Fix marshalling generators using 0 as cleanup length for ManagedToUnmanaged collections with NoCountInfo

src/libraries/System.Runtime.InteropServices/gen/Microsoft.Interop.SourceGeneration/Marshalling/ElementsMarshalling.cs

@@ -105,6 +105,16 @@ ExpressionSyntax GetExpressionForParam(TypePositionInfo paramInfo)
 
         public abstract StatementSyntax GenerateUnmarshalStatement(StubIdentifierContext context);
         public abstract StatementSyntax GenerateElementCleanupStatement(StubIdentifierContext context);
+
+        /// <summary>
+        /// <code>
+        /// &lt;numElements&gt; = &lt;GetManagedValuesSource&gt;.Length;
+        /// </code>
+        /// </summary>
+        public StatementSyntax GenerateNumElementsAssignmentFromManagedValuesSource(StubIdentifierContext context)
+        {
+            return CollectionSource.GetNumElementsAssignmentFromManagedValuesSource(CollectionSource.TypeInfo, context);
+        }
     }
 
     file static class ElementsMarshallingCollectionSourceExtensions

src/libraries/System.Runtime.InteropServices/gen/Microsoft.Interop.SourceGeneration/Marshalling/StatelessMarshallingStrategy.cs

@@ -581,15 +581,9 @@ public IEnumerable<StatementSyntax> GenerateCleanupCallerAllocatedResourcesState
                     if (countInfo is NoCountInfo && MarshallerHelpers.GetMarshalDirection(TypeInfo, CodeContext) == MarshalDirection.ManagedToUnmanaged)
                     {
                         // When marshalling from managed to unmanaged, we may not have count info.
-                        // For now, just set <numElements> to 0.
-                        // See https://github.com/dotnet/runtime/issues/93423 for a tracking issue.
-
-                        // <numElements> = 0;
-                        yield return ExpressionStatement(
-                            AssignmentExpression(
-                                SyntaxKind.SimpleAssignmentExpression,
-                                IdentifierName(numElementsIdentifier),
-                                LiteralExpression(SyntaxKind.NumericLiteralExpression, Literal(0))));
+                        // Use the managed collection's length to determine the number of elements to clean up.
+                        // <numElements> = <GetManagedValuesSource>.Length;
+                        yield return elementsMarshalling.GenerateNumElementsAssignmentFromManagedValuesSource(context);
                     }
                     else
                     {

src/libraries/System.Runtime.InteropServices/tests/ComInterfaceGenerator.Unit.Tests/Compiles.cs

@@ -314,11 +314,13 @@ public static IEnumerable<object[]> CustomCollectionsManagedToUnmanaged(Generato
             yield return new[] { ID(), customCollectionMarshallingCodeSnippetsManagedToUnmanaged.Stateless.NativeToManagedOnlyOutParameter<int>() };
             yield return new[] { ID(), customCollectionMarshallingCodeSnippetsManagedToUnmanaged.Stateless.NativeToManagedOnlyReturnValue<int>() };
             yield return new[] { ID(), customCollectionMarshallingCodeSnippetsManagedToUnmanaged.Stateless.NonBlittableElementByValue };
+            yield return new[] { ID(), customCollectionMarshallingCodeSnippetsManagedToUnmanaged.Stateless.NonBlittableElementWithFreeByValue };
             yield return new[] { ID(), customCollectionMarshallingCodeSnippetsManagedToUnmanaged.Stateless.NonBlittableElementNativeToManagedOnlyOutParameter };
             yield return new[] { ID(), customCollectionMarshallingCodeSnippetsManagedToUnmanaged.Stateless.NonBlittableElementNativeToManagedOnlyReturnValue };
             yield return new[] { ID(), customCollectionMarshallingCodeSnippetsManagedToUnmanaged.Stateful.NativeToManagedOnlyOutParameter<int>() };
             yield return new[] { ID(), customCollectionMarshallingCodeSnippetsManagedToUnmanaged.Stateful.NativeToManagedOnlyReturnValue<int>() };
             yield return new[] { ID(), customCollectionMarshallingCodeSnippetsManagedToUnmanaged.Stateful.NonBlittableElementByValue };
+            yield return new[] { ID(), customCollectionMarshallingCodeSnippetsManagedToUnmanaged.Stateful.NonBlittableElementWithFreeByValue };
             yield return new[] { ID(), customCollectionMarshallingCodeSnippetsManagedToUnmanaged.Stateful.NonBlittableElementNativeToManagedOnlyOutParameter };
             yield return new[] { ID(), customCollectionMarshallingCodeSnippetsManagedToUnmanaged.Stateful.NonBlittableElementNativeToManagedOnlyReturnValue };
         }

src/libraries/System.Runtime.InteropServices/tests/Common/CustomCollectionMarshallingCodeSnippets.cs

@@ -54,6 +54,16 @@ public struct Native { }
                 public static Element ConvertToManaged(Native n) => throw null;
             }
             """;
+        public const string ElementInWithFree = """
+            [CustomMarshaller(typeof(Element), MarshalMode.ElementIn, typeof(ElementMarshaller))]
+            static class ElementMarshaller
+            {
+                public struct Native { }
+                public static Native ConvertToUnmanaged(Element e) => throw null;
+                public static Element ConvertToManaged(Native n) => throw null;
+                public static void Free(Native unmanaged) { }
+            }
+            """;
         public const string ElementOut = """
             [CustomMarshaller(typeof(Element), MarshalMode.ElementOut, typeof(ElementMarshaller))]
             static class ElementMarshaller
@@ -252,6 +262,10 @@ public string NestedMarshallerParametersAndModifiers(string elementType) => _pro
                 + NonBlittableElement
                 + ElementIn;
 
+            public string NonBlittableElementWithFreeByValue => ByValue("Element")
+                + NonBlittableElement
+                + ElementInWithFree;
+
             public string NonBlittableElementNativeToManagedOnlyOutParameter => NativeToManagedOnlyOutParameter("Element")
                 + NonBlittableElement
                 + ElementOut;
@@ -508,6 +522,10 @@ public string NativeToManagedFinallyOnlyReturnValue(string elementType) => _snip
                 + NonBlittableElement
                 + ElementIn;
 
+            public string NonBlittableElementWithFreeByValue => ByValue("Element")
+                + NonBlittableElement
+                + ElementInWithFree;
+
             public string NonBlittableElementNativeToManagedOnlyOutParameter => NativeToManagedOnlyOutParameter("Element")
                 + NonBlittableElement
                 + ElementOut;

src/libraries/System.Runtime.InteropServices/tests/LibraryImportGenerator.UnitTests/Compiles.cs

@@ -394,6 +394,7 @@ public static IEnumerable<object[]> CustomCollections()
             yield return new[] { ID(), customCollectionMarshallingCodeSnippets.Stateless.NativeToManagedFinallyOnlyReturnValue<int>() };
             yield return new[] { ID(), customCollectionMarshallingCodeSnippets.Stateless.NestedMarshallerParametersAndModifiers<int>() };
             yield return new[] { ID(), customCollectionMarshallingCodeSnippets.Stateless.NonBlittableElementByValue };
+            yield return new[] { ID(), customCollectionMarshallingCodeSnippets.Stateless.NonBlittableElementWithFreeByValue };
             yield return new[] { ID(), customCollectionMarshallingCodeSnippets.Stateless.NonBlittableElementParametersAndModifiers };
             yield return new[] { ID(), customCollectionMarshallingCodeSnippets.Stateless.NonBlittableElementNativeToManagedOnlyOutParameter };
             yield return new[] { ID(), customCollectionMarshallingCodeSnippets.Stateless.NonBlittableElementNativeToManagedFinallyOnlyOutParameter };
@@ -432,6 +433,7 @@ public static IEnumerable<object[]> CustomCollections()
             yield return new[] { ID(), customCollectionMarshallingCodeSnippets.Stateful.NativeToManagedOnlyReturnValue<int>() };
             yield return new[] { ID(), customCollectionMarshallingCodeSnippets.Stateful.NativeToManagedFinallyOnlyReturnValue<int>() };
             yield return new[] { ID(), customCollectionMarshallingCodeSnippets.Stateful.NonBlittableElementByValue };
+            yield return new[] { ID(), customCollectionMarshallingCodeSnippets.Stateful.NonBlittableElementWithFreeByValue };
             yield return new[] { ID(), customCollectionMarshallingCodeSnippets.Stateful.NonBlittableElementParametersAndModifiers };
             yield return new[] { ID(), customCollectionMarshallingCodeSnippets.Stateful.NonBlittableElementNativeToManagedOnlyOutParameter };
             yield return new[] { ID(), customCollectionMarshallingCodeSnippets.Stateful.NonBlittableElementNativeToManagedFinallyOnlyOutParameter };