[Vue warn]: Property undefined was accessed during render but is not defined on instance.

[rhengles]

Without this change, I'm getting a lot of this error:

https://prnt.sc/wchiz8

Related to #2270 , but I'm already using @vue/compiler-dom.

[LinusBorg]

Could you maybe explain the actual problem ? The references issue is not really helpful in understanding the context you are experiencing your issue in.

And I don't think we will accept a change that removes a warning that is otherwise considered useful from our perspective, unless we understand how it actually causes a problem, and under which circumstances.

[rhengles]

@LinusBorg I understand. The issue is that no application ever would use Symbol.unscopables as a key to its own data, this access is coming from the with(_ctx) {} that is generated by the template compiler, not from my application, so me as a user shouldn't have to see this warning that I can't do anything about.

Please also notice that the message itself is misleading. There is no Property undefined, but that is because JSON.stringify can't translate a symbol.

[LinusBorg]

That helps a bit but I still don't see how you are seeing a lot of these errors in your app caused by this. an reproduction from a real use case would help us understand what the actual issue and impact is.

[rhengles]

@LinusBorg Here is a link to a fiddle: https://jsfiddle.net/s5dtoy7v/

Really, if you simply use a compiled render function from a template, you get this because of the with(_ctx){}.

[LinusBorg]

You are missing an implementation detail:

https://jsfiddle.net/Linusborg/3tkae0jd/

With that flag, you don't get any more warnings. That's also why the render function works if you let Vue compile it itself, the way it's intended:

https://jsfiddle.net/Linusborg/5xL86wuz/

[rhengles]

@LinusBorg Thank you for your help!

Of course my fiddle wasn't "intended" to be a way to build production apps, only to show the issue. Now someone else who tries to use the Vue compiler as a step of their workflow can search for this issue and know what they need to do to remove this warning message. ❤

Do you or someone else know what is the rationale for this flag to not be active by default? Or why would someone ever need it disabled?