fix: Remove trailing nulls for optional enums

Author: sbernauer

kube-core/src/schema/mod.rs

@@ -4,6 +4,7 @@
 
 mod transform_any_of;
 mod transform_one_of;
+mod transform_optional_enum_with_null;
 mod transform_properties;
 
 // Used in docs
@@ -13,6 +14,7 @@ use schemars::{transform::Transform, JsonSchema};
 use serde::{Deserialize, Serialize};
 use serde_json::Value;
 use std::collections::{BTreeMap, BTreeSet};
+use transform_optional_enum_with_null::remove_optional_enum_null_variant;
 
 use crate::schema::{
     transform_any_of::hoist_any_of_subschema_with_a_nullable_variant,
@@ -278,6 +280,7 @@ impl Transform for StructuralSchemaRewriter {
         hoist_one_of_enum_with_unit_variants(&mut schema);
         hoist_any_of_subschema_with_a_nullable_variant(&mut schema);
         hoist_properties_for_any_of_subschemas(&mut schema);
+        remove_optional_enum_null_variant(&mut schema);
 
         // check for maps without with properties (i.e. flattened maps)
         // and allow these to persist dynamically

kube-core/src/schema/transform_optional_enum_with_null.rs

@@ -0,0 +1,64 @@
+use serde_json::Value;
+
+use super::SchemaObject;
+
+#[cfg(test)]
+#[test]
+fn optional_enum_with_null() {
+    let original_schema_object_value = serde_json::json!({
+        "description": "A very simple enum with unit variants without descriptions",
+        "enum": [
+            "A",
+            "B",
+            "C",
+            "D",
+            null
+        ],
+        "nullable": true
+    });
+
+    let expected_converted_schema_object_value = serde_json::json!({
+        "description": "A very simple enum with unit variants without descriptions",
+        "enum": [
+            "A",
+            "B",
+            "C",
+            "D"
+        ],
+        "nullable": true
+    });
+
+    let original_schema_object: SchemaObject =
+        serde_json::from_value(original_schema_object_value).expect("valid JSON");
+    let expected_converted_schema_object: SchemaObject =
+        serde_json::from_value(expected_converted_schema_object_value).expect("valid JSON");
+
+    let mut actual_converted_schema_object = original_schema_object.clone();
+    remove_optional_enum_null_variant(&mut actual_converted_schema_object);
+
+    assert_json_diff::assert_json_eq!(actual_converted_schema_object, expected_converted_schema_object);
+}
+
+/// A Option<Enum> without any descriptions has `nullable` set to `true` as well as a trailing
+/// `null` enum variant. We remove the trailing enum variant as it's not needed for Kubernetes and
+/// makes the CRD more compact by removing duplicated information.
+pub(crate) fn remove_optional_enum_null_variant(kube_schema: &mut SchemaObject) {
+    let SchemaObject {
+        enum_values: Some(enum_values),
+        extensions,
+        ..
+    } = kube_schema
+    else {
+        return;
+    };
+
+    // It only makes sense to remove `null` enum values in case the enum is
+    // nullable (thus optional).
+    if let Some(Value::Bool(true)) = extensions.get("nullable")
+        // Don't remove the single last enum variant. This often happens for
+        // `Option<XXX>`, which is represented as
+        // `"anyOf": [XXX, {"enum": [null], "optional": true}]`
+        && enum_values.len() > 1 {
+            enum_values.retain(|enum_value| enum_value != &Value::Null);
+    }
+}