Don't emit friendly overload of Span<byte> param for flexible array structs (#1541)

Author: jevansaks

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

@@ -191,6 +191,7 @@ private IEnumerable<MethodDeclarationSyntax> DeclareFriendlyOverload(
             bool isManagedParameterType = this.IsManagedType(parameterTypeInfo);
             MemorySize? memorySize = null;
             bool mustRemainAsPointer = false;
+            bool isPointerToStructWithFlexibleArray = parameterTypeInfo is PointerTypeHandleInfo { ElementType: HandleTypeHandleInfo pointedElement } && pointedElement.Generator.IsStructWithFlexibleArray(pointedElement);
             if (this.FindInteropDecorativeAttribute(paramAttributes, MemorySizeAttribute) is CustomAttribute memorySizeAttribute)
             {
                 memorySize = DecodeMemorySizeAttribute(memorySizeAttribute);
@@ -206,7 +207,7 @@ private IEnumerable<MethodDeclarationSyntax> DeclareFriendlyOverload(
             else if (memorySize is null)
             {
                 // If there's no MemorySize attribute, we may still need to keep this parameter as a pointer if it's a struct with a flexible array.
-                mustRemainAsPointer = parameterTypeInfo is PointerTypeHandleInfo { ElementType: HandleTypeHandleInfo pointedElement } && pointedElement.Generator.IsStructWithFlexibleArray(pointedElement);
+                mustRemainAsPointer = isPointerToStructWithFlexibleArray;
             }
             else if (!improvePointersToSpansAndRefs)
             {
@@ -477,7 +478,7 @@ private IEnumerable<MethodDeclarationSyntax> DeclareFriendlyOverload(
                     if (!isPointerToPointer && TryHandleCountParam(elementType, nullableSource: true))
                     {
                         // If we used a Span, we might also want to generate a struct helper.
-                        if (memorySize is not null)
+                        if (memorySize is not null && !isPointerToStructWithFlexibleArray)
                         {
                             countOfBytesStructParameters ??= new();
                             countOfBytesStructParameters.Add(param);

test/CsWin32Generator.Tests/CsWin32GeneratorTests.cs

@@ -176,13 +176,15 @@ public async Task PointerReturnValueIsPreserved()
         ["InitializeAcl", "InitializeAcl", "Span<byte> pAcl, winmdroot.Security.ACE_REVISION dwAclRevision"],
         // MemorySized-struct param should also have a version with `out struct` parameter.
         ["InitializeAcl", "InitializeAcl", "out winmdroot.Security.ACL pAcl, winmdroot.Security.ACE_REVISION dwAclRevision"],
-        ["SetDefaultCommConfig", "SetDefaultCommConfig", "string lpszName, in winmdroot.Devices.Communication.COMMCONFIG lpCC"],
+        ["SetDefaultCommConfig", "SetDefaultCommConfig", "string lpszName, in winmdroot.Devices.Communication.COMMCONFIG lpCC", false],
         ["ID3D11DeviceChild", "GetPrivateData", "this winmdroot.Graphics.Direct3D11.ID3D11DeviceChild @this, in global::System.Guid guid, ref uint pDataSize, Span<byte> pData"],
         ["WriteFile", "WriteFile", "SafeHandle hFile, in byte lpBuffer, uint* lpNumberOfBytesWritten, global::System.Threading.NativeOverlapped* lpOverlapped", false],
         // All params included
         ["SetupDiGetDeviceInterfaceDetail", "SetupDiGetDeviceInterfaceDetail", "SafeHandle DeviceInfoSet, in winmdroot.Devices.DeviceAndDriverInstallation.SP_DEVICE_INTERFACE_DATA DeviceInterfaceData, Span<byte> DeviceInterfaceDetailData, out uint RequiredSize, ref winmdroot.Devices.DeviceAndDriverInstallation.SP_DEVINFO_DATA DeviceInfoData"],
         // Optional params omitted
         ["SetupDiGetDeviceInterfaceDetail", "SetupDiGetDeviceInterfaceDetail", "SafeHandle DeviceInfoSet, in winmdroot.Devices.DeviceAndDriverInstallation.SP_DEVICE_INTERFACE_DATA DeviceInterfaceData, Span<byte> DeviceInterfaceDetailData"],
+        // We should _not_ have a struct param overload for flexible arrays
+        ["SetupDiGetDeviceInterfaceDetail", "SetupDiGetDeviceInterfaceDetail", "SafeHandle DeviceInfoSet, in winmdroot.Devices.DeviceAndDriverInstallation.SP_DEVICE_INTERFACE_DATA DeviceInterfaceData, out winmdroot.Devices.DeviceAndDriverInstallation.SP_DEVICE_INTERFACE_DETAIL_DATA_W DeviceInterfaceDetailData, out uint RequiredSize, ref winmdroot.Devices.DeviceAndDriverInstallation.SP_DEVINFO_DATA DeviceInfoData", false],
         ["WinHttpReadData", "WinHttpReadData", "void* hRequest, Span<byte> lpBuffer, ref uint lpdwNumberOfBytesRead"],
         ["IsTextUnicode", "IsTextUnicode", "ReadOnlySpan<byte> lpv, ref winmdroot.Globalization.IS_TEXT_UNICODE_RESULT lpiResult"],
         // Omitted ref param