Vuetify: [Bug Report] Lazy ExpansionPanel not animating

[oliveiracdz]

Versions and Environment

Vuetify: 1.4.2
Last working version: 1.3.7
Vue: 2.5.22
Browsers: Chrome 71.0.3578.98
OS: Windows 10

Steps to reproduce

Create a ExpansionPainel with lazy ExpansionPainelContents.

Expected Behavior

The opening animation to work initially, even with lazy content.
This used to work with v1.3.7, like in this codepen .

Actual Behavior

The opening animation do not work.

Reproduction Link

https://codepen.io/oliveiracdz/pen/OrYaKQ

[sh7dm]

@oliveiracdz In which version it broke?

[oliveiracdz]

@sh7dm, version 1.3.10.
Maybe something related with this commit d0ffc88a75a2179bc5fbdb5578405863acfb47eb?

[sh7dm]

@oliveiracdz It works in both directions in v1.3.7 https://codepen.io/sh7dm/pen/XOrZad
Only on open: v1.3.8 / v1.3.9 https://codepen.io/sh7dm/pen/ErYQwg
Doesn't work at all 🤬: v1.3.10 https://codepen.io/sh7dm/pen/pGzadz

[sh7dm]

Looks like close anim was removed in 97053db

[sh7dm]

These commits between v1.3.9 and v1.3.10 are related to VExpansionPanel: ebc5aaf cb605ac a039846

[sh7dm]

Hmm... it only doesn't work for first time, then anim works good. It's very strange

[sh7dm]

@oliveiracdz you were right! when I removed !! it works good. Looks like this was for Boolean() conversion

[sh7dm]

After I do this:

     toggle (active: boolean) {
-      if (active) this.isBooted = true
+      if (active !== undefined && active) this.isBooted = true

       this.isActive = active
     }

and this:

     register (content: VExpansionPanelContentInstance) {
       const i = this.items.push(content) - 1
       this.value !== null && this.updateFromValue(this.value)
-      content.toggle(!!this.open[i])
+      content.toggle(this.open[i])
     },

it works

[sh7dm]

@oliveiracdz Thanks

[oliveiracdz]

@sh7dm, this fix breaks #5703 again. =/
Now the lazy content renders before open the expansion, like in this
codepen with v1.4.5.

[sh7dm]

:boom: It's very difficult to fix. I think we need @johnleider's help!

[johnleider]

I have a fix for this going up

[oliveiracdz]

Thanks!

But I think that d3937e05228474844d764c55ef6c23ca0a58dfb1 broke this another https://github.com/vuetifyjs/vuetify/issues/4483 now.

https://codepen.io/oliveiracdz/pen/aXyajL

[AlexeyKot]

This change broke my expansion-list with a component containing dynamic chart. Code Example:
https://codesandbox.io/s/98wo5r0664