Custom extensions cannot import models/widgets/widget

As part of panel we are shipping various custom models, generally that works perfectly but it seems when I export a plot containing custom models to a static HTML file it fails to resolve certain modules, specifically this line raises errors:

      var widget_1 = require("models/widgets/widget"); 

while other imports seem to work just fine, e.g.:

      var p = require("core/properties");

I’m really not quite sure how best to provide a minimal reproducible example, so here is the exported HTML file, here is the custom model definition and here is the traceback:

Uncaught Error: Cannot find module 'models/widgets/widget'
    at s (Panel.html:93)
    at Object.custom/panel.models.widgets.audio (Panel.html:358)
    at s (Panel.html:93)
    at Object.custom/main (Panel.html:147)
    at s (Panel.html:93)
    at Object.t.Bokeh.r.register_plugin (Panel.html:93)
    at outer (Panel.html:137)
    at Panel.html:142
    at Panel.html:132
    at Panel.html:133

[mattpap]

Actually I’m finishing a PR right now.

[philippjfr]

You’re amazing!