bug fix: When generating the get accessor for a field composed of an embedded array of structs use __GetOrCreateInstance to initialize the managed array wrapper rather than __CreateInstance so that __Instance holds a pointer to the memory allocated for the array in the outer struct rather than an independent copy of that memory.

Added a test.

TODO: once allocated, we may want to cache the managed array. Does this
issue exist in other generators as well?

Author: jpnoir

src/Generator/Generators/CSharp/CSharpMarshal.cs

@@ -91,8 +91,8 @@ public override bool VisitArrayType(ArrayType array, TypeQualifiers quals)
                         {
                             if (arrayType == finalArrayType)
                                 supportBefore.WriteLineIndent(
-                                    "{0}[i] = {1}.{2}(*(({1}.{3}*)&({4}[i * sizeof({1}.{3})])));",
-                                    value, array.Type, Helpers.CreateInstanceIdentifier,
+                                    "{0}[i] = {1}.{2}((IntPtr)(({1}.{3}*)&({4}[i * sizeof({1}.{3})])), true, true);",
+                                    value, array.Type, Helpers.GetOrCreateInstanceIdentifier,
                                     Helpers.InternalStruct, Context.ReturnVarName);
                             else
                                 supportBefore.WriteLineIndent(

src/Generator/Generators/CodeGenerator.cs

@@ -1301,6 +1301,7 @@ public static class Helpers
         public static readonly string OwnsNativeInstanceIdentifier = Generator.GeneratedIdentifier("ownsNativeInstance");
 
         public static readonly string CreateInstanceIdentifier = Generator.GeneratedIdentifier("CreateInstance");
+        public static readonly string GetOrCreateInstanceIdentifier = Generator.GeneratedIdentifier("GetOrCreateInstance");
 
         public static string GetSuffixForInternal(DeclarationContext @class)
         {

tests/CSharp/CSharp.Tests.cs

@@ -767,6 +767,22 @@ public void TestAlignment()
         }
     }
 
+    [Test]
+    public void TestEmbeddedArrayOfStructAccessor()
+    {
+        const ulong firstLong =  0xC92EEDE87AAB4FECul;
+        const ulong secondLong = 0xAD5FB16491935522ul;
+
+        var testStruct = new StructWithEmbeddedArrayOfStructObjectAlignment();
+        testStruct.EmbeddedStruct[0].Ui64 = firstLong;
+        testStruct.EmbeddedStruct[1].Ui64 = secondLong;
+
+        // Since the memory allocated for EmbeddedStruct is generally uninintialized, I suppose it _could_
+        // just happen to match, but it seems very unlikely.
+        Assert.That(firstLong, Is.EqualTo(testStruct.EmbeddedStruct[0].Ui64));
+        Assert.That(secondLong, Is.EqualTo(testStruct.EmbeddedStruct[1].Ui64));
+    }
+
     public void TestClassSize()
     {
         Assert.That(Marshal.SizeOf<HasSecondaryBaseWithAbstractWithDefaultArg.__Internal>, Is.EqualTo(Marshal.SizeOf<IntPtr>() * 2));

tests/CSharp/CSharp.h

@@ -1504,7 +1504,7 @@ struct DLL_API ClassMicrosoftObjectAlignment : ClassMicrosoftObjectAlignmentBase
 
 struct DLL_API EmbeddedStruct
 {
-    int64_t i64;
+    uint64_t ui64;
 };
 struct DLL_API StructWithEmbeddedArrayOfStructObjectAlignment
 {