githubusercontent.com/dotnet/runtime/753648476b64946b8f5f4d25e1294adbabd3165b/src/libraries/System.Private.CoreLib/src/System/Diagnostics/CodeAnalysis/NullableAttributes.cs
 
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
-// See the LICENSE file in the project root for more information.
 
 namespace System.Diagnostics.CodeAnalysis
 {
-#if NETSTANDARD2_0 || NETCOREAPP2_0 || NETCOREAPP2_1 || NETCOREAPP2_2 || NET45 || NET451 || NET452 || NET6 || NET461 || NET462 || NET47 || NET471 || NET472 || NET48
+#if !NET6_0_OR_GREATER
     /// <summary>Specifies that null is allowed as an input even if the corresponding type disallows it.</summary>
     [AttributeUsage(AttributeTargets.Field | AttributeTargets.Parameter | AttributeTargets.Property, Inherited = false)]
-#if INTERNAL_NULLABLE_ATTRIBUTES
-    internal
-#else
-    public
-#endif
-        sealed class AllowNullAttribute : Attribute
-    { }
+    internal sealed class AllowNullAttribute : Attribute { }
 
     /// <summary>Specifies that null is disallowed as an input even if the corresponding type allows it.</summary>
     [AttributeUsage(AttributeTargets.Field | AttributeTargets.Parameter | AttributeTargets.Property, Inherited = false)]
-#if INTERNAL_NULLABLE_ATTRIBUTES
-    internal
-#else
-    public
-#endif
-        sealed class DisallowNullAttribute : Attribute
-    { }
+    internal sealed class DisallowNullAttribute : Attribute { }
 
     /// <summary>Specifies that an output may be null even if the corresponding type disallows it.</summary>
     [AttributeUsage(AttributeTargets.Field | AttributeTargets.Parameter | AttributeTargets.Property | AttributeTargets.ReturnValue, Inherited = false)]
-#if INTERNAL_NULLABLE_ATTRIBUTES
-    internal
-#else
-    public
-#endif
-        sealed class MaybeNullAttribute : Attribute
-    { }
+    internal sealed class MaybeNullAttribute : Attribute { }
 
-    /// <summary>Specifies that an output will not be null even if the corresponding type allows it.</summary>
+    /// <summary>Specifies that an output will not be null even if the corresponding type allows it. Specifies that an input argument was not null when the call returns.</summary>
     [AttributeUsage(AttributeTargets.Field | AttributeTargets.Parameter | AttributeTargets.Property | AttributeTargets.ReturnValue, Inherited = false)]
-#if INTERNAL_NULLABLE_ATTRIBUTES
-    internal
-#else
-    public
-#endif
-        sealed class NotNullAttribute : Attribute
-    { }
+    internal sealed class NotNullAttribute : Attribute { }
 
     /// <summary>Specifies that when a method returns <see cref="ReturnValue"/>, the parameter may be null even if the corresponding type disallows it.</summary>
     [AttributeUsage(AttributeTargets.Parameter, Inherited = false)]
-#if INTERNAL_NULLABLE_ATTRIBUTES
-    internal
-#else
-    public
-#endif
-        sealed class MaybeNullWhenAttribute : Attribute
+    internal sealed class MaybeNullWhenAttribute : Attribute
     {
         /// <summary>Initializes the attribute with the specified return value condition.</summary>
         /// <param name="returnValue">
@@ -71,12 +38,7 @@ namespace System.Diagnostics.CodeAnalysis
 
     /// <summary>Specifies that when a method returns <see cref="ReturnValue"/>, the parameter will not be null even if the corresponding type allows it.</summary>
     [AttributeUsage(AttributeTargets.Parameter, Inherited = false)]
-#if INTERNAL_NULLABLE_ATTRIBUTES
-    internal
-#else
-    public
-#endif
-        sealed class NotNullWhenAttribute : Attribute
+    internal sealed class NotNullWhenAttribute : Attribute
     {
         /// <summary>Initializes the attribute with the specified return value condition.</summary>
         /// <param name="returnValue">
@@ -90,12 +52,7 @@ namespace System.Diagnostics.CodeAnalysis
 
     /// <summary>Specifies that the output will be non-null if the named parameter is non-null.</summary>
     [AttributeUsage(AttributeTargets.Parameter | AttributeTargets.Property | AttributeTargets.ReturnValue, AllowMultiple = true, Inherited = false)]
-#if INTERNAL_NULLABLE_ATTRIBUTES
-    internal
-#else
-    public
-#endif
-        sealed class NotNullIfNotNullAttribute : Attribute
+    internal sealed class NotNullIfNotNullAttribute : Attribute
     {
         /// <summary>Initializes the attribute with the associated parameter name.</summary>
         /// <param name="parameterName">
@@ -109,22 +66,11 @@ namespace System.Diagnostics.CodeAnalysis
 
     /// <summary>Applied to a method that will never return under any circumstance.</summary>
     [AttributeUsage(AttributeTargets.Method, Inherited = false)]
-#if INTERNAL_NULLABLE_ATTRIBUTES
-    internal
-#else
-    public
-#endif
-        sealed class DoesNotReturnAttribute : Attribute
-    { }
+    internal sealed class DoesNotReturnAttribute : Attribute { }
 
     /// <summary>Specifies that the method will not return if the associated Boolean parameter is passed the specified value.</summary>
     [AttributeUsage(AttributeTargets.Parameter, Inherited = false)]
-#if INTERNAL_NULLABLE_ATTRIBUTES
-    internal
-#else
-    public
-#endif
-        sealed class DoesNotReturnIfAttribute : Attribute
+    internal sealed class DoesNotReturnIfAttribute : Attribute
     {
         /// <summary>Initializes the attribute with the specified parameter value.</summary>
         /// <param name="parameterValue">
@@ -136,82 +82,62 @@ namespace System.Diagnostics.CodeAnalysis
         /// <summary>Gets the condition parameter value.</summary>
         public bool ParameterValue { get; }
     }
-#endif // NETSTANDARD2_0 attributes
 
-#if NETSTANDARD2_1 || NETSTANDARD2_0 || NETCOREAPP2_0 || NETCOREAPP2_1 || NETCOREAPP2_2 || NETCOREAPP3_1 || NET45 || NET451 || NET452 || NET6 || NET461 || NET462 || NET47 || NET471 || NET472 || NET48
-    /// <summary>
-    /// Specifies that the method or property will ensure that the listed field and property members have
-    /// not-<see langword="null"/> values.
-    /// </summary>
+    /// <summary>Specifies that the method or property will ensure that the listed field and property members have not-null values.</summary>
     [AttributeUsage(AttributeTargets.Method | AttributeTargets.Property, Inherited = false, AllowMultiple = true)]
-#if INTERNAL_NULLABLE_ATTRIBUTES
-    internal
-#else
-    public
-#endif
-    sealed class MemberNotNullAttribute : Attribute
+    internal sealed class MemberNotNullAttribute : Attribute
     {
-        /// <summary>Gets field or property member names.</summary>
-        public string[] Members { get; }
-
         /// <summary>Initializes the attribute with a field or property member.</summary>
-        /// <param name="member">The field or property member that is promised to be not-null.</param>
-        public MemberNotNullAttribute(string member)
-        {
-            Members = new[] { member };
-        }
+        /// <param name="member">
+        /// The field or property member that is promised to be not-null.
+        /// </param>
+        public MemberNotNullAttribute(string member) => Members = [member];
 
         /// <summary>Initializes the attribute with the list of field and property members.</summary>
-        /// <param name="members">The list of field and property members that are promised to be not-null.</param>
-        public MemberNotNullAttribute(params string[] members)
-        {
-            Members = members;
-        }
-    }
-
-    /// <summary>
-    /// Specifies that the method or property will ensure that the listed field and property members have
-    /// non-<see langword="null"/> values when returning with the specified return value condition.
-    /// </summary>
-    [AttributeUsage(AttributeTargets.Method | AttributeTargets.Property, Inherited = false, AllowMultiple = true)]
-#if INTERNAL_NULLABLE_ATTRIBUTES
-    internal
-#else
-    public
-#endif
-    sealed class MemberNotNullWhenAttribute : Attribute
-    {
-        /// <summary>Gets the return value condition.</summary>
-        public bool ReturnValue { get; }
+        /// <param name="members">
+        /// The list of field and property members that are promised to be not-null.
+        /// </param>
+        public MemberNotNullAttribute(params string[] members) => Members = members;
 
         /// <summary>Gets field or property member names.</summary>
         public string[] Members { get; }
+    }
 
+    /// <summary>Specifies that the method or property will ensure that the listed field and property members have not-null values when returning with the specified return value condition.</summary>
+    [AttributeUsage(AttributeTargets.Method | AttributeTargets.Property, Inherited = false, AllowMultiple = true)]
+    internal sealed class MemberNotNullWhenAttribute : Attribute
+    {
         /// <summary>Initializes the attribute with the specified return value condition and a field or property member.</summary>
         /// <param name="returnValue">
-        /// The return value condition. If the method returns this value,
-        /// the associated parameter will not be <see langword="null"/>.
+        /// The return value condition. If the method returns this value, the associated parameter will not be null.
+        /// </param>
+        /// <param name="member">
+        /// The field or property member that is promised to be not-null.
         /// </param>
-        /// <param name="member">The field or property member that is promised to be not-<see langword="null"/>.</param>
         public MemberNotNullWhenAttribute(bool returnValue, string member)
         {
             ReturnValue = returnValue;
-            Members = new[] { member };
+            Members = [member];
         }
 
-        /// <summary>Initializes the attribute with the specified return value condition and list of field and property members.
-        /// </summary>
+        /// <summary>Initializes the attribute with the specified return value condition and list of field and property members.</summary>
         /// <param name="returnValue">
-        /// The return value condition. If the method returns this value,
-        /// the associated parameter will not be <see langword="null"/>.
+        /// The return value condition. If the method returns this value, the associated parameter will not be null.
+        /// </param>
+        /// <param name="members">
+        /// The list of field and property members that are promised to be not-null.
         /// </param>
-        /// <param name="members">The list of field and property members that are promised to be not-null.</param>
         public MemberNotNullWhenAttribute(bool returnValue, params string[] members)
         {
             ReturnValue = returnValue;
             Members = members;
         }
+
+        /// <summary>Gets the return value condition.</summary>
+        public bool ReturnValue { get; }
+
+        /// <summary>Gets field or property member names.</summary>
+        public string[] Members { get; }
     }
-#endif // NETSTANDARD2_1 attributes
+#endif
 }
-

src/Avalonia.Build.Tasks/Avalonia.Build.Tasks.csproj

@@ -1,6 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
     <PropertyGroup>
-      <TargetFrameworks>netstandard2.0</TargetFrameworks>
+      <TargetFramework>netstandard2.0</TargetFramework>
+      <Nullable>enable</Nullable>
       <GenerateDocumentationFile>false</GenerateDocumentationFile>
       <BuildOutputTargetFolder>tools</BuildOutputTargetFolder>
       <DefineConstants>$(DefineConstants);BUILDTASK;XAMLX_CECIL_INTERNAL;XAMLX_INTERNAL</DefineConstants>
@@ -114,16 +115,18 @@
       <Compile Include="../Avalonia.Base/RelativePoint.cs">
         <Link>Markup/%(RecursiveDir)%(FileName)%(Extension)</Link>
       </Compile>
-      <Compile Include="..\Avalonia.Base\Metadata\NullableAttributes.cs" Link="NullableAttributes.cs" />
-      <Compile Include="..\Avalonia.Base\Compatibility\TrimmingAttributes.cs" Link="TrimmingAttributes.cs" Visible="False" />
-      <Compile Include="..\Avalonia.Base\Utilities\SpanHelpers.cs" Link="Utilities\SpanHelpers.cs" />
-      <Compile Include="..\Shared\StringCompatibilityExtensions.cs" Link="Compatibility\StringCompatibilityExtensions.cs" />
-      <Compile Include="..\Shared\IsExternalInit.cs" Link="Compatibility\IsExternalInit.cs" />
-      <Compile Remove="../Markup/Avalonia.Markup.Xaml.Loader\xamlil.github\**\obj\**\*.cs" />
-      <Compile Remove="../Markup/Avalonia.Markup.Xaml.Loader\xamlil.github\src\XamlX\IL\SreTypeSystem.cs" />
+      <Compile Include="../Avalonia.Base/Compatibility/NullableAttributes.cs" Link="Compatibility/NullableAttributes.cs" />
+      <Compile Include="../Avalonia.Base/Compatibility/TrimmingAttributes.cs" Link="Compatibility/TrimmingAttributes.cs" />
+      <Compile Include="../Avalonia.Base/Utilities/SpanHelpers.cs" Link="Utilities/SpanHelpers.cs" />
+      <Compile Include="../Shared/StringCompatibilityExtensions.cs" Link="Compatibility/StringCompatibilityExtensions.cs" />
+      <Compile Include="../Shared/IsExternalInit.cs" Link="Compatibility/IsExternalInit.cs" />
+      <Compile Remove="../Markup/Avalonia.Markup.Xaml.Loader/xamlil.github/**/obj/**/*.cs" />
+      <Compile Remove="../Markup/Avalonia.Markup.Xaml.Loader/xamlil.github/src/XamlX/Compatibility/*.cs" />
+      <Compile Remove="../Markup/Avalonia.Markup.Xaml.Loader/xamlil.github/src/XamlX/IL/SreTypeSystem.cs" />
       <PackageReference Include="Mono.Cecil" Version="0.11.5" />
       <PackageReference Include="Microsoft.Build.Framework" Version="15.1.548" PrivateAssets="All" />
       <PackageReference Include="System.Numerics.Vectors" Version="4.5.0" />
     </ItemGroup>
-  <Import Project="..\..\build\SourceGenerators.props" />
+  <Import Project="../../build/SourceGenerators.props" />
+  <Import Project="../../build/NullableEnable.props" />
 </Project>

src/Avalonia.Controls.ColorPicker/Avalonia.Controls.ColorPicker.csproj

@@ -4,7 +4,7 @@
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
   </PropertyGroup>
   <ItemGroup>
-    <Compile Include="..\Avalonia.Base\Metadata\NullableAttributes.cs" Link="NullableAttributes.cs" />
+    <Compile Include="..\Avalonia.Base\Compatibility\NullableAttributes.cs" Link="NullableAttributes.cs" />
   </ItemGroup>
   <ItemGroup>
     <ProjectReference Include="..\Avalonia.Base\Avalonia.Base.csproj" />

src/Markup/Avalonia.Markup.Xaml.Loader/Avalonia.Markup.Xaml.Loader.csproj

@@ -14,4 +14,5 @@
   <Import Project="..\..\..\build\DevAnalyzers.props" />
   <Import Project="..\..\..\build\TrimmingEnable.props" />
   <Import Project="..\..\..\build\SourceGenerators.props" />
+  <Import Project="..\..\..\build\NullableEnable.props" />
 </Project>

src/Markup/Avalonia.Markup.Xaml.Loader/AvaloniaXamlIlRuntimeCompiler.cs

@@ -33,14 +33,14 @@ namespace Avalonia.Markup.Xaml.XamlIl
     internal static class AvaloniaXamlIlRuntimeCompiler
     {
 #if !RUNTIME_XAML_CECIL
-        private static SreTypeSystem _sreTypeSystem;
-        private static Type _ignoresAccessChecksFromAttribute;
-        private static ModuleBuilder _sreBuilder;
-        private static IXamlType _sreContextType; 
-        private static XamlLanguageTypeMappings _sreMappings;
-        private static XamlLanguageEmitMappings<IXamlILEmitter, XamlILNodeEmitResult> _sreEmitMappings;
-        private static XamlXmlnsMappings _sreXmlns;
-        private static AssemblyBuilder _sreAsm;
+        private static SreTypeSystem? _sreTypeSystem;
+        private static Type? _ignoresAccessChecksFromAttribute;
+        private static ModuleBuilder? _sreBuilder;
+        private static IXamlType? _sreContextType;
+        private static XamlLanguageTypeMappings? _sreMappings;
+        private static XamlLanguageEmitMappings<IXamlILEmitter, XamlILNodeEmitResult>? _sreEmitMappings;
+        private static XamlXmlnsMappings? _sreXmlns;
+        private static AssemblyBuilder? _sreAsm;
         private static bool _sreCanSave;
 
         [UnconditionalSuppressMessage("Trimming", "IL2026", Justification = XamlX.TrimmingMessages.CanBeSafelyTrimmed)]
@@ -48,7 +48,7 @@ namespace Avalonia.Markup.Xaml.XamlIl
         {
             if (_sreBuilder == null)
                 return;
-            var saveMethod = _sreAsm.GetType().GetMethods()
+            var saveMethod = _sreAsm!.GetType().GetMethods()
                 .FirstOrDefault(m => m.Name == "Save" && m.GetParameters().Length == 1);
             if (saveMethod == null)
                 return;
@@ -65,6 +65,13 @@ namespace Avalonia.Markup.Xaml.XamlIl
 
         [CompilerDynamicDependencies]
         [UnconditionalSuppressMessage("Trimming", "IL2072", Justification = XamlX.TrimmingMessages.GeneratedTypes)]
+        [MemberNotNull(nameof(_sreTypeSystem))]
+        [MemberNotNull(nameof(_sreBuilder))]
+        [MemberNotNull(nameof(_sreMappings))]
+        [MemberNotNull(nameof(_sreEmitMappings))]
+        [MemberNotNull(nameof(_sreXmlns))]
+        [MemberNotNull(nameof(_sreContextType))]
+        [MemberNotNull(nameof(_ignoresAccessChecksFromAttribute))]
         static void InitializeSre()
         {
             if (_sreTypeSystem == null)
@@ -81,8 +88,8 @@ namespace Avalonia.Markup.Xaml.XamlIl
                         {
                             name, (AssemblyBuilderAccess)3,
                             Path.GetDirectoryName(typeof(AvaloniaXamlIlRuntimeCompiler).Assembly.GetModules()[0]
-                                .FullyQualifiedName)
-                        });
+                                .FullyQualifiedName)!
+                        })!;
                     else
                         _sreCanSave = false;
                 }
@@ -94,7 +101,7 @@ namespace Avalonia.Markup.Xaml.XamlIl
                 _sreBuilder = _sreAsm.DefineDynamicModule("XamlIlLoader.ildump");
             }
 
-            if (_sreMappings == null)
+            if (_sreMappings is null || _sreEmitMappings is null)
                 (_sreMappings, _sreEmitMappings) = AvaloniaXamlIlLanguage.Configure(_sreTypeSystem);
             if (_sreXmlns == null)
                 _sreXmlns = XamlXmlnsMappings.Resolve(_sreTypeSystem, _sreMappings);
@@ -108,7 +115,7 @@ namespace Avalonia.Markup.Xaml.XamlIl
         }
 
         [UnconditionalSuppressMessage("Trimming", "IL2026", Justification = XamlX.TrimmingMessages.CanBeSafelyTrimmed)]
-        static MethodInfo GetDefineDynamicAssembly() => AppDomain.CurrentDomain.GetType().GetMethods()
+        static MethodInfo? GetDefineDynamicAssembly() => AppDomain.CurrentDomain.GetType().GetMethods()
             .FirstOrDefault(m => m.Name == "DefineDynamicAssembly"
                                  && m.GetParameters().Length == 3 &&
                                  m.GetParameters()[2].ParameterType == typeof(string));
@@ -142,12 +149,12 @@ namespace Avalonia.Markup.Xaml.XamlIl
             ctorIl.Emit(OpCodes.Ret);
 
             tb.SetCustomAttribute(new CustomAttributeBuilder(
-                typeof(AttributeUsageAttribute).GetConstructor(new[] { typeof(AttributeTargets) }),
+                typeof(AttributeUsageAttribute).GetConstructor(new[] { typeof(AttributeTargets) })!,
                 new object[] { AttributeTargets.Assembly },
-                new[] { typeof(AttributeUsageAttribute).GetProperty("AllowMultiple") },
+                new[] { typeof(AttributeUsageAttribute).GetProperty(nameof(AttributeUsageAttribute.AllowMultiple))! },
                 new object[] { true }));
             
-            return tb.CreateTypeInfo();
+            return tb.CreateTypeInfo()!;
         }
 
         [UnconditionalSuppressMessage("Trimming", "IL2080", Justification = XamlX.TrimmingMessages.GeneratedTypes)]
@@ -159,8 +166,8 @@ namespace Avalonia.Markup.Xaml.XamlIl
             var key = assemblyName.GetPublicKey();
             if (key != null && key.Length != 0)
                 name += ", PublicKey=" + BitConverter.ToString(key).Replace("-", "").ToUpperInvariant();
-            _sreAsm.SetCustomAttribute(new CustomAttributeBuilder(
-                _ignoresAccessChecksFromAttribute.GetConstructors()[0],
+            _sreAsm!.SetCustomAttribute(new CustomAttributeBuilder(
+                _ignoresAccessChecksFromAttribute!.GetConstructors()[0],
                 new object[] { name }));
         }
 
@@ -267,7 +274,7 @@ namespace Avalonia.Markup.Xaml.XamlIl
                 using (var sr = new StreamReader(document.XamlStream))
                     xaml = sr.ReadToEnd();
                 
-                IXamlType overrideType = null;
+                IXamlType? overrideType = null;
                 if (document.RootInstance != null)
                 {
                     overrideType = _sreTypeSystem.GetType(document.RootInstance.GetType());
@@ -326,13 +333,16 @@ namespace Avalonia.Markup.Xaml.XamlIl
 
         [UnconditionalSuppressMessage("Trimming", "IL2075", Justification = XamlX.TrimmingMessages.GeneratedTypes)]
         [UnconditionalSuppressMessage("Trimming", "IL2072", Justification = XamlX.TrimmingMessages.GeneratedTypes)]
-        static object LoadOrPopulate([DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.All)] Type created, object rootInstance, IServiceProvider parentServiceProvider)
+        static object LoadOrPopulate(
+            [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.All)] Type created,
+            object? rootInstance,
+            IServiceProvider? parentServiceProvider)
         {
             var isp = Expression.Parameter(typeof(IServiceProvider));
 
 
             var epar = Expression.Parameter(typeof(object));
-            var populate = created.GetMethod(AvaloniaXamlIlCompiler.PopulateName);
+            var populate = created.GetMethod(AvaloniaXamlIlCompiler.PopulateName)!;
             isp = Expression.Parameter(typeof(IServiceProvider));
             var populateCb = Expression.Lambda<Action<IServiceProvider, object>>(
                 Expression.Call(populate, isp, Expression.Convert(epar, populate.GetParameters()[1].ParameterType)),
@@ -353,7 +363,7 @@ namespace Avalonia.Markup.Xaml.XamlIl
                             target => { populateCb(serviceProvider, target); }));
                     try
                     {
-                        return Activator.CreateInstance(targetType);
+                        return Activator.CreateInstance(targetType)!;
                     }
                     finally
                     {
@@ -363,7 +373,7 @@ namespace Avalonia.Markup.Xaml.XamlIl
                 
                 var createCb = Expression.Lambda<Func<IServiceProvider, object>>(
                     Expression.Convert(Expression.Call(
-                        created.GetMethod(AvaloniaXamlIlCompiler.BuildName), isp), typeof(object)), isp).Compile();
+                        created.GetMethod(AvaloniaXamlIlCompiler.BuildName)!, isp), typeof(object)), isp).Compile();
                 return createCb(serviceProvider);
             }
             else
@@ -394,7 +404,7 @@ namespace Avalonia.Markup.Xaml.XamlIl
 #endif
         }
 
-        private static string GetSafeUriIdentifier(Uri uri)
+        private static string? GetSafeUriIdentifier(Uri? uri)
         {
             return uri?.ToString()
                 .Replace(":", "_")

src/Markup/Avalonia.Markup.Xaml.Loader/CompilerExtensions/AstNodes/AvaloniaXamlIlFontFamilyAstNode.cs

@@ -28,8 +28,8 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.AstNodes
         {
             codeGen
                 .Ldloc(context.ContextLocal)
-                .Castclass(context.Configuration.TypeMappings.UriContextProvider)
-                .EmitCall(context.Configuration.TypeMappings.UriContextProvider.FindMethod(
+                .Castclass(context.Configuration.TypeMappings.UriContextProvider!)
+                .EmitCall(context.Configuration.TypeMappings.UriContextProvider!.GetMethod(
                     "get_BaseUri", _types.Uri, false))
                 .Ldstr(_text)
                 .Newobj(_types.FontFamilyConstructorUriName);

src/Markup/Avalonia.Markup.Xaml.Loader/CompilerExtensions/AvaloniaXamlIlCompiler.cs

@@ -17,7 +17,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions
 {
     class AvaloniaXamlIlCompiler : XamlILCompiler
     {
-        private readonly IXamlType _contextType;
+        private readonly IXamlType _contextType = null!;
         private readonly AvaloniaXamlIlDesignPropertiesTransformer _designTransformer;
         private readonly AvaloniaBindingExtensionTransformer _bindingTransformer;
 
@@ -156,7 +156,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions
 #if !XAMLX_CECIL_INTERNAL
         [RequiresUnreferencedCode(XamlX.TrimmingMessages.DynamicXamlReference)]
 #endif
-        public XamlDocument Parse(string xaml, IXamlType overrideRootType)
+        public XamlDocument Parse(string xaml, IXamlType? overrideRootType)
         {
             var parsed = XDocumentXamlParser.Parse(xaml, new Dictionary<string, string>
             {
@@ -192,7 +192,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions
             return parsed;
         }
 
-        public void Compile(XamlDocument document, XamlDocumentTypeBuilderProvider typeBuilderProvider, string baseUri, IFileSource fileSource)
+        public void Compile(XamlDocument document, XamlDocumentTypeBuilderProvider typeBuilderProvider, string? baseUri, IFileSource? fileSource)
         {
             Compile(
                 document,
@@ -211,7 +211,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions
 #if !XAMLX_CECIL_INTERNAL
         [RequiresUnreferencedCode(XamlX.TrimmingMessages.DynamicXamlReference)]
 #endif
-        public void ParseAndCompile(string xaml, string baseUri, IFileSource fileSource, IXamlTypeBuilder<IXamlILEmitter> tb, IXamlType overrideRootType)
+        public void ParseAndCompile(string xaml, string? baseUri, IFileSource fileSource, IXamlTypeBuilder<IXamlILEmitter> tb, IXamlType overrideRootType)
         {
             var parsed = Parse(xaml, overrideRootType);
 

src/Markup/Avalonia.Markup.Xaml.Loader/CompilerExtensions/AvaloniaXamlIlCompilerConfiguration.cs

@@ -9,16 +9,17 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions
         public XamlIlPropertyInfoAccessorFactoryEmitter AccessorFactoryEmitter { get; }
         public XamlIlTrampolineBuilder TrampolineBuilder { get; }
 
-        public AvaloniaXamlIlCompilerConfiguration(IXamlTypeSystem typeSystem, 
-            IXamlAssembly defaultAssembly, 
+        public AvaloniaXamlIlCompilerConfiguration(
+            IXamlTypeSystem typeSystem,
+            IXamlAssembly? defaultAssembly,
             XamlLanguageTypeMappings typeMappings,
-            XamlXmlnsMappings xmlnsMappings,
-            XamlValueConverter customValueConverter,
+            XamlXmlnsMappings? xmlnsMappings,
+            XamlValueConverter? customValueConverter,
             XamlIlClrPropertyInfoEmitter clrPropertyEmitter,
             XamlIlPropertyInfoAccessorFactoryEmitter accessorFactoryEmitter,
             XamlIlTrampolineBuilder trampolineBuilder,
-            IXamlIdentifierGenerator identifierGenerator,
-            XamlDiagnosticsHandler diagnosticsHandler)
+            IXamlIdentifierGenerator? identifierGenerator,
+            XamlDiagnosticsHandler? diagnosticsHandler)
             : base(typeSystem, defaultAssembly, typeMappings, xmlnsMappings, customValueConverter, identifierGenerator, diagnosticsHandler)
         {
             ClrPropertyEmitter = clrPropertyEmitter;

src/Markup/Avalonia.Markup.Xaml.Loader/CompilerExtensions/AvaloniaXamlIlLanguage.cs

@@ -1,5 +1,6 @@
 using System;
 using System.Collections.Generic;
+using System.Diagnostics.CodeAnalysis;
 using System.Linq;
 using Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers;
 using XamlX.Ast;
@@ -21,8 +22,6 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions
         public static (XamlLanguageTypeMappings language, XamlLanguageEmitMappings<IXamlILEmitter, XamlILNodeEmitResult> emit) Configure(IXamlTypeSystem typeSystem)
         {
             var runtimeHelpers = typeSystem.GetType("Avalonia.Markup.Xaml.XamlIl.Runtime.XamlIlRuntimeHelpers");
-            var assignBindingAttribute = typeSystem.GetType("Avalonia.Data.AssignBindingAttribute");
-            var bindingType = typeSystem.GetType("Avalonia.Data.IBinding");
             var rv = new XamlLanguageTypeMappings(typeSystem)
             {
                 SupportInitialize = typeSystem.GetType("System.ComponentModel.ISupportInitialize"),
@@ -89,7 +88,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions
             IXamlTypeSystem typeSystem,
             IXamlILContextDefinition<IXamlILEmitter> definition)
         {
-            var nameScopeType = typeSystem.FindType("Avalonia.Controls.INameScope");
+            var nameScopeType = typeSystem.GetType("Avalonia.Controls.INameScope");
             var field = definition.TypeBuilder.DefineField(nameScopeType,
                 ContextNameScopeFieldName, XamlVisibility.Public, false);
             definition.ConstructorBuilder.Generator
@@ -97,7 +96,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions
                 .Ldarg(1)
                 .Ldtype(nameScopeType)
                 .EmitCall(mappings.ServiceProvider.GetMethod(new FindMethodMethodSignature("GetService",
-                    typeSystem.FindType("System.Object"), typeSystem.FindType("System.Type"))))
+                    typeSystem.GetType("System.Object"), typeSystem.GetType("System.Type"))))
                 .Stfld(field);
         }
 
@@ -107,26 +106,26 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions
             IXamlILContextDefinition<IXamlILEmitter> definition,
             IXamlType runtimeHelpers)
         {
-            var interfaceType = typeSystem.FindType("Avalonia.Markup.Xaml.XamlIl.Runtime.IAvaloniaXamlIlEagerParentStackProvider");
+            var interfaceType = typeSystem.GetType("Avalonia.Markup.Xaml.XamlIl.Runtime.IAvaloniaXamlIlEagerParentStackProvider");
 
             definition.TypeBuilder.AddInterfaceImplementation(interfaceType);
 
             // IReadOnlyList<object> DirectParentsStack => (IReadOnlyList<object>)ParentsStack;
             var directParentsGetter = ImplementInterfacePropertyGetter("DirectParentsStack");
             directParentsGetter.Generator
-                .LdThisFld(definition.ParentListField)
+                .LdThisFld(definition.ParentListField!)
                 .Castclass(directParentsGetter.ReturnType)
                 .Ret();
 
             var serviceProviderGetServiceMethod = mappings.ServiceProvider.GetMethod(new FindMethodMethodSignature(
                 "GetService",
-                typeSystem.FindType("System.Object"),
-                typeSystem.FindType("System.Type")));
+                typeSystem.GetType("System.Object"),
+                typeSystem.GetType("System.Type")));
 
             var asEagerParentStackProviderMethod = runtimeHelpers.GetMethod(new FindMethodMethodSignature(
                 "AsEagerParentStackProvider",
                 interfaceType,
-                mappings.ParentStackProvider)
+                mappings.ParentStackProvider!)
             {
                 IsStatic = true
             });
@@ -136,14 +135,14 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions
             var parentProviderGetter = ImplementInterfacePropertyGetter("ParentProvider");
             parentProviderGetter.Generator
                 .LdThisFld(definition.ParentServiceProviderField)
-                .Ldtype(mappings.ParentStackProvider)
+                .Ldtype(mappings.ParentStackProvider!)
                 .EmitCall(serviceProviderGetServiceMethod)
                 .EmitCall(asEagerParentStackProviderMethod)
                 .Ret();
 
             IXamlMethodBuilder<IXamlILEmitter> ImplementInterfacePropertyGetter(string propertyName)
             {
-                var interfaceGetter = interfaceType.FindMethod(m => m.Name == "get_" + propertyName);
+                var interfaceGetter = interfaceType.GetMethod(m => m.Name == "get_" + propertyName);
 
                 var getter = definition.TypeBuilder.DefineMethod(
                     interfaceGetter.ReturnType,
@@ -193,7 +192,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions
                 _avaloniaListConverter = typeSystem.GetType("Avalonia.Collections.AvaloniaListConverter`1");
             }
 
-            IXamlType LookupConverter(IXamlType type)
+            IXamlType? LookupConverter(IXamlType type)
             {
                 foreach(var p in _converters)
                     if (p.Key.Equals(type))
@@ -205,41 +204,44 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions
 
             class ConstructedAttribute : IXamlCustomAttribute
             {
-                public bool Equals(IXamlCustomAttribute other) => false;
+                public bool Equals(IXamlCustomAttribute? other) => false;
                 
                 public IXamlType Type { get; }
-                public List<object> Parameters { get; }
-                public Dictionary<string, object> Properties { get; }
+                public List<object?> Parameters { get; }
+                public Dictionary<string, object?> Properties { get; }
 
-                public ConstructedAttribute(IXamlType type, List<object> parameters, Dictionary<string, object> properties)
+                public ConstructedAttribute(IXamlType type, List<object?>? parameters, Dictionary<string, object?>? properties)
                 {
                     Type = type;
-                    Parameters = parameters ?? new List<object>();
-                    Properties = properties ?? new Dictionary<string, object>();
+                    Parameters = parameters ?? new List<object?>();
+                    Properties = properties ?? new Dictionary<string, object?>();
                 }
             }
             
-            public IXamlCustomAttribute GetCustomAttribute(IXamlType type, IXamlType attributeType)
+            public IXamlCustomAttribute? GetCustomAttribute(IXamlType type, IXamlType attributeType)
             {
                 if (attributeType.Equals(_typeConverterAttribute))
                 {
                     var conv = LookupConverter(type);
                     if (conv != null)
-                        return new ConstructedAttribute(_typeConverterAttribute, new List<object>() {conv}, null);
+                        return new ConstructedAttribute(_typeConverterAttribute, [conv], null);
                 }
 
                 return null;
             }
 
-            public IXamlCustomAttribute GetCustomAttribute(IXamlProperty property, IXamlType attributeType)
+            public IXamlCustomAttribute? GetCustomAttribute(IXamlProperty property, IXamlType attributeType)
             {
                 return null;
             }
         }
 
-        public static bool CustomValueConverter(AstTransformationContext context,
-            IXamlAstValueNode node, IReadOnlyList<IXamlCustomAttribute> customAttributes, IXamlType type,
-            out IXamlAstValueNode result)
+        public static bool CustomValueConverter(
+            AstTransformationContext context,
+            IXamlAstValueNode node,
+            IReadOnlyList<IXamlCustomAttribute>? customAttributes,
+            IXamlType type,
+            [NotNullWhen(true)] out IXamlAstValueNode? result)
         {
             if (node is AvaloniaXamlIlOptionMarkupExtensionTransformer.OptionsMarkupExtensionNode optionsNode)
             {

src/Markup/Avalonia.Markup.Xaml.Loader/CompilerExtensions/AvaloniaXamlIlLanguageParseIntrinsics.cs

@@ -1,5 +1,6 @@
 using System;
 using System.Collections.Generic;
+using System.Diagnostics.CodeAnalysis;
 using System.Globalization;
 using System.Linq;
 using Avalonia.Controls;
@@ -15,9 +16,15 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions
 {
     class AvaloniaXamlIlLanguageParseIntrinsics
     {
-        public static bool TryConvert(AstTransformationContext context, IXamlAstValueNode node, string text, IXamlType type, AvaloniaXamlIlWellKnownTypes types, out IXamlAstValueNode result)
+        public static bool TryConvert(
+            AstTransformationContext context,
+            IXamlAstValueNode node,
+            string text,
+            IXamlType type,
+            AvaloniaXamlIlWellKnownTypes types,
+            [NotNullWhen(true)] out IXamlAstValueNode? result)
         {
-            bool ReturnOnParseError(string title, out IXamlAstValueNode result)
+            bool ReturnOnParseError(string title, out IXamlAstValueNode? result)
             {
                 context.ReportDiagnostic(new XamlDiagnostic(
                     AvaloniaXamlDiagnosticCodes.AvaloniaIntrinsicsError,
@@ -50,7 +57,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions
                 }
 
                 result = new XamlStaticOrTargetedReturnMethodCallNode(node,
-                    type.FindMethod("FromTicks", type, false, types.Long),
+                    type.GetMethod("FromTicks", type, false, types.Long),
                     new[] { new XamlConstantNode(node, types.Long, timeSpan.Ticks) });
                 return true;
             }
@@ -272,7 +279,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions
                 {
                     if (property.PropertyType == types.TextTrimming && property.Name.Equals(text, StringComparison.OrdinalIgnoreCase))
                     {
-                        result = new XamlStaticOrTargetedReturnMethodCallNode(node, property.Getter, Enumerable.Empty<IXamlAstValueNode>());
+                        result = new XamlStaticOrTargetedReturnMethodCallNode(node, property.Getter!, Enumerable.Empty<IXamlAstValueNode>());
 
                         return true;
                     }
@@ -285,7 +292,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions
                 {
                     if (property.PropertyType == types.TextDecorationCollection && property.Name.Equals(text, StringComparison.OrdinalIgnoreCase))
                     {
-                        result = new XamlStaticOrTargetedReturnMethodCallNode(node, property.Getter, Enumerable.Empty<IXamlAstValueNode>());
+                        result = new XamlStaticOrTargetedReturnMethodCallNode(node, property.Getter!, Enumerable.Empty<IXamlAstValueNode>());
 
                         return true;
                     }
@@ -298,7 +305,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions
                 {
                     if (property.PropertyType == types.WindowTransparencyLevel && property.Name.Equals(text, StringComparison.OrdinalIgnoreCase))
                     {
-                        result = new XamlStaticOrTargetedReturnMethodCallNode(node, property.Getter, Enumerable.Empty<IXamlAstValueNode>());
+                        result = new XamlStaticOrTargetedReturnMethodCallNode(node, property.Getter!, Enumerable.Empty<IXamlAstValueNode>());
 
                         return true;
                     }
@@ -309,7 +316,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions
             {
                 var uriText = text.Trim();
 
-                var kind = ((!uriText?.StartsWith("/") == true) ? UriKind.RelativeOrAbsolute : UriKind.Relative);
+                var kind = !uriText.StartsWith("/") ? UriKind.RelativeOrAbsolute : UriKind.Relative;
 
                 if (string.IsNullOrWhiteSpace(uriText) || !Uri.TryCreate(uriText, kind, out var _))
                 {
@@ -373,12 +380,12 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions
                     {
                         if (attribute.Properties.TryGetValue("Separators", out var separatorsArray))
                         {
-                            separators = ((Array)separatorsArray)?.OfType<string>().ToArray();
+                            separators = ((Array?)separatorsArray)?.OfType<string>().ToArray();
                         }
 
                         if (attribute.Properties.TryGetValue("SplitOptions", out var splitOptionsObj))
                         {
-                            splitOptions = (StringSplitOptions)splitOptionsObj;
+                            splitOptions = (StringSplitOptions)splitOptionsObj!;
                         }
                     }
 
@@ -403,7 +410,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions
                         return false;
                     }
 
-                    nodes[index] = itemNode;
+                    nodes[index] = itemNode!;
                 }
 
                 foreach (var element in nodes)
@@ -440,7 +447,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions
             return false;
         }
 
-        private static IXamlType GetElementType(IXamlType type, XamlTypeWellKnownTypes types)
+        private static IXamlType? GetElementType(IXamlType type, XamlTypeWellKnownTypes types)
         {
             if (type.IsArray)
             {

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

@@ -1,7 +1,4 @@
-using System;
-using System.Collections.Generic;
-using System.Xml;
-using XamlX;
+using System.Collections.Generic;
 using XamlX.Ast;
 using XamlX.Transform;
 
@@ -18,7 +15,7 @@ internal class AstGroupTransformationContext : AstTransformationContext
     }
 
     public override string Document => CurrentDocument?.FileSource?.FilePath ?? "{unknown document}";
-    public IXamlDocumentResource CurrentDocument { get; set; }
+    public IXamlDocumentResource? CurrentDocument { get; set; }
     
     public IReadOnlyCollection<IXamlDocumentResource> Documents { get; }
 

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

@@ -192,7 +192,7 @@ internal class AvaloniaXamlIncludeTransformer : IXamlAstGroupTransformer
         var uriPath = new Uri(originalAssetPath, (UriKind)uriKind);
         if (!uriPath.IsAbsoluteUri)
         {
-            var baseUrl = context.CurrentDocument.Uri ?? throw new InvalidOperationException("CurrentDocument URI is null.");
+            var baseUrl = context.CurrentDocument?.Uri ?? throw new InvalidOperationException("CurrentDocument URI is null.");
             uriPath = new Uri(new Uri(baseUrl, UriKind.Absolute), uriPath);
         }
         else if (!uriPath.Scheme.Equals("avares", StringComparison.CurrentCultureIgnoreCase))
@@ -218,7 +218,7 @@ internal class AvaloniaXamlIncludeTransformer : IXamlAstGroupTransformer
         {
             codeGen.Ldloc(context.ContextLocal);
             var method = context.GetAvaloniaTypes().RuntimeHelpers
-                .FindMethod(m => m.Name == "CreateRootServiceProviderV3");
+                .GetMethod(m => m.Name == "CreateRootServiceProviderV3");
             codeGen.EmitCall(method);
 
             return XamlILNodeEmitResult.Type(0, Type.GetClrType());

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

@@ -7,7 +7,6 @@ using XamlX.Ast;
 using XamlX.TypeSystem;
 
 namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.GroupTransformers;
-#nullable enable
 
 internal class XamlMergeResourceGroupTransformer : IXamlAstGroupTransformer
 {
@@ -94,7 +93,7 @@ internal class XamlMergeResourceGroupTransformer : IXamlAstGroupTransformer
                     $"Node MergeResourceInclude is unable to resolve \"{originalAssetPath}\" path.", propertyNode, node);
             }
 
-            var singleRootObject = ((XamlManipulationGroupNode)targetDocumentRoot.Manipulation)
+            var singleRootObject = ((XamlManipulationGroupNode)targetDocumentRoot.Manipulation!)
                 .Children.OfType<XamlObjectInitializationNode>().Single();
             if (singleRootObject.Type != resourceDictionaryType)
             {

src/Markup/Avalonia.Markup.Xaml.Loader/CompilerExtensions/Transformers/AddNameScopeRegistration.cs

@@ -22,7 +22,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
                         && mg.Children.OfType<AvaloniaNameScopeRegistrationXamlIlNode>().Any())
                         return node;
 
-                    IXamlAstValueNode value = null;
+                    IXamlAstValueNode? value = null;
                     for (var c = 0; c < pa.Values.Count; c++)
                         if (pa.Values[c].Type.GetClrType().Equals(context.Configuration.WellKnownTypes.String))
                         {
@@ -73,9 +73,9 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
     class AvaloniaNameScopeRegistrationXamlIlNode : XamlAstNode, IXamlAstManipulationNode
     {
         public IXamlAstValueNode Name { get; set; }
-        public IXamlType TargetType { get; }
+        public IXamlType? TargetType { get; }
 
-        public AvaloniaNameScopeRegistrationXamlIlNode(IXamlAstValueNode name, IXamlType targetType) : base(name)
+        public AvaloniaNameScopeRegistrationXamlIlNode(IXamlAstValueNode name, IXamlType? targetType) : base(name)
         {
             TargetType = targetType;
             Name = name;
@@ -87,7 +87,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
 
     class AvaloniaNameScopeRegistrationXamlIlNodeEmitter : IXamlAstLocalsNodeEmitter<IXamlILEmitter, XamlILNodeEmitResult>
     {
-        public XamlILNodeEmitResult Emit(IXamlAstNode node, XamlEmitContextWithLocals<IXamlILEmitter, XamlILNodeEmitResult> context, IXamlILEmitter codeGen)
+        public XamlILNodeEmitResult? Emit(IXamlAstNode node, XamlEmitContextWithLocals<IXamlILEmitter, XamlILNodeEmitResult> context, IXamlILEmitter codeGen)
         {
             if (node is AvaloniaNameScopeRegistrationXamlIlNode registration)
             {
@@ -114,7 +114,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
 
                 return XamlILNodeEmitResult.Void(1);
             }
-            return default;
+            return null;
         }
     }
 }

src/Markup/Avalonia.Markup.Xaml.Loader/CompilerExtensions/Transformers/AvaloniaBindingExtensionTransformer.cs

@@ -4,14 +4,11 @@ using XamlX;
 using XamlX.Ast;
 using XamlX.Transform;
 
-
-using XamlParseException = XamlX.XamlParseException;
-
 namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
 {
     class XamlBindingsTransformException : XamlTransformException
     {
-        public XamlBindingsTransformException(string message, IXamlLineInfo lineInfo, Exception innerException = null)
+        public XamlBindingsTransformException(string message, IXamlLineInfo lineInfo, Exception? innerException = null)
             : base(message, lineInfo, innerException)
         {
         }

src/Markup/Avalonia.Markup.Xaml.Loader/CompilerExtensions/Transformers/AvaloniaXamlIlBindingPathParser.cs

@@ -1,15 +1,13 @@
 using System;
 using System.Collections.Generic;
+using System.Diagnostics.CodeAnalysis;
 using System.Linq;
-using System.Text;
 using Avalonia.Markup.Parsers;
 using Avalonia.Utilities;
-using XamlX;
 using XamlX.Ast;
 using XamlX.Transform;
 using XamlX.Transform.Transformers;
 using XamlX.TypeSystem;
-using XamlParseException = XamlX.XamlParseException;
 
 namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
 {
@@ -81,11 +79,11 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
             return node;
         }
 
-        private static BindingExpressionGrammar.INode ConvertLongFormPropertiesToBindingExpressionNode(
+        private static BindingExpressionGrammar.INode? ConvertLongFormPropertiesToBindingExpressionNode(
             AstTransformationContext context,
             XamlAstObjectNode binding)
         {
-            BindingExpressionGrammar.INode convertedNode = null;
+            BindingExpressionGrammar.INode? convertedNode = null;
 
             var syntheticCompiledBindingProperties = binding.Children.OfType<XamlAstXamlPropertyValueNode>()
                 .Where(v => v.Property is AvaloniaSyntheticCompiledBindingProperty)
@@ -195,17 +193,15 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
 
                     if (treeType == "Visual")
                     {
-                        convertedNode = new VisualAncestorBindingExpressionNode
+                        convertedNode = new VisualAncestorBindingExpressionNode(ancestorType!)
                         {
-                            Type = ancestorType,
                             Level = ancestorLevel
                         };
                     }
                     else if (treeType == "Logical")
                     {
-                        convertedNode = new LogicalAncestorBindingExpressionNode
+                        convertedNode = new LogicalAncestorBindingExpressionNode(ancestorType!)
                         {
-                            Type = ancestorType,
                             Level = ancestorLevel
                         };
                     }
@@ -238,7 +234,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
                         throw new XamlBindingsTransformException("TargetType has to be set on ControlTemplate or it should be defined inside of a Style.", binding);
                     } 
 
-                    convertedNode = new TemplatedParentBindingExpressionNode { Type = parentType };
+                    convertedNode = new TemplatedParentBindingExpressionNode(parentType);
                 }
                 else
                 {
@@ -260,8 +256,8 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
 
         private static bool GetRelativeSourceObjectFromAssignment(
             AstTransformationContext context,
-            XamlAstXamlPropertyValueNode relativeSourceProperty,
-            out XamlAstObjectNode relativeSourceObject)
+            XamlAstXamlPropertyValueNode? relativeSourceProperty,
+            [NotNullWhen(true)] out XamlAstObjectNode? relativeSourceObject)
         {
             relativeSourceObject = null;
             if (relativeSourceProperty is null)
@@ -320,20 +316,20 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
         }
     }
 
-    class VisualAncestorBindingExpressionNode : BindingExpressionGrammar.INode
+    class VisualAncestorBindingExpressionNode(IXamlType type) : BindingExpressionGrammar.INode
     {
-        public IXamlType Type { get; set; }
+        public IXamlType Type { get; set; } = type;
         public int Level { get; set; }
     }
 
-    class LogicalAncestorBindingExpressionNode : BindingExpressionGrammar.INode
+    class LogicalAncestorBindingExpressionNode(IXamlType type) : BindingExpressionGrammar.INode
     {
-        public IXamlType Type { get; set; }
+        public IXamlType Type { get; set; } = type;
         public int Level { get; set; }
     }
 
-    class TemplatedParentBindingExpressionNode : BindingExpressionGrammar.INode
+    class TemplatedParentBindingExpressionNode(IXamlType type) : BindingExpressionGrammar.INode
     {
-        public IXamlType Type { get; set; }
+        public IXamlType Type { get; set; } = type;
     }
 }

src/Markup/Avalonia.Markup.Xaml.Loader/CompilerExtensions/Transformers/AvaloniaXamlIlBindingPathTransformer.cs

@@ -14,7 +14,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
         {
             if (node is XamlAstConstructableObjectNode binding && binding.Type.GetClrType().Equals(context.GetAvaloniaTypes().CompiledBindingExtension))
             {
-                IXamlType startType = null;
+                IXamlType? startType = null;
                 var sourceProperty = binding.Children.OfType<XamlPropertyAssignmentNode>().FirstOrDefault(c => c.Property.Name == "Source");
                 var dataTypeProperty = binding.Children.OfType<XamlPropertyAssignmentNode>().FirstOrDefault(c => c.Property.Name == "DataType");
                 if (sourceProperty?.Values.Count is 1)
@@ -23,11 +23,11 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
                     switch (sourceValue)
                     {
                         case XamlAstTextNode textNode:
-                            startType = textNode.Type?.GetClrType();
+                            startType = textNode.Type.GetClrType();
                             break;
 
                         case XamlMarkupExtensionNode extension:
-                            startType = extension.Type?.GetClrType();
+                            startType = extension.Type.GetClrType();
 
                             //let's try to infer StaticResource type from parent resources in xaml
                             if (extension.Value.Type.GetClrType().FullName == "Avalonia.Markup.Xaml.MarkupExtensions.StaticResourceExtension" &&
@@ -47,7 +47,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
                                 string getResourceValue_xKey(XamlPropertyAssignmentNode node)
                                     => node.Values.Count == 2 && node.Values[0] is XamlAstTextNode t ? t.Text : "";
 
-                                IXamlType getResourceValue_Type(XamlPropertyAssignmentNode node, IXamlType xamlType)
+                                IXamlType? getResourceValue_Type(XamlPropertyAssignmentNode node, IXamlType? xamlType)
                                     => node.Values.Count == 2 ? node.Values[1].Type.GetClrType() : xamlType;
 
                                 IEnumerable<XamlPropertyAssignmentNode> getResourceValues(IXamlAstNode node)
@@ -85,7 +85,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
                                                         .Where(o => styledElement.IsAssignableFrom(o.Type.GetClrType()))
                                                         .Select(o => o.Children.FirstOrDefault(p => matchProperty(p, styledElement, "Resources")))
                                                         .Where(r => r != null)
-                                                        .SelectMany(r => getResourceValues(r))
+                                                        .SelectMany(r => getResourceValues(r!))
                                                         .FirstOrDefault(r => getResourceValue_xKey(r) == key);
 
                                 if (resource != null)
@@ -96,7 +96,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
                             break;
 
                         case XamlStaticExtensionNode staticExtension:
-                            startType = staticExtension.Type?.GetClrType();
+                            startType = staticExtension.Type.GetClrType();
                             break;
                     }
                 }

src/Markup/Avalonia.Markup.Xaml.Loader/CompilerExtensions/Transformers/AvaloniaXamlIlClassesPropertyResolver.cs

@@ -49,7 +49,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
                 {
                     emitter
                         .Stloc(value.Local)
-                        .EmitCall(_types.StyledElementClassesProperty.Getter)
+                        .EmitCall(_types.StyledElementClassesProperty.Getter!)
                         .Ldstr(_className)
                         .Ldloc(value.Local)
                         .EmitCall(_types.Classes.GetMethod(new FindMethodMethodSignature("Set",

src/Markup/Avalonia.Markup.Xaml.Loader/CompilerExtensions/Transformers/AvaloniaXamlIlDataContextTypeTransformer.cs

@@ -12,7 +12,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
 {
     class XamlDataContextException : XamlTransformException
     {
-        public XamlDataContextException(string message, IXamlLineInfo lineInfo, Exception innerException = null)
+        public XamlDataContextException(string message, IXamlLineInfo lineInfo, Exception? innerException = null)
             : base(message, lineInfo, innerException)
         {
         }
@@ -30,8 +30,8 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
 
             if (node is XamlAstConstructableObjectNode on)
             {
-                AvaloniaXamlIlDataContextTypeMetadataNode inferredDataContextTypeNode = null;
-                AvaloniaXamlIlDataContextTypeMetadataNode directiveDataContextTypeNode = null;
+                AvaloniaXamlIlDataContextTypeMetadataNode? inferredDataContextTypeNode = null;
+                AvaloniaXamlIlDataContextTypeMetadataNode? directiveDataContextTypeNode = null;
 
                 for (int i = 0; i < on.Children.Count; ++i)
                 {
@@ -81,13 +81,13 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
                     // Infer data type from collection binding on a control that displays items.
                     var property = context.ParentNodes().OfType<XamlPropertyAssignmentNode>().FirstOrDefault();
                     var attributeType = context.GetAvaloniaTypes().InheritDataTypeFromItemsAttribute;
-                    var attribute = property?.Property?.GetClrProperty().CustomAttributes
+                    var attribute = property?.Property.GetClrProperty().CustomAttributes
                         .FirstOrDefault(a => a.Type == attributeType);
     
                     if (attribute is not null)
                     {
-                        var propertyName = (string)attribute.Parameters.First();
-                        XamlAstConstructableObjectNode parentObject;
+                        var propertyName = (string?)attribute.Parameters.First();
+                        XamlAstConstructableObjectNode? parentObject;
                         if (attribute.Properties.TryGetValue("AncestorType", out var type)
                             && type is IXamlType xamlType)
                         {
@@ -99,7 +99,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
                             parentObject = context.ParentNodes().OfType<XamlAstConstructableObjectNode>().FirstOrDefault();
                         }
                             
-                        if (parentObject != null)
+                        if (parentObject != null && !string.IsNullOrEmpty(propertyName))
                         {
                             inferredDataContextTypeNode = InferDataContextOfPresentedItem(context, on, parentObject, propertyName);
                         }
@@ -122,7 +122,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
             return node;
         }
         
-        private static AvaloniaXamlIlDataContextTypeMetadataNode InferDataContextOfPresentedItem(
+        private static AvaloniaXamlIlDataContextTypeMetadataNode? InferDataContextOfPresentedItem(
             AstTransformationContext context, XamlAstConstructableObjectNode on,
             XamlAstConstructableObjectNode parentObject, string propertyName)
         {
@@ -135,7 +135,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
                 return null;
             }
 
-            IXamlType itemsCollectionType = null;
+            IXamlType? itemsCollectionType = null;
             if (context.GetAvaloniaTypes().IBinding.IsAssignableFrom(parentItemsValue.Type.GetClrType()))
             {
                 if (parentItemsValue.Type.GetClrType().Equals(context.GetAvaloniaTypes().CompiledBindingExtension)
@@ -217,7 +217,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
     [DebuggerDisplay("DataType = {DataContextType}")]
     class AvaloniaXamlIlDataContextTypeMetadataNode : XamlValueWithSideEffectNodeBase
     {
-        public virtual IXamlType DataContextType { get; }
+        public IXamlType DataContextType { get; }
 
         public AvaloniaXamlIlDataContextTypeMetadataNode(IXamlAstValueNode value, IXamlType targetType)
             : base(value, value)
@@ -230,10 +230,8 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
     class AvaloniaXamlIlUninferrableDataContextMetadataNode : AvaloniaXamlIlDataContextTypeMetadataNode
     {
         public AvaloniaXamlIlUninferrableDataContextMetadataNode(IXamlAstValueNode value)
-            : base(value, null)
+            : base(value, XamlPseudoType.Unknown)
         {
         }
-
-        public override IXamlType DataContextType => XamlPseudoType.Unknown;
     }
 }

src/Markup/Avalonia.Markup.Xaml.Loader/CompilerExtensions/Transformers/AvaloniaXamlIlDeferredResourceTransformer.cs

@@ -28,7 +28,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
                     new XamlDirectCallPropertySetter(types.ResourceDictionaryDeferredAdd),
                 };
             }
-            else if (pa.Property.Name == "Resources" && pa.Property.Getter.ReturnType.Equals(types.IResourceDictionary)
+            else if (pa.Property.Name == "Resources" && pa.Property.Getter?.ReturnType.Equals(types.IResourceDictionary) == true
                 && ShouldBeDeferred(pa.Values[1]))
             {
                 pa.Values[1] = new XamlDeferredContentNode(pa.Values[1], types.XamlIlTypes.Object, context.Configuration);
@@ -132,7 +132,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
                 emitter.EmitCall(_adder, true);
             }
 
-            public bool Equals(AdderSetter other)
+            public bool Equals(AdderSetter? other)
             {
                 if (ReferenceEquals(null, other))
                     return false;
@@ -142,7 +142,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
                 return _getter.Equals(other._getter) && _adder.Equals(other._adder);
             }
 
-            public override bool Equals(object obj)
+            public override bool Equals(object? obj)
                 => Equals(obj as AdderSetter);
 
             public override int GetHashCode()

src/Markup/Avalonia.Markup.Xaml.Loader/CompilerExtensions/Transformers/AvaloniaXamlIlEnsureResourceDictionaryCapacityTransformer.cs

@@ -70,8 +70,8 @@ internal sealed class AvaloniaXamlIlEnsureResourceDictionaryCapacityTransformer
         {
             "Content" when node.Property.DeclaringType == types.ResourceDictionary
                 => new ResourcesInfo(ResourcesMode.ResourceDictionaryContent, null) { Count = 1 },
-            "Resources" when types.IResourceDictionary.IsAssignableFrom(node.Property.Getter.ReturnType)
-                => new ResourcesInfo(ResourcesMode.ElementResources, node.Property.Getter) { Count = 1 },
+            "Resources" when node.Property.Getter is { } getter && types.IResourceDictionary.IsAssignableFrom(getter.ReturnType)
+                => new ResourcesInfo(ResourcesMode.ElementResources, getter) { Count = 1 },
             _
                 => default
         };

src/Markup/Avalonia.Markup.Xaml.Loader/CompilerExtensions/Transformers/AvaloniaXamlIlOptionMarkupExtensionTransformer.cs

@@ -1,5 +1,6 @@
 using System;
 using System.Collections.Generic;
+using System.Diagnostics.CodeAnalysis;
 using System.Linq;
 using System.Reflection.Emit;
 using XamlX;
@@ -25,9 +26,9 @@ internal class AvaloniaXamlIlOptionMarkupExtensionTransformer : IXamlAstTransfor
             var optionAttribute = context.GetAvaloniaTypes().MarkupExtensionOptionAttribute;
             var defaultOptionAttribute = context.GetAvaloniaTypes().MarkupExtensionDefaultOptionAttribute;
 
-            var typeArgument = type.GenericArguments?.FirstOrDefault();
+            var typeArgument = type.GenericArguments.FirstOrDefault();
 
-            IXamlAstValueNode defaultValue = null;
+            IXamlAstValueNode? defaultValue = null;
             var values = new List<OptionsMarkupExtensionBranch>();
 
             if (objectNode.Arguments.FirstOrDefault() is { } argument)
@@ -64,7 +65,7 @@ internal class AvaloniaXamlIlOptionMarkupExtensionTransformer : IXamlAstTransfor
                         var optionsPropNode = onObj.Children.OfType<XamlAstXamlPropertyValueNode>()
                             .SingleOrDefault(v => v.Property.GetClrProperty().Name == "Options")
                             ?.Values.Single();
-                        var options = (optionsPropNode as XamlAstTextNode)?.Text?.Split(new[] { ',', ' ' }, StringSplitOptions.RemoveEmptyEntries)
+                        var options = (optionsPropNode as XamlAstTextNode)?.Text.Split(new[] { ',', ' ' }, StringSplitOptions.RemoveEmptyEntries)
                             ?? Array.Empty<string>();
                         if (options.Length == 0)
                         {
@@ -128,8 +129,8 @@ internal class AvaloniaXamlIlOptionMarkupExtensionTransformer : IXamlAstTransfor
                         throw new XamlTransformException("MarkupExtension option must not be null", li);
                     }
 
-                    var optionAsString = option.ToString();
-                    IXamlAstValueNode optionNode = null;
+                    var optionAsString = option.ToString() ?? string.Empty;
+                    IXamlAstValueNode? optionNode = null;
                     foreach (var method in methods)
                     {
                         try
@@ -184,7 +185,7 @@ internal class AvaloniaXamlIlOptionMarkupExtensionTransformer : IXamlAstTransfor
 
         IXamlAstValueNode TransformNode(
             IReadOnlyCollection<IXamlAstValueNode> values,
-            IXamlType suggestedType,
+            IXamlType? suggestedType,
             IXamlLineInfo line)
         {
             if (suggestedType is not null)
@@ -212,7 +213,7 @@ internal class AvaloniaXamlIlOptionMarkupExtensionTransformer : IXamlAstTransfor
         public OptionsMarkupExtensionNode(
             XamlMarkupExtensionNode original,
             OptionsMarkupExtensionBranch[] branches,
-            IXamlAstValueNode defaultNode,
+            IXamlAstValueNode? defaultNode,
             IXamlType contextParameter)
             : base(
             original.Value,
@@ -232,9 +233,9 @@ internal class AvaloniaXamlIlOptionMarkupExtensionTransformer : IXamlAstTransfor
             base.VisitChildren(visitor);
         }
 
-        public bool ConvertToReturnType(AstTransformationContext context, IXamlType type, out OptionsMarkupExtensionNode res)
+        public bool ConvertToReturnType(AstTransformationContext context, IXamlType type, [NotNullWhen(true)] out OptionsMarkupExtensionNode? res)
         {
-            IXamlAstValueNode convertedDefaultNode = null;
+            IXamlAstValueNode? convertedDefaultNode = null;
 
             if (ProvideValue.ExtensionNodeContainer.DefaultNode is { } defaultNode)
             {
@@ -255,7 +256,7 @@ internal class AvaloniaXamlIlOptionMarkupExtensionTransformer : IXamlAstTransfor
                 return false;
             }
 
-            res = new OptionsMarkupExtensionNode(this, convertedBranches, convertedDefaultNode, _contextParameter);
+            res = new OptionsMarkupExtensionNode(this, convertedBranches!, convertedDefaultNode, _contextParameter);
             return true;
         }
     }
@@ -264,19 +265,19 @@ internal class AvaloniaXamlIlOptionMarkupExtensionTransformer : IXamlAstTransfor
     {
         public OptionsMarkupExtensionNodesContainer(
             OptionsMarkupExtensionBranch[] branches,
-            IXamlAstValueNode defaultNode) : base(branches.FirstOrDefault()?.Value ?? defaultNode)
+            IXamlAstValueNode? defaultNode) : base((branches.FirstOrDefault()?.Value ?? defaultNode)!)
         {
             Branches = branches;
             DefaultNode = defaultNode;
         }
 
         public OptionsMarkupExtensionBranch[] Branches { get; }
-        public IXamlAstValueNode DefaultNode { get; private set; }
+        public IXamlAstValueNode? DefaultNode { get; private set; }
 
         public override void VisitChildren(IXamlAstVisitor visitor)
         {
             VisitList(Branches, visitor);
-            DefaultNode = (IXamlAstValueNode)DefaultNode?.Visit(visitor);
+            DefaultNode = (IXamlAstValueNode?)DefaultNode?.Visit(visitor);
         }
 
         public IXamlType GetReturnType()
@@ -351,7 +352,7 @@ internal class AvaloniaXamlIlOptionMarkupExtensionTransformer : IXamlAstTransfor
             // - markup ext "@this" instance (always)
             // We always pop context from the stack, as this method decide by itself either context is needed.
             // We store "@this" as a local variable. But only if any conditional method is an instance method.
-            IXamlLocal @this = null;
+            IXamlLocal? @this = null;
             if (Parameters.Count > 0)
             {
                 codeGen.Pop();
@@ -377,7 +378,7 @@ internal class AvaloniaXamlIlOptionMarkupExtensionTransformer : IXamlAstTransfor
                 }
                 if (!branch.ConditionMethod.IsStatic)
                 {
-                    codeGen.Ldloc(@this);
+                    codeGen.Ldloc(@this!);
                 }
                 context.Emit(branch.Option, codeGen, branch.Option.Type.GetClrType());
                 codeGen.EmitCall(branch.ConditionMethod);
@@ -402,7 +403,7 @@ internal class AvaloniaXamlIlOptionMarkupExtensionTransformer : IXamlAstTransfor
             codeGen.MarkLabel(ret);
         }
 
-        public bool Equals(IXamlMethod other) => ReferenceEquals(this, other);
+        public bool Equals(IXamlMethod? other) => ReferenceEquals(this, other);
     }
 }
 

src/Markup/Avalonia.Markup.Xaml.Loader/CompilerExtensions/Transformers/AvaloniaXamlIlPropertyPathTransformer.cs

@@ -14,7 +14,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
 {
     class XamlPropertyPathException : XamlTransformException
     {
-        public XamlPropertyPathException(string message, IXamlLineInfo lineInfo, Exception innerException = null)
+        public XamlPropertyPathException(string message, IXamlLineInfo lineInfo, Exception? innerException = null)
             : base(message, lineInfo, innerException)
         {
         }
@@ -50,7 +50,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
                 }
 
                 var elements = new List<IXamlIlPropertyPathElementNode>();
-                IXamlType currentType = parentScope.TargetType.GetClrType();
+                var currentType = parentScope.TargetType.GetClrType();
                 
                 
                 var expectProperty = true;
@@ -58,13 +58,13 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
                 var expectTraversal = false;
                 var types = context.GetAvaloniaTypes();
                 
-                IXamlType GetType(string ns, string name)
+                IXamlType GetType(string? ns, string name)
                 {
                     return TypeReferenceResolver.ResolveType(context, $"{ns}:{name}", false,
                         text, true).GetClrType();
                 }
 
-                void HandleProperty(string name, string typeNamespace, string typeName)
+                void HandleProperty(string name, string? typeNamespace, string? typeName)
                 {
                     if(!expectProperty || currentType == null)
                         throw new XamlPropertyPathException("Unexpected property node", text);
@@ -72,7 +72,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
                     var propertySearchType =
                         typeName != null ? GetType(typeNamespace, typeName) : currentType;
 
-                    IXamlIlPropertyPathElementNode prop = null;
+                    IXamlIlPropertyPathElementNode? prop = null;
                     var avaloniaPropertyFieldName = name + "Property";
                     var avaloniaPropertyField = propertySearchType.GetAllFields().FirstOrDefault(f =>
                         f.IsStatic && f.IsPublic && f.Name == avaloniaPropertyFieldName);
@@ -84,7 +84,8 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
                     else
                     {
                         var clrProperty = propertySearchType.GetAllProperties().FirstOrDefault(p => p.Name == name);
-                        prop = new XamlIClrPropertyPathElementNode(clrProperty);
+                        if (clrProperty is not null)
+                            prop = new XamlIClrPropertyPathElementNode(clrProperty);
                     }
 
                     if (prop == null)
@@ -151,7 +152,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
         interface IXamlIlPropertyPathElementNode
         {
             void Emit(XamlEmitContext<IXamlILEmitter, XamlILNodeEmitResult> context, IXamlILEmitter codeGen);
-            IXamlType Type { get; }
+            IXamlType? Type { get; }
         }
 
         class XamlIlChildTraversalPropertyPathElementNode : IXamlIlPropertyPathElementNode
@@ -159,9 +160,9 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
             public void Emit(XamlEmitContext<IXamlILEmitter, XamlILNodeEmitResult> context, IXamlILEmitter codeGen)
                 => codeGen.EmitCall(
                     context.GetAvaloniaTypes()
-                        .PropertyPathBuilder.FindMethod(m => m.Name == "ChildTraversal"));
+                        .PropertyPathBuilder.GetMethod(m => m.Name == "ChildTraversal"));
 
-            public IXamlType Type => null;
+            public IXamlType? Type => null;
         }
         
         class XamlIlAvaloniaPropertyPropertyPathElementNode : IXamlIlPropertyPathElementNode
@@ -178,7 +179,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
                 => codeGen
                     .Ldsfld(_field)
                     .EmitCall(context.GetAvaloniaTypes()
-                        .PropertyPathBuilder.FindMethod(m => m.Name == "Property"));
+                        .PropertyPathBuilder.GetMethod(m => m.Name == "Property"));
 
             public IXamlType Type { get; }
         }
@@ -198,10 +199,10 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
                     .Emit(context, codeGen, _property);
 
                 codeGen.EmitCall(context.GetAvaloniaTypes()
-                    .PropertyPathBuilder.FindMethod(m => m.Name == "Property"));
+                    .PropertyPathBuilder.GetMethod(m => m.Name == "Property"));
             }
 
-            public IXamlType Type => _property.Getter?.ReturnType ?? _property.Setter?.Parameters[0];
+            public IXamlType Type => _property.PropertyType;
         }
 
         class XamlIlCastPropertyPathElementNode : IXamlIlPropertyPathElementNode
@@ -220,7 +221,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
                 codeGen
                     .Ldtype(_type)
                     .EmitCall(context.GetAvaloniaTypes()
-                        .PropertyPathBuilder.FindMethod(m => m.Name == (_ensureType ? "EnsureType" : "Cast")));
+                        .PropertyPathBuilder.GetMethod(m => m.Name == (_ensureType ? "EnsureType" : "Cast")));
             }
 
             public IXamlType Type => _type;
@@ -241,14 +242,14 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
             }
 
             public IXamlAstTypeReference Type { get; }
-            public IXamlType PropertyType => _elements.LastOrDefault()?.Type;
+            public IXamlType? PropertyType => _elements.LastOrDefault()?.Type;
             public XamlILNodeEmitResult Emit(XamlEmitContext<IXamlILEmitter, XamlILNodeEmitResult> context, IXamlILEmitter codeGen)
             {
                 codeGen
-                    .Newobj(_types.PropertyPathBuilder.FindConstructor());
+                    .Newobj(_types.PropertyPathBuilder.GetConstructor());
                 foreach(var e in _elements)
                     e.Emit(context, codeGen);
-                codeGen.EmitCall(_types.PropertyPathBuilder.FindMethod(m => m.Name == "Build"));
+                codeGen.EmitCall(_types.PropertyPathBuilder.GetMethod(m => m.Name == "Build"));
                 return XamlILNodeEmitResult.Type(0, _types.PropertyPath);
             }
         }
@@ -256,6 +257,6 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
 
     interface IXamlIlPropertyPathNode : IXamlAstValueNode
     {
-        IXamlType PropertyType { get; }
+        IXamlType? PropertyType { get; }
     }
 }

src/Markup/Avalonia.Markup.Xaml.Loader/CompilerExtensions/Transformers/AvaloniaXamlIlReorderClassesPropertiesTransformer.cs

@@ -9,8 +9,8 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
         {
             if (node is XamlAstObjectNode obj)
             {
-                IXamlAstNode classesNode = null;
-                IXamlAstNode firstSingleClassNode = null;
+                IXamlAstNode? classesNode = null;
+                IXamlAstNode? firstSingleClassNode = null;
                 var types = context.GetAvaloniaTypes();
                 foreach (var child in obj.Children)
                 {

src/Markup/Avalonia.Markup.Xaml.Loader/CompilerExtensions/Transformers/AvaloniaXamlIlRootObjectScopeTransformer.cs

@@ -19,7 +19,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
                 mnode.Manipulation = new XamlManipulationGroupNode(mnode,
                     new[]
                     {
-                        mnode.Manipulation,
+                        mnode.Manipulation!,
                         new HandleRootObjectScopeNode(mnode, context.GetAvaloniaTypes())
                     });
             }
@@ -37,7 +37,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
         }
         internal class Emitter : IXamlILAstNodeEmitter
         {
-            public XamlILNodeEmitResult Emit(IXamlAstNode node, XamlEmitContext<IXamlILEmitter, XamlILNodeEmitResult> context, IXamlILEmitter codeGen)
+            public XamlILNodeEmitResult? Emit(IXamlAstNode node, XamlEmitContext<IXamlILEmitter, XamlILNodeEmitResult> context, IXamlILEmitter codeGen)
             {
                 if (!(node is HandleRootObjectScopeNode))
                 {

src/Markup/Avalonia.Markup.Xaml.Loader/CompilerExtensions/Transformers/AvaloniaXamlIlSelectorTransformer.cs

@@ -15,7 +15,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
 {
     internal class XamlSelectorsTransformException : XamlTransformException
     {
-        public XamlSelectorsTransformException(string message, IXamlLineInfo lineInfo, Exception innerException = null)
+        public XamlSelectorsTransformException(string message, IXamlLineInfo lineInfo, Exception? innerException = null)
             : base(message, lineInfo, innerException)
         {
         }
@@ -46,14 +46,14 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
             if (!(pn.Values[0] is XamlAstTextNode tn))
                 throw new XamlSelectorsTransformException("Selector property should be a text node", node);
 
-            var selectorType = pn.Property.GetClrProperty().Getter.ReturnType;
+            var selectorType = pn.Property.GetClrProperty().Getter!.ReturnType;
             var initialNode = new XamlIlSelectorInitialNode(node, selectorType);
             var avaloniaAttachedPropertyT = context.GetAvaloniaTypes().AvaloniaAttachedPropertyT;
             XamlIlSelectorNode Create(IEnumerable<SelectorGrammar.ISyntax> syntax,
                 Func<string, string, XamlAstClrTypeReference> typeResolver)
             {
                 XamlIlSelectorNode result = initialNode;
-                XamlIlOrSelectorNode results = null;
+                XamlIlOrSelectorNode? results = null;
                 foreach (var i in syntax)
                 {
                     switch (i)
@@ -73,7 +73,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
                             break;
                         case SelectorGrammar.PropertySyntax property:
                         {
-                            var type = result?.TargetType;
+                            var type = result.TargetType;
 
                             if (type == null)
                                 throw new XamlTransformException("Property selectors must be applied to a type.", node);
@@ -96,7 +96,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
                         }
                         case SelectorGrammar.AttachedPropertySyntax attachedProperty:
                             {
-                                var targetType = result?.TargetType;
+                                var targetType = result.TargetType;
                                 if (targetType == null)
                                 {
                                     throw new XamlTransformException("Attached Property selectors must be applied to a type.",node);
@@ -172,7 +172,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
                     }
                 }
 
-                if (results != null && result != null)
+                if (results != null)
                 {
                     results.Add(result);
                 }
@@ -191,14 +191,13 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
             }
 
             var selector = Create(parsed, (p, n) 
-                => TypeReferenceResolver.ResolveType(context, $"{p}:{n}", true, node, true)
-                    ?? new XamlAstClrTypeReference(node, XamlPseudoType.Unknown, false));
+                => TypeReferenceResolver.ResolveType(context, $"{p}:{n}", true, node, true));
             pn.Values[0] = selector;
 
             var templateType = GetLastTemplateTypeFromSelector(selector);
             
             var styleNode = new AvaloniaXamlIlTargetTypeMetadataNode(on,
-                new XamlAstClrTypeReference(selector, selector.TargetType, false),
+                new XamlAstClrTypeReference(selector, selector.TargetType!, false),
                 AvaloniaXamlIlTargetTypeMetadataNode.ScopeTypes.Style);
 
             return templateType switch
@@ -210,7 +209,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
             };
         }
 
-        private static IXamlType GetLastTemplateTypeFromSelector(XamlIlSelectorNode node)
+        private static IXamlType? GetLastTemplateTypeFromSelector(XamlIlSelectorNode? node)
         {
             while (node is not null)
             {
@@ -219,7 +218,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
                         SelectorType: XamlIlCombinatorSelector.CombinatorSelectorType.Template
                     })
                 {
-                    return node.Previous.TargetType;
+                    return node.Previous?.TargetType;
                 }
                 node = node.Previous;
             }
@@ -230,15 +229,15 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
 
     abstract class XamlIlSelectorNode : XamlAstNode, IXamlAstValueNode, IXamlAstEmitableNode<IXamlILEmitter, XamlILNodeEmitResult>
     {
-        internal XamlIlSelectorNode Previous { get; }
-        public abstract IXamlType TargetType { get; }
+        internal XamlIlSelectorNode? Previous { get; }
+        public abstract IXamlType? TargetType { get; }
 
-        public XamlIlSelectorNode(XamlIlSelectorNode previous,
-            IXamlLineInfo info = null,
-            IXamlType selectorType = null) : base(info ?? previous)
+        public XamlIlSelectorNode(XamlIlSelectorNode? previous,
+            IXamlLineInfo? info = null,
+            IXamlType? selectorType = null) : base((info ?? previous)!)
         {
             Previous = previous;
-            Type = selectorType == null ? previous.Type : new XamlAstClrTypeReference(this, selectorType, false);
+            Type = selectorType == null ? previous!.Type : new XamlAstClrTypeReference(this, selectorType, false);
         }
 
         public IXamlAstTypeReference Type { get; }
@@ -256,7 +255,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
         protected void EmitCall(XamlEmitContext<IXamlILEmitter, XamlILNodeEmitResult> context, IXamlILEmitter codeGen, Func<IXamlMethod, bool> method)
         {
             var selectors = context.Configuration.TypeSystem.GetType("Avalonia.Styling.Selectors");
-            var found = selectors.FindMethod(m => m.IsStatic && m.Parameters.Count > 0 && method(m));
+            var found = selectors.GetMethod(m => m.IsStatic && m.Parameters.Count > 0 && method(m));
             codeGen.EmitCall(found);
         }
     }
@@ -268,7 +267,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
         {
         }
 
-        public override IXamlType TargetType => null;
+        public override IXamlType? TargetType => null;
         protected override void DoEmit(XamlEmitContext<IXamlILEmitter, XamlILNodeEmitResult> context, IXamlILEmitter codeGen) => codeGen.Ldnull();
     }
 
@@ -310,7 +309,8 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
         }
 
 
-        public override IXamlType TargetType => Previous?.TargetType;
+        public override IXamlType? TargetType => Previous?.TargetType;
+
         protected override void DoEmit(XamlEmitContext<IXamlILEmitter, XamlILNodeEmitResult> context, IXamlILEmitter codeGen)
         {
             codeGen.Ldstr(String);
@@ -336,7 +336,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
         }
 
         public CombinatorSelectorType SelectorType => _type;
-        public override IXamlType TargetType => null;
+        public override IXamlType? TargetType => null;
         protected override void DoEmit(XamlEmitContext<IXamlILEmitter, XamlILNodeEmitResult> context, IXamlILEmitter codeGen)
         {
             var name = _type.ToString();
@@ -354,7 +354,8 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
             Argument = argument;
         }
 
-        public override IXamlType TargetType => Previous?.TargetType;
+        public override IXamlType? TargetType => Previous?.TargetType;
+
         protected override void DoEmit(XamlEmitContext<IXamlILEmitter, XamlILNodeEmitResult> context, IXamlILEmitter codeGen)
         {
             context.Emit(Argument, codeGen, Type.GetClrType());
@@ -382,7 +383,8 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
             _type = type;
         }
 
-        public override IXamlType TargetType => Previous?.TargetType;
+        public override IXamlType? TargetType => Previous?.TargetType;
+
         protected override void DoEmit(XamlEmitContext<IXamlILEmitter, XamlILNodeEmitResult> context, IXamlILEmitter codeGen)
         {
             codeGen.Ldc_I4(_step);
@@ -406,12 +408,13 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
         public IXamlProperty Property { get; set; }
         public IXamlAstValueNode Value { get; set; }
         
-        public override IXamlType TargetType => Previous?.TargetType;
+        public override IXamlType? TargetType => Previous?.TargetType;
+
         protected override void DoEmit(XamlEmitContext<IXamlILEmitter, XamlILNodeEmitResult> context, IXamlILEmitter codeGen)
         {
             if (!XamlIlAvaloniaPropertyHelper.Emit(context, codeGen, Property))
                 throw new XamlX.XamlLoadException(
-                    $"{Property.Name} of {(Property.Setter ?? Property.Getter).DeclaringType.GetFqn()} doesn't seem to be an AvaloniaProperty",
+                    $"{Property.Name} of {Property.DeclaringType.GetFqn()} doesn't seem to be an AvaloniaProperty",
                     this);
             context.Emit(Value, codeGen, context.Configuration.WellKnownTypes.Object);
             EmitCall(context, codeGen,
@@ -437,7 +440,8 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
         public IXamlField PropertyFiled { get; set; }
         public IXamlAstValueNode Value { get; set; }
 
-        public override IXamlType TargetType => Previous?.TargetType;
+        public override IXamlType? TargetType => Previous?.TargetType;
+
         protected override void DoEmit(XamlEmitContext<IXamlILEmitter, XamlILNodeEmitResult> context, IXamlILEmitter codeGen)
         {
             codeGen.Ldsfld(PropertyFiled);
@@ -462,25 +466,25 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
             _selectors.Add(node);
         }
         
-        public override IXamlType TargetType
+        public override IXamlType? TargetType
         {
             get
             {
-                IXamlType result = null;
+                IXamlType? result = null;
 
                 foreach (var selector in _selectors)
                 {
-                    if (selector.TargetType == null)
+                    if (selector.TargetType is not { } targetType)
                     {
                         return null;
                     }
                     else if (result == null)
                     {
-                        result = selector.TargetType;
+                        result = targetType;
                     }
                     else
                     {
-                        while (!result.IsAssignableFrom(selector.TargetType))
+                        while (result is not null && !result.IsAssignableFrom(selector.TargetType))
                         {
                             result = result.BaseType;
                         }
@@ -500,11 +504,11 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
                 _selectors[0].Emit(context, codeGen);
                 return;
             }
-            var listType = context.Configuration.TypeSystem.FindType("System.Collections.Generic.List`1")
+            var listType = context.Configuration.TypeSystem.GetType("System.Collections.Generic.List`1")
                 .MakeGenericType(base.Type.GetClrType());
-            var add = listType.FindMethod("Add", context.Configuration.WellKnownTypes.Void, false, Type.GetClrType());
+            var add = listType.GetMethod("Add", context.Configuration.WellKnownTypes.Void, false, Type.GetClrType());
             codeGen
-                .Newobj(listType.FindConstructor());
+                .Newobj(listType.GetConstructor());
             foreach (var s in _selectors)
             {
                 codeGen.Dup();

src/Markup/Avalonia.Markup.Xaml.Loader/CompilerExtensions/Transformers/AvaloniaXamlIlSetterTransformer.cs

@@ -12,7 +12,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
 {
     class XamlStyleTransformException : XamlTransformException
     {
-        public XamlStyleTransformException(string message, IXamlLineInfo lineInfo, Exception innerException = null)
+        public XamlStyleTransformException(string message, IXamlLineInfo lineInfo, Exception? innerException = null)
             : base(message, lineInfo, innerException)
         {
         }
@@ -26,8 +26,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
                   && on.Type.GetClrType().FullName == "Avalonia.Styling.Setter"))
                 return node;
 
-            IXamlType targetType = null;
-            IXamlLineInfo lineInfo = null;
+            IXamlType? targetType = null;
 
             var avaloniaTypes = context.GetAvaloniaTypes();
 
@@ -39,7 +38,6 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
             {
                 targetType = styleParent.TargetType.GetClrType()
                              ?? throw new XamlStyleTransformException("Can not find parent Style Selector or ControlTemplate TargetType. If setter is not part of the style, you can set x:SetterTargetType directive on its parent.", node);
-                lineInfo = on;
             }
 
             if (targetType == null)
@@ -47,13 +45,12 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
                 throw new XamlStyleTransformException("Could not determine target type of Setter", node);
             }
 
-            IXamlType propType = null;
-            IXamlIlAvaloniaPropertyNode avaloniaPropertyNode = null;
+            IXamlType? propType;
             var property = @on.Children.OfType<XamlAstXamlPropertyValueNode>()
                 .FirstOrDefault(x => x.Property.GetClrProperty().Name == "Property");
             if (property != null)
             {
-                avaloniaPropertyNode = property.Values.OfType<IXamlIlAvaloniaPropertyNode>().FirstOrDefault();
+                var avaloniaPropertyNode = property.Values.OfType<IXamlIlAvaloniaPropertyNode>().FirstOrDefault();
                 if (avaloniaPropertyNode is null)
                 {
                     var propertyName = property.Values.OfType<XamlAstTextNode>().FirstOrDefault()?.Text;
@@ -61,7 +58,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
                         throw new XamlStyleTransformException("Setter.Property must be a string.", node);
 
                     avaloniaPropertyNode = XamlIlAvaloniaPropertyHelper.CreateNode(context, propertyName,
-                        new XamlAstClrTypeReference(lineInfo, targetType, false), property.Values[0]);
+                        new XamlAstClrTypeReference(on, targetType, false), property.Values[0]);
 
                     property.Values = new List<IXamlAstValueNode> {avaloniaPropertyNode};
                 }
@@ -90,9 +87,8 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
                 && XamlTransformHelpers.TryGetCorrectlyTypedValue(context, textValue,
                     propType, out _))
             {
-                
                 var setterValueProperty = new SetterValueProperty(
-                    (IXamlLineInfo)valueProperty?.Property ?? textValue,
+                    (IXamlLineInfo?)valueProperty?.Property ?? textValue,
                     on.Type.GetClrType(), propType, avaloniaTypes);
                 if (valueProperty is not null)
                 {
@@ -116,8 +112,8 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
             // but we have better validation in runtime for TemplatedBinding.
             // See Correctly_Resolve_TemplateBinding_In_Theme_Detached_Template test.
             if (!avaloniaTypes.ITemplateOfControl.IsAssignableFrom(propType)
-                && on.Children.OfType<XamlAstObjectNode>()?.FirstOrDefault() is { } valueObj
-                && avaloniaTypes.ITemplateOfControl.IsAssignableFrom(valueObj?.Type.GetClrType()))
+                && on.Children.OfType<XamlAstObjectNode>().FirstOrDefault() is { } valueObj
+                && avaloniaTypes.ITemplateOfControl.IsAssignableFrom(valueObj.Type.GetClrType()))
             {
                 on.Children[on.Children.IndexOf(valueObj)] = new AvaloniaXamlIlTargetTypeMetadataNode(valueObj,
                     new XamlAstClrTypeReference(on, targetType, false),
@@ -169,10 +165,10 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
                     };
                 }
 
-                private bool Equals(XamlIlDirectCallPropertySetter other) 
-                    => Equals(_method, other._method) && Equals(_type, other._type);
+                private bool Equals(XamlIlDirectCallPropertySetter? other)
+                    => other is not null && Equals(_method, other._method) && Equals(_type, other._type);
 
-                public override bool Equals(object obj) 
+                public override bool Equals(object? obj)
                     => Equals(obj as XamlIlDirectCallPropertySetter);
 
                 public override int GetHashCode() 

src/Markup/Avalonia.Markup.Xaml.Loader/CompilerExtensions/Transformers/AvaloniaXamlIlThemeVariantProviderTransformer.cs

@@ -24,7 +24,8 @@ internal class AvaloniaXamlIlThemeVariantProviderTransformer : IXamlAstTransform
 
         var themeDictionariesColl = avTypes.IDictionaryT.MakeGenericType(avTypes.ThemeVariant, avTypes.IThemeVariantProvider);
         if (context.ParentNodes().FirstOrDefault() is not XamlAstXamlPropertyValueNode propertyValueNode
-            || !themeDictionariesColl.IsAssignableFrom(propertyValueNode.Property.GetClrProperty().Getter.ReturnType))
+            || propertyValueNode.Property.GetClrProperty().Getter is not { } getter
+            || !themeDictionariesColl.IsAssignableFrom(getter.ReturnType))
         {
             return node;
         }

src/Markup/Avalonia.Markup.Xaml.Loader/CompilerExtensions/Transformers/AvaloniaXamlIlTransformInstanceAttachedProperties.cs

@@ -30,7 +30,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
                     if (clrProp != null
                         && (clrProp.Getter?.IsStatic == false || clrProp.Setter?.IsStatic == false))
                     {
-                        var declaringType = (clrProp.Getter ?? clrProp.Setter)?.DeclaringType;
+                        var declaringType = clrProp.DeclaringType;
                         var avaloniaPropertyFieldName = prop.Name + "Property";
                         var avaloniaPropertyField = declaringType.Fields.FirstOrDefault(f => f.IsStatic && f.Name == avaloniaPropertyFieldName);
                         if (avaloniaPropertyField != null)
@@ -52,10 +52,10 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
                             if (avaloniaPropertyType == null)
                                 return node;
 
-                            if (avaloniaPropertyType.GenericArguments?.Count > 1)
+                            if (avaloniaPropertyType.GenericArguments.Count > 1)
                                 return node;
 
-                            var propertyType = avaloniaPropertyType.GenericArguments?.Count == 1 ?
+                            var propertyType = avaloniaPropertyType.GenericArguments.Count == 1 ?
                                 avaloniaPropertyType.GenericArguments[0] :
                                 context.Configuration.WellKnownTypes.Object;
 
@@ -97,8 +97,8 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
                 _avaloniaPropertyType = avaloniaPropertyType;
                 
                 // XamlIl doesn't support generic methods yet
-                if (_avaloniaPropertyType.GenericArguments?.Count > 0)
-                    _avaloniaPropertyType = _avaloniaPropertyType.BaseType;
+                if (_avaloniaPropertyType.GenericArguments.Count > 0)
+                    _avaloniaPropertyType = _avaloniaPropertyType.BaseType!;
                 
                 _avaloniaObject = avaloniaObject;
                 _field = field;
@@ -173,9 +173,9 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
                 public IXamlMethod MakeGenericMethod(IReadOnlyList<IXamlType> typeArguments) 
                     => throw new System.NotSupportedException();
 
-
-                public bool Equals(IXamlMethod other) =>
+                public bool Equals(IXamlMethod? other) =>
                     other is GetterMethod m && m.Name == Name && m.DeclaringType.Equals(DeclaringType);
+
                 public IXamlType ReturnType => Parent.PropertyType;
                 public IReadOnlyList<IXamlType> Parameters { get; }
 

src/Markup/Avalonia.Markup.Xaml.Loader/CompilerExtensions/Transformers/AvaloniaXamlIlWellKnownTypes.cs

@@ -28,7 +28,6 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
         public IXamlType IDisposable { get; }
         public IXamlType ICommand { get; }
         public XamlTypeWellKnownTypes XamlIlTypes { get; }
-        public XamlLanguageTypeMappings XamlIlMappings { get; }
         public IXamlType Transitions { get; }
         public IXamlType AssignBindingAttribute { get; }
         public IXamlType DependsOnAttribute { get; }
@@ -143,12 +142,12 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
             internal InteractivityWellKnownTypes(TransformerConfiguration cfg)
             {
                 var ts = cfg.TypeSystem;
-                Interactive = ts.FindType("Avalonia.Interactivity.Interactive");
-                RoutedEvent = ts.FindType("Avalonia.Interactivity.RoutedEvent");
-                RoutedEventArgs = ts.FindType("Avalonia.Interactivity.RoutedEventArgs");
-                var eventHanlderT = ts.FindType("System.EventHandler`1");
+                Interactive = ts.GetType("Avalonia.Interactivity.Interactive");
+                RoutedEvent = ts.GetType("Avalonia.Interactivity.RoutedEvent");
+                RoutedEventArgs = ts.GetType("Avalonia.Interactivity.RoutedEventArgs");
+                var eventHanlderT = ts.GetType("System.EventHandler`1");
                 RoutedEventHandler = eventHanlderT.MakeGenericType(RoutedEventArgs);
-                AddHandler = Interactive.FindMethod(m => m.IsPublic
+                AddHandler = Interactive.GetMethod(m => m.IsPublic
                     && !m.IsStatic
                     && m.Name == "AddHandler"
                     && m.Parameters.Count == 4
@@ -157,15 +156,15 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
                     && m.Parameters[2].IsEnum
                     && m.Parameters[3].Equals(cfg.WellKnownTypes.Boolean)
                     );
-                AddHandlerT = Interactive.FindMethod(m => m.IsPublic
+                AddHandlerT = Interactive.GetMethod(m => m.IsPublic
                     && !m.IsStatic
                     && m.Name == "AddHandler"
                     && m.Parameters.Count == 4
                     && RoutedEvent.IsAssignableFrom(m.Parameters[0])
-                    && m.Parameters[0].GenericArguments?.Count == 1 // This is specific this case  workaround to check is generic method
+                    && m.Parameters[0].GenericArguments.Count == 1 // This is specific this case  workaround to check is generic method
                     && (cfg.WellKnownTypes.Delegate).IsAssignableFrom(m.Parameters[1])
                     && m.Parameters[2].IsEnum
-                    && m.Parameters[3].Equals(cfg.WellKnownTypes.Boolean) == true
+                    && m.Parameters[3].Equals(cfg.WellKnownTypes.Boolean)
                 );
 
             }
@@ -186,7 +185,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
             AvaloniaAttachedPropertyT = cfg.TypeSystem.GetType("Avalonia.AttachedProperty`1");
             BindingPriority = cfg.TypeSystem.GetType("Avalonia.Data.BindingPriority");
             AvaloniaObjectSetStyledPropertyValue = AvaloniaObject
-                .FindMethod(m => m.IsPublic && !m.IsStatic && m.Name == "SetValue"
+                .GetMethod(m => m.IsPublic && !m.IsStatic && m.Name == "SetValue"
                                  && m.Parameters.Count == 3
                                  && m.Parameters[0].Name == "StyledProperty`1"
                                  && m.Parameters[2].Equals(BindingPriority));
@@ -205,7 +204,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
             AvaloniaListAttribute = cfg.TypeSystem.GetType("Avalonia.Metadata.AvaloniaListAttribute");
             AvaloniaList = cfg.TypeSystem.GetType("Avalonia.Collections.AvaloniaList`1");
             OnExtensionType = cfg.TypeSystem.GetType("Avalonia.Markup.Xaml.MarkupExtensions.On");
-            AvaloniaObjectBindMethod = AvaloniaObjectExtensions.FindMethod("Bind", IDisposable, false, AvaloniaObject,
+            AvaloniaObjectBindMethod = AvaloniaObjectExtensions.GetMethod("Bind", IDisposable, false, AvaloniaObject,
                 AvaloniaProperty,
                 IBinding, cfg.WellKnownTypes.Object);
             UnsetValueType = cfg.TypeSystem.GetType("Avalonia.UnsetValueType");
@@ -230,7 +229,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
             NameScopeSetNameScope = NameScope.GetMethod(new FindMethodMethodSignature("SetNameScope",
                 XamlIlTypes.Void, StyledElement, INameScope)
             { IsStatic = true });
-            AvaloniaObjectSetValueMethod = AvaloniaObject.FindMethod("SetValue", IDisposable,
+            AvaloniaObjectSetValueMethod = AvaloniaObject.GetMethod("SetValue", IDisposable,
                 false, AvaloniaProperty, XamlIlTypes.Object, BindingPriority);
             IPropertyInfo = cfg.TypeSystem.GetType("Avalonia.Data.Core.IPropertyInfo");
             ClrPropertyInfo = cfg.TypeSystem.GetType("Avalonia.Data.Core.ClrPropertyInfo");
@@ -292,7 +291,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
             StyledElementClassesProperty =
                 StyledElement.Properties.First(x => x.Name == "Classes" && x.PropertyType.Equals(Classes));
             ClassesBindMethod = cfg.TypeSystem.GetType("Avalonia.StyledElementExtensions")
-                .FindMethod("BindClass", IDisposable, false, StyledElement,
+                .GetMethod("BindClass", IDisposable, false, StyledElement,
                 cfg.WellKnownTypes.String,
                 IBinding, cfg.WellKnownTypes.Object);
 
@@ -311,10 +310,10 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
             MergeResourceInclude = cfg.TypeSystem.GetType("Avalonia.Markup.Xaml.Styling.MergeResourceInclude");
             IResourceDictionary = cfg.TypeSystem.GetType("Avalonia.Controls.IResourceDictionary");
             ResourceDictionary = cfg.TypeSystem.GetType("Avalonia.Controls.ResourceDictionary");
-            ResourceDictionaryDeferredAdd = ResourceDictionary.FindMethod("AddDeferred", XamlIlTypes.Void, true, XamlIlTypes.Object,
+            ResourceDictionaryDeferredAdd = ResourceDictionary.GetMethod("AddDeferred", XamlIlTypes.Void, true, XamlIlTypes.Object,
                 cfg.TypeSystem.GetType("Avalonia.Controls.IDeferredContent"));
-            ResourceDictionaryEnsureCapacity = ResourceDictionary.FindMethod("EnsureCapacity", XamlIlTypes.Void, true, XamlIlTypes.Int32);
-            ResourceDictionaryGetCount = ResourceDictionary.FindMethod("get_Count", XamlIlTypes.Int32, true);
+            ResourceDictionaryEnsureCapacity = ResourceDictionary.GetMethod("EnsureCapacity", XamlIlTypes.Void, true, XamlIlTypes.Int32);
+            ResourceDictionaryGetCount = ResourceDictionary.GetMethod("get_Count", XamlIlTypes.Int32, true);
             IThemeVariantProvider = cfg.TypeSystem.GetType("Avalonia.Controls.IThemeVariantProvider");
             UriKind = cfg.TypeSystem.GetType("System.UriKind");
             UriConstructor = Uri.GetConstructor(new List<IXamlType>() { cfg.WellKnownTypes.String, UriKind });

src/Markup/Avalonia.Markup.Xaml.Loader/CompilerExtensions/Visitors/NameScopeRegistrationVisitor.cs

@@ -25,7 +25,7 @@ internal class NameScopeRegistrationVisitor : Dictionary<string, (IXamlType type
             && node is AvaloniaNameScopeRegistrationXamlIlNode nameScopeRegistration
             && nameScopeRegistration.Name is XamlAstTextNode textNode)
         {
-            this[textNode.Text] = (nameScopeRegistration.TargetType, textNode);
+            this[textNode.Text] = (nameScopeRegistration.TargetType ?? XamlPseudoType.Unknown, textNode);
         }
 
         return node;

src/Markup/Avalonia.Markup.Xaml.Loader/CompilerExtensions/XamlIlAvaloniaPropertyHelper.cs

@@ -51,9 +51,8 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions
         
         public static bool Emit(XamlIlEmitContext context, IXamlILEmitter emitter, IXamlProperty property)
         {
-            var type = (property.Getter ?? property.Setter).DeclaringType;
             var name = property.Name + "Property";
-            var found = type.Fields.FirstOrDefault(f => f.IsStatic && f.Name == name);
+            var found = property.DeclaringType.Fields.FirstOrDefault(f => f.IsStatic && f.Name == name);
             if (found == null)
                 return false;
 
@@ -225,11 +224,13 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions
                 AvaloniaXamlIlWellKnownTypes types,
                 IXamlType declaringType,
                 IXamlField avaloniaProperty,
-                bool allowNull)
+                bool allowNull,
+                IReadOnlyList<IXamlType> parameters)
             {
                 Types = types;
                 AvaloniaProperty = avaloniaProperty;
                 TargetType = declaringType;
+                Parameters = parameters;
                 BinderParameters = new PropertySetterBinderParameters
                 {
                     AllowXNull = allowNull,
@@ -241,7 +242,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions
 
             public PropertySetterBinderParameters BinderParameters { get; }
 
-            public IReadOnlyList<IXamlType> Parameters { get; set; }
+            public IReadOnlyList<IXamlType> Parameters { get; }
             public IReadOnlyList<IXamlCustomAttribute> CustomAttributes => Array.Empty<IXamlCustomAttribute>();
 
             public abstract void Emit(IXamlILEmitter emitter);
@@ -251,7 +252,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions
                 IXamlILEmitter emitter,
                 IReadOnlyList<IXamlAstValueNode> arguments);
 
-            public bool Equals(AvaloniaPropertyCustomSetter other)
+            public bool Equals(AvaloniaPropertyCustomSetter? other)
             {
                 if (ReferenceEquals(null, other))
                     return false;
@@ -261,7 +262,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions
                 return GetType() == other.GetType() && AvaloniaProperty.Equals(other.AvaloniaProperty);
             }
 
-            public override bool Equals(object obj)
+            public override bool Equals(object? obj)
                 => Equals(obj as AvaloniaPropertyCustomSetter);
 
             public override int GetHashCode() 
@@ -270,11 +271,12 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions
 
         class BindingSetter : AvaloniaPropertyCustomSetter
         {
-            public BindingSetter(AvaloniaXamlIlWellKnownTypes types,
+            public BindingSetter(
+                AvaloniaXamlIlWellKnownTypes types,
                 IXamlType declaringType,
-                IXamlField avaloniaProperty) : base(types, declaringType, avaloniaProperty, false)
+                IXamlField avaloniaProperty)
+                : base(types, declaringType, avaloniaProperty, false, [types.IBinding])
             {
-                Parameters = new[] { types.IBinding };
             }
 
             public override void Emit(IXamlILEmitter emitter)
@@ -307,11 +309,12 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions
 
         class BindingWithPrioritySetter : AvaloniaPropertyCustomSetter
         {
-            public BindingWithPrioritySetter(AvaloniaXamlIlWellKnownTypes types,
+            public BindingWithPrioritySetter(
+                AvaloniaXamlIlWellKnownTypes types,
                 IXamlType declaringType,
-                IXamlField avaloniaProperty) : base(types, declaringType, avaloniaProperty, false)
+                IXamlField avaloniaProperty)
+                : base(types, declaringType, avaloniaProperty, false, [types.BindingPriority, types.IBinding])
             {
-                Parameters = new[] { types.BindingPriority, types.IBinding };
             }
 
             public override void Emit(IXamlILEmitter emitter)
@@ -345,11 +348,13 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions
 
         class SetValueWithPrioritySetter : AvaloniaPropertyCustomSetter
         {
-            public SetValueWithPrioritySetter(AvaloniaXamlIlWellKnownTypes types, IXamlType declaringType, IXamlField avaloniaProperty,
+            public SetValueWithPrioritySetter(
+                AvaloniaXamlIlWellKnownTypes types,
+                IXamlType declaringType,
+                IXamlField avaloniaProperty,
                 IXamlType propertyType)
-                : base(types, declaringType, avaloniaProperty, propertyType.AcceptsNull())
+                : base(types, declaringType, avaloniaProperty, propertyType.AcceptsNull(), [types.BindingPriority, propertyType])
             {
-                Parameters = new[] { types.BindingPriority, propertyType };
             }
 
             public override void Emit(IXamlILEmitter emitter)
@@ -393,10 +398,12 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions
 
         class UnsetValueSetter : AvaloniaPropertyCustomSetter
         {
-            public UnsetValueSetter(AvaloniaXamlIlWellKnownTypes types, IXamlType declaringType, IXamlField avaloniaProperty) 
-                : base(types, declaringType, avaloniaProperty, false)
+            public UnsetValueSetter(
+                AvaloniaXamlIlWellKnownTypes types,
+                IXamlType declaringType,
+                IXamlField avaloniaProperty)
+                : base(types, declaringType, avaloniaProperty, false, [types.UnsetValueType])
             {
-                Parameters = new[] { types.UnsetValueType };
             }
 
             public override void Emit(IXamlILEmitter codegen)

src/Markup/Avalonia.Markup.Xaml.Loader/CompilerExtensions/XamlIlBindingPathHelper.cs

@@ -21,7 +21,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions
     {
         public static IXamlType UpdateCompiledBindingExtension(AstTransformationContext context, XamlAstConstructableObjectNode binding, Func<IXamlType> startTypeResolver, IXamlType selfType)
         {
-            IXamlType bindingResultType = null;
+            IXamlType? bindingResultType;
             if (binding.Arguments.Count > 0 && binding.Arguments[0] is ParsedBindingPathNode bindingPath)
             {
                 var transformed = TransformBindingPath(
@@ -90,8 +90,12 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions
             
             if (GetPropertyType(context, parentNode) == context.GetAvaloniaTypes().ICommand && lastElement is XamlIlClrMethodPathElementNode methodPathElement)
             {
-                IXamlMethod executeMethod = methodPathElement.Method;
-                IXamlMethod canExecuteMethod = executeMethod.DeclaringType.FindMethod(new FindMethodMethodSignature($"Can{executeMethod.Name}", context.Configuration.WellKnownTypes.Boolean, context.Configuration.WellKnownTypes.Object));
+                var executeMethod = methodPathElement.Method;
+                var canExecuteMethod = executeMethod.DeclaringType.FindMethod(new FindMethodMethodSignature(
+                    $"Can{executeMethod.Name}",
+                    context.Configuration.WellKnownTypes.Boolean,
+                    context.Configuration.WellKnownTypes.Object));
+
                 List<string> dependsOnProperties = new();
                 if (canExecuteMethod is not null)
                 {
@@ -99,7 +103,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions
                     {
                         if (attr.Type == context.GetAvaloniaTypes().DependsOnAttribute)
                         {
-                            dependsOnProperties.Add((string)attr.Parameters[0]);
+                            dependsOnProperties.Add((string)attr.Parameters[0]!);
                         }
                     }
                 }
@@ -110,7 +114,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions
             return transformed;
         }
 
-        private static IXamlType GetPropertyType(AstTransformationContext context, XamlPropertyAssignmentNode node)
+        private static IXamlType? GetPropertyType(AstTransformationContext context, XamlPropertyAssignmentNode node)
         {
             var setterType = context.GetAvaloniaTypes().Setter;
 
@@ -126,11 +130,11 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions
                     .FirstOrDefault(x => x.Property.GetClrProperty().Name == "Property");
                 var property = propertyAssignment?.Values.FirstOrDefault() as IXamlIlAvaloniaPropertyNode;
 
-                if (property.AvaloniaPropertyType is { } propertyType)
+                if (property?.AvaloniaPropertyType is { } propertyType)
                     return propertyType;
             }
 
-            return node.Property?.Getter?.ReturnType;
+            return node.Property.Getter?.ReturnType;
         }
 
         private static XamlIlBindingPathNode TransformBindingPath(AstTransformationContext context, IXamlLineInfo lineInfo, Func<IXamlType> startTypeResolver, IXamlType selfType, IEnumerable<BindingExpressionGrammar.INode> bindingExpression)
@@ -150,7 +154,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions
                     case BindingExpressionGrammar.StreamNode _:
                         {
                             IXamlType targetType = targetTypeResolver();
-                            IXamlType observableType;
+                            IXamlType? observableType;
                             if (targetType.GenericTypeDefinition?.Equals(context.Configuration.TypeSystem.FindType("System.IObservable`1")) == true)
                             {
                                 observableType = targetType;
@@ -165,10 +169,13 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions
                                 nodes.Add(new XamlIlStreamObservablePathElementNode(observableType.GenericArguments[0]));
                                 break;
                             }
+
                             bool foundTask = false;
+                            var taskType = context.Configuration.TypeSystem.GetType("System.Threading.Tasks.Task`1");
+
                             for (var currentType = targetType; currentType != null; currentType = currentType.BaseType)
                             {
-                                if (currentType.GenericTypeDefinition.Equals(context.Configuration.TypeSystem.GetType("System.Threading.Tasks.Task`1")))
+                                if (currentType.GenericTypeDefinition?.Equals(taskType) == true)
                                 {
                                     foundTask = true;
                                     nodes.Add(new XamlIlStreamTaskPathElementNode(currentType.GenericArguments[0]));
@@ -216,13 +223,13 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions
                                 break;
                             }
 
-                            IXamlProperty property = null;
+                            IXamlProperty? property = null;
                             foreach (var currentType in TraverseTypeHierarchy(targetType))
                             {
                                 var defaultMemberAttribute = currentType.CustomAttributes.FirstOrDefault(x => x.Type.Namespace == "System.Reflection" && x.Type.Name == "DefaultMemberAttribute");
                                 if (defaultMemberAttribute != null)
                                 {
-                                    property = currentType.GetAllProperties().FirstOrDefault(x => x.Name == (string)defaultMemberAttribute.Parameters[0]);
+                                    property = currentType.GetAllProperties().FirstOrDefault(x => x.Name == (string)defaultMemberAttribute.Parameters[0]!);
                                     break;
                                 }
                             }
@@ -255,8 +262,17 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions
                         }
                     case BindingExpressionGrammar.AttachedPropertyNameNode attachedProp:
                         var avaloniaPropertyFieldName = attachedProp.PropertyName + "Property";
-                        var avaloniaPropertyField = GetType(attachedProp.Namespace, attachedProp.TypeName).GetAllFields().FirstOrDefault(f =>
+                        var propertyOwnerType = GetType(attachedProp.Namespace, attachedProp.TypeName);
+                        var avaloniaPropertyField = propertyOwnerType.GetAllFields().FirstOrDefault(f =>
                             f.IsStatic && f.IsPublic && f.Name == avaloniaPropertyFieldName);
+
+                        if (avaloniaPropertyField is null)
+                        {
+                            throw new XamlTransformException(
+                                $"Unable to find {avaloniaPropertyFieldName} field on type {propertyOwnerType.GetFullName()}",
+                                lineInfo);
+                        }
+
                         nodes.Add(new XamlIlAvaloniaPropertyPropertyPathElementNode(avaloniaPropertyField,
                             XamlIlAvaloniaPropertyHelper.GetAvaloniaPropertyType(avaloniaPropertyField, context.GetAvaloniaTypes(), lineInfo)));
                         break;
@@ -305,7 +321,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions
                         }
                         break;
                     case BindingExpressionGrammar.NameNode elementName:
-                        IXamlType elementType = null;
+                        IXamlType? elementType = null;
                         foreach (var deferredContent in context.ParentNodes().OfType<NestedScopeMetadataNode>())
                         {
                             elementType = ScopeRegistrationFinder.GetTargetType(deferredContent, elementName.Name);
@@ -340,7 +356,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions
 
             return new XamlIlBindingPathNode(lineInfo, context.GetAvaloniaTypes().CompiledBindingPath, transformNodes, nodes);
 
-            IXamlType GetType(string ns, string name)
+            IXamlType GetType(string? ns, string? name)
             {
                 return TypeReferenceResolver.ResolveType(context, $"{ns}:{name}", false,
                     lineInfo, true).GetClrType();
@@ -403,9 +419,9 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions
 
             string Name { get; }
 
-            IXamlType TargetType { get; set; }
+            IXamlType? TargetType { get; set; }
 
-            public static IXamlType GetTargetType(IXamlAstNode namescopeRoot, string name)
+            public static IXamlType? GetTargetType(IXamlAstNode namescopeRoot, string name)
             {
                 // If we start from the nested scope - skip it.
                 if (namescopeRoot is NestedScopeMetadataNode scope)
@@ -468,7 +484,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions
 
             public void Emit(XamlIlEmitContext context, IXamlILEmitter codeGen)
             {
-                codeGen.EmitCall(context.GetAvaloniaTypes().CompiledBindingPathBuilder.FindMethod(m => m.Name == "Not"));
+                codeGen.EmitCall(context.GetAvaloniaTypes().CompiledBindingPathBuilder.GetMethod(m => m.Name == "Not"));
             }
         }
 
@@ -483,7 +499,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions
 
             public void Emit(XamlIlEmitContext context, IXamlILEmitter codeGen)
             {
-                codeGen.EmitCall(context.GetAvaloniaTypes().CompiledBindingPathBuilder.FindMethod(m => m.Name == "StreamObservable").MakeGenericMethod(new[] { Type }));
+                codeGen.EmitCall(context.GetAvaloniaTypes().CompiledBindingPathBuilder.GetMethod(m => m.Name == "StreamObservable").MakeGenericMethod(new[] { Type }));
             }
         }
 
@@ -498,7 +514,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions
 
             public void Emit(XamlIlEmitContext context, IXamlILEmitter codeGen)
             {
-                codeGen.EmitCall(context.GetAvaloniaTypes().CompiledBindingPathBuilder.FindMethod(m => m.Name == "StreamTask").MakeGenericMethod(new[] { Type }));
+                codeGen.EmitCall(context.GetAvaloniaTypes().CompiledBindingPathBuilder.GetMethod(m => m.Name == "StreamTask").MakeGenericMethod(new[] { Type }));
             }
         }
 
@@ -513,7 +529,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions
 
             public void Emit(XamlIlEmitContext context, IXamlILEmitter codeGen)
             {
-                codeGen.EmitCall(context.GetAvaloniaTypes().CompiledBindingPathBuilder.FindMethod(m => m.Name == "Self"));
+                codeGen.EmitCall(context.GetAvaloniaTypes().CompiledBindingPathBuilder.GetMethod(m => m.Name == "Self"));
             }
         }
 
@@ -533,7 +549,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions
             {
                 codeGen.Ldtype(Type)
                     .Ldc_I4(_level)
-                    .EmitCall(context.GetAvaloniaTypes().CompiledBindingPathBuilder.FindMethod(m => m.Name == "Ancestor"));
+                    .EmitCall(context.GetAvaloniaTypes().CompiledBindingPathBuilder.GetMethod(m => m.Name == "Ancestor"));
             }
         }
 
@@ -553,7 +569,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions
             {
                 codeGen.Ldtype(Type)
                     .Ldc_I4(_level)
-                    .EmitCall(context.GetAvaloniaTypes().CompiledBindingPathBuilder.FindMethod(m => m.Name == "VisualAncestor"));
+                    .EmitCall(context.GetAvaloniaTypes().CompiledBindingPathBuilder.GetMethod(m => m.Name == "VisualAncestor"));
             }
         }
 
@@ -578,7 +594,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions
                     .Ldloc(context.ContextLocal)
                     .Ldfld(scopeField)
                     .Ldstr(_name)
-                    .EmitCall(context.GetAvaloniaTypes().CompiledBindingPathBuilder.FindMethod(m => m.Name == "ElementName"));
+                    .EmitCall(context.GetAvaloniaTypes().CompiledBindingPathBuilder.GetMethod(m => m.Name == "ElementName"));
             }
         }
 
@@ -594,7 +610,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions
             public void Emit(XamlIlEmitContext context, IXamlILEmitter codeGen)
             {
                 codeGen
-                    .EmitCall(context.GetAvaloniaTypes().CompiledBindingPathBuilder.FindMethod(m => m.Name == "TemplatedParent"));
+                    .EmitCall(context.GetAvaloniaTypes().CompiledBindingPathBuilder.GetMethod(m => m.Name == "TemplatedParent"));
             }
         }
 
@@ -614,7 +630,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions
                 context.Configuration.GetExtra<XamlIlPropertyInfoAccessorFactoryEmitter>()
                     .EmitLoadAvaloniaPropertyAccessorFactory(context, codeGen);
                 codeGen.EmitCall(context.GetAvaloniaTypes()
-                    .CompiledBindingPathBuilder.FindMethod(m => m.Name == "Property"));
+                    .CompiledBindingPathBuilder.GetMethod(m => m.Name == "Property"));
             }
 
             public IXamlType Type { get; }
@@ -639,10 +655,10 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions
 
                 codeGen
                     .EmitCall(context.GetAvaloniaTypes()
-                        .CompiledBindingPathBuilder.FindMethod(m => m.Name == "Property"));
+                        .CompiledBindingPathBuilder.GetMethod(m => m.Name == "Property"));
             }
 
-            public IXamlType Type => _property.Getter?.ReturnType ?? _property.Setter?.Parameters[0];
+            public IXamlType Type => _property.PropertyType;
         }
 
         class XamlIlClrMethodPathElementNode : IXamlIlBindingPathElementNode
@@ -659,7 +675,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions
 
             public void Emit(XamlIlEmitContext context, IXamlILEmitter codeGen)
             {
-                IXamlTypeBuilder<IXamlILEmitter> newDelegateTypeBuilder = null;
+                IXamlTypeBuilder<IXamlILEmitter>? newDelegateTypeBuilder = null;
                 IXamlType specificDelegateType;
                 if (Method.ReturnType == context.Configuration.WellKnownTypes.Void && Method.Parameters.Count == 0)
                 {
@@ -696,7 +712,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions
                     .Ldtoken(Method)
                     .Ldtoken(specificDelegateType)
                     .EmitCall(context.GetAvaloniaTypes()
-                        .CompiledBindingPathBuilder.FindMethod(m => m.Name == "Method"));
+                        .CompiledBindingPathBuilder.GetMethod(m => m.Name == "Method"));
 
                 newDelegateTypeBuilder?.CreateType();
             }
@@ -705,10 +721,14 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions
         class XamlIlClrMethodAsCommandPathElementNode : IXamlIlBindingPathElementNode
         {
             private readonly IXamlMethod _executeMethod;
-            private readonly IXamlMethod _canExecuteMethod;
+            private readonly IXamlMethod? _canExecuteMethod;
             private readonly IReadOnlyList<string> _dependsOnProperties;
 
-            public XamlIlClrMethodAsCommandPathElementNode(IXamlType iCommandType, IXamlMethod executeMethod, IXamlMethod canExecuteMethod, IReadOnlyList<string> dependsOnProperties)
+            public XamlIlClrMethodAsCommandPathElementNode(
+                IXamlType iCommandType,
+                IXamlMethod executeMethod,
+                IXamlMethod? canExecuteMethod,
+                IReadOnlyList<string> dependsOnProperties)
             {
                 Type = iCommandType;
                 _executeMethod = executeMethod;
@@ -716,7 +736,6 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions
                 _dependsOnProperties = dependsOnProperties;
             }
 
-
             public IXamlType Type { get; }
 
             public void Emit(XamlIlEmitContext context, IXamlILEmitter codeGen)
@@ -770,7 +789,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions
 
                 codeGen
                     .EmitCall(context.GetAvaloniaTypes()
-                        .CompiledBindingPathBuilder.FindMethod(m => m.Name == "Command"));
+                        .CompiledBindingPathBuilder.GetMethod(m => m.Name == "Command"));
             }
         }
 
@@ -810,10 +829,10 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions
                 }
 
                 codeGen.EmitCall(context.GetAvaloniaTypes()
-                    .CompiledBindingPathBuilder.FindMethod(m => m.Name == "Property"));
+                    .CompiledBindingPathBuilder.GetMethod(m => m.Name == "Property"));
             }
 
-            public IXamlType Type => _property.Getter?.ReturnType ?? _property.Setter?.Parameters[0];
+            public IXamlType Type => _property.PropertyType;
         }
 
         class XamlIlArrayIndexerPathElementNode : IXamlIlBindingPathElementNode
@@ -853,10 +872,10 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions
                 codeGen.Ldloc(indices)
                     .Ldtype(Type)
                     .EmitCall(context.GetAvaloniaTypes()
-                    .CompiledBindingPathBuilder.FindMethod(m => m.Name == "ArrayElement"));
+                    .CompiledBindingPathBuilder.GetMethod(m => m.Name == "ArrayElement"));
             }
 
-            public IXamlType Type => _arrayType.ArrayElementType;
+            public IXamlType Type => _arrayType.ArrayElementType!;
         }
 
         class TypeCastPathElementNode : IXamlIlBindingPathElementNode
@@ -870,7 +889,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions
 
             public void Emit(XamlIlEmitContext context, IXamlILEmitter codeGen)
             {
-                codeGen.EmitCall(context.GetAvaloniaTypes().CompiledBindingPathBuilder.FindMethod(m => m.Name == "TypeCast").MakeGenericMethod(new[] { Type }));
+                codeGen.EmitCall(context.GetAvaloniaTypes().CompiledBindingPathBuilder.GetMethod(m => m.Name == "TypeCast").MakeGenericMethod(new[] { Type }));
             }
         }
 
@@ -906,7 +925,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions
                 // of 1 to indicate that we don't want TemplatedParent compatibility hacks enabled.
                 codeGen
                     .Ldc_I4(1)
-                    .Newobj(types.CompiledBindingPathBuilder.FindConstructor(new() { intType }));
+                    .Newobj(types.CompiledBindingPathBuilder.GetConstructor(new() { intType }));
 
                 foreach (var transform in _transformElements)
                 {
@@ -918,7 +937,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions
                     element.Emit(context, codeGen);
                 }
 
-                codeGen.EmitCall(types.CompiledBindingPathBuilder.FindMethod(m => m.Name == "Build"));
+                codeGen.EmitCall(types.CompiledBindingPathBuilder.GetMethod(m => m.Name == "Build"));
                 return XamlILNodeEmitResult.Type(0, types.CompiledBindingPath);
             }
 

src/Markup/Avalonia.Markup.Xaml.Loader/CompilerExtensions/XamlIlClrPropertyInfoHelper.cs

@@ -3,7 +3,6 @@ using System.Collections.Generic;
 using System.Linq;
 using Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers;
 using XamlX.Ast;
-using XamlX.Transform;
 using XamlX.TypeSystem;
 using XamlX.IL;
 using XamlX.Emit;
@@ -22,9 +21,12 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions
             _builder = builder;
         }
 
-        static string GetKey(IXamlProperty property, string indexerArgumentsKey)
+        static string GetKey(IXamlProperty property, string? indexerArgumentsKey)
         {
-            var baseKey = property.Getter.DeclaringType.GetFullName() + "." + property.Name;
+            var declaringType = (property.Getter ?? property.Setter)?.DeclaringType
+                ?? throw new InvalidOperationException($"Couldn't get declaring type for property {property}");
+
+            var baseKey = declaringType.GetFullName() + "." + property.Name;
 
             if (indexerArgumentsKey is null)
             {
@@ -34,9 +36,14 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions
             return baseKey + $"[{indexerArgumentsKey}]";
         }
 
-        public IXamlType Emit(XamlEmitContext<IXamlILEmitter, XamlILNodeEmitResult> context, IXamlILEmitter codeGen, IXamlProperty property, IReadOnlyCollection<IXamlAstValueNode> indexerArguments = null, string indexerArgumentsKey = null)
+        public IXamlType Emit(
+            XamlEmitContext<IXamlILEmitter, XamlILNodeEmitResult> context,
+            IXamlILEmitter codeGen,
+            IXamlProperty property,
+            IReadOnlyCollection<IXamlAstValueNode>? indexerArguments = null,
+            string? indexerArgumentsKey = null)
         {
-            indexerArguments = indexerArguments ?? Array.Empty<IXamlAstValueNode>();
+            indexerArguments ??= [];
             var types = context.GetAvaloniaTypes();
             IXamlMethod Get()
             {
@@ -83,7 +90,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions
                         new[] {types.XamlIlTypes.Object}, name + "!Getter", XamlVisibility.Private, true, false);
                 if (getter != null)
                 {
-                    Load(property.Getter, getter.Generator, !property.Getter.IsStatic);
+                    Load(property.Getter!, getter.Generator, !property.Getter!.IsStatic);
                     
                     getter.Generator.EmitCall(property.Getter);
                     if (property.Getter.ReturnType.IsValueType)
@@ -98,7 +105,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions
                         name + "!Setter", XamlVisibility.Private, true, false);
                 if (setter != null)
                 {
-                    Load(property.Setter, setter.Generator, !property.Getter.IsStatic);
+                    Load(property.Setter!, setter.Generator, !property.Setter!.IsStatic);
                     
                     setter.Generator.Ldarg(1);
 
@@ -128,7 +135,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions
                     .MarkLabel(cacheMiss)
                     .Ldstr(property.Name);
 
-                void EmitFunc(IXamlILEmitter emitter, IXamlMethod method, IXamlType del)
+                void EmitFunc(IXamlILEmitter emitter, IXamlMethod? method, IXamlType del)
                 {
                     if (method == null)
                         emitter.Ldnull();

src/Markup/Avalonia.Markup.Xaml.Loader/CompilerExtensions/XamlIlPropertyInfoAccessorFactoryEmitter.cs

@@ -17,7 +17,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions
     {
         private const string IndexerClosureFactoryMethodName = "CreateAccessor";
         private readonly IXamlTypeBuilder<IXamlILEmitter> _indexerClosureTypeBuilder;
-        private IXamlType _indexerClosureType;
+        private IXamlType? _indexerClosureType;
         public XamlIlPropertyInfoAccessorFactoryEmitter(IXamlTypeBuilder<IXamlILEmitter> indexerClosureType)
         {
             _indexerClosureTypeBuilder = indexerClosureType;
@@ -57,7 +57,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions
             }
 
             context.Emit(value, codeGen, intType);
-            codeGen.Newobj(_indexerClosureType.FindConstructor(new List<IXamlType> { intType }));
+            codeGen.Newobj(_indexerClosureType.GetConstructor(new List<IXamlType> { intType }));
             EmitLoadPropertyAccessorFactory(context, codeGen, _indexerClosureType, IndexerClosureFactoryMethodName, isStatic: false);
             return EmitCreateAccessorFactoryDelegate(context, codeGen);
         }

src/Markup/Avalonia.Markup.Xaml.Loader/CompilerExtensions/XamlIlTrampolineBuilder.cs

@@ -54,10 +54,10 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions
                     var convertedValue = gen.DefineLocal(context.Configuration.WellKnownTypes.Object);
                     gen.Ldtype(executeMethod.Parameters[0])
                         .Ldarg(1)
-                        .EmitCall(context.Configuration.WellKnownTypes.CultureInfo.FindMethod(m => m.Name == "get_CurrentCulture"))
+                        .EmitCall(context.Configuration.WellKnownTypes.CultureInfo.GetMethod(m => m.Name == "get_CurrentCulture"))
                         .Ldloca(convertedValue)
                         .EmitCall(
-                            context.GetAvaloniaTypes().TypeUtilities.FindMethod(m => m.Name == "TryConvert"),
+                            context.GetAvaloniaTypes().TypeUtilities.GetMethod(m => m.Name == "TryConvert"),
                             swallowResult: true)
                         .Ldloc(convertedValue)
                         .Unbox_Any(executeMethod.Parameters[0]);

src/Markup/Avalonia.Markup.Xaml.Loader/xamlil.github

@@ -1 +1 @@
-Subproject commit 941dafce490ffd21178f4493a7f0425e9d478e60
+Subproject commit 14fed0cb0666a9b3f71cb635cf61eb6010d4ff64

src/Markup/Avalonia.Markup.Xaml/XamlIl/Runtime/XamlIlRuntimeHelpers.cs

@@ -361,7 +361,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.Runtime
         {
             return new RootServiceProvider(new NameScope(), null);
         }
-        public static IServiceProvider CreateRootServiceProviderV3(IServiceProvider parentServiceProvider)
+        public static IServiceProvider CreateRootServiceProviderV3(IServiceProvider? parentServiceProvider)
         {
             return new RootServiceProvider(new NameScope(), parentServiceProvider);
         }

src/tools/Avalonia.Designer.HostApp/Avalonia.Designer.HostApp.csproj

@@ -14,11 +14,12 @@
     <Compile Include="..\..\..\src\Markup\Avalonia.Markup.Xaml.Loader\CompilerExtensions\**\*.cs" />
     <Compile Include="..\..\..\src\Markup\Avalonia.Markup.Xaml.Loader\AvaloniaXamlIlRuntimeCompiler.cs" />
     <Compile Include="..\..\..\src\Markup\Avalonia.Markup.Xaml.Loader\CompilerDynamicDependencies.cs" />
-    <Compile Include="..\..\..\src\Avalonia.Base\Metadata\NullableAttributes.cs" Link="Compatibility\NullableAttributes.cs" />
+    <Compile Include="..\..\..\src\Avalonia.Base\Compatibility\NullableAttributes.cs" Link="Compatibility\NullableAttributes.cs" />
     <Compile Include="..\..\..\src\Avalonia.Base\Compatibility\TrimmingAttributes.cs" Link="Compatibility\TrimmingAttributes.cs" />
     <Compile Include="..\..\..\src\Shared\IsExternalInit.cs" Link="Compatibility\IsExternalInit.cs" />
   </ItemGroup>
   <Import Project="..\..\..\src\Markup\Avalonia.Markup.Xaml.Loader\IncludeXamlIlSre.props" />
   <Import Project="..\..\..\build\DevAnalyzers.props" />
   <Import Project="..\..\..\build\TrimmingEnable.props" />
+  <Import Project="..\..\..\build\NullableEnable.props" />
 </Project>

src/tools/Avalonia.Designer.HostApp/DesignXamlLoader.cs

@@ -19,11 +19,11 @@ class DesignXamlLoader : AvaloniaXamlLoader.IRuntimeXamlLoader
         return AvaloniaXamlIlRuntimeCompiler.Load(document, configuration);
     }
 
-    private void PreloadDepsAssemblies(Assembly targetAssembly)
+    private void PreloadDepsAssemblies(Assembly? targetAssembly)
     {
         // Assemblies loaded in memory (e.g. single file) return empty string from Location.
         // In these cases, don't try probing next to the assembly.
-        var assemblyLocation = targetAssembly.Location;
+        var assemblyLocation = targetAssembly?.Location;
         if (string.IsNullOrEmpty(assemblyLocation))
         {
             return;
@@ -32,7 +32,7 @@ class DesignXamlLoader : AvaloniaXamlLoader.IRuntimeXamlLoader
         var depsJsonFile = Path.ChangeExtension(assemblyLocation, ".deps.json");
         if (!File.Exists(depsJsonFile))
         {
-            var sameDir = Path.GetDirectoryName(depsJsonFile);
+            var sameDir = Path.GetDirectoryName(depsJsonFile)!;
             var fallbackDepsFiles = Directory.GetFiles(sameDir, "*.deps.json");
             if (fallbackDepsFiles.Length == 1)
             {

src/tools/Avalonia.Generators/Avalonia.Generators.csproj

@@ -8,6 +8,7 @@
     <IncludeSymbols>false</IncludeSymbols>
     <IsRoslynComponent>true</IsRoslynComponent>
     <EnforceExtendedAnalyzerRules>true</EnforceExtendedAnalyzerRules>
+    <Nullable>enable</Nullable>
   </PropertyGroup>
 
   <ItemGroup>
@@ -16,20 +17,21 @@
   </ItemGroup>
 
   <ItemGroup>
-    <Compile Link="Compiler\XamlX\filename" Include="../../Markup/Avalonia.Markup.Xaml.Loader/xamlil.github/src/XamlX/**/*.cs" />
+    <Compile Link="Compiler/XamlX/filename" Include="../../Markup/Avalonia.Markup.Xaml.Loader/xamlil.github/src/XamlX/**/*.cs" />
     <Compile Remove="../../Markup/Avalonia.Markup.Xaml.Loader/xamlil.github/src/XamlX/obj/**/*.cs" />
     <Compile Remove="../../Markup/Avalonia.Markup.Xaml.Loader/xamlil.github/src/XamlX/**/SreTypeSystem.cs" />
-    <Compile Include="..\..\Shared\IsExternalInit.cs" Link="IsExternalInit.cs" Visible="False" />
-    <Compile Include="..\..\Avalonia.Base\Compatibility\TrimmingAttributes.cs" Link="TrimmingAttributes.cs" Visible="False" />
+    <Compile Include="../../Shared/IsExternalInit.cs" Link="IsExternalInit.cs" Visible="False" />
+    <Compile Include="../../Avalonia.Base/Compatibility/TrimmingAttributes.cs" Link="TrimmingAttributes.cs" Visible="False" />
+    <Compile Include="../../Avalonia.Base/Compatibility/NullableAttributes.cs" Link="TrimmingAttributes.cs" Visible="False" />
   </ItemGroup>
 
   <ItemGroup>
-    <None Include="$(OutputPath)\$(AssemblyName).dll" Pack="true" PackagePath="analyzers/dotnet/cs" Visible="false" />
+    <None Include="$(OutputPath)/$(AssemblyName).dll" Pack="true" PackagePath="analyzers/dotnet/cs" Visible="false" />
   </ItemGroup>
 
   <ItemGroup Label="InternalsVisibleTo">
     <InternalsVisibleTo Include="Avalonia.Generators.Tests, PublicKey=$(AvaloniaPublicKey)" />
   </ItemGroup>
 
-  <Import Project="..\..\..\build\TrimmingEnable.props" />
+  <Import Project="../../../build/TrimmingEnable.props" />
 </Project>

src/tools/Avalonia.Generators/Common/Domain/IViewResolver.cs

@@ -5,7 +5,7 @@ namespace Avalonia.Generators.Common.Domain;
 
 internal interface IViewResolver
 {
-    ResolvedView ResolveView(string xaml);
+    ResolvedView? ResolveView(string xaml);
 }
 
 internal record ResolvedView(string ClassName, IXamlType XamlType, string Namespace, XamlDocument Xaml);

src/tools/Avalonia.Generators/Common/XamlXViewResolver.cs

@@ -14,18 +14,18 @@ internal class XamlXViewResolver : IViewResolver, IXamlAstVisitor
     private readonly RoslynTypeSystem _typeSystem;
     private readonly MiniCompiler _compiler;
     private readonly bool _checkTypeValidity;
-    private readonly Action<string> _onTypeInvalid;
-    private readonly Action<Exception> _onUnhandledError;
+    private readonly Action<string>? _onTypeInvalid;
+    private readonly Action<Exception>? _onUnhandledError;
 
-    private ResolvedView _resolvedClass;
-    private XamlDocument _xaml;
+    private ResolvedView? _resolvedClass;
+    private XamlDocument? _xaml;
 
     public XamlXViewResolver(
         RoslynTypeSystem typeSystem,
         MiniCompiler compiler,
         bool checkTypeValidity = false,
-        Action<string> onTypeInvalid = null,
-        Action<Exception> onUnhandledError = null)
+        Action<string>? onTypeInvalid = null,
+        Action<Exception>? onUnhandledError = null)
     {
         _checkTypeValidity = checkTypeValidity;
         _onTypeInvalid = onTypeInvalid;
@@ -34,7 +34,7 @@ internal class XamlXViewResolver : IViewResolver, IXamlAstVisitor
         _compiler = compiler;
     }
 
-    public ResolvedView ResolveView(string xaml)
+    public ResolvedView? ResolveView(string xaml)
     {
         try
         {
@@ -86,7 +86,7 @@ internal class XamlXViewResolver : IViewResolver, IXamlAstVisitor
                 var nameSpace = string.Join(".", split.Take(split.Length - 1));
                 var className = split.Last();
 
-                _resolvedClass = new ResolvedView(className, clrType, nameSpace, _xaml);
+                _resolvedClass = new ResolvedView(className, clrType, nameSpace, _xaml!);
                 return node;
             }
         }

src/tools/Avalonia.Generators/Compiler/RoslynTypeSystem.cs

@@ -28,18 +28,18 @@ internal class RoslynTypeSystem : IXamlTypeSystem
 
     public IEnumerable<IXamlAssembly> Assemblies => _assemblies;
 
-    public IXamlAssembly FindAssembly(string name) =>
+    public IXamlAssembly? FindAssembly(string name) =>
         Assemblies
             .FirstOrDefault(a => string.Equals(a.Name, name, StringComparison.OrdinalIgnoreCase));
 
     [UnconditionalSuppressMessage("Trimming", "IL2092", Justification = TrimmingMessages.Roslyn)]
-    public IXamlType FindType(string name) =>
+    public IXamlType? FindType(string name) =>
         _assemblies
             .Select(assembly => assembly.FindType(name))
             .FirstOrDefault(type => type != null);
 
     [UnconditionalSuppressMessage("Trimming", "IL2092", Justification = TrimmingMessages.Roslyn)]
-    public IXamlType FindType(string name, string assembly) =>
+    public IXamlType? FindType(string name, string assembly) =>
         _assemblies
             .Select(assemblyInstance => assemblyInstance.FindType(name))
             .FirstOrDefault(type => type != null);
@@ -62,7 +62,7 @@ internal class RoslynAssembly : IXamlAssembly
             .Select(data => new RoslynAttribute(data, this))
             .ToList();
 
-    public IXamlType FindType(string fullName)
+    public IXamlType? FindType(string fullName)
     {
         var type = _symbol.GetTypeByMetadataName(fullName);
         return type is null ? null : new RoslynType(type, this);
@@ -84,14 +84,14 @@ internal class RoslynAttribute : IXamlCustomAttribute
         other is RoslynAttribute attribute &&
         _data == attribute._data;
 
-    public IXamlType Type => new RoslynType(_data.AttributeClass, _assembly);
+    public IXamlType Type => new RoslynType(_data.AttributeClass!, _assembly);
 
-    public List<object> Parameters =>
+    public List<object?> Parameters =>
         _data.ConstructorArguments
             .Select(argument => argument.Value)
             .ToList();
 
-    public Dictionary<string, object> Properties =>
+    public Dictionary<string, object?> Properties =>
         _data.NamedArguments.ToDictionary(
             pair => pair.Key,
             pair => pair.Value.Value);
@@ -132,7 +132,7 @@ internal class RoslynType : IXamlType
 
     public bool IsNestedPrivate => _symbol.DeclaredAccessibility == Accessibility.Private;
 
-    public IXamlType DeclaringType =>
+    public IXamlType? DeclaringType =>
         _symbol.ContainingType is { } containingType ? new RoslynType(containingType, _assembly) : null;
 
     public IReadOnlyList<IXamlProperty> Properties =>
@@ -142,18 +142,18 @@ internal class RoslynType : IXamlType
             .Select(property => new RoslynProperty(property, _assembly))
             .ToList();
 
-    public IReadOnlyList<IXamlEventInfo> Events { get; } = new List<IXamlEventInfo>();
+    public IReadOnlyList<IXamlEventInfo> Events => [];
         
-    public IReadOnlyList<IXamlField> Fields { get; } = new List<IXamlField>();
+    public IReadOnlyList<IXamlField> Fields => [];
         
-    public IReadOnlyList<IXamlMethod> Methods { get; } = new List<IXamlMethod>();
+    public IReadOnlyList<IXamlMethod> Methods => [];
 
     public IReadOnlyList<IXamlConstructor> Constructors =>
         _symbol.Constructors
             .Select(method => new RoslynConstructor(method, _assembly))
             .ToList();
 
-    public IReadOnlyList<IXamlCustomAttribute> CustomAttributes { get; } = Array.Empty<IXamlCustomAttribute>();
+    public IReadOnlyList<IXamlCustomAttribute> CustomAttributes => [];
 
     public IReadOnlyList<IXamlType> GenericArguments { get; private set; } = new List<IXamlType>();
 
@@ -169,15 +169,15 @@ internal class RoslynType : IXamlType
         
     public bool IsArray => false;
 
-    public IXamlType ArrayElementType { get; } = null;
+    public IXamlType? ArrayElementType => null;
         
-    public IXamlType MakeArrayType(int dimensions) => null;
+    public IXamlType MakeArrayType(int dimensions) => throw new NotSupportedException();
 
-    public IXamlType BaseType => _symbol.BaseType == null ? null : new RoslynType(_symbol.BaseType, _assembly);
+    public IXamlType? BaseType => _symbol.BaseType is { } baseType ? new RoslynType(baseType, _assembly) : null;
 
-    public bool IsValueType { get; } = false;
+    public bool IsValueType => false;
 
-    public bool IsEnum { get; } = false;
+    public bool IsEnum => false;
 
     public IReadOnlyList<IXamlType> Interfaces =>
         _symbol.AllInterfaces
@@ -186,9 +186,9 @@ internal class RoslynType : IXamlType
 
     public bool IsInterface => _symbol.IsAbstract;
         
-    public IXamlType GetEnumUnderlyingType() => null;
+    public IXamlType GetEnumUnderlyingType() => throw new NotSupportedException();
 
-    public IReadOnlyList<IXamlType> GenericParameters { get; } = new List<IXamlType>();
+    public IReadOnlyList<IXamlType> GenericParameters => [];
 
     public bool IsFunctionPointer => false;
 }
@@ -217,6 +217,10 @@ internal class RoslynConstructor : IXamlConstructor
             .Select(parameter => new RoslynParameter(_assembly, parameter).ParameterType)
             .ToList();
 
+    public string Name => _symbol.Name;
+
+    public IXamlType DeclaringType => new RoslynType(_symbol.ContainingType, _assembly);
+
     public IXamlParameterInfo GetParameterInfo(int index) => new RoslynParameter(_assembly, _symbol.Parameters[index]);
 }
 
@@ -237,18 +241,20 @@ internal class RoslynProperty : IXamlProperty
 
     public string Name => _symbol.Name;
 
+    public IXamlType DeclaringType => new RoslynType(_symbol.ContainingType, _assembly);
+
     public IXamlType PropertyType =>
         _symbol.Type is INamedTypeSymbol namedTypeSymbol
             ? new RoslynType(namedTypeSymbol, _assembly)
-            : null;
+            : XamlPseudoType.Unknown;
 
-    public IXamlMethod Getter => _symbol.GetMethod == null ? null : new RoslynMethod(_symbol.GetMethod, _assembly);
+    public IXamlMethod? Getter => _symbol.GetMethod == null ? null : new RoslynMethod(_symbol.GetMethod, _assembly);
         
-    public IXamlMethod Setter => _symbol.SetMethod == null ? null : new RoslynMethod(_symbol.SetMethod, _assembly); 
+    public IXamlMethod? Setter => _symbol.SetMethod == null ? null : new RoslynMethod(_symbol.SetMethod, _assembly);
 
-    public IReadOnlyList<IXamlCustomAttribute> CustomAttributes { get; } = Array.Empty<IXamlCustomAttribute>();
+    public IReadOnlyList<IXamlCustomAttribute> CustomAttributes => [];
 
-    public IReadOnlyList<IXamlType> IndexerParameters { get; } = new List<IXamlType>();
+    public IReadOnlyList<IXamlType> IndexerParameters => [];
 }
 
 internal class RoslynParameter : IXamlParameterInfo
@@ -298,10 +304,11 @@ internal class RoslynMethod : IXamlMethod
         _symbol.Parameters.Select(parameter => new RoslynParameter(_assembly, parameter).ParameterType)
             .ToList();
 
-    public IXamlType DeclaringType => new RoslynType((INamedTypeSymbol)_symbol.ReceiverType, _assembly);
-        
-    public IXamlMethod MakeGenericMethod(IReadOnlyList<IXamlType> typeArguments) => null;
+    public IXamlType DeclaringType => new RoslynType(_symbol.ContainingType, _assembly);
+
+    public IXamlMethod MakeGenericMethod(IReadOnlyList<IXamlType> typeArguments) => throw new NotSupportedException();
+
+    public IReadOnlyList<IXamlCustomAttribute> CustomAttributes => [];
 
-    public IReadOnlyList<IXamlCustomAttribute> CustomAttributes { get; } = Array.Empty<IXamlCustomAttribute>();
     public IXamlParameterInfo GetParameterInfo(int index) => new RoslynParameter(_assembly, _symbol.Parameters[index]);
 }

src/tools/Avalonia.Generators/GeneratorContextExtensions.cs

@@ -29,7 +29,7 @@ internal static class GeneratorContextExtensions
             $"Avalonia x:Name generator was unable to generate names for type '{typeName}'. " +
             $"The type '{typeName}' does not exist in the assembly.");
 
-    private static void Report(this GeneratorExecutionContext context, string id, string title, string message = null, string description = null) =>
+    private static void Report(this GeneratorExecutionContext context, string id, string title, string? message = null, string? description = null) =>
         context.ReportDiagnostic(
             Diagnostic.Create(
                 new DiagnosticDescriptor(

src/tools/Avalonia.Generators/NameGenerator/AvaloniaNameSourceGenerator.cs

@@ -57,7 +57,7 @@ public class AvaloniaNameSourceGenerator : ISourceGenerator
                 && sourceItemGroup == "AvaloniaXaml");
     }
 
-    private static INameGenerator CreateNameGenerator(GeneratorExecutionContext context)
+    private static INameGenerator? CreateNameGenerator(GeneratorExecutionContext context)
     {
         var options = new GeneratorOptions(context);
         if (!options.AvaloniaNameGeneratorIsEnabled)

tests/Avalonia.Generators.Tests/InitializeComponent/InitializeComponentTests.cs

@@ -44,11 +44,12 @@ public class InitializeComponentTests
 
         var xaml = await View.Load(markup);
         var classInfo = classResolver.ResolveView(xaml);
+        Assert.NotNull(classInfo);
         var nameResolver = new XamlXNameResolver();
         var names = nameResolver.ResolveNames(classInfo.Xaml);
 
         var generator = new InitializeComponentCodeGenerator(types, devToolsMode);
-        var generatorVersion = typeof(InitializeComponentCodeGenerator).Assembly.GetName().Version.ToString();
+        var generatorVersion = typeof(InitializeComponentCodeGenerator).Assembly.GetName().Version?.ToString();
 
         var code = generator
             .GenerateCode("SampleView", "Sample.App",  classInfo.XamlType, names)

tests/Avalonia.Generators.Tests/OnlyProperties/OnlyPropertiesTests.cs

@@ -37,11 +37,12 @@ public class OnlyPropertiesTests
 
         var xaml = await View.Load(markup);
         var classInfo = classResolver.ResolveView(xaml);
+        Assert.NotNull(classInfo);
         var nameResolver = new XamlXNameResolver();
         var names = nameResolver.ResolveNames(classInfo.Xaml);
 
         var generator = new OnlyPropertiesCodeGenerator();
-        var generatorVersion = typeof(OnlyPropertiesCodeGenerator).Assembly.GetName().Version.ToString();
+        var generatorVersion = typeof(OnlyPropertiesCodeGenerator).Assembly.GetName().Version?.ToString();
 
         var code = generator
             .GenerateCode("SampleView", "Sample.App",  classInfo.XamlType, names)

tests/Avalonia.Generators.Tests/XamlXClassResolverTests.cs

@@ -34,6 +34,7 @@ public class XamlXClassResolverTests
             MiniCompiler.CreateDefault(types, MiniCompiler.AvaloniaXmlnsDefinitionAttribute));
 
         var resolvedClass = resolver.ResolveView(xaml);
+        Assert.NotNull(resolvedClass);
         Assert.Equal(className, resolvedClass.ClassName);
         Assert.Equal(nameSpace, resolvedClass.Namespace);
     }

tests/Avalonia.Generators.Tests/XamlXNameResolverTests.cs

@@ -135,6 +135,7 @@ public class XamlXNameResolverTests
                 MiniCompiler.AvaloniaXmlnsDefinitionAttribute));
 
         var classInfo = classResolver.ResolveView(xaml);
+        Assert.NotNull(classInfo);
         var nameResolver = new XamlXNameResolver();
         return nameResolver.ResolveNames(classInfo.Xaml);
     }