Support DisplayNameAttribute for name resolution in AI libraries

src/Libraries/Microsoft.Extensions.AI.Abstractions/Functions/AIFunctionFactory.cs

@@ -729,7 +729,7 @@ private ReflectionAIFunctionDescriptor(DescriptorKey key, JsonSerializerOptions
 
             ReturnParameterMarshaller = GetReturnParameterMarshaller(key, serializerOptions, out Type? returnType);
             Method = key.Method;
-            Name = key.Name ?? GetFunctionName(key.Method);
+            Name = key.Name ?? key.Method.GetCustomAttribute<DisplayNameAttribute>(inherit: true)?.DisplayName ?? GetFunctionName(key.Method);
             Description = key.Description ?? key.Method.GetCustomAttribute<DescriptionAttribute>(inherit: true)?.Description ?? string.Empty;
             JsonSerializerOptions = serializerOptions;
             ReturnJsonSchema = returnType is null || key.ExcludeResultSchema ? null : AIJsonUtilities.CreateJsonSchema(

test/Libraries/Microsoft.Extensions.AI.Tests/Functions/AIFunctionFactoryTest.cs

@@ -237,6 +237,39 @@ public void Metadata_DerivedFromLambda()
             p => Assert.Equal("This is B", p.GetCustomAttribute<DescriptionAttribute>()?.Description));
     }
 
+    [Fact]
+    public void Metadata_DisplayNameAttribute()
+    {
+        // Test DisplayNameAttribute on a delegate method
+        Func<string> funcWithDisplayName = [DisplayName("get_user_id")] () => "test";
+        AIFunction func = AIFunctionFactory.Create(funcWithDisplayName);
+        Assert.Equal("get_user_id", func.Name);
+        Assert.Empty(func.Description);
+
+        // Test DisplayNameAttribute with DescriptionAttribute
+        Func<string> funcWithBoth = [DisplayName("my_function")][Description("A test function")] () => "test";
+        func = AIFunctionFactory.Create(funcWithBoth);
+        Assert.Equal("my_function", func.Name);
+        Assert.Equal("A test function", func.Description);
+
+        // Test that explicit name parameter takes precedence over DisplayNameAttribute
+        func = AIFunctionFactory.Create(funcWithDisplayName, name: "explicit_name");
+        Assert.Equal("explicit_name", func.Name);
+
+        // Test DisplayNameAttribute with options
+        func = AIFunctionFactory.Create(funcWithDisplayName, new AIFunctionFactoryOptions());
+        Assert.Equal("get_user_id", func.Name);
+
+        // Test that options.Name takes precedence over DisplayNameAttribute
+        func = AIFunctionFactory.Create(funcWithDisplayName, new AIFunctionFactoryOptions { Name = "options_name" });
+        Assert.Equal("options_name", func.Name);
+
+        // Test function without DisplayNameAttribute falls back to method name
+        Func<string> funcWithoutDisplayName = () => "test";
+        func = AIFunctionFactory.Create(funcWithoutDisplayName);
+        Assert.Contains("Metadata_DisplayNameAttribute", func.Name); // Will contain the lambda method name
+    }
+
     [Fact]
     public void AIFunctionFactoryCreateOptions_ValuesPropagateToAIFunction()
     {