Adapt to future ReadTheDocs changes (#1317)

https://about.readthedocs.com/blog/2024/07/addons-by-default/

Author: hynek

doc/conf.py

@@ -15,6 +15,8 @@
 import re
 import sys
 
+import sphinx_rtd_theme
+
 HERE = os.path.abspath(os.path.dirname(__file__))
 
 
@@ -122,13 +124,15 @@ def find_version(*file_paths):
 
 # The theme to use for HTML and HTML Help pages.  See the documentation for
 # a list of builtin themes.
-on_rtd = os.environ.get("READTHEDOCS", None) == "True"
+if os.environ.get("READTHEDOCS", None) == "True":
+    html_baseurl = os.environ.get("READTHEDOCS_CANONICAL_URL", "")
 
-if not on_rtd:  # only import and set the theme if we're building docs locally
-    import sphinx_rtd_theme
+    if "html_context" not in globals():
+        html_context = {}
+    html_context["READTHEDOCS"] = True
 
-    html_theme = "sphinx_rtd_theme"
-    html_theme_path = [sphinx_rtd_theme.get_html_theme_path()]
+html_theme = "sphinx_rtd_theme"
+html_theme_path = [sphinx_rtd_theme.get_html_theme_path()]
 
 # Theme options are theme-specific and customize the look and feel of a theme
 # further.  For a list of options available for each theme, see the