feat: Add typed scale argument to derive macro

examples/crd_api.rs

@@ -19,7 +19,10 @@ use kube::{
 #[derive(CustomResource, Deserialize, Serialize, Clone, Debug, Validate, JsonSchema)]
 #[kube(group = "clux.dev", version = "v1", kind = "Foo", namespaced)]
 #[kube(status = "FooStatus")]
-#[kube(scale = r#"{"specReplicasPath":".spec.replicas", "statusReplicasPath":".status.replicas"}"#)]
+#[kube(scale(
+    spec_replicas_path = ".spec.replicas",
+    status_replicas_path = ".status.replicas"
+))]
 #[kube(printcolumn = r#"{"name":"Team", "jsonPath": ".spec.metadata.team", "type": "string"}"#)]
 pub struct FooSpec {
     #[schemars(length(min = 3))]

examples/crd_derive.rs

@@ -22,7 +22,10 @@ use serde::{Deserialize, Serialize};
     derive = "PartialEq",
     derive = "Default",
     shortname = "f",
-    scale = r#"{"specReplicasPath":".spec.replicas", "statusReplicasPath":".status.replicas"}"#,
+    scale(
+        spec_replicas_path = ".spec.replicas",
+        status_replicas_path = ".status.replicas"
+    ),
     printcolumn = r#"{"name":"Spec", "type":"string", "description":"name of foo", "jsonPath":".spec.name"}"#,
     selectable = "spec.name"
 )]

kube-derive/Cargo.toml

@@ -19,6 +19,7 @@ proc-macro2.workspace = true
 quote.workspace = true
 syn = { workspace = true, features = ["extra-traits"] }
 serde_json.workspace = true
+k8s-openapi = { workspace = true, features = ["latest"] }
 darling.workspace = true
 
 [lib]

kube-derive/src/custom_resource.rs

@@ -2,6 +2,7 @@
 #![allow(clippy::manual_unwrap_or_default)]
 
 use darling::{FromDeriveInput, FromMeta};
+use k8s_openapi::apiextensions_apiserver::pkg::apis::apiextensions::v1::CustomResourceSubresourceScale;
 use proc_macro2::{Ident, Literal, Span, TokenStream};
 use quote::{ToTokens, TokenStreamExt};
 use syn::{parse_quote, Data, DeriveInput, Path, Visibility};
@@ -34,7 +35,12 @@
     printcolums: Vec<String>,
     #[darling(multiple)]
     selectable: Vec<String>,
-    scale: Option<String>,
+
+    /// Customize the scale subresource, see [Kubernetes docs][1].
+    ///
+    /// [1]: https://kubernetes.io/docs/tasks/extend-kubernetes/custom-resources/custom-resource-definitions/#scale-subresource
+    scale: Option<Scale>,
+
     #[darling(default)]
     crates: Crates,
     #[darling(multiple, rename = "annotation")]
@@ -185,6 +191,107 @@
     }
 }
 
+/// A new-type wrapper around [`CustomResourceSubresourceScale`] to support parsing from the
+/// `#[kube]` attribute.
+#[derive(Debug)]
+struct Scale(CustomResourceSubresourceScale);
+
+// This custom FromMeta implementation is needed for two reasons:
+//
+// - To enable backwards-compatibility. Up to version 0.97.0 it was only possible to set scale
+//   subresource values as a JSON string.
+// - k8s_openapi types don't support being parsed directly from attributes using darling. This
+//   would require an upstream change, which is highly unlikely to occur. The from_list impl uses
+//   the derived implementation as inspiration.
+impl FromMeta for Scale {
+    /// This is implemented for backwards-compatibility. It allows that the scale subresource can
+    /// be deserialized from a JSON string.
+    fn from_string(value: &str) -> darling::Result<Self> {
+        let scale = serde_json::from_str(value).map_err(|err| darling::Error::custom(err))?;
+        Ok(Self(scale))
+    }
+
+    fn from_list(items: &[darling::ast::NestedMeta]) -> darling::Result<Self> {
+        let mut errors = darling::Error::accumulator();
+
+        let mut label_selector_path: (bool, Option<Option<String>>) = (false, None);
+        let mut spec_replicas_path: (bool, Option<String>) = (false, None);
+        let mut status_replicas_path: (bool, Option<String>) = (false, None);
+
+        for item in items {
+            match item {
+                darling::ast::NestedMeta::Meta(meta) => {
+                    let name = darling::util::path_to_string(meta.path());
+
+                    match name.as_str() {
+                        "label_selector_path" => {
+                            let path = errors.handle(darling::FromMeta::from_meta(meta));
+                            label_selector_path = (true, Some(path))
+                        }
+                        "spec_replicas_path" => {
+                            let path = errors.handle(darling::FromMeta::from_meta(meta));
+                            spec_replicas_path = (true, path)
+                        }
+                        "status_replicas_path" => {
+                            let path = errors.handle(darling::FromMeta::from_meta(meta));
+                            status_replicas_path = (true, path)
+                        }
+                        other => return Err(darling::Error::unknown_field(other)),
+                    }
+                }
+                darling::ast::NestedMeta::Lit(lit) => {
+                    errors.push(darling::Error::unsupported_format("literal").with_span(&lit.span()))
+                }
+            }
+        }
+
+        if !label_selector_path.0 {
+            match <Option<String> as darling::FromMeta>::from_none() {
+                Some(fallback) => label_selector_path.1 = Some(fallback),
+                None => errors.push(darling::Error::missing_field("spec_replicas_path")),
+            }
+        }
+
+        if !spec_replicas_path.0 && spec_replicas_path.1.is_none() {
+            errors.push(darling::Error::missing_field("spec_replicas_path"));
+        }
+
+        if !status_replicas_path.0 && status_replicas_path.1.is_none() {
+            errors.push(darling::Error::missing_field("status_replicas_path"));
+        }
+
+        errors.finish_with(Self(CustomResourceSubresourceScale {
+            label_selector_path: label_selector_path.1.unwrap(),
+            spec_replicas_path: spec_replicas_path.1.unwrap(),
+            status_replicas_path: status_replicas_path.1.unwrap(),
+        }))
+    }
+}
+
+impl Scale {
+    fn to_tokens(&self, k8s_openapi: &Path) -> TokenStream {
+        let apiext = quote! {
+            #k8s_openapi::apiextensions_apiserver::pkg::apis::apiextensions::v1
+        };
+
+        let label_selector_path = self
+            .0
+            .label_selector_path
+            .as_ref()
+            .map_or_else(|| quote! { None }, |p| quote! { #p.into() });
+        let spec_replicas_path = &self.0.spec_replicas_path;
+        let status_replicas_path = &self.0.status_replicas_path;
+
+        quote! {
+            #apiext::CustomResourceSubresourceScale {
+                label_selector_path: #label_selector_path,
+                spec_replicas_path: #spec_replicas_path.into(),
+                status_replicas_path: #status_replicas_path.into()
+            }
+        }
+    }
+}
+
 pub(crate) fn derive(input: proc_macro2::TokenStream) -> proc_macro2::TokenStream {
     let derive_input: DeriveInput = match syn::parse2(input) {
         Err(err) => return err.to_compile_error(),
@@ -439,7 +546,13 @@
         .map(|s| format!(r#"{{ "jsonPath": "{s}" }}"#))
         .collect();
     let fields = format!("[ {} ]", fields.join(","));
-    let scale_code = if let Some(s) = scale { s } else { "".to_string() };
+    let scale = scale.map_or_else(
+        || quote! { None },
+        |s| {
+            let scale = s.to_tokens(&k8s_openapi);
+            quote! { Some(#scale) }
+        },
+    );
 
     // Ensure it generates for the correct CRD version (only v1 supported now)
     let apiext = quote! {
@@ -551,11 +664,7 @@
                 #k8s_openapi::k8s_if_ge_1_30! {
                     let fields : Vec<#apiext::SelectableField> = #serde_json::from_str(#fields).expect("valid selectableField column json");
                 }
-                let scale: Option<#apiext::CustomResourceSubresourceScale> = if #scale_code.is_empty() {
-                    None
-                } else {
-                    #serde_json::from_str(#scale_code).expect("valid scale subresource json")
-                };
+                let scale: Option<#apiext::CustomResourceSubresourceScale> = #scale;
                 let categories: Vec<String> = #serde_json::from_str(#categories_json).expect("valid categories");
                 let shorts : Vec<String> = #serde_json::from_str(#short_json).expect("valid shortnames");
                 let subres = if #has_status {

kube/src/lib.rs

@@ -223,7 +223,10 @@ mod test {
     #[derive(CustomResource, Deserialize, Serialize, Clone, Debug, JsonSchema)]
     #[kube(group = "clux.dev", version = "v1", kind = "Foo", namespaced)]
     #[kube(status = "FooStatus")]
-    #[kube(scale = r#"{"specReplicasPath":".spec.replicas", "statusReplicasPath":".status.replicas"}"#)]
+    #[kube(scale(
+        spec_replicas_path = ".spec.replicas",
+        status_replicas_path = ".status.replicas"
+    ))]
     #[kube(crates(kube_core = "crate::core"))] // for dev-dep test structure
     pub struct FooSpec {
         name: String,