Improve terminalable directive

[kazupon]

There are times when we want to use the arg and modifires in custom terminal directive, and control the priority.

e.g.

<input type="text" v-validate:feild1.input-off="['required']">

Recently, in the following related issues or PR, we became able to define the terminal directive.

• allow empty expression in terminal directives
  allow empty expression in terminal directives #2137
• transfer DOM
  transfer DOM #2130

However, we can not yet.

I fixed this issues.
I hope that this PR are merged with you.

Please check the codes.

[yyx990803]

Thanks for the PR! This one takes some time to review, but I'll do it as soon as I can 👍

[kazupon]

Thanks!! 😺

[blake-newman]

Perhaps assign the args[0] to a variable.

[kazupon]

ping @yyx990803

[yyx990803]

These change seems pretty expensive since it's now map + sort + nested for loop for every single element compiled. Ideally we want to move as much work out of this function as possible.

[yyx990803]

Here's what I think what should be the ideal API: the custom directive should just declare terminal: true instead of monkey patching the internal terminalDirectives array. We should also change v-if and v-for to use the same terminal: true contract.

With this, the checkTerminalDirectives function would largely be the same with compileDirectives - pseudo code:

let A = "current terminal directive found with highest priority"
- for each attribute on current element:
  - if it's a directive, and has `terminal: true`:
    - if A doesn't exist, or it has higher priority than A:
      - assign it to A
- If A exists, return a terminalLinkFn for it.

Does this make sense? I may have overlooked something but I think this could make it more efficient and more consistent.

[simplesmiler]

custom directive should just declare terminal: true

Do want. This will allow to make things like vue-transfer-dom truly reusable (i.e. without Vue.use(...)).

[blake-newman]

I totally agree with the approach not to monkey patch parts of the core API. This clearly has a use case that makes sense to easily implement, with future extentions this will become ever more requested.

[kazupon]

@yyx990803
Thank you for your code review , new API proposal for terminal directive, and pseudo code.

When I'm implementing the patch of this PR, I felt that terminalDirectives array is monkey patch. I think that your API proposal make sense.

I'll try to challenge based on your feedback. 😸

[kazupon]

@yyx990803 updated

[yyx990803]

we can already extract arg as matched[2] here, and can just use that and pass it to makeTerminalNodeLinkFn instead of using argRE.

[kazupon]

@yyx990803
Updated Done.

This PR is breaking change of custom terminal directives.
We need to write the document terminal directive feature.

[yyx990803]

@kazupon yes. Custom terminal directives were not publicly documented though, so technically this is a new feature. One case I can think of is https://github.com/rhyzx/vue-transfer-dom may need to be updated to use the new API. /cc @rhyzx

[yyx990803]

Merged! 🎉
I think this is the first PR that makes non-trivial updates to the compiler mechanism, great job @kazupon !

[kazupon]

@yyx990803
Thanks !!

As next step, I'll try to write the documentation.