Append a hash ?digest to CSS files for cache-busting

[hugovk]

Fix https://github.com/python/python-docs-theme/issues/78.

Append a ?digest=hash to the end of the pydoctheme.css, computed from the file contents, so when a new CSS file is deployed, the old one is no longer used from the browser cache.

For example:

<link rel="stylesheet" type="text/css" href="_static/pydoctheme.css?digest=afc8307635b40ad4bb21df93e5fc348bcdad7f27" />

This is based on how @pradyunsg's Furo theme does it:

https://github.com/pradyunsg/furo/blob/193643fdb6787501195555244f4a9e953ef544bb/src/furo/__init__.py#L149-L161

Demo

View the source of pages at https://python-docs-theme-previews--108.org.readthedocs.build/en/108/

[m-aciek]

This changes break backwards compatibility with Sphinx 3.4.3 which is pinned for Python 3.10 documentation. Following is seen in the stdout when trying to build (example):

% make html
…
Extension error:
Handler <function _html_page_context at 0x110466020> for event 'html-page-context' threw an exception (exception: This documentation is not using `pydoctheme.css` as the stylesheet. If you have set `html_style` in your conf.py file, remove it.)

Does the same for compatibility with Sphinx 2.4.4 pinned for Python 3.9 and Python 3.8 docs:

% make html
…

Exception occurred:
  File "/Users/maciej.olko/projects/cpython/Doc/venv/lib/python3.12/site-packages/python_docs_theme/__init__.py", line 42, in _html_page_context
    raise ValueError(
    ^^^^^^^^^^^^^^^^^
ValueError: This documentation is not using `pydoctheme.css` as the stylesheet. If you have set `html_style` in your conf.py file, remove it.
The full traceback has been saved in /var/folders/c0/vxg8dn6n28105qpdxmg3kblc0000gq/T/sphinx-err-psaoa2co.log, if you want to report the issue to the developers.
Please also report this if it was a user error, so that a better error message can be provided next time.
A bug report can be filed in the tracker at <https://github.com/sphinx-doc/sphinx/issues>. Thanks!

(Theme seems compatible with Sphinx 2.3.1 which is used for Python 3.7.)

Would it be possible to tweak the theme to support Sphinx 3.4.3 and 2.4.4 for older Python docs?

[hugovk]

Thanks for reporting.

Sphinx 3.4.3: context["css_files"]=[]

Sphinx 6.1.3: context["css_files"]=['_static/pygments.css', '_static/pydoctheme.css']

---

Options include pinning python-docs-theme, or ideally upgrading Sphinx for the other version branches.

But from a practical maintenance point of view, shall we just skip this for older Sphinx versions?

commit 8b88430553fdaa1d7a85296a106158b5faf99a4b
Author: Hugo van Kemenade <hugovk@users.noreply.github.com>
Date:   Sat Mar 11 13:32:42 2023 +0200

    Skip cache-busting for old Sphinx

diff --git a/python_docs_theme/__init__.py b/python_docs_theme/__init__.py
index 62b16f0..bbe1352 100644
--- a/python_docs_theme/__init__.py
+++ b/python_docs_theme/__init__.py
@@ -37,7 +37,7 @@ def _html_page_context(

     assert isinstance(app.builder, StandaloneHTMLBuilder)

-    if "css_files" in context:
+    if sphinx.version_info >= (4,) and "css_files" in context:
         if "_static/pydoctheme.css" not in context["css_files"]:
             raise ValueError(
                 "This documentation is not using `pydoctheme.css` as the stylesheet. "

[m-aciek]

I think skipping is most pragmatic solution. 👍 I was also thinking about pinning, but the downside is it would prevent users from having another fixes from this release. When having similar conversation earlier, upgrading Sphinx wasn't told to be good option for already published stable releases, because of Linux distributions that provide Sphinx as a system package, if I recall correctly.

[hugovk]

Please see PR https://github.com/python/python-docs-theme/pull/113.