Fix Application.EnableVisualStyles in single file publishing mode

src/System.Windows.Forms.Primitives/src/Interop/Kernel32/Interop.ACTCTXW.cs

@@ -1,4 +1,4 @@
-// Licensed to the .NET Foundation under one or more agreements.
+// 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.
 
@@ -9,6 +9,7 @@ internal partial class Interop
 {
     internal partial class Kernel32
     {
+        [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Unicode)]
         public unsafe struct ACTCTXW
         {
             public uint cbSize;
@@ -19,6 +20,7 @@ public unsafe struct ACTCTXW
             public char* lpAssemblyDirectory;
             public IntPtr lpResourceName;
             public char* lpApplicationName;
+            public IntPtr hModule;
         }
     }
 }

src/System.Windows.Forms.Primitives/src/Interop/Kernel32/Interop.ACTCTX_FLAG.cs

@@ -1,4 +1,4 @@
-// Licensed to the .NET Foundation under one or more agreements.
+// 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.
 
@@ -11,14 +11,14 @@ internal partial class Kernel32
         [Flags]
         public enum ACTCTX_FLAG : uint
         {
-            PROCESSOR_ARCHITECTURE_VALID = 0x00000001,
-            LANGID_VALID = 0x00000002,
-            ASSEMBLY_DIRECTORY_VALID = 0x00000004,
-            RESOURCE_NAME_VALID = 0x00000008,
-            SET_PROCESS_DEFAULT = 0x00000010,
-            APPLICATION_NAME_VALID = 0x00000020,
-            SOURCE_IS_ASSEMBLYREF = 0x00000040,
-            HMODULE_VALID = 0x00000080,
+            PROCESSOR_ARCHITECTURE_VALID    = 0x00000001,
+            LANGID_VALID                    = 0x00000002,
+            ASSEMBLY_DIRECTORY_VALID        = 0x00000004,
+            RESOURCE_NAME_VALID             = 0x00000008,
+            SET_PROCESS_DEFAULT             = 0x00000010,
+            APPLICATION_NAME_VALID          = 0x00000020,
+            SOURCE_IS_ASSEMBLYREF           = 0x00000040,
+            HMODULE_VALID                   = 0x00000080,
         }
     }
 }

src/System.Windows.Forms.Primitives/src/System/Windows/Forms/Internals/ThemingScope.cs

@@ -2,7 +2,7 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
-using System.Runtime.InteropServices;
+using System.IO;
 using static Interop;
 
 namespace System.Windows.Forms
@@ -59,25 +59,68 @@ public static IntPtr Deactivate(IntPtr userCookie)
             return userCookie;
         }
 
-        public unsafe static bool CreateActivationContext(string dllPath, int nativeResourceManifestID)
+        public unsafe static bool CreateActivationContext(IntPtr module, int nativeResourceManifestID)
         {
             lock (typeof(ThemingScope))
             {
                 if (!s_contextCreationSucceeded)
                 {
-                    fixed (char* pDllPath = dllPath)
+                    s_enableThemingActivationContext = new Kernel32.ACTCTXW
+                    {
+                        cbSize = (uint)sizeof(Kernel32.ACTCTXW),
+                        lpResourceName = (IntPtr)nativeResourceManifestID,
+                        dwFlags = Kernel32.ACTCTX_FLAG.HMODULE_VALID | Kernel32.ACTCTX_FLAG.RESOURCE_NAME_VALID,
+                        hModule = module
+                    };
+
+                    s_hActCtx = Kernel32.CreateActCtxW(ref s_enableThemingActivationContext);
+
+                    s_contextCreationSucceeded = (s_hActCtx != new IntPtr(-1));
+                }
+
+                return s_contextCreationSucceeded;
+            }
+        }
+
+        public unsafe static bool CreateActivationContext(Stream manifest)
+        {
+            lock (typeof(ThemingScope))
+            {
+                if (!s_contextCreationSucceeded)
+                {
+                    string tempFilePath = Path.Join(Path.GetTempPath(), Path.GetRandomFileName());
+                    using FileStream tempFileStream = new FileStream(
+                        tempFilePath,
+                        FileMode.CreateNew,
+                        FileAccess.ReadWrite,
+                        FileShare.Delete | FileShare.ReadWrite);
+
+                    manifest.CopyTo(tempFileStream);
+
+                    // CreateActCtxW gives a sharing violation if we have the handle open
+                    tempFileStream.Close();
+
+                    fixed (char* p = tempFilePath)
                     {
                         s_enableThemingActivationContext = new Kernel32.ACTCTXW
                         {
-                            cbSize = (uint)Marshal.SizeOf<Kernel32.ACTCTXW>(),
-                            lpSource = pDllPath,
-                            lpResourceName = (IntPtr)nativeResourceManifestID,
-                            dwFlags = Kernel32.ACTCTX_FLAG.RESOURCE_NAME_VALID
+                            cbSize = (uint)sizeof(Kernel32.ACTCTXW),
+                            lpSource = p
                         };
 
                         s_hActCtx = Kernel32.CreateActCtxW(ref s_enableThemingActivationContext);
                     }
+
                     s_contextCreationSucceeded = (s_hActCtx != new IntPtr(-1));
+
+                    try
+                    {
+                        File.Delete(tempFilePath);
+                    }
+                    catch (Exception e) when (e is UnauthorizedAccessException or IOException)
+                    {
+                        // Don't want to take down WinForms if we can't delete is file
+                    }
                 }
 
                 return s_contextCreationSucceeded;

src/System.Windows.Forms/src/System.Windows.Forms.csproj

@@ -1,4 +1,4 @@
-<Project Sdk="Microsoft.NET.Sdk">
+<Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
     <AssemblyName>System.Windows.Forms</AssemblyName>
@@ -13,6 +13,10 @@
     <UsePublicApiAnalyzers>true</UsePublicApiAnalyzers>
   </PropertyGroup>
 
+  <ItemGroup>
+    <None Remove="Resources\System\Windows\Forms\XPThemes.manifest" />
+  </ItemGroup>
+
   <ItemGroup>
     <ProjectReference Include="..\..\System.Windows.Forms.SourceGenerators\src\System.Windows.Forms.SourceGenerators.csproj" 
                       ReferenceOutputAssembly="false"
@@ -634,6 +638,9 @@
     <EmbeddedResource Include="Resources\System\Windows\Forms\ToolStrip\BlankToolstrip.ico">
       <LogicalName>System.Windows.Forms.blank</LogicalName>
     </EmbeddedResource>
+    <EmbeddedResource Include="Resources\System\Windows\Forms\XPThemes.manifest">
+      <LogicalName>System.Windows.Forms.XPThemes.manifest</LogicalName>
+    </EmbeddedResource>
   </ItemGroup>
 
   <ItemGroup>

src/System.Windows.Forms/src/System/Windows/Forms/Application.cs

@@ -820,15 +820,27 @@ internal static void DoEventsModal()
         public static void EnableVisualStyles()
         {
             // Pull manifest from our resources
-            string assemblyLoc = typeof(Application).Assembly.Location;
-            if (assemblyLoc != null)
-            {
-                // CSC embeds DLL manifests as resource ID 2
-                UseVisualStyles = ThemingScope.CreateActivationContext(assemblyLoc, nativeResourceManifestID: 2);
-                Debug.Assert(UseVisualStyles, "Enable Visual Styles failed");
+            Module module = typeof(Application).Module;
+            IntPtr moduleHandle = Kernel32.GetModuleHandleW(module.Name);
 
-                s_comCtlSupportsVisualStylesInitialized = false;
+            if (moduleHandle != IntPtr.Zero)
+            {
+                // We have a native module, point to our native embedded manifest resource.
+                // CSC embeds DLL manifests as native resource ID 2
+                UseVisualStyles = ThemingScope.CreateActivationContext(moduleHandle, nativeResourceManifestID: 2);
             }
+            else
+            {
+                // We couldn't grab the module handle, likely we're running from a single file package.
+                // Extract the manifest from managed resources.
+                using Stream stream = module.Assembly.GetManifestResourceStream(
+                    "System.Windows.Forms.XPThemes.manifest");
+                UseVisualStyles = ThemingScope.CreateActivationContext(stream);
+            }
+
+            Debug.Assert(UseVisualStyles, "Enable Visual Styles failed");
+
+            s_comCtlSupportsVisualStylesInitialized = false;
         }
 
         /// <summary>

src/System.Windows.Forms/tests/UnitTests/System/Windows/Forms/ApplicationTests.cs

@@ -4,6 +4,7 @@
 
 using System.Collections.Generic;
 using System.Globalization;
+using System.IO;
 using System.Threading;
 using System.Windows.Forms.VisualStyles;
 using Microsoft.DotNet.RemoteExecutor;
@@ -140,6 +141,15 @@ public void Application_VisualStyleState_Set_ReturnsExpected(VisualStyleState va
             }, valueParam.ToString());
         }
 
+        [Fact]
+        public void Application_EnableVisualStyles_ManifestResourceExists()
+        {
+            // Check to make sure the manifest we use for single file publishing is present
+            using Stream stream = typeof(Application).Module.Assembly.GetManifestResourceStream(
+                "System.Windows.Forms.XPThemes.manifest");
+            Assert.NotNull(stream);
+        }
+
         private class CustomLCIDCultureInfo : CultureInfo
         {
             private readonly int _lcid;