SystemAPI generating wrong code

[lone forge]

There seems to be some kind of issue when using SystemAPI.QueryBuilder inside system properties. The generated query is missing the WithAll parameter and not working properly.
When defining the query inside a method instead of a property it works correctly.

Am I doing something wrong or is this a Unity bug?

Code:

public partial class TestSystem : SystemBase
{
    public struct TestComponent : IComponentData
    {
        public int A;
    }

    public Entity MyEntity => SystemAPI.QueryBuilder().WithAll<TestComponent>().Build().GetSingletonEntity();

    protected override void OnUpdate() { }
}

Generated Code:

[global::System.Runtime.CompilerServices.CompilerGenerated]
public partial class TestSystem
{
    [global::Unity.Entities.DOTSCompilerPatchedProperty("TestSystem.MyEntity")]

    Entity __MyEntity_6A13DB69 =>  __query_1809747855_0.GetSingletonEntity();
    
    TypeHandle __TypeHandle;
     Unity.Entities.EntityQuery __query_1809747855_0;
// ...
    [global::System.Runtime.CompilerServices.MethodImpl(global::System.Runtime.CompilerServices.MethodImplOptions.AggressiveInlining)]
    void __AssignQueries(ref global::Unity.Entities.SystemState state)
    {
        var entityQueryBuilder = new global::Unity.Entities.EntityQueryBuilder(global::Unity.Collections.Allocator.Temp);
        __query_1809747855_0 = entityQueryBuilder.Build(ref state);
        entityQueryBuilder.Reset();
        entityQueryBuilder.Dispose();
    }
// ...
}

[willow hornet]

first problem is you are using a property on an ISystem 🙈

[lone forge]

yeah, for the ISystem it doesn't actually makes sense... I've updated the post
but I don't see any reason for it not working on SystemBase?

[celest moth]

I assume because code generation is finicky, and properties are finicky, so combining the two is just a bad idea from the get-go.

Though to begin with, I would suggest not having heavy logic / slow code inside a property, since it hides a bit of logic and doesn't make it obvious that you shouldn't be calling it over and over instead of just caching the result

[lone forge]

I don't see why would properties would be finicky though, it's a pretty common language feature
I'll file a bug report soon... there should at least be a warning in case they don't intend to support proper code gen on properties

[serene notch]

In ECS Systems aren't really represented as objects. It's more of a C# thing. In some ECS frameworks, systems are written as literally static functions