Allow serializing/deserializing Entity outside World

[Rua]

When trying to serialise a type that contains an Entity reference, outside a World, I get a panic with the error "No entity serializer set". Serializing an Entity reference requires run_as_context to be called in order to provide the thread-local variable containing the Canon. This function is private, which means it's not possible to serialize/deserialize any type that contains Entity if it's not in a component in the World.

Could something be added to allow serde of Entity outside a World?

[Uriopass]

I think #221 solves this but I'm not sure what idiomatic code looks like using it. (note that this PR isn't part of the last released version)

[Rua]

Unfortunately it doesn't. The way to serialise Entity or types containing it would be something like this:

registry.with_entity_serializer(|canon| {
    run_as_context(canon, || {
        // do serialising here...
    });
});

This is more or less what the code here does. But with run_as_context being private, non-Legion code can't replicate it.

[matthewjberger]

I am seeing this as well

I'm storing copies of Entity in a scene graph outside of the legion::World. When the scene graph is empty (containing no copies of Entity) serialization works properly, but otherwise I get the No entity serializer set panic when serializing

[Uriopass]

Well, in the meantime, I have a workaround for this.

Just before serializing, put structs containing entities in the world as single-component entities and serialize as normal. Then remove them from the world.

When deserializing extract theses structs and remove them from the world. Note that this workaround does a lot of copying :/