fix(dotnet): Fix property set for nested Dictionaries (#736)

* fix(dotnet) Fix property set for complex Dictionaries

* Explicit assert type

packages/jsii-dotnet-runtime-test/test/Amazon.JSII.Runtime.IntegrationTests/ComplianceTests.cs

@@ -91,6 +91,19 @@ public void CollectionTypes()
             types.MapProperty = map;
             Assert.Equal((double) 123, types.MapProperty["Foo"].Value);
         }
+
+        [Fact(DisplayName = Prefix + nameof(ComplexCollectionTypes))]
+        public void ComplexCollectionTypes()
+        {
+            // See https://github.com/aws/aws-cdk/issues/2496
+            AllTypes types = new AllTypes();
+            // complex map
+            IDictionary<string, object> map = new Dictionary<string, object>();
+            map.Add("Foo", new Dictionary<string, object>() { {"Key", 123d}});
+            types.AnyMapProperty = map;
+            var dict = (Dictionary<string, object>)types.AnyMapProperty["Foo"];
+            Assert.Equal(123d, dict["Key"]);
+        }
 
         [Fact(DisplayName = Prefix + nameof(DynamicTypes))]
         public void DynamicTypes()

packages/jsii-dotnet-runtime/src/Amazon.JSII.Runtime/Services/Converters/FrameworkToJsiiConverter.cs

@@ -263,7 +263,16 @@ protected override bool TryConvertMap(IReferenceMap referenceMap, TypeReference
             foreach (string key in keys)
             {
                 object element = indexer.GetValue(value, new object[] {key});
-                if (!TryConvert(elementType, referenceMap, element, out object convertedElement))
+
+                TypeReference childElementType = InferType(referenceMap, element);
+
+                // We should not pass the parent element type as we are in a map
+                // A map<string, object> could be a map<string, map<string, object> etc
+                // If we pass the parent referenceMap then it will try to convert it as Any
+                // So by inferring the child element type we are always converting the correct type.
+                // See https://github.com/aws/aws-cdk/issues/2496
+
+                if (!TryConvert(childElementType, referenceMap, element, out object convertedElement))
                 {
                     result = null;
                     return false;