Adjust fork form visibility logic

Dynamically creating the allowed visibility logic.
This will make it easier to support issues:
- https://gitlab.com/gitlab-org/gitlab/-/issues/329575
- https://gitlab.com/gitlab-org/gitlab/-/issues/331620

app/assets/javascripts/pages/projects/forks/new/components/fork_form.vue

@@ -26,10 +26,10 @@ const PRIVATE_VISIBILITY = 'private';
 const INTERNAL_VISIBILITY = 'internal';
 const PUBLIC_VISIBILITY = 'public';
 
-const ALLOWED_VISIBILITY = {
-  private: [PRIVATE_VISIBILITY],
-  internal: [INTERNAL_VISIBILITY, PRIVATE_VISIBILITY],
-  public: [INTERNAL_VISIBILITY, PRIVATE_VISIBILITY, PUBLIC_VISIBILITY],
+const VISIBILITY_LEVEL = {
+  [PRIVATE_VISIBILITY]: 0,
+  [INTERNAL_VISIBILITY]: 10,
+  [PUBLIC_VISIBILITY]: 20,
 };
 
 const initFormField = ({ value, required = true, skipValidation = false }) => ({
@@ -124,14 +124,23 @@ export default {
     projectUrl() {
       return `${gon.gitlab_url}/`;
     },
-    projectAllowedVisibility() {
-      return ALLOWED_VISIBILITY[this.projectVisibility];
+    projectVisibilityLevel() {
+      return VISIBILITY_LEVEL[this.projectVisibility];
     },
-    namespaceAllowedVisibility() {
-      return (
-        ALLOWED_VISIBILITY[this.form.fields.namespace.value?.visibility] ||
-        ALLOWED_VISIBILITY[PUBLIC_VISIBILITY]
-      );
+    namespaceVisibilityLevel() {
+      const visibility = this.form.fields.namespace.value?.visibility || PUBLIC_VISIBILITY;
+      return VISIBILITY_LEVEL[visibility];
+    },
+    visibilityLevelCap() {
+      return Math.min(this.projectVisibilityLevel, this.namespaceVisibilityLevel);
+    },
+    allowedVisibilityLevels() {
+      return Object.entries(VISIBILITY_LEVEL).reduce((levels, [levelName, levelValue]) => {
+        if (levelValue <= this.visibilityLevelCap) {
+          levels.push(levelName);
+        }
+        return levels;
+      }, []);
     },
     visibilityLevels() {
       return [
@@ -179,11 +188,8 @@ export default {
       const { data } = await axios.get(this.endpoint);
       this.namespaces = data.namespaces;
     },
-    isVisibilityLevelDisabled(visibilityLevel) {
-      return !(
-        this.projectAllowedVisibility.includes(visibilityLevel) &&
-        this.namespaceAllowedVisibility.includes(visibilityLevel)
-      );
+    isVisibilityLevelDisabled(visibility) {
+      return !this.allowedVisibilityLevels.includes(visibility);
     },
     async onSubmit() {
       this.form.showValidation = true;