Generate cocreatable types as classes with [ComImport]

src/Microsoft.Windows.CsWin32/Generator.cs

@@ -2588,6 +2588,10 @@ private bool IsCompilerGenerated(TypeDefinition typeDef)
                     {
                         typeDeclaration = this.DeclareTypeDefStruct(typeDef);
                     }
+                    else if (this.IsEmptyStructWithGuid(typeDef))
+                    {
+                        typeDeclaration = this.DeclareCocreatableClass(typeDef);
+                    }
                     else
                     {
                         StructDeclarationSyntax structDeclaration = this.DeclareStruct(typeDef);
@@ -2635,6 +2639,12 @@ private bool IsCompilerGenerated(TypeDefinition typeDef)
 
         private bool IsTypeDefStruct(TypeDefinition typeDef) => typeDef.GetCustomAttributes().Any(att => this.IsAttribute(this.Reader.GetCustomAttribute(att), InteropDecorationNamespace, NativeTypedefAttribute));
 
+        private bool IsEmptyStructWithGuid(TypeDefinition typeDef)
+        {
+            return typeDef.GetCustomAttributes().Any(att => this.IsAttribute(this.Reader.GetCustomAttribute(att), InteropDecorationNamespace, nameof(GuidAttribute)))
+                && typeDef.GetFields().Count == 0;
+        }
+
         private void DeclareExternMethod(MethodDefinitionHandle methodDefinitionHandle)
         {
             MethodDefinition methodDefinition = this.Reader.GetMethodDefinition(methodDefinitionHandle);
@@ -3427,6 +3437,24 @@ private StructDeclarationSyntax DeclareStruct(TypeDefinition typeDef)
             return result;
         }
 
+        /// <summary>
+        /// Creates an empty class that when instantiated, creates a cocreatable Windows object
+        /// that may implement a number of interfaces at runtime, discoverable only by documentation.
+        /// </summary>
+        private ClassDeclarationSyntax DeclareCocreatableClass(TypeDefinition typeDef)
+        {
+            IdentifierNameSyntax name = IdentifierName(this.Reader.GetString(typeDef.Name));
+            Guid guid = this.FindGuidFromAttribute(typeDef) ?? throw new ArgumentException("Type does not have a GuidAttribute.");
+            var classModifiers = TokenList(TokenWithSpace(this.Visibility));
+            classModifiers = classModifiers.Add(TokenWithSpace(SyntaxKind.PartialKeyword));
+            ClassDeclarationSyntax result = ClassDeclaration(name.Identifier)
+                .WithModifiers(classModifiers)
+                .AddAttributeLists(AttributeList().AddAttributes(GUID(guid), ComImportAttribute));
+
+            result = this.AddApiDocumentation(name.Identifier.ValueText, result);
+            return result;
+        }
+
         /// <summary>
         /// Creates a struct that emulates a typedef in the C language headers.
         /// </summary>

test/GenerationSandbox.Tests/BasicTests.cs

@@ -11,8 +11,10 @@
 using Windows.Win32.Foundation;
 using Windows.Win32.Media.DirectShow;
 using Windows.Win32.Storage.FileSystem;
+using Windows.Win32.System.Com;
 using Windows.Win32.System.Console;
 using Windows.Win32.System.ErrorReporting;
+using Windows.Win32.UI.Shell;
 using Xunit;
 using Xunit.Abstractions;
 
@@ -428,4 +430,12 @@ public void CHAR_MarshaledAsUtf8()
     {
         Assert.Equal(1, Marshal.SizeOf<CHAR>());
     }
+
+    [Fact]
+    public void CocreatableClassesWithImplicitInterfaces()
+    {
+        ShellLink shellLink = new ShellLink();
+        IPersistFile persistFile = (IPersistFile)shellLink;
+        Assert.NotNull(persistFile);
+    }
 }

test/GenerationSandbox.Tests/NativeMethods.txt

@@ -9,12 +9,14 @@ GetWindowText
 GetWindowTextLength
 HDC_UserSize
 IEnumDebugPropertyInfo
+IPersistFile
 KEY_EVENT_RECORD
 LoadLibrary
 MainAVIHeader
 NTSTATUS
+RegLoadAppKey
 RM_PROCESS_INFO
+ShellLink
 WER_REPORT_INFORMATION
 wglGetProcAddress
 WPARAM
-RegLoadAppKey

test/Microsoft.Windows.CsWin32.Tests/GeneratorTests.cs

@@ -2227,6 +2227,17 @@ public async Task UnparseableNativeMethodsJson()
         }.RunAsync();
     }
 
+    [Fact]
+    public void CocreatableStructs()
+    {
+        this.generator = this.CreateGenerator();
+        Assert.True(this.generator.TryGenerate("ShellLink", CancellationToken.None));
+        this.CollectGeneratedCode(this.generator);
+        this.AssertNoDiagnostics();
+        ClassDeclarationSyntax classDecl = Assert.IsType<ClassDeclarationSyntax>(this.FindGeneratedType("ShellLink").Single());
+        Assert.Contains(classDecl.AttributeLists, al => al.Attributes.Any(a => a.Name.ToString().Contains("ComImport")));
+    }
+
     private static string ConstructGlobalConfigString(bool omitDocs = false)
     {
         StringBuilder globalConfigBuilder = new();