Deprecate {{partial}}

[GavinJoyce]

closes #390

Rendered

[rwjblue]

👏 awesome, thank you for putting this together @GavinJoyce!

I'm 1000000% in favor...

[andremalan]

This is an RFC that I'd assumed had happened already! We've been treating partials as deprecated for years!

[ngouy]

I guess it's more appropriate to post it here :

• They are hard to reason about as they inherit the scope of the calling template -> i'm not sure to understand. Isn't it their reason to be ?

the idea of a "kind of component" having the same context as the caller was sometimes very helpful :
https://blog.nathangouy.com/emberjs-full-component-inheritance/

I understand the reason of deprecating this for simplifications and performence reasons, I just wonder how it will be possible to do something like that later on... passing all attributes with a=a b=b c=c. (Not sure but did an RFC or smt opened for passing argument with ... notation ? I have the impression I saw something like this)

[rwjblue]

Not sure but did an RFC or smt opened for passing argument with ... notation ? I have the impression I saw something like thi

There is ...attributes, but it does not work for arguments. It would probably be possible to allow something akin to ...arguments to angle bracket invocation, but it hasn't been done (or designed) just yet.

[ngouy]

Ok my bad I thought I saw something like this in a RFC. It would have been a great tool to have a smooth transition on this one, but giant thing to implement due to bunch of corner cases I guess.

[tomdale]

Great writeup, @GavinJoyce. This is long overdue, and perhaps one of the least controversial deprecations RFCs to ever come across the core team desk. 😉 We're moving this one to Final Comment Period, so please chime in now if you've got concerns with the proposal as written.

[mixonic]

Regarding the migration script: Mostly the use cases considered are looking at downward data flow. We should consider <button {{action 'foo'}}> inside a partial- I presume once you move that into a glimmer component the action won't behave the same way it did in the partial.

[chancancode]

@mixonic yep that would break because this form of action implicitly closes over this, we should make sure the migration guide mentions that (and accounted for in the codemod, if there is one?), and suggest passing it in as an argument:

{{!--outside--}}
<ConvertedFromPartial ... @action={{action 'foo'}} .../>

{{!--inside--}}
<button {{action @action}}>

[omairvaiyani]

I'm fully in favour of this deprecation, but I don't think a codemod that fully automates the migration will land. There is too much implicit two-day data flow going on with partials to be safely handled by static analysis. If this library was still active, it may have been possible, but probably beyond difficult for smaller teams to manage.

I think a codemod that superficially converts partials to components (and generates the placeholder component files), followed by a list of items migrated, would greatly help with the migration process, but a large part of it will most likely be arduous and manual. Still worth it as we've noted that partials are a point of incredible confusion when we onboard a new developer into our team.

[rwjblue]

There is too much implicit two-day data flow going on with partials to be safely handled by static analysis.

@omairvaiyani agree to disagree 😸, I believe the codemod steps discussed in this RFC would work fine and the number of cases that were not possible would be limited to those where you have partial usage inside of a partial.

However, I also agree with you that even without codemod support, this RFC is still worthwhile.

[chancancode]

@GavinJoyce can you update the RFC to include the {{action "name"}} example? Today at the core team meeting, we agreed to accept the RFC with that minor modification, so I'll merge when that's sorted.

[GavinJoyce]

@chancancode I've updated the deprecation details to include an example action:

---

app/templates/application.hbs

{{#let (hash title="Don't use partials" body="Components are always better") as |tip|}}
  {{partial "partials/quick-tip"}}
{{/let}}

app/templates/partials/quick-tip.hbs

<h1>Tip: {{tip.title}}</h1>
<p>{{tip.body}}</p>
<button {{action 'dismissTip'}}>OK</button>

Here's the same template code after migrating the partials/quick-tip partial to be a component.

app/templates/application.hbs

{{#let (hash title="Don't use partials" body="Components are always better") as |tip|}}
  <QuickTip @tip={{tip}} @onDismiss={{action 'dismissTip'}} />
{{/let}}

app/templates/components/quick-tip.hbs

<h1>Tip: {{@tip.title}}</h1>
<p>{{@tip.body}}</p>
<button {{action @onDismiss}}>OK</button>

[chancancode]

🎉 Thanks @GavinJoyce!