Prefer pointers over out/ref for optional parameters

src/Microsoft.Windows.CsWin32/PointerTypeHandleInfo.cs

@@ -16,7 +16,8 @@ internal override TypeSyntaxAndMarshaling ToTypeSyntax(TypeSyntaxSettings inputs
         }
 
         TypeSyntaxAndMarshaling elementTypeDetails = this.ElementType.ToTypeSyntax(inputs with { PreferInOutRef = false }, customAttributes);
-        if (elementTypeDetails.MarshalAsAttribute is object || inputs.Generator?.IsManagedType(this.ElementType) is true || (inputs.PreferInOutRef && this.ElementType is PrimitiveTypeHandleInfo { PrimitiveTypeCode: not PrimitiveTypeCode.Void }))
+        bool xOptional = (parameterAttributes & ParameterAttributes.Optional) == ParameterAttributes.Optional;
+        if (elementTypeDetails.MarshalAsAttribute is object || inputs.Generator?.IsManagedType(this.ElementType) is true || (inputs.PreferInOutRef && !xOptional && this.ElementType is PrimitiveTypeHandleInfo { PrimitiveTypeCode: not PrimitiveTypeCode.Void }))
         {
             bool xIn = (parameterAttributes & ParameterAttributes.In) == ParameterAttributes.In;
             bool xOut = (parameterAttributes & ParameterAttributes.Out) == ParameterAttributes.Out;

test/GenerationSandbox.Tests/GeneratedForm.cs

@@ -6,6 +6,7 @@
 using Windows.Win32;
 using Windows.Win32.Foundation;
 using Windows.Win32.Networking.ActiveDirectory;
+using Windows.Win32.System.Com;
 using Windows.Win32.System.Diagnostics.Debug;
 using Windows.Win32.System.Threading;
 
@@ -79,4 +80,65 @@ private static void WriteFile()
         uint written = 0;
         PInvoke.WriteFile((SafeHandle?)null, new byte[2], &written, (NativeOverlapped*)null);
     }
+
+    private class MyStream : IStream
+    {
+        public HRESULT Read(void* pv, uint cb, uint* pcbRead)
+        {
+            // the last parameter should be a pointer because it is optional, and using `out uint` makes it very cumbersome
+            // for C# implementation of this interface to detect a null argument before setting the out parameter,
+            // which would throw NRE in such a case.
+            throw new NotImplementedException();
+        }
+
+        public HRESULT Write(void* pv, uint cb, uint* pcbWritten)
+        {
+            throw new NotImplementedException();
+        }
+
+        public void Seek(long dlibMove, SeekOrigin dwOrigin, ulong* plibNewPosition)
+        {
+            throw new NotImplementedException();
+        }
+
+        public void SetSize(ulong libNewSize)
+        {
+            throw new NotImplementedException();
+        }
+
+        public void CopyTo(IStream pstm, ulong cb, ulong* pcbRead, ulong* pcbWritten)
+        {
+            throw new NotImplementedException();
+        }
+
+        public void Commit([MarshalAs(UnmanagedType.U4)] STGC grfCommitFlags)
+        {
+            throw new NotImplementedException();
+        }
+
+        public void Revert()
+        {
+            throw new NotImplementedException();
+        }
+
+        public void LockRegion(ulong libOffset, ulong cb, [MarshalAs(UnmanagedType.U4)] LOCKTYPE dwLockType)
+        {
+            throw new NotImplementedException();
+        }
+
+        public void UnlockRegion(ulong libOffset, ulong cb, uint dwLockType)
+        {
+            throw new NotImplementedException();
+        }
+
+        public void Stat(Windows.Win32.System.Com.STATSTG* pstatstg, [MarshalAs(UnmanagedType.U4)] STATFLAG grfStatFlag)
+        {
+            throw new NotImplementedException();
+        }
+
+        public void Clone(out IStream ppstm)
+        {
+            throw new NotImplementedException();
+        }
+    }
 }

test/GenerationSandbox.Tests/NativeMethods.txt

@@ -19,6 +19,7 @@ IEnumDebugPropertyInfo
 IPersistFile
 IServiceProvider
 IShellWindows
+IStream
 KEY_EVENT_RECORD
 LoadLibrary
 MainAVIHeader

test/SpellChecker/Program.cs

@@ -56,7 +56,7 @@
                 IEnumString suggestions = spellChecker.Suggest(word);
                 do
                 {
-                    suggestions.Next(suggestionResult, out _);
+                    suggestions.Next(suggestionResult, null);
                     if (suggestionResult[0].Value is not null)
                     {
                         Console.WriteLine($"\t{suggestionResult[0]}");