Add `Sphinx.add_html_assets_in_all_pages`

This new method in the `Sphinx` object allows extensions to communicate to
Sphinx that it's preferred to include HTML assets in all the pages. However,
it's extensions developers' responsability to follow this config and decide
whether or not include the assets required.

Extensions developers' can check `Sphinx.html_assets_in_all_pages` together with
any other logic they may have to decide if the assets will be included in the
rendered page or not.

Closes #9115

1 files changed, 1 insertions, 1 deletions

diff --git a/sphinx/ext/mathjax.py b/sphinx/ext/mathjax.py
index 301c0d699..8fc63cb9e 100644
--- a/sphinx/ext/mathjax.py
+++ b/sphinx/ext/mathjax.py
@@ -79,7 +79,7 @@ def install_mathjax(app: Sphinx, pagename: str, templatename: str, context: Dict
                              'mathjax extension to work')
 
     domain = cast(MathDomain, app.env.get_domain('math'))
-    if domain.has_equations(pagename):
+    if app.html_assets_in_all_pages or domain.has_equations(pagename):
         # Enable mathjax only if equations exists
         options = {'async': 'async'}
         if app.config.mathjax_options: