V4 Vue 2.7.x support

[dparish]

Now that Vue officially supports the composition API is it possible for Vee Validate 4.0 to support Vue 2.7.x?

That would make migrating from Vue 2 to Vue 3 much easier.

[tinyfly]

Ya, this has been a huge headache. My other third-party libraries made their existing apis work with vue 3. Then made major changes after the fact in the next version making the upgrade fairly painless. This one, if you want to use vue 3 you've got to completely rewrite your validation code.

[logaretm]

I'm not sure since I haven't checked if Vue 2.7 has the same VNode API which was the main reason for the breaking change. The old API wasn't possible with Vue 3 so v4 had to be something different, unfortunately.

Now even if 2.7 worked with v4, I don't see that helping your migration efforts (well maybe if you want to slowly migrate to Vue 3) as you will still need to change your validation API. But the opposite like @tinyfly mentioned would be if it was possible.

If you are curious to know the reason specifically. In Vue 3, the VNode API doesn't tell you which node has v-model on it as directives were converted to functions and event handlers. So that means the ValidationProvider won't be able to tell which field to validate so that breaks the whole premise of vee-validate v3 API.

[dparish]

That helps a great deal and explains why you had to boil the ocean to get things to work :(

well maybe if you want to slowly migrate to Vue 3

This point EXACTLY. In our app we have 135 occurrences of ValidationProvider and ValidationObserver. That's alot to fix during an upgrade. If we can migrate those to the new Vee Validate we can move with much less risk.

[strokirk]

@dparish / @logaretm Did you end up figuring out which version of vee-validate is the correct one to use to be compatible with Vue 2 and Vue 3 versions at the same time, while doing a safe upgrade?

[logaretm]

vee-validate v3 used private VDOM API, not the public Vue API. Which is not backward compatible between Vue 3 -> Vue 2. This is the main blocker. So there is no way v3 API works in Vue 3.

However, the reverse is a different story. In theory, vee-validate v4 could work with Vue 2 if you are using composables only but I don't have the time to experiment with that unfortunately.