Implement stub .exe support for apps + WinRT components

.gitignore

@@ -4,6 +4,7 @@
 *_i.c
 *_p.c
 *.c
+!nuget/sources/*.c
 *.winmd
 *test*.xml
 obj

nuget/Microsoft.Windows.CsWinRT.BeforeMicrosoftNetSdk.targets

@@ -0,0 +1,27 @@
+<!--
+***********************************************************************************************
+Copyright (C) Microsoft Corporation. All rights reserved.
+***********************************************************************************************
+-->
+<Project ToolsVersion="14.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
+
+  <PropertyGroup>
+
+    <!-- We need to set the final value of this property here, as if that's set, we need to do additional work before the .NET SDK .targets -->
+    <CsWinRTMergeReferencedActivationFactories Condition="'$(CsWinRTMergeReferencedActivationFactories)' == ''">false</CsWinRTMergeReferencedActivationFactories>
+  </PropertyGroup>
+
+  <!--
+    If we need to merge activation factories and the project is an executable, we need to emit a stub .exe,
+    so in order to do that we need to tell the .NET SDK to export a custom main, and compile to a .dll instead.
+    These two properties have to be set before the Native AOT toolchain runs, that's why it's done from here.
+  -->
+  <PropertyGroup Condition="'$(CsWinRTMergeReferencedActivationFactories)' == 'true' AND ('$(OutputType)' == 'Exe' OR '$(OutputType)' == 'WinExe')">
+    <NativeLib>Shared</NativeLib>
+    <CustomNativeMain>true</CustomNativeMain>
+
+    <!-- Activate our custom target to produce the stub .exe after the publish step -->
+    <_CsWinRTEnableStubExeGeneration>true</_CsWinRTEnableStubExeGeneration>
+  </PropertyGroup>
+
+</Project>

nuget/Microsoft.Windows.CsWinRT.nuspec

@@ -22,6 +22,7 @@
     <file src="NOTICE.txt"/>
     <file src="$cswinrt_exe$"/>
     <file src="Microsoft.Windows.CsWinRT.props" target="build"/>
+    <file src="Microsoft.Windows.CsWinRT.BeforeMicrosoftNetSdk.targets" target="build"/>
     <file src="Microsoft.Windows.CsWinRT.targets" target="build"/>
     <file src="Microsoft.Windows.CsWinRT.Authoring.targets" target="build"/>
     <file src="Microsoft.Windows.CsWinRT.Embedded.targets" target="build"/>
@@ -68,6 +69,8 @@
 
     <file src="..\src\WinRT.Runtime\Configuration\*.cs" exclude="..\src\WinRT.Runtime\Configuration\*.net*.cs"  target="embedded\any\" />
 
-    <file src="$guid_patch$" target ="build\tools\IIDOptimizer"/>
+    <file src="sources\StubExe.c" target="build\sources"/>
+
+    <file src="$guid_patch$" target="build\tools\IIDOptimizer"/>
   </files>
 </package>

nuget/Microsoft.Windows.CsWinRT.props

@@ -8,6 +8,9 @@ Copyright (C) Microsoft Corporation. All rights reserved.
   <PropertyGroup>
     <CsWinRTPath Condition="'$(CsWinRTPath)'==''">$([MSBuild]::NormalizeDirectory('$(MSBuildThisFileDirectory)', '..'))</CsWinRTPath>
     <CsWinRTExe>$(CsWinRTPath)cswinrt.exe</CsWinRTExe>
+
+    <!-- Wire up the .targets that should be imported before the .NET SDK -->
+    <BeforeMicrosoftNETSdkTargets>$(BeforeMicrosoftNETSdkTargets);$(MSBuildThisFileDirectory)Microsoft.Windows.CsWinRT.BeforeMicrosoftNetSdk.targets</BeforeMicrosoftNETSdkTargets>
   </PropertyGroup>
 
 </Project>

nuget/readme.md

@@ -50,6 +50,7 @@ C#/WinRT behavior can be customized with these project properties:
 | CsWinRTMergeReferencedActivationFactories | true \| *false | Makes the native `DllGetActivationFactory` exported function for AOT scenarios also forward the activation call to all referenced WinRT components, allowing them to all be merged into a single executable or shared library |
 | CsWinRTEnableManifestFreeActivation | *true \| false | Enables the manifest-free WinRT activation path as fallback when `RoGetActivationFactory` fails to resolve a WinRT type |
 | CsWinRTManifestFreeActivationReportOriginalException | true \| *false | If 'CsWinRTEnableManifestFreeActivation' is set and activating a type fails, ensures the original exception is thrown, rather than 'NotSupportedException' |
+| CsWinRTUseEnvironmentalTools | *true \| false | Makes the invocation of MSVC to produce a stub .exe (for Native AOT scenarios) rely on environmental tools, rather than looking up the MSVC install path. This is enabled by default when running in a Visual Studio Developer Command Prompt (or PowerShell), and false otherwise. |
 | CsWinRTAotWarningLevel | 0 \| *1 \| 2 | Specifies the warning level used by the code fixer for trimming and AOT compat (0 - no warnings, 1 - warnings for scenarios involving non built-in types, 2 - warnings for all scenarios) |
 \*Default value
 

nuget/sources/StubExe.c

@@ -0,0 +1,13 @@
+#include <wchar.h>
+
+// Declare the import for '__managed__Main', which is a special export produced by the
+// Native AOT runtime to allow jumping into the real 'Main' of an application. This is
+// exported automatically when the 'CustomNativeMain' property is set to 'true'.
+__declspec(dllimport)
+int __stdcall __managed__Main(int argc, wchar_t** argv);
+
+// Our entry point is simply a direct jump into the entry point from Native AOT
+int wmain(int argc, wchar_t** argv)
+{
+    return __managed__Main(argc, argv);
+}

src/Authoring/WinRT.SourceGenerator/Generator.cs

@@ -271,13 +271,16 @@ public static int DllGetActivationFactory(void* activatableClassId, void** facto
 
                 """);
 
-            // There's three possible cases for this method:
+            // There's four possible cases for this method:
             //   1a) The project is a standalone WinRT component
             //   1b) The project is a WinRT component, and we're chaining other WinRT components
             //   2)  The project is an app/library, but we also want to chain other WinRT components
+            //   4)  There's no possible types to activate (ie. no authored ones, no dependent ones)
             if (context.IsCsWinRTComponent())
             {
-                builder.AppendLine("IntPtr obj = GetActivationFactory(fullyQualifiedTypeName);");
+                builder.AppendLine("""
+                                    IntPtr obj = GetActivationFactory(fullyQualifiedTypeName);
+                    """);
                 builder.AppendLine();
 
                 // Only emit this call if we have actually generated that. We want to avoid generating
@@ -295,7 +298,18 @@ public static int DllGetActivationFactory(void* activatableClassId, void** facto
             }
             else if (ShouldEmitCallToTryGetDependentActivationFactory(context))
             {
-                builder.AppendLine("IntPtr obj = TryGetDependentActivationFactory(fullyQualifiedTypeName);");
+                builder.AppendLine("""
+                                   IntPtr obj = TryGetDependentActivationFactory(fullyQualifiedTypeName);
+                    """);
+                builder.AppendLine();
+            }
+            else
+            {
+                // This ensures we don't get build errors if someone sets 'CsWinRTMergeReferencedActivationFactories'
+                // but there's no referenced activation factories defined yet (ie. no WinRT components referenced).
+                builder.AppendLine("""
+                                   IntPtr obj = IntPtr.Zero;
+                    """);
                 builder.AppendLine();
             }