Fix: Exclude read-only properties from KernelJsonSchema generation

Author: sajidkamaljoy

dotnet/src/InternalUtilities/src/Schema/KernelJsonSchemaBuilder.cs

@@ -67,7 +67,10 @@ private static JsonSerializerOptions GetDefaultOptions()
         {
             JsonSerializerOptions options = new()
             {
-                TypeInfoResolver = new DefaultJsonTypeInfoResolver(),
+                TypeInfoResolver = new DefaultJsonTypeInfoResolver
+                {
+                    Modifiers = { ExcludeReadOnlyProperties }
+                },
                 Converters = { new JsonStringEnumConverter() },
             };
             options.MakeReadOnly();
@@ -76,4 +79,19 @@ private static JsonSerializerOptions GetDefaultOptions()
 
         return s_options;
     }
+
+    private static void ExcludeReadOnlyProperties(JsonTypeInfo typeInfo)
+    {
+        if (typeInfo.Kind != JsonTypeInfoKind.Object) return;
+
+        for (int i = 0; i < typeInfo.Properties.Count; i++)
+        {
+            var property = typeInfo.Properties[i];
+
+            if (property.Set == null)
+            {
+                typeInfo.Properties.RemoveAt(i--);
+            }
+        }
+    }
 }

dotnet/src/SemanticKernel.UnitTests/Functions/KernelJsonSchemaTests.cs

@@ -1,6 +1,7 @@
 // Copyright (c) Microsoft. All rights reserved.
 
 using System;
+using System.ComponentModel;
 using System.Text;
 using System.Text.Json;
 using Microsoft.SemanticKernel;
@@ -91,6 +92,39 @@ public void ItThrowsOnInvalidJson()
         Assert.ThrowsAny<JsonException>(() => KernelJsonSchema.Parse(Encoding.UTF8.GetBytes(InvalidJsonSchema)));
     }
 
+    [Fact]
+    public void ItShouldExcludeReadOnlyPropertiesFromSchema()
+    {
+        var function = KernelFunctionFactory.CreateFromMethod(
+            (MyComplexType input) => { },
+            "TestFunction");
+
+        var schema = function.Metadata.Parameters[0].Schema;
+        var jsonSchemaString = schema?.ToString();
+
+        Assert.NotNull(jsonSchemaString);
+        Assert.Contains("Status", jsonSchemaString); 
+        Assert.DoesNotContain("Derived", jsonSchemaString); 
+    }
+
+    /// <summary>
+    /// A helper class specific to this test case.
+    /// Used to verify that read-only properties are ignored by the schema generator.
+    /// </summary>
+    private class MyComplexType
+    {
+        [Description("The current status of the user account")]
+        public MyStatus Status { get; set; }
+
+        public string Derived => $"Status is {Status}";
+    }
+
+    private enum MyStatus
+    {
+        Active,
+        Inactive
+    }
+
     // TODO: KernelJsonSchema currently validates that the input is valid JSON but not that it's valid JSON schema.
     //[Theory]
     //[InlineData("{ \"type\":\"invalid\" }")]