Allow specifying multiple CSS files in themes (#10465)

Co-authored-by: Adam Turner <9087854+aa-turner@users.noreply.github.com>

CHANGES

@@ -79,6 +79,9 @@ Deprecated
 Features added
 --------------
 
+* #10444: html theme: Allow specifying multiple CSS files through the ``stylesheet``
+  setting in ``theme.conf`` or by setting ``html_style`` to an iterable of strings.
+
 Bugs fixed
 ----------
 

doc/development/theming.rst

@@ -56,10 +56,10 @@ Python :mod:`ConfigParser` module) and has the following structure:
   want to also inherit the stylesheet, include it via CSS' ``@import`` in your
   own.
 
-* The **stylesheet** setting gives the name of a CSS file which will be
-  referenced in the HTML header.  If you need more than one CSS file, either
-  include one from the other via CSS' ``@import``, or use a custom HTML template
-  that adds ``<link rel="stylesheet">`` tags as necessary.  Setting the
+* The **stylesheet** setting gives a list of CSS filenames separated commas which
+  will be referenced in the HTML header.  You can also use CSS' ``@import``
+  technique to include one from the other, or use a custom HTML template that
+  adds ``<link rel="stylesheet">`` tags as necessary.  Setting the
   :confval:`html_style` config value will override this setting.
 
 * The **pygments_style** setting gives the name of a Pygments style to use for
@@ -82,6 +82,9 @@ Python :mod:`ConfigParser` module) and has the following structure:
 .. versionadded:: 1.7
    sidebar settings
 
+.. versionchanged:: 5.1
+
+   The stylesheet setting accepts multiple CSS filenames
 
 .. _distribute-your-theme:
 

doc/templating.rst

@@ -392,11 +392,29 @@ in the future.
 
    .. versionadded:: 5.0.2
 
+.. data:: styles
+
+   A list of the names of the main stylesheets as given by the theme or
+   :confval:`html_style`.
+
+   .. versionadded:: 5.1
+
 .. data:: style
 
    The name of the main stylesheet, as given by the theme or
    :confval:`html_style`.
 
+   .. versionchanged:: 5.1
+
+      The theme or :confval:`html_style` are now able to specify multiple
+      stylesheets, the ``style`` key returns the last stylesheet when more than
+      one is specified.
+
+   .. deprecated:: 5.1
+
+      Use the :data:`styles` key instead, as there is no longer a single main
+      stylesheet. The ``style`` key will be removed in Sphinx 7.0.
+
 .. data:: title
 
    The title of the current document, as used in the ``<title>`` tag.

sphinx/builders/html/__init__.py

@@ -279,13 +279,16 @@ class StandaloneHTMLBuilder(Builder):
                 return jsfile
         return None
 
-    def _get_style_filename(self) -> str:
-        if self.config.html_style is not None:
-            return self.config.html_style
+    def _get_style_filenames(self) -> Iterator[str]:
+        if isinstance(self.config.html_style, str):
+            yield self.config.html_style
+        elif self.config.html_style is not None:
+            yield from self.config.html_style
         elif self.theme:
-            return self.theme.get_config('theme', 'stylesheet')
+            stylesheet = self.theme.get_config('theme', 'stylesheet')
+            yield from map(str.strip, stylesheet.split(','))
         else:
-            return 'default.css'
+            yield 'default.css'
 
     def get_theme_config(self) -> Tuple[str, Dict]:
         return self.config.html_theme, self.config.html_theme_options
@@ -324,7 +327,9 @@ class StandaloneHTMLBuilder(Builder):
     def init_css_files(self) -> None:
         self.css_files = []
         self.add_css_file('pygments.css', priority=200)
-        self.add_css_file(self._get_style_filename(), priority=200)
+
+        for filename in self._get_style_filenames():
+            self.add_css_file(filename, priority=200)
 
         for filename, attrs in self.app.registry.css_files:
             self.add_css_file(filename, **attrs)
@@ -525,6 +530,7 @@ class StandaloneHTMLBuilder(Builder):
         # 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)
+        styles = list(self._get_style_filenames())
 
         self.globalcontext = {
             'embedded': self.embedded,
@@ -552,7 +558,8 @@ class StandaloneHTMLBuilder(Builder):
             'sphinx_version': __display_version__,
             'sphinx_version_tuple': sphinx_version,
             'docutils_version_info': docutils.__version_info__[:5],
-            'style': self._get_style_filename(),
+            'styles': styles,
+            'style': styles[-1],  # xref RemovedInSphinx70Warning
             'rellinks': rellinks,
             'builder': self.name,
             'parents': [],
@@ -1356,7 +1363,7 @@ def setup(app: Sphinx) -> Dict[str, Any]:
                          lambda self: _('%s %s documentation') % (self.project, self.release),
                          'html', [str])
     app.add_config_value('html_short_title', lambda self: self.html_title, 'html')
-    app.add_config_value('html_style', None, 'html', [str])
+    app.add_config_value('html_style', None, 'html', [list, str])
     app.add_config_value('html_logo', None, 'html', [str])
     app.add_config_value('html_favicon', None, 'html', [str])
     app.add_config_value('html_css_files', [], 'html')

tests/roots/test-build-html-theme-having-multiple-stylesheets/_themes/mytheme/theme.conf

@@ -0,0 +1,3 @@
+[theme]
+inherit = basic
+stylesheet = mytheme.css, extra.css

tests/roots/test-build-html-theme-having-multiple-stylesheets/conf.py

@@ -0,0 +1,2 @@
+html_theme_path = ['_themes']
+html_theme = 'mytheme'

tests/roots/test-build-html-theme-having-multiple-stylesheets/index.rst

@@ -0,0 +1,2 @@
+test-build-html-theme-having-multiple-stylesheets
+=================================================

tests/test_build_html.py

@@ -1782,3 +1782,12 @@ def test_theme_options_with_override(app, status, warning):
     result = (app.outdir / '_static' / 'documentation_options.js').read_text(encoding='utf8')
     assert 'NAVIGATION_WITH_KEYS: true' in result
     assert 'ENABLE_SEARCH_SHORTCUTS: false' in result
+
+
+@pytest.mark.sphinx('html', testroot='build-html-theme-having-multiple-stylesheets')
+def test_theme_having_multiple_stylesheets(app):
+    app.build()
+    content = (app.outdir / 'index.html').read_text(encoding='utf-8')
+
+    assert '<link rel="stylesheet" type="text/css" href="_static/mytheme.css" />' in content
+    assert '<link rel="stylesheet" type="text/css" href="_static/extra.css" />' in content