Doesn't work:

* plugin loading in App.xaml.cs (#if NET472)
* OSVersionHelper bombs with PlatformNotSupportedException (#if NET472)
* ILSpyTraceListener - this needs something different in net5

ILSpy.BamlDecompiler/ILSpy.BamlDecompiler.csproj

@@ -3,7 +3,7 @@
   <Import Sdk="Microsoft.NET.Sdk" Project="Sdk.props" />
 
   <PropertyGroup>
-    <TargetFramework>net472</TargetFramework>
+    <TargetFrameworks>net472;net5.0-windows</TargetFrameworks>
     <AssemblyName>ILSpy.BamlDecompiler.Plugin</AssemblyName>
     <LangVersion>8.0</LangVersion>
 

ILSpy.ReadyToRun/ILSpy.ReadyToRun.csproj

@@ -2,7 +2,7 @@
 <Project Sdk="MSBuild.Sdk.Extras">
 
   <PropertyGroup>
-    <TargetFramework>net472</TargetFramework>
+    <TargetFrameworks>net472;net5.0-windows</TargetFrameworks>
     <AssemblyName>ILSpy.ReadyToRun.Plugin</AssemblyName>
     <LangVersion>8.0</LangVersion>
 

ILSpy.Tests/ILSpy.Tests.csproj

@@ -2,7 +2,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFramework>net472</TargetFramework>
+    <TargetFrameworks>net472;net5.0-windows</TargetFrameworks>
     <LangVersion>8.0</LangVersion>
 
     <AllowUnsafeBlocks>True</AllowUnsafeBlocks>

ILSpy/AboutPage.cs

@@ -62,7 +62,11 @@ namespace ICSharpCode.ILSpy
 				EnableHyperlinks = true
 			};
 			output.WriteLine(Resources.ILSpyVersion + RevisionClass.FullVersion);
-			if (WindowsVersionHelper.HasPackageIdentity)
+			bool hasPackageIdentity = false;
+#if NET472
+			hasPackageIdentity = WindowsVersionHelper.HasPackageIdentity;
+#endif
+			if (hasPackageIdentity)
 			{
 				output.WriteLine($"Package Name: {WindowsVersionHelper.GetPackageFamilyName()}");
 			}

ILSpy/Analyzers/AnalyzerScope.cs

@@ -23,11 +23,12 @@ using System.Threading;
 
 using ICSharpCode.Decompiler;
 using ICSharpCode.Decompiler.Metadata;
-using ICSharpCode.Decompiler.TypeSystem;
 using ICSharpCode.Decompiler.Util;
 
 namespace ICSharpCode.ILSpy.Analyzers
 {
+	using ICSharpCode.Decompiler.TypeSystem;
+
 	public class AnalyzerScope
 	{
 		readonly ITypeDefinition typeScope;

ILSpy/Analyzers/Builtin/TypeExposedByAnalyzer.cs

@@ -24,10 +24,11 @@ using System.Linq;
 using System.Text;
 using System.Threading.Tasks;
 
-using ICSharpCode.Decompiler.TypeSystem;
 
 namespace ICSharpCode.ILSpy.Analyzers.Builtin
 {
+	using ICSharpCode.Decompiler.TypeSystem;
+
 	/// <summary>
 	/// Finds all entities that expose a type.
 	/// </summary>

ILSpy/Analyzers/TreeNodes/AnalyzedEventTreeNode.cs

@@ -19,11 +19,12 @@
 using System;
 using System.Linq;
 
-using ICSharpCode.Decompiler.TypeSystem;
 using ICSharpCode.ILSpy.TreeNodes;
 
 namespace ICSharpCode.ILSpy.Analyzers.TreeNodes
 {
+	using ICSharpCode.Decompiler.TypeSystem;
+
 	internal sealed class AnalyzedEventTreeNode : AnalyzerEntityTreeNode
 	{
 		readonly IEvent analyzedEvent;

ILSpy/App.xaml.cs

@@ -94,6 +94,7 @@ namespace ICSharpCode.ILSpy
 				var discovery = new AttributedPartDiscoveryV1(Resolver.DefaultInstance);
 				var catalog = ComposableCatalog.Create(Resolver.DefaultInstance);
 				var pluginDir = Path.GetDirectoryName(typeof(App).Module.FullyQualifiedName);
+#if NET472
 				if (pluginDir != null)
 				{
 					foreach (var plugin in Directory.GetFiles(pluginDir, "*.Plugin.dll"))
@@ -111,6 +112,7 @@ namespace ICSharpCode.ILSpy
 						}
 					}
 				}
+#endif
 				// Add the built-in parts
 				var createdParts = await discovery.CreatePartsAsync(Assembly.GetExecutingAssembly());
 				catalog = catalog.AddParts(createdParts);

ILSpy/Commands/CheckForUpdatesCommand.cs

@@ -28,11 +28,12 @@ namespace ICSharpCode.ILSpy
 	{
 		public override bool CanExecute(object parameter)
 		{
+#if NET472
 			if (WindowsVersionHelper.HasPackageIdentity)
 			{
 				return false;
 			}
-
+#endif
 			return base.CanExecute(parameter);
 		}
 

ILSpy/Commands/SearchMsdnContextMenuEntry.cs

@@ -19,11 +19,12 @@
 using System.Linq;
 using System.Threading;
 
-using ICSharpCode.Decompiler.TypeSystem;
 using ICSharpCode.ILSpy.Properties;
 using ICSharpCode.ILSpy.TreeNodes;
 namespace ICSharpCode.ILSpy
 {
+	using ICSharpCode.Decompiler.TypeSystem;
+
 	[ExportContextMenuEntry(Header = nameof(Resources.SearchMSDN), Icon = "images/SearchMsdn", Order = 9999)]
 	internal sealed class SearchMsdnContextMenuEntry : IContextMenuEntry
 	{

ILSpy/ILSpy.csproj

@@ -2,7 +2,7 @@
 <Project Sdk="MSBuild.Sdk.Extras">
 
   <PropertyGroup>
-    <TargetFramework>net472</TargetFramework>
+    <TargetFrameworks>net472;net5.0-windows</TargetFrameworks>
     <OutputType>WinExe</OutputType>
     <LangVersion>9.0</LangVersion>
     <GenerateAssemblyInfo>False</GenerateAssemblyInfo>

ILSpy/ILSpyTraceListener.cs

@@ -31,8 +31,10 @@ namespace ICSharpCode.ILSpy
 		[Conditional("DEBUG")]
 		public static void Install()
 		{
+#if NET472
 			Debug.Listeners.Clear();
 			Debug.Listeners.Add(new ILSpyTraceListener());
+#endif
 		}
 
 		public ILSpyTraceListener()

ILSpy/MainWindow.xaml.cs

@@ -678,12 +678,13 @@ namespace ICSharpCode.ILSpy
 
 		public async Task ShowMessageIfUpdatesAvailableAsync(ILSpySettings spySettings, bool forceCheck = false)
 		{
+#if NET472
 			// Don't check for updates if we're in an MSIX since they work differently
 			if (WindowsVersionHelper.HasPackageIdentity)
 			{
 				return;
 			}
-
+#endif
 			string downloadUrl;
 			if (forceCheck)
 			{

ILSpy/Search/AbstractEntitySearchStrategy.cs

@@ -5,11 +5,12 @@ using System.Threading;
 using System.Windows.Media;
 
 using ICSharpCode.Decompiler.Metadata;
-using ICSharpCode.Decompiler.TypeSystem;
 using ICSharpCode.ILSpy.TreeNodes;
 
 namespace ICSharpCode.ILSpy.Search
 {
+	using ICSharpCode.Decompiler.TypeSystem;
+
 	abstract class AbstractEntitySearchStrategy : AbstractSearchStrategy
 	{
 		protected readonly Language language;

ILSpy/TreeNodes/DerivedTypesEntryNode.cs

@@ -21,10 +21,11 @@ using System.Linq;
 using System.Threading;
 
 using ICSharpCode.Decompiler;
-using ICSharpCode.Decompiler.TypeSystem;
 
 namespace ICSharpCode.ILSpy.TreeNodes
 {
+	using ICSharpCode.Decompiler.TypeSystem;
+
 	class DerivedTypesEntryNode : ILSpyTreeNode, IMemberTreeNode
 	{
 		readonly AssemblyList list;

ILSpy/TreeNodes/EventTreeNode.cs

@@ -20,10 +20,11 @@ using System;
 using System.Windows.Media;
 
 using ICSharpCode.Decompiler;
-using ICSharpCode.Decompiler.TypeSystem;
 
 namespace ICSharpCode.ILSpy.TreeNodes
 {
+	using ICSharpCode.Decompiler.TypeSystem;
+
 	/// <summary>
 	/// Represents an event in the TreeView.
 	/// </summary>

ILSpy/TreeNodes/FieldTreeNode.cs

@@ -20,10 +20,11 @@ using System;
 using System.Windows.Media;
 
 using ICSharpCode.Decompiler;
-using ICSharpCode.Decompiler.TypeSystem;
 
 namespace ICSharpCode.ILSpy.TreeNodes
 {
+	using ICSharpCode.Decompiler.TypeSystem;
+
 	/// <summary>
 	/// Represents a field in the TreeView.
 	/// </summary>

ILSpy/TreeNodes/MethodTreeNode.cs

@@ -20,10 +20,11 @@ using System;
 using System.Windows.Media;
 
 using ICSharpCode.Decompiler;
-using ICSharpCode.Decompiler.TypeSystem;
 
 namespace ICSharpCode.ILSpy.TreeNodes
 {
+	using ICSharpCode.Decompiler.TypeSystem;
+
 	/// <summary>
 	/// Tree Node representing a field, method, property, or event.
 	/// </summary>

ILSpy/TreeNodes/PropertyTreeNode.cs

@@ -23,12 +23,13 @@ using System.Windows.Media;
 
 using ICSharpCode.Decompiler;
 using ICSharpCode.Decompiler.Metadata;
-using ICSharpCode.Decompiler.TypeSystem;
 
 using SRM = System.Reflection.Metadata;
 
 namespace ICSharpCode.ILSpy.TreeNodes
 {
+	using ICSharpCode.Decompiler.TypeSystem;
+
 	/// <summary>
 	/// Represents a property in the TreeView.
 	/// </summary>

ILSpy/TreeNodes/TypeTreeNode.cs

@@ -22,12 +22,12 @@ using System.Reflection;
 using System.Windows.Media;
 
 using ICSharpCode.Decompiler;
-using ICSharpCode.Decompiler.TypeSystem;
 
 using SRM = System.Reflection.Metadata;
 
 namespace ICSharpCode.ILSpy.TreeNodes
 {
+	using ICSharpCode.Decompiler.TypeSystem;
 	public sealed class TypeTreeNode : ILSpyTreeNode, IMemberTreeNode
 	{
 		public TypeTreeNode(ITypeDefinition typeDefinition, AssemblyTreeNode parentAssemblyNode)

SharpTreeView/ICSharpCode.TreeView.csproj

@@ -2,7 +2,7 @@
 <Project Sdk="MSBuild.Sdk.Extras">
 
   <PropertyGroup>
-    <TargetFramework>net472</TargetFramework>
+    <TargetFrameworks>net472;net5.0-windows</TargetFrameworks>
 
     <GenerateAssemblyInfo>False</GenerateAssemblyInfo>
 

TestPlugin/TestPlugin.csproj

@@ -2,7 +2,7 @@
 <Project Sdk="MSBuild.Sdk.Extras">
 
   <PropertyGroup>
-    <TargetFramework>net472</TargetFramework>
+    <TargetFrameworks>net472;net5.0-windows</TargetFrameworks>
     <AssemblyName>Test.Plugin</AssemblyName>
 
     <GenerateAssemblyInfo>False</GenerateAssemblyInfo>

global.json

@@ -1,9 +1,9 @@
 {
 	"msbuild-sdks": {
-		"MSBuild.Sdk.Extras": "2.0.54"
+		"MSBuild.Sdk.Extras": "3.0.23"
 	},
 	"sdk": {
-		"version": "3.1.100",
+		"version": "5.0.100",
 		"rollForward": "latestFeature"
 	}
 }