Here is how to repro:

1. 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

2. 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
   

3. 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

4. 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:

This patch would fix it cilium@d944deb.

When type Alias is its own type, it goes to:

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!