Should .vue file need access modifiers? like public/protected/private in Java

[xuyimingwork]

vuejs/rfcs#96
vuejs/rfcs#517

VueUse now has createReusableTemplate function to create sub component in a file.

But I think break large component into sub component is a real requirement, the key problem is:

• sub component is only used by large component, if I define sub component in another .vue, it exposed to the outside of the large component, which is not what I need.
• if I keep sub component in large component file, making large component file even larger, which is not what I need either.

So, my idea is: this is a problem of js missing access modifiers, unlike Java, we don't have public protected private access modifiers.
A component in Vue is like a class in Java, a .vue file in Vue is like a .java file in Java.
Why not just introduce the best practice of access modifiers in Java, which examined by millions of developer, to solve the problem we facing? Just using tools like eslint, add a new rule and config .vue's access modifiers by comment, maybe enough.

[xuyimingwork]

Draft Specification: Vue File-Level Access Control

1. The Modifier Matrix

Level	Syntax	Scope
Private	/** @access private(File.vue) **/	Accessible only by the specific parent file.
Strict Protected	/** @access protected(Folder) strict **/	Accessible only by files in the Folder/ root.
Protected	/** @access protected(Folder) **/	Accessible by Folder/ and all its sub-directories.
Public	/** @access public **/	Accessible by any file in the project.

2. Project Example & Enforcement

Imagine a User Management feature which has a UserList.vue component. We want to break it down without leaking internal parts:

A. The Private

UserListItem.vue is a small part of the UserList.vue

<script setup>  
/** @access private(UserList.vue) **/  
</script>

• Allowed: UserList.vue
• Blocked: Any other component

B. The Strict Protected (Same Folder)

UserTheme.vue defines the look for the whole feature.

<script setup>  
/** @access protected(User) strict **/  
</script>

• Allowed: components under User folder, like User/UserDashboard.vue
• Blocked: any other components not directly under User, like: User/Reports/WeeklyReport.vue or Other/OtherReport.vue

C. The Protected

UserIcon.vue is used by all components under the User/ folder.

<script setup>  
/** @access protected(User) **/  
</script>

• Allowed: User/UserDashboard.vue AND User/Reports/WeeklyReport.vue.
• Blocked: any other components not under User, like: Other/OtherReport.vue

. The Public

a component can import by any component in project.

<script setup>  
/** @access public **/  
</script>

or no comment(default behavior).

• Allowed: all component can import
• Blocked: None

3. ESLint Implementation Logic

To enforce this, a custom ESLint rule would perform these three checks whenever an import is detected:

1. Tag Discovery: Read the first 10 lines of the imported file to find the @access comment.
2. Path Resolution: Resolve the (Name) parameter to a physical directory path.
3. Boundary Check:
   • If Private: Is the importer's filename exactly Name?
   • If Protected: Does the importer's path start with Name's path?
   • If Strict: Does the importer's path start with Name's path and have the same folder depth?

4. Why this works for the Vue Ecosystem

• No Runtime Cost: The browser never sees these comments; it only affects the development/build phase.
• Incremental Adoption: You can add this to just one folder in your project without needing to update the whole app.
• Zero Boilerplate: It replaces the need for complex index.js export files or "Barrel" files which often slow down build times.

[aniruddhaadak80]

Hey @xuyimingwork,

Working with Vue reactivity system and compilers can sometimes present interesting edge cases. A few quick things to consider regarding this topic:

1. Reactivity & Refs: Remember that reactive() unwraps refs automatically, but accessing private properties of proxy classes inherently breaks proxy traps. Always interact with the standard exposed endpoints.
2. Component Lifecycle & state: If you are mixing <script setup>, ensure you aren???t trying to mutate props directly or losing reactivity when destructuring (use toRefs if needed).

I highly recommend checking out the Vue DevTools extension to inspect the component tree and verify if the state is updating as expected. Let me know if you want to dig deeper into the specific component logic.

Hope this points you in the right direction! Let me know how it goes. Happy coding!