Widgets do not render in static documentation

[astrojuanlu]

Problem

I was following the ipywidgets tutorial in preparation of SciPy US 2021 and, when told to go to https://ipywidgets.readthedocs.io/en/latest/examples/Widget%20Events.html to see the differences between link and jslink, saw that no widgets appeared at all. This is both in latest Firefox and Chromium on Linux Mint 20.2.

In both browsers with all extensions disabled I see a process is not defined error. Chromium:

Uncaught (in promise) ReferenceError: process is not defined
    at Object.7482 (embed-amd.js:8)
    at __webpack_require__ (embed-amd.js:14)
    at Object.62207 (embed-amd.js:8)
    at __webpack_require__ (embed-amd.js:14)
    at Object.37552 (embed-amd.js:8)
    at __webpack_require__ (embed-amd.js:14)
    at Object.57850 (embed-amd.js:8)
    at __webpack_require__ (embed-amd.js:14)
    at Object.25741 (embed-amd.js:8)
    at __webpack_require__ (embed-amd.js:14)

Firefox:

Uncaught (in promise) ReferenceError: process is not defined
    7482 https://cdn.jsdelivr.net/npm/@jupyter-widgets/html-manager@^0.21.0-alpha.0/dist/embed-amd.js:8
    __webpack_require__ https://cdn.jsdelivr.net/npm/@jupyter-widgets/html-manager@^0.21.0-alpha.0/dist/embed-amd.js:14
    62207 https://cdn.jsdelivr.net/npm/@jupyter-widgets/html-manager@^0.21.0-alpha.0/dist/embed-amd.js:8
    __webpack_require__ https://cdn.jsdelivr.net/npm/@jupyter-widgets/html-manager@^0.21.0-alpha.0/dist/embed-amd.js:14
    37552 https://cdn.jsdelivr.net/npm/@jupyter-widgets/html-manager@^0.21.0-alpha.0/dist/embed-amd.js:8
    __webpack_require__ https://cdn.jsdelivr.net/npm/@jupyter-widgets/html-manager@^0.21.0-alpha.0/dist/embed-amd.js:14
    57850 https://cdn.jsdelivr.net/npm/@jupyter-widgets/html-manager@^0.21.0-alpha.0/dist/embed-amd.js:8
    __webpack_require__ https://cdn.jsdelivr.net/npm/@jupyter-widgets/html-manager@^0.21.0-alpha.0/dist/embed-amd.js:14
    25741 https://cdn.jsdelivr.net/npm/@jupyter-widgets/html-manager@^0.21.0-alpha.0/dist/embed-amd.js:8
    __webpack_require__ https://cdn.jsdelivr.net/npm/@jupyter-widgets/html-manager@^0.21.0-alpha.0/dist/embed-amd.js:14
    45705 https://cdn.jsdelivr.net/npm/@jupyter-widgets/html-manager@^0.21.0-alpha.0/dist/embed-amd.js:8
    __webpack_require__ https://cdn.jsdelivr.net/npm/@jupyter-widgets/html-manager@^0.21.0-alpha.0/dist/embed-amd.js:14
    93920 https://cdn.jsdelivr.net/npm/@jupyter-widgets/html-manager@^0.21.0-alpha.0/dist/embed-amd.js:8
    __webpack_require__ https://cdn.jsdelivr.net/npm/@jupyter-widgets/html-manager@^0.21.0-alpha.0/dist/embed-amd.js:14
    <anonymous> https://cdn.jsdelivr.net/npm/@jupyter-widgets/html-manager@^0.21.0-alpha.0/dist/embed-amd.js:14
    <anonymous> https://cdn.jsdelivr.net/npm/@jupyter-widgets/html-manager@^0.21.0-alpha.0/dist/embed-amd.js:14
    <anonymous> https://cdn.jsdelivr.net/npm/@jupyter-widgets/html-manager@^0.21.0-alpha.0/dist/embed-amd.js:14
    execCb https://cdnjs.cloudflare.com/ajax/libs/require.js/2.3.4/require.min.js:1
    check https://cdnjs.cloudflare.com/ajax/libs/require.js/2.3.4/require.min.js:1
    enable https://cdnjs.cloudflare.com/ajax/libs/require.js/2.3.4/require.min.js:1
    enable https://cdnjs.cloudflare.com/ajax/libs/require.js/2.3.4/require.min.js:1
    enable https://cdnjs.cloudflare.com/ajax/libs/require.js/2.3.4/require.min.js:1
    bind https://cdnjs.cloudflare.com/ajax/libs/require.js/2.3.4/require.min.js:1
    each https://cdnjs.cloudflare.com/ajax/libs/require.js/2.3.4/require.min.js:1
    enable https://cdnjs.cloudflare.com/ajax/libs/require.js/2.3.4/require.min.js:1
    init https://cdnjs.cloudflare.com/ajax/libs/require.js/2.3.4/require.min.js:1
    o https://cdnjs.cloudflare.com/ajax/libs/require.js/2.3.4/require.min.js:1

However, this seemed to work fine in the 7.6.3 docs, see https://ipywidgets.readthedocs.io/en/7.6.3/examples/Widget%20Events.html.

Suggested Improvement

[astrojuanlu]

It looks like 7.6.3 was built with conda on a newer Sphinx version https://readthedocs.org/projects/ipywidgets/builds/12954552/
whereas latest was built with Sphinx 1.8 https://readthedocs.org/projects/ipywidgets/builds/14178439/.

The change was made in #2708 right after 7.6.3 was released, about one year and a half ago. However, that pull request looks fine: https://ipywidgets--2708.org.readthedocs.build/en/2708/examples/Widget%20Events.html

Doing a rough binary search, I think this broke somewhere between #3107 (February, good) and #3167 (March, bad).

[astrojuanlu]

I confirm that:

• The problem is not time-dependent, but code-dependent. In other words: rebuilding the 7.6.3 docs today doesn't exhibit the problem, there are no dependency issues.
• The problem can be reproduced locally. Therefore, it is not a Read the Docs issue.
• Doing a git bisect I identified eadb5ef as the first bad commit. No widgets are seen locally.
  • Its first parent, 60c88a5, looks good
  • Its second parent, 5532c91, corresponds to ipywidgets 7.6.3 and shows the widgets, but there is a bug and they appear twice (this can still be seen online)
  • ❓

That's how far I can go with my limited knowledge of ipywidgets.

[jasongrout]

Thanks for tracking this down! Adding it to the 8.0 milestone.

[martinRenou]

Assigning myself