Adds an Unknown variant to the list of possible mirrord targets for future compat.

[meowjesty]

• Issue: Add Unknown variant for Target #2515

1. Changes the TargetSpec from having an Option<Target> field to an KubeTarget enum, which can take either a Known(Target) or an Unknown(String):
   • custom deserialization, allowing us to convert a valid kubernetes target, which we don't know about in mirrord, into an KubeTarget::Unknown;

[Razz4780]

Have you tried changing TargetCrd instead? Maybe we can wrap Target in there into some enum :V
Sth like:

#[derive(Deserialize, ...)
#[serde(untagged)]
pub enum SafeTarget {
  KnownTarget(Target),
  UnknownTarget {
    #[serde(rename = "type")]
    type_: String,
  },
}

The necessary use of unreachables here is uncanny and I'm sad :<
Also Unknown being displayed as an empty string and other code depending on it :<

[meowjesty]

Changed it to an enum, please look into the operator PR to see if it's better now.

Name suggestions are welcome, I was thinking KubeTarget, as this type encapsulates any kube target, known and unknown to us.

[Razz4780]

Changed it to an enum, please look into the operator PR to see if it's better now.

Name suggestions are welcome, I was thinking KubeTarget, as this type encapsulates any kube target, known and unknown to us.

Looks better imho ^^

[Razz4780]

I think this change could touch only mirrord_operator. Would be nice, because unknown targets are only relevant for maintaining forward compatibility with the operator. New wrapper type could be moved to mirrord_operator::crd and the rest of OSS code could stay unaware of its existence. You wouldn't need to change mirrord_config or mirrord_kube

[Razz4780]

Some nits + could you add a unit tests asserting that this change is backwards compatible? In test submodule, you could declare a struct like TargetSpecLegacy (with all the derives) that matches previous format and check how:

1. Serialized legacy type with target None deserializes into new type
2. Serialized legacy type with some target deserializes into new type
3. New type deserializes from some unknown target type
4. Legacy type deserializes from the serialized new type

[Razz4780]

Neat!