validation on type alias is ignored when `GODEBUG=gotypealias=0` (Go < 1.23)

Here is how to repro:

Create a a repro directory mkdir repro and put repro.go inside of it with:

// +groupName=repro.io
package repro

import (
metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
)

type Repro struct {
metav1.TypeMeta   `json:",inline"`
metav1.ObjectMeta `json:"metadata"`

Reproducer StringAlias `json:"reproducer"`
}

// +kubebuilder:validation:MaxLength=12
type StringAlias = string

Run controller-gen with:

go run ./cmd/controller-gen/ crd paths=./repro output:stdout

The output should be similar to

---
apiVersion: apiextensions.k8s.io/v1
kind: CustomResourceDefinition
metadata:
  annotations:
    controller-gen.kubebuilder.io/version: (devel)
  name: reproes.repro.io
spec:
  group: repro.io
  names:
    kind: Repro
    listKind: ReproList
    plural: reproes
    singular: repro
  scope: Namespaced
  versions:
  - name: repro
    schema:
      openAPIV3Schema:
        properties:
          apiVersion:
            description: |-
              APIVersion defines the versioned schema of this representation of an object.
              Servers should convert recognized schemas to the latest internal value, and
              may reject unrecognized values.
              More info: https://git.k8s.io/community/contributors/devel/sig-architecture/api-conventions.md#resources
            type: string
          kind:
            description: |-
              Kind is a string value representing the REST resource this object represents.
              Servers may infer this from the endpoint the client submits requests to.
              Cannot be updated.
              In CamelCase.
              More info: https://git.k8s.io/community/contributors/devel/sig-architecture/api-conventions.md#types-kinds
            type: string
          metadata:
            type: object
          reproducer:
            type: string
        required:
        - metadata
        - reproducer
        type: object
    served: true
    storage: true

Now bump the go directive to Go 1.23.0 in go.mod or put godebug gotypesalias=1 in the go.mod with Go 1.22:

diff --git a/go.mod b/go.mod
index 790a5a11..c9e19176 100644
--- a/go.mod
+++ b/go.mod
@@ -1,6 +1,6 @@
module sigs.k8s.io/controller-tools

-go 1.22.0
+ go 1.23.0

Run controller-gen with:

go run ./cmd/controller-gen/ crd paths=./repro output:stdout

The output should be similar to

---
apiVersion: apiextensions.k8s.io/v1
kind: CustomResourceDefinition
metadata:
  annotations:
    controller-gen.kubebuilder.io/version: (devel)
  name: reproes.repro.io
spec:
  group: repro.io
  names:
    kind: Repro
    listKind: ReproList
    plural: reproes
    singular: repro
  scope: Namespaced
  versions:
  - name: repro
    schema:
      openAPIV3Schema:
        properties:
          apiVersion:
            description: |-
              APIVersion defines the versioned schema of this representation of an object.
              Servers should convert recognized schemas to the latest internal value, and
              may reject unrecognized values.
              More info: https://git.k8s.io/community/contributors/devel/sig-architecture/api-conventions.md#resources
            type: string
          kind:
            description: |-
              Kind is a string value representing the REST resource this object represents.
              Servers may infer this from the endpoint the client submits requests to.
              Cannot be updated.
              In CamelCase.
              More info: https://git.k8s.io/community/contributors/devel/sig-architecture/api-conventions.md#types-kinds
            type: string
          metadata:
            type: object
          reproducer:
+           maxLength: 12
            type: string
        required:
        - metadata
        - reproducer
        type: object
    served: true
    storage: true

Explanation: without the type Alias being its own type (Go 1.22), in localNamedToSchema, the link is missing: https://github.com/kubernetes-sigs/controller-tools/blob/1d40d792491f708409229c554022de59b90637a7/pkg/crd/schema.go#L245-L254

This patch would fix it https://github.com/cilium/controller-tools/commit/d944debcff34ea02a9506bc5911b2bb64ee61dd6.

When type Alias is its own type, it goes to: https://github.com/kubernetes-sigs/controller-tools/blob/1d40d792491f708409229c554022de59b90637a7/pkg/crd/schema.go#L255-L267

And then the link is properly made.

Should we have the patch for the version so that type Alias validation works with Go 1.22 or should we just wait for this project to use Go 1.23 and thus gotypesalias=1? Thanks!

kubernetes-sigs / controller-tools

validation on type alias is ignored when `GODEBUG=gotypealias=0` (Go < 1.23) #1071