ReactiveHTML does not rerender loop in _template

[MarcSkovMadsen]

Current Panel master branch (latest release is 0.12.6).

Motivated by the discussion https://discourse.holoviz.org/t/sortable-widget/2877/15?u=marc

It seems the ReactiveHTML does not rerender the _template when using parameter in loop. I guess its not a bug. It's the way the feature works by jinja templating. So maybe this is a feature request.

We expect and need the text section to update when the value of the parameter rows changes. It does not.

loop_not_working.mp4

import param
import panel as pn
pn.extension(js_files={'sortablelist': "https://raw.githack.com/SortableJS/Sortable/master/Sortable.js"})

class Sortable(pn.reactive.ReactiveHTML):

    rows = param.List(default=[0,1,2,3,4,5])

    _template = """
<div id="simpleList" class="list-group" style="font-size:48px">
    {% for row in rows %}
    <div class="list-group-item">${row}</div>
    {% endfor %}
</div>
"""
    
sortable = Sortable(rows=["Panel", "New", "Year", "Happy", "Friends", ])


update_list = pn.widgets.Button(name="Update")

@pn.depends(value=update_list, watch=True)
def update(value):
    sortable.rows=["Some", "New", "Values"]

pn.Column(
    update_list, sortable, sortable.param.rows
).servable()