feat: Add EnumMemberAttribute and .NET 9's JsonStringEnumMemberNameAttribute (#833)

Adds support for deriving the proper possible values for enum members
from EnumMemberAttribute and JsonStringEnumMemberNameAttribute.

Author: wasabii

src/KubeOps.Transpiler/Crds.cs

@@ -1,6 +1,7 @@
 using System.Collections;
 using System.Collections.ObjectModel;
 using System.Reflection;
+using System.Runtime.Serialization;
 using System.Text.Json.Serialization;
 
 using k8s;
@@ -339,12 +340,46 @@ private static V1JSONSchemaProps Map(this MetadataLoadContext context, Type type
             "System.Enum" => new V1JSONSchemaProps
             {
                 Type = String,
-                EnumProperty = Enum.GetNames(type).Cast<object>().ToList(),
+                EnumProperty = GetEnumNames(context, type),
             },
             _ => throw InvalidType(type),
         };
     }
 
+    private static IList<object> GetEnumNames(this MetadataLoadContext context, Type type)
+    {
+#if NET9_0_OR_GREATER
+        var attributeNameByFieldName = new Dictionary<string, string>();
+
+        foreach (var field in type.GetFields(BindingFlags.Public | BindingFlags.Static))
+        {
+            if (field.GetCustomAttributeData<JsonStringEnumMemberNameAttribute>() is { } jsonMemberNameAttribute &&
+                jsonMemberNameAttribute.GetCustomAttributeCtorArg<string>(context, 0) is { } jsonMemberNameAtributeName)
+            {
+                attributeNameByFieldName.Add(field.Name, jsonMemberNameAtributeName);
+            }
+        }
+
+        var enumNames = new List<object>();
+
+        foreach (var value in Enum.GetNames(type))
+        {
+            if (attributeNameByFieldName.TryGetValue(value, out var name))
+            {
+                enumNames.Add(name);
+            }
+            else
+            {
+                enumNames.Add(value);
+            }
+        }
+
+        return enumNames;
+#else
+        return Enum.GetNames(type);
+#endif
+    }
+
     private static V1JSONSchemaProps MapObjectType(this MetadataLoadContext context, Type type)
     {
         switch (type.FullName)

src/KubeOps.Transpiler/Utilities.cs

@@ -20,6 +20,18 @@ public static class Utilities
             .GetCustomAttributes(type)
             .FirstOrDefault(a => a.AttributeType.Name == typeof(TAttribute).Name);
 
+    /// <summary>
+    /// Load a custom attribute from a read-only-reflected field.
+    /// </summary>
+    /// <param name="field">The field.</param>
+    /// <typeparam name="TAttribute">The type of the attribute to load.</typeparam>
+    /// <returns>The custom attribute data if an attribute is found.</returns>
+    public static CustomAttributeData? GetCustomAttributeData<TAttribute>(this FieldInfo field)
+        where TAttribute : Attribute
+        => CustomAttributeData
+            .GetCustomAttributes(field)
+            .FirstOrDefault(a => a.AttributeType.Name == typeof(TAttribute).Name);
+
     /// <summary>
     /// Load a custom attribute from a read-only-reflected property.
     /// </summary>

test/KubeOps.Transpiler.Test/Crds.Mlc.Test.cs

@@ -40,6 +40,7 @@ public class CrdsMlcTest(MlcProvider provider) : TranspilerTestBase(provider)
     [InlineData(typeof(SetIntEntity), "array", null, null)]
     [InlineData(typeof(InheritedEnumerableEntity), "array", null, null)]
     [InlineData(typeof(EnumEntity), "string", null, null)]
+    [InlineData(typeof(NamedEnumEntity), "string", null, null)]
     [InlineData(typeof(NullableEnumEntity), "string", null, true)]
     [InlineData(typeof(DictionaryEntity), "object", null, null)]
     [InlineData(typeof(EnumerableKeyPairsEntity), "object", null, null)]
@@ -475,6 +476,14 @@ public void Should_Correctly_Use_Entity_Scope_Attribute()
         clusterCrd.Spec.Scope.Should().Be("Cluster");
     }
 
+    [Fact]
+    public void Should_Correctly_Get_Enum_Value_From_JsonStringEnumMemberNameAttribute()
+    {
+        var crd = _mlc.Transpile(typeof(NamedEnumEntity));
+        var specProperties = crd.Spec.Versions.First().Schema.OpenAPIV3Schema.Properties["property"];
+        specProperties.EnumProperty.Should().BeEquivalentTo(["enumValue1", "enumValue2"]);
+    }
+
     #region Test Entity Classes
 
     [KubernetesEntity(Group = "testing.dev", ApiVersion = "v1", Kind = "TestEntity")]
@@ -659,6 +668,20 @@ public enum TestSpecEnum
         }
     }
 
+    [KubernetesEntity(Group = "testing.dev", ApiVersion = "v1", Kind = "TestEntity")]
+    private class NamedEnumEntity : CustomKubernetesEntity
+    {
+        public TestSpecEnum Property { get; set; }
+
+        public enum TestSpecEnum
+        {
+            [JsonStringEnumMemberName("enumValue1")]
+            Value1,
+            [JsonStringEnumMemberName("enumValue2")]
+            Value2,
+        }
+    }
+
     [KubernetesEntity(Group = "testing.dev", ApiVersion = "v1", Kind = "TestEntity")]
     private class SimpleDictionaryEntity : CustomKubernetesEntity
     {