From afc3f01a100fc5981a69eef22ff21855add9c572 Mon Sep 17 00:00:00 2001
From: Will Gunaratne <will@avius.com>
Date: Wed, 26 Feb 2025 11:13:29 +0000
Subject: [PATCH] Fix generic base codec generic type parameter resolution

---
 .../Serializers/CodecProvider.cs              |  2 +-
 .../GenericBaseClassTest.cs                   | 30 +++++++++++++++++++
 2 files changed, 31 insertions(+), 1 deletion(-)
 create mode 100644 test/Orleans.Serialization.UnitTests/GenericBaseClassTest.cs

diff --git a/src/Orleans.Serialization/Serializers/CodecProvider.cs b/src/Orleans.Serialization/Serializers/CodecProvider.cs
index 18b8b5363d2..0aa26a41c83 100644
--- a/src/Orleans.Serialization/Serializers/CodecProvider.cs
+++ b/src/Orleans.Serialization/Serializers/CodecProvider.cs
@@ -543,7 +543,7 @@ private IFieldCodec CreateCodecInstance(Type fieldType, Type searchType)
             }
             else if (searchType.BaseType is object
                 && CreateCodecInstance(
-                    fieldType,
+                    fieldType.BaseType,
                     searchType.BaseType switch
                     {
                         { IsConstructedGenericType: true } => searchType.BaseType.GetGenericTypeDefinition(),
diff --git a/test/Orleans.Serialization.UnitTests/GenericBaseClassTest.cs b/test/Orleans.Serialization.UnitTests/GenericBaseClassTest.cs
new file mode 100644
index 00000000000..bb5bff30261
--- /dev/null
+++ b/test/Orleans.Serialization.UnitTests/GenericBaseClassTest.cs
@@ -0,0 +1,30 @@
+using Microsoft.Extensions.DependencyInjection;
+using Xunit;
+
+namespace Orleans.Serialization.UnitTests
+{
+    [GenerateSerializer]
+    abstract class Base<T>;
+
+    class Derived : Base<int>;
+
+    [Trait("Category", "BVT")]
+    public class GenericBaseClassTest
+    {
+        private readonly ServiceProvider _services;
+        private readonly Serializer _serializer;
+        public GenericBaseClassTest()
+        {
+            _services = new ServiceCollection()
+                .AddSerializer()
+                .BuildServiceProvider();
+            _serializer = _services.GetRequiredService<Serializer>();
+        }
+
+        [Fact]
+        public void DerivedNoGeneric()
+        {
+            Assert.False(_serializer.CanSerialize(typeof(Derived)));
+        }
+    }
+}