Close #6241: html: Allow to add JS/CSS files to the specific page

Allow to add JS/CSS files to the specific page when an extension calls
`app.add_js_file()` or `app.add_css_file()` on `html-page-context`
event.

CHANGES

@@ -22,8 +22,12 @@ Features added
 * #8619: html: kbd role generates customizable HTML tags for compound keys
 * #8634: html: Allow to change the order of JS/CSS via ``priority`` parameter
   for :meth:`Sphinx.add_js_file()` and :meth:`Sphinx.add_css_file()`
+* #6241: html: Allow to add JS/CSS files to the specific page when an extension
+  calls ``app.add_js_file()`` or ``app.add_css_file()`` on
+  :event:`html-page-context` event
 * #8649: imgconverter: Skip availability check if builder supports the image
   type
+* #6241: mathjax: Include mathjax.js only on the document using equations
 * #8132: Add :confval:`project_copyright` as an alias of :confval:`copyright`
 
 Bugs fixed

doc/extdev/appapi.rst

@@ -369,6 +369,9 @@ Here is a more detailed list of these events.
    You can return a string from the handler, it will then replace
    ``'page.html'`` as the HTML template for this page.
 
+   .. note:: You can install JS/CSS files for the specific page via
+             :meth:`Sphinx.add_js_file` and :meth:`Sphinx.add_css_file` since v4.0.
+
    .. versionadded:: 0.4
 
    .. versionchanged:: 1.3

sphinx/application.py

@@ -965,7 +965,10 @@ def add_js_file(self, filename: str, priority: int = 500, **kwargs: Any) -> None
            And it allows keyword arguments as attributes of script tag.
 
         .. versionchanged:: 3.5
-           Take priority argument.
+
+           * Take priority argument.
+           * Allowed to add a JavaScript file to the specific HTML page when an
+             extension calls this on :event:`html-page-context` event.
         """
         self.registry.add_js_file(filename, priority=priority, **kwargs)
         if hasattr(self.builder, 'add_js_file'):
@@ -1018,7 +1021,9 @@ def add_css_file(self, filename: str, priority: int = 500, **kwargs: Any) -> Non
            And it allows keyword arguments as attributes of link tag.
 
         .. versionchanged:: 3.5
-           Take priority argument.
+           * Take priority argument.
+           * Allowed to add a stylesheet file to the specific HTML page when an
+             extension calls this on :event:`html-page-context` event.
         """
         logger.debug('[app] adding stylesheet: %r', filename)
         self.registry.add_css_files(filename, priority=priority, **kwargs)

sphinx/builders/html/__init__.py

@@ -466,6 +466,10 @@ def prepare_writing(self, docnames: Set[str]) -> None:
                 rellinks.append((indexname, indexcls.localname,
                                  '', indexcls.shortname))
 
+        # back up script_files and css_files to allow adding JS/CSS files to a specific page.
+        self._script_files = list(self.script_files)
+        self._css_files = list(self.css_files)
+
         if self.config.html_style is not None:
             stylename = self.config.html_style
         elif self.theme:
@@ -1016,6 +1020,10 @@ def hasdoc(name: str) -> bool:
         self.add_sidebars(pagename, ctx)
         ctx.update(addctx)
 
+        # revert script_files and css_files
+        self.script_files[:] = self._script_files
+        self.css_files[:] = self.css_files
+
         self.update_page_context(pagename, templatename, ctx, event_arg)
         newtmpl = self.app.emit_firstresult('html-page-context', pagename,
                                             templatename, ctx, event_arg)

sphinx/domains/math.py

@@ -157,8 +157,11 @@ def get_next_equation_number(self, docname: str) -> int:
         targets = [eq for eq in self.equations.values() if eq[0] == docname]
         return len(targets) + 1
 
-    def has_equations(self) -> bool:
-        return any(self.data['has_equations'].values())
+    def has_equations(self, docname: str = None) -> bool:
+        if docname:
+            return self.data['has_equations'].get(docname, False)
+        else:
+            return any(self.data['has_equations'].values())
 
 
 def setup(app: "Sphinx") -> Dict[str, Any]:

sphinx/ext/mathjax.py

@@ -17,9 +17,7 @@
 
 import sphinx
 from sphinx.application import Sphinx
-from sphinx.builders.html import StandaloneHTMLBuilder
 from sphinx.domains.math import MathDomain
-from sphinx.environment import BuildEnvironment
 from sphinx.errors import ExtensionError
 from sphinx.locale import _
 from sphinx.util.math import get_node_equation_number
@@ -71,25 +69,25 @@ def html_visit_displaymath(self: HTMLTranslator, node: nodes.math_block) -> None
     raise nodes.SkipNode
 
 
-def install_mathjax(app: Sphinx, env: BuildEnvironment) -> None:
+def install_mathjax(app: Sphinx, pagename: str, templatename: str, context: Dict,
+                    event_arg: Any) -> None:
     if app.builder.format != 'html' or app.builder.math_renderer_name != 'mathjax':  # type: ignore  # NOQA
         return
     if not app.config.mathjax_path:
         raise ExtensionError('mathjax_path config value must be set for the '
                              'mathjax extension to work')
 
-    builder = cast(StandaloneHTMLBuilder, app.builder)
-    domain = cast(MathDomain, env.get_domain('math'))
-    if domain.has_equations():
+    domain = cast(MathDomain, app.env.get_domain('math'))
+    if domain.has_equations(pagename):
         # Enable mathjax only if equations exists
         options = {'async': 'async'}
         if app.config.mathjax_options:
             options.update(app.config.mathjax_options)
-        builder.add_js_file(app.config.mathjax_path, **options)
+        app.add_js_file(app.config.mathjax_path, **options)  # type: ignore
 
         if app.config.mathjax_config:
             body = "MathJax.Hub.Config(%s)" % json.dumps(app.config.mathjax_config)
-            builder.add_js_file(None, type="text/x-mathjax-config", body=body)
+            app.add_js_file(None, type="text/x-mathjax-config", body=body)
 
 
 def setup(app: Sphinx) -> Dict[str, Any]:
@@ -102,6 +100,6 @@ def setup(app: Sphinx) -> Dict[str, Any]:
     app.add_config_value('mathjax_inline', [r'\(', r'\)'], 'html')
     app.add_config_value('mathjax_display', [r'\[', r'\]'], 'html')
     app.add_config_value('mathjax_config', None, 'html')
-    app.connect('env-updated', install_mathjax)
+    app.connect('html-page-context', install_mathjax)
 
     return {'version': sphinx.__display_version__, 'parallel_read_safe': True}

tests/roots/test-ext-math/index.rst

@@ -6,6 +6,7 @@ Test Math
 
    math
    page
+   nomath
 
 .. math:: a^2+b^2=c^2
 

tests/test_ext_math.py

@@ -15,6 +15,7 @@
 import pytest
 from docutils import nodes
 
+from sphinx.ext.mathjax import MATHJAX_URL
 from sphinx.testing.util import assert_node
 
 
@@ -224,6 +225,18 @@ def test_mathjax_config(app, status, warning):
             '</script>' in content)
 
 
+@pytest.mark.sphinx('html', testroot='ext-math',
+                    confoverrides={'extensions': ['sphinx.ext.mathjax']})
+def test_mathjax_is_installed_only_if_document_having_math(app, status, warning):
+    app.builder.build_all()
+
+    content = (app.outdir / 'index.html').read_text()
+    assert MATHJAX_URL in content
+
+    content = (app.outdir / 'nomath.html').read_text()
+    assert MATHJAX_URL not in content
+
+
 @pytest.mark.sphinx('html', testroot='basic',
                     confoverrides={'extensions': ['sphinx.ext.mathjax']})
 def test_mathjax_is_not_installed_if_no_equations(app, status, warning):