Automatically marshal COM outputs as WinRT

.github/workflows/build.yml

@@ -308,9 +308,8 @@ jobs:
         & $msbuild "${{ runner.temp }}\integration-tests\buildtask-sdk\buildtask-sdk.slnx" /r
       shell: pwsh
     - name: 🧪 dotnet publish buildtask-sdk-style
-      run: dotnet publish -r win-x64
+      run: dotnet publish -c Release -r win-x64
       working-directory: ${{ runner.temp }}/integration-tests/buildtask-sdk
-      shell: pwsh
 
   validate:
     name: ✅ Validate

Microsoft.Windows.CsWin32.sln

@@ -60,6 +60,18 @@ Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "GenerationSandbox.BuildTask
 		{DBA19B76-E786-297A-C44F-6121CA5FFCDC} = {DBA19B76-E786-297A-C44F-6121CA5FFCDC}
 	EndProjectSection
 EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "GenerationSandbox.AutoWinRTDisabled.Tests", "test\GenerationSandbox.AutoWinRTDisabled.Tests\GenerationSandbox.AutoWinRTDisabled.Tests.csproj", "{A3AACB6C-0398-4325-B1C7-D9CE72A909DA}"
+	ProjectSection(ProjectDependencies) = postProject
+		{D3363193-DE88-5AFE-BA2D-CAF66280F243} = {D3363193-DE88-5AFE-BA2D-CAF66280F243}
+		{DBA19B76-E786-297A-C44F-6121CA5FFCDC} = {DBA19B76-E786-297A-C44F-6121CA5FFCDC}
+	EndProjectSection
+EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "GenerationSandbox.BuiltInCom.Tests", "test\GenerationSandbox.BuiltInCom.Tests\GenerationSandbox.BuiltInCom.Tests.csproj", "{1D316174-9568-4128-AE4C-B1A01EBA65FE}"
+	ProjectSection(ProjectDependencies) = postProject
+		{D3363193-DE88-5AFE-BA2D-CAF66280F243} = {D3363193-DE88-5AFE-BA2D-CAF66280F243}
+		{DBA19B76-E786-297A-C44F-6121CA5FFCDC} = {DBA19B76-E786-297A-C44F-6121CA5FFCDC}
+	EndProjectSection
+EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
 		Debug|Any CPU = Debug|Any CPU
@@ -162,6 +174,22 @@ Global
 		{A0253377-BC40-63BD-F41A-AC7EBA7A3C54}.Release|Any CPU.Build.0 = Release|Any CPU
 		{A0253377-BC40-63BD-F41A-AC7EBA7A3C54}.Release|NonWindows.ActiveCfg = Release|Any CPU
 		{A0253377-BC40-63BD-F41A-AC7EBA7A3C54}.Release|NonWindows.Build.0 = Release|Any CPU
+		{A3AACB6C-0398-4325-B1C7-D9CE72A909DA}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{A3AACB6C-0398-4325-B1C7-D9CE72A909DA}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{A3AACB6C-0398-4325-B1C7-D9CE72A909DA}.Debug|NonWindows.ActiveCfg = Debug|Any CPU
+		{A3AACB6C-0398-4325-B1C7-D9CE72A909DA}.Debug|NonWindows.Build.0 = Debug|Any CPU
+		{A3AACB6C-0398-4325-B1C7-D9CE72A909DA}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{A3AACB6C-0398-4325-B1C7-D9CE72A909DA}.Release|Any CPU.Build.0 = Release|Any CPU
+		{A3AACB6C-0398-4325-B1C7-D9CE72A909DA}.Release|NonWindows.ActiveCfg = Release|Any CPU
+		{A3AACB6C-0398-4325-B1C7-D9CE72A909DA}.Release|NonWindows.Build.0 = Release|Any CPU
+		{1D316174-9568-4128-AE4C-B1A01EBA65FE}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{1D316174-9568-4128-AE4C-B1A01EBA65FE}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{1D316174-9568-4128-AE4C-B1A01EBA65FE}.Debug|NonWindows.ActiveCfg = Debug|Any CPU
+		{1D316174-9568-4128-AE4C-B1A01EBA65FE}.Debug|NonWindows.Build.0 = Debug|Any CPU
+		{1D316174-9568-4128-AE4C-B1A01EBA65FE}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{1D316174-9568-4128-AE4C-B1A01EBA65FE}.Release|Any CPU.Build.0 = Release|Any CPU
+		{1D316174-9568-4128-AE4C-B1A01EBA65FE}.Release|NonWindows.ActiveCfg = Release|Any CPU
+		{1D316174-9568-4128-AE4C-B1A01EBA65FE}.Release|NonWindows.Build.0 = Release|Any CPU
 	EndGlobalSection
 	GlobalSection(SolutionProperties) = preSolution
 		HideSolutionNode = FALSE
@@ -178,6 +206,8 @@ Global
 		{168AF67E-678E-FDC9-7C20-7407D58A37FE} = {36CCE840-6FE5-4DB9-A8D5-8CF3CB6D342A}
 		{DC26E9DC-DFB1-19BD-6BAA-38B23E99C3C6} = {36CCE840-6FE5-4DB9-A8D5-8CF3CB6D342A}
 		{A0253377-BC40-63BD-F41A-AC7EBA7A3C54} = {36CCE840-6FE5-4DB9-A8D5-8CF3CB6D342A}
+		{A3AACB6C-0398-4325-B1C7-D9CE72A909DA} = {36CCE840-6FE5-4DB9-A8D5-8CF3CB6D342A}
+		{1D316174-9568-4128-AE4C-B1A01EBA65FE} = {36CCE840-6FE5-4DB9-A8D5-8CF3CB6D342A}
 	EndGlobalSection
 	GlobalSection(ExtensibilityGlobals) = postSolution
 		SolutionGuid = {E3944F6A-384B-4B0F-B93F-3BD513DC57BD}

azure-pipelines/integration-test.yml

@@ -58,7 +58,7 @@ jobs:
       solution: $(Pipeline.Workspace)\integration-tests\buildtask-sdk\buildtask-sdk.slnx
       msbuildArguments: /r
     condition: eq(variables.currentSdk, 'true')
-  - pwsh: dotnet publish -r win-x64
+  - pwsh: dotnet publish -c Release -r win-x64
     displayName: 🧪 dotnet publish
     workingDirectory: $(Pipeline.Workspace)\integration-tests\buildtask-sdk
     condition: eq(variables.currentSdk, 'true')

docs/design/adaptive-com-winrt-object-marshalling.md

@@ -0,0 +1,168 @@
+# Automatic COM and Windows Runtime object out-parameter marshalling
+
+## Status
+
+Accepted.
+
+CsWin32 will automatically detect Windows Runtime objects returned through recognized COM `IID`/`void**` out-parameter pairs. The automatic behavior is enabled by default and can be disabled globally in `NativeMethods.json`.
+
+The caller-selected policy was considered but not selected. Unique COM wrapper ownership remains separate work.
+
+## Motivation
+
+CsWin32 projects COM object outputs as COM wrappers. That is correct for ordinary COM, but it prevents an object returned through an `IID`/`void**` pair from being used as a C#/WinRT projection:
+
+```csharp
+shellItem.BindToHandler<IStorageItem>(
+    null,
+    bhidStorageItem,
+    out IStorageItem storageItem);
+```
+
+The native object returned by `BindToHandler` implements `IInspectable`, but COM-only marshalling creates a `ComObject`. That wrapper cannot safely provide the C#/WinRT `IStorageItem` behavior. The problem also occurs when the immediate output type is `object` or a COM interface and the caller casts to a WinRT interface later.
+
+Callers should not have to know which wrapper family to request. The returned native identity already provides the authoritative answer:
+
+- An identity that implements `IInspectable` should be projected through C#/WinRT.
+- An identity that returns `E_NOINTERFACE` for `IInspectable` should use normal COM projection.
+
+The extra `QueryInterface(IInspectable)` is accepted in exchange for automatic behavior and substantially simpler generated APIs.
+
+## Decision
+
+For each eligible COM object output:
+
+1. Request the native interface identified by the friendly method's `T`.
+2. Query the returned identity for `IInspectable`.
+3. On success, project the value with `WinRT.MarshalInspectable<object>.FromAbi`.
+4. On `E_NOINTERFACE`, use the normal COM projection.
+5. Propagate every other QI failure.
+
+This rule applies to source-generated flat P/Invokes, generated COM calls, and built-in COM friendly overloads.
+
+The generated friendly signature remains:
+
+```csharp
+public static void BindToHandler<T>(
+    this IShellItem @this,
+    IBindCtx? pbc,
+    in Guid bhid,
+    out T ppv)
+    where T : class;
+```
+
+No caller-visible marshalling enum, raw companion method, same-IID companion interface, or analyzer is required.
+
+## Configuration
+
+Automatic projection is enabled by default:
+
+```json
+{
+  "comInterop": {
+    "autoWinRTMarshalling": true
+  }
+}
+```
+
+Set the option to `false` to preserve COM-only projection and avoid the additional `QI(IInspectable)`.
+
+The option has no effect when marshaling is disabled, C#/WinRT is absent, or the target framework lacks required custom-marshalling support.
+
+## Eligible methods
+
+The initial implementation recognizes a final metadata pair:
+
+```text
+Guid* riid, [ComOutPtr] void** ppv
+```
+
+Non-final pairs and the one SDK method with two pairs remain future work. Disabling generic COM out-pointer friendly overloads does not disable source-generated ABI marshalling.
+
+## IID selection
+
+- `object` uses `IID_IUnknown`.
+- C#/WinRT types use `WinRT.GuidGenerator.CreateIID(typeof(T))`.
+- Generated COM types use `typeof(T).GUID`.
+
+The generic `T` is annotated with `DynamicallyAccessedMembers(PublicFields)` for trimming and Native AOT.
+
+IID selection chooses the native interface. The returned identity chooses the managed wrapper family.
+
+## Adaptive output marshaller
+
+Source-generated interop uses one object marshaller for `ManagedToUnmanagedOut` and `UnmanagedToManagedOut`.
+
+Native-to-managed conversion queries `IInspectable`, uses C#/WinRT on success, falls back to `ComInterfaceMarshaller<object>` only for `E_NOINTERFACE`, and releases the original and temporary QI references independently.
+
+Eligible `[LibraryImport]` declarations apply `[MarshalUsing]` directly to `out object`; no duplicate raw P/Invoke is generated.
+
+## Generated COM interfaces
+
+CsWin32 applies the adaptive marshaller to the object output without changing the IID parameter:
+
+```csharp
+void BindToHandler(
+    IBindCtx? pbc,
+    Guid* bhid,
+    Guid* riid,
+    [MarshalUsing(typeof(ComOrWinRTObjectMarshaller))]
+    out object ppv);
+```
+
+For managed implementations, the output marshaller returns the object's COM identity. A generated
+managed consumer then applies the adaptive input projection, and the friendly overload casts the
+projected object to `T`. That cast performs the required interface QI, so no sibling-parameter state
+is needed.
+
+Managed implementations may return WinRT objects, inspectable COM objects, non-inspectable COM
+objects, or `null`. Producing the exact interface pointer named by `riid` for arbitrary native callers
+of managed implementations is a separate generated COM marshalling concern and is not added by this
+proposal.
+
+## Built-in COM interop
+
+Classic `[ComImport]` and `DllImport` do not honor source-generated custom marshallers. Their friendly overloads post-process the built-in wrapper:
+
+1. Obtain its identity with `Marshal.GetIUnknownForObject`.
+2. Query `IInspectable`.
+3. Project through C#/WinRT on success.
+4. Return the original built-in wrapper on `E_NOINTERFACE`.
+5. Release temporary references.
+
+This creates a transient built-in RCW. CsWin32 does not final-release it because it may be identity-cached and shared.
+
+Runtime coverage invokes a WinRT member after adaptation; a cast alone is not sufficient to prove correct vtable dispatch.
+
+## Inspectable objects used through COM interfaces
+
+C#/WinRT wrappers on .NET 8 and later can dynamically expose source-generated COM interfaces. An inspectable shell stream can therefore be projected as `WinRT.IInspectable`, cast to CsWin32's `IStream`, and invoked.
+
+Consumers that disable C#/WinRT dynamic interface casting cannot rely on this behavior.
+
+## Native AOT
+
+The design uses generated COM metadata and custom marshallers. Native AOT callers rely on interface contracts rather than concrete runtime-class wrapper types.
+
+The integration suite publishes a Native AOT package-consumption app.
+
+## Behavior and cost
+
+Inspectable values that previously appeared as COM wrappers now appear as C#/WinRT wrappers. Non-inspectable values remain COM wrappers.
+
+Each eligible output adds one `QI(IInspectable)`. Only `E_NOINTERFACE` selects COM fallback; other failures propagate.
+
+CsWin32 projections are primarily internal, so preserving previous generated source or managed ABI signatures is not a requirement. The native ABI remains unchanged.
+
+## Non-goals
+
+- Unique COM wrapper ownership.
+- Input marshalling changes.
+- Every fixed-type COM output.
+- Non-final or multiple IID/output pairs in the initial implementation.
+- Concrete WinRT runtime-class wrapper identity.
+- Exact-`riid` output pointers from managed implementations consumed directly by arbitrary native callers.
+
+## Validation
+
+Coverage includes generator-shape tests, source-generated and built-in runtime tests, enabled and disabled behavior, WinRT and COM outputs, managed round trips, null output, and Native AOT package publication.

integration-tests/buildtask-sdk/app/buildtask-sdk.csproj

@@ -3,7 +3,7 @@
   <PropertyGroup>
     <OutputType>Exe</OutputType>
     <TargetFramework>net9.0-windows</TargetFramework>
-    <LangVersion>9</LangVersion>
+    <LangVersion>12</LangVersion>
     <PublishAot>true</PublishAot>
     <CsWin32RunAsBuildTask>true</CsWin32RunAsBuildTask>
     <DisableRuntimeMarshalling>true</DisableRuntimeMarshalling>

src/Microsoft.Windows.CsWin32/Generator.Com.cs

@@ -1017,6 +1017,10 @@ static ExpressionSyntax ThisPointer(PointerTypeSyntax? typedPointer = null)
                         methodDeclaration = methodDeclaration.AddModifiers(TokenWithSpace(SyntaxKind.UnsafeKeyword));
                     }
 
+                    methodDeclaration = methodDefinition.Generator.ApplyAutoWinRTMarshalling(
+                        methodDefinition.Method,
+                        signature,
+                        methodDeclaration);
                     propertyOrMethod = methodDeclaration;
                 }