You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: crd.rs
    path of file: ./repos/kube/kube-core/src
    
    the code of the file until where you have to start completion: //! Traits and tyes for CustomResources

use k8s_openapi::apiextensions_apiserver::pkg::apis::apiextensions as apiexts;

/// Types for v1 CustomResourceDefinitions
pub mod v1 {
    use super::apiexts::v1::CustomResourceDefinition as Crd;
    /// Extension trait that is implemented by kube-derive
    pub trait CustomResourceExt {
        /// Helper to generate the CRD including the JsonSchema
        ///
        /// This is using the stable v1::CustomResourceDefinitions (present in kubernetes >= 1.16)
        fn crd() -> Crd;
        /// Helper to return the name of this `CustomResourceDefinition` in kubernetes.
        ///
        /// This is not the name of an _instance_ of this custom resource but the `CustomResourceDefinition` object itself.
        fn crd_name() -> &'static str;
        /// Helper to generate the api information type for use with the dynamic `Api`
        fn api_resource() -> crate::discovery::ApiResource;
        /// Shortnames of this resource type.
        ///
        /// For example: [`Pod`] has the shortname alias `po`.
        ///
        /// NOTE: This function returns *declared* short names (at compile-time, using the `#[kube(shortname = "foo")]`), not the
        /// shortnames registered with the Kubernetes API (which is what tools such as `kubectl` look at).
        ///
        /// [`Pod`]: `k8s_openapi::api::core::v1::Pod`
        fn shortnames() -> &'static [&'static str];
    }

    /// Possible errors when merging CRDs
    #[derive(Debug, thiserror::Error)]
    pub enum MergeErro
    
        fn crd_merge() {
            use super::{merge_crds, Crd};
            let crd1 = r#"
            apiVersion: apiextensions.k8s.io/v1
            kind: CustomResourceDefinition
            metadata:
              name: multiversions.kube.rs
            spec:
              group: kube.rs
              names:
                categories: []
                kind: MultiVersion
                plural: multiversions
                shortNames: []
                singular: multiversion
              scope: Namespaced
              versions:
              - additionalPrinterColumns: []
                name: v1
                schema:
                  openAPIV3Schema:
                    type: object
                    x-kubernetes-preserve-unknown-fields: true
                served: true
                storage: true"#;

            let crd2 = r#"
            apiVersion: apiextensions.k8s.io/v1
            kind: CustomResourceDefinition
            metadata:
              name: multiversions.kube.rs
            spec:
              group: kube.rs
              names:
                categories: []
                kind: MultiVersion
                plural: multiversions
                shortNames: []
                singular: multiversion
              scope: Namespaced
              versions:
              - additionalPrinterColumns: []
                name: v2
                schema:
                  openAPIV3Schema:
                    type: object
                    x-kubernetes-preserve-unknown-fields: true
                served: true
                storage: true"#;

            let expected = r#"
            apiVersion: apiextensions.k8s.io/v1
            kind: CustomResourceDefinition
            metadata:
              name: multiversions.kube.rs
            spec:
              group: kube.rs
              names:
                categories: []
                kind: MultiVersion
                plural: multiversions
                shortNames: []
                singular: multiversion
              scope: Namespaced
              versions:
              - additionalPrinterColumns: []
                name: v2
                schema:
                  openAPIV3Schema:
                    type: object
                    x-kubernetes-preserve-unknown-fields: true
                served: true
                storage: true
              - additionalPrinterColumns: []
                name: v1
                schema:
                  openAPIV3Schema:
                    type: object
                    x-kubernetes-preserve-unknown-fields: true
                served: true
                storage: false"#;

            let c1: Crd = serde_yaml::from_str(crd1).unwrap();
            let c2: Crd = serde_yaml::from_str(crd2).unwrap();
            let ce: Crd = serde_yaml::from_str(expected).unwrap();
            let combined = merge_crds(vec![c1, c2], "v2").unwrap();

            let combo_json = serde_json::to_value(&combined).unwrap();
            let exp_json = serde_json::to_value(&ce).unwrap();
            assert_json_diff::assert_json_eq!(combo_json, exp_json);
        }