template ref with reactive in v-for always empty in production mode

[Filin3]

Vue version

3.4.21

Link to minimal reproduction

https://play.vuejs.org/#eNp9kF9LwzAUxb/KJS/rYLZOfRrdQGUPCv5BfTMipb2t2dokJGmtlH53b1pW9yCjFMK5v5ycezp2rXXY1MhWLHZY6TJxuOESIM5EA81ZrsyaMwFCwvKcM1jt8ccLnA0UcRoM5iRpkroOBPR9HOnRIyITOsXRkbX/YpsaoR1YdLVHRaWVcdCBkg+qlg6zBbkmqRMNQg+5URXMKOWMy1RJ60DDegKC94+5N53uBsEc1hvofASPqxLDUhWBJqynP47G5zdswZwlIhdFuLNKUgnDJc5SVWlRonnSTpADZ6vRzs+SslTf94PmTI2Lg55+Ybr/R9/Z1mucPRu0aBrkbJq5xBToxvH29RFbOk/DSmV1SfSJ4QvSdrXPOGI3tcwo9hE3pL0b+hWyeLPb1qG0h6V8UE/2A88ZdXx7YvW/uJfh1XCPGqUWPxs03pMKpEF4sWT9Ly2kxOo=

Steps to reproduce

Open vue playground then open devtools console and change prod\dev mode

What is expected?

The same behavior is expected in prod and dev mode. Reactive const will be filled in both cases

What is actually happening?

The Reactive constant is filled in dev mode, but always empty in prod

System Info

No response

Any additional comments?

No response

[LinusBorg]

The production behaviour is correct as the template ref gets a new array reassigned - and const variables are not re-assignable.

However we should look into how to warn about this in dev mode

[quiteeasy]

In the prod mode, reactive values are not exposed in the setupResult object as the script setup gets inlined when using the script setup syntax. However, this does not occur in development mode or when using the regular setup() function that returns reactive values.

To address this, I have added a warning in the PR for this specific case. One potential solution could be to forbid the use of reactive as a ref completely. However, this approach might have implications for existing code and developer workflows, so it's essential to gather feedback from the team and carefully evaluate the trade-offs.

I'm looking forward to the team's input and suggestions on how to best resolve this issue. In the meantime, I am opening a PR proposing a potential solution, which I'm happy to discuss further with the team.

[quiteeasy]

PR to add a warning for this case #10784

[scottbell]

Just ran into this - thanks to all for the ticket & the PR! Note this error is difficult to debug, as the error is rather cryptic.

[edison1105]

fixed via #12051