Allow attributes to be used on enums

src/gaemstone/ECS/Attributes.cs

@@ -16,7 +16,7 @@ public interface ICreateEntityAttribute {  }
 /// (a globally unique identifier) set equal to their name. If they
 /// are also marked with this attribute, the symbol won't be set.
 /// </summary>
-[AttributeUsage(AttributeTargets.Class | AttributeTargets.Struct)]
+[AttributeUsage(AttributeTargets.Class | AttributeTargets.Struct | AttributeTargets.Enum)]
 public class PrivateAttribute : Attribute {  }
 
 /// <summary>
@@ -51,15 +51,15 @@ public class TagAttribute : AddAttribute<Tag>, ICreateEntityAttribute {  }
 /// the "relation" in a pair. However, this attribute is purely informational.
 /// </summary>
 /// <remarks>
-///   The relationship may have component data associated with
-///   it when added to an entity under these circumstances:
-///   <list type="bullet">
-///     <item>If marked as a <see cref="TagAttribute"/>, does not carry data.</item>
-///     <item>If marked as a <see cref="ComponentAttribute"/>, carries the relation's data.</item>
-///     <item>If marked with neither, will carry the target's data, if it's a component.</item>
-///   </list>
+/// The relationship may have component data associated with
+/// it when added to an entity under these circumstances:
+/// <list type="bullet">
+///   <item>If marked as a <see cref="TagAttribute"/>, does not carry data.</item>
+///   <item>If marked as a <see cref="ComponentAttribute"/>, carries the relation's data.</item>
+///   <item>If marked with neither, will carry the target's data, if it's a component.</item>
+/// </list>
 /// </remarks>
-[AttributeUsage(AttributeTargets.Class | AttributeTargets.Struct)]
+[AttributeUsage(AttributeTargets.Class | AttributeTargets.Struct | AttributeTargets.Enum)]
 public class RelationAttribute : Attribute, ICreateEntityAttribute {  }
 
 
@@ -67,7 +67,7 @@ public class RelationAttribute : Attribute, ICreateEntityAttribute {  }
 public class IsAAttribute<TTarget> : AddAttribute<IsA, TTarget> {  }
 
 /// <seealso cref="ChildOf"/>
-[AttributeUsage(AttributeTargets.Class | AttributeTargets.Struct)]
+[AttributeUsage(AttributeTargets.Class | AttributeTargets.Struct | AttributeTargets.Enum)]
 public class ChildOfAttribute<TTarget> : AddAttribute<ChildOf, TTarget> {  }
 
 /// <seealso cref="DependsOn"/>
@@ -90,14 +90,14 @@ public class ProxyAttribute : Attribute
 	internal ProxyAttribute(Type type) => Type = type;
 }
 
-[AttributeUsage(AttributeTargets.Class | AttributeTargets.Struct, AllowMultiple = true)]
+[AttributeUsage(AttributeTargets.Class | AttributeTargets.Struct | AttributeTargets.Enum, AllowMultiple = true)]
 public class AddEntityAttribute : Attribute
 {
 	public Type Entity { get; }
 	internal AddEntityAttribute(Type entity) => Entity = entity;
 }
 
-[AttributeUsage(AttributeTargets.Class | AttributeTargets.Struct, AllowMultiple = true)]
+[AttributeUsage(AttributeTargets.Class | AttributeTargets.Struct | AttributeTargets.Enum, AllowMultiple = true)]
 public class AddRelationAttribute : Attribute
 {
 	public Type Relation { get; }

src/gaemstone/ECS/Component.cs

@@ -5,7 +5,7 @@ using static flecs_hub.flecs;
 
 namespace gaemstone.ECS;
 
-[AttributeUsage(AttributeTargets.Class | AttributeTargets.Struct)]
+[AttributeUsage(AttributeTargets.Class | AttributeTargets.Struct | AttributeTargets.Enum)]
 public class ComponentAttribute : EntityAttribute {  }
 
 public static class ComponentExtensions
@@ -17,7 +17,13 @@ public static class ComponentExtensions
 		// TODO: Do some additional sanity checking for this type.
 
 		var typeInfo = default(ecs_type_info_t);
-		if (type.IsValueType) {
+		if (type.IsPrimitive) throw new ArgumentException(
+			"Must not be primitive", nameof(type));
+		else if (type.IsEnum) {
+			var wrapper = TypeWrapper.For(type);
+			typeInfo.size      = wrapper.Size;
+			typeInfo.alignment = wrapper.Size;
+		} else if (type.IsValueType) {
 			var wrapper = TypeWrapper.For(type);
 			if (!wrapper.IsUnmanaged) throw new Exception(
 				"Struct component must satisfy the unmanaged constraint. " +

src/gaemstone/ECS/Entity.cs

@@ -12,6 +12,7 @@ public class EntityAttribute : Attribute, ICreateEntityAttribute
 /// without explicitly specifying an entity in a query, where it is equivalent
 /// to <see cref="SourceAttribute{}"/> with itself as the generic type parameter.
 /// </summary>
+[AttributeUsage(AttributeTargets.Class | AttributeTargets.Struct | AttributeTargets.Enum)]
 public class SingletonAttribute : EntityAttribute {  }
 
 public readonly struct Entity