Fix #11756 (#11758)

Author: jfbu

CHANGES.rst

@@ -43,6 +43,10 @@ Bugs fixed
   Patch by James Addison.
 * #11678: Fix a possible ``ZeroDivisionError`` in ``sphinx.ext.coverage``.
   Patch by Stephen Finucane.
+* #11756: LaTeX: build error with recent TeXLive due to missing ``substitutefont``
+  package (triggered if using ``fontenc`` with ``T2A`` option and document
+  language is not a Cyrillic one).
+  Patch by Jean-François B.
 
 Testing
 -------

sphinx/builders/latex/__init__.py

@@ -215,15 +215,18 @@ def init_multilingual(self) -> None:
         if self.context['latex_engine'] == 'pdflatex':
             if not self.babel.uses_cyrillic():
                 if 'X2' in self.context['fontenc']:
-                    self.context['substitutefont'] = '\\usepackage{substitutefont}'
+                    self.context['substitutefont'] = ('\\usepackage'
+                                                      '{sphinxpackagesubstitutefont}')
                     self.context['textcyrillic'] = ('\\usepackage[Xtwo]'
                                                     '{sphinxpackagecyrillic}')
                 elif 'T2A' in self.context['fontenc']:
-                    self.context['substitutefont'] = '\\usepackage{substitutefont}'
+                    self.context['substitutefont'] = ('\\usepackage'
+                                                      '{sphinxpackagesubstitutefont}')
                     self.context['textcyrillic'] = ('\\usepackage[TtwoA]'
                                                     '{sphinxpackagecyrillic}')
             if 'LGR' in self.context['fontenc']:
-                self.context['substitutefont'] = '\\usepackage{substitutefont}'
+                self.context['substitutefont'] = ('\\usepackage'
+                                                  '{sphinxpackagesubstitutefont}')
             else:
                 self.context['textgreek'] = ''
             if self.context['substitutefont'] == '':

sphinx/texinputs/sphinxpackagesubstitutefont.sty

@@ -0,0 +1,21 @@
+%% a stub for obsoleted LaTeX package substitutefont
+% The package substitutefont stopped being distributed with TeXLive
+% around August 2023 and was moved to "obsolete" section.
+% cf https://ctan.org/pkg/substitutefont
+% Trying to load it raises a LaTeX build error since.
+
+% The \substitutefont has a LaTeX kernel replacement
+%     \DeclareFontFamilySubstitution
+% which was added to LaTeX 2020-02-02
+% The aim of this stub is to do that replacement silently.
+
+% change this info string if making any custom modification
+\ProvidesPackage{sphinxpackagesubstitutefont}[2023/15/11 v7.3.0 advanced colored boxes]
+
+\ifdefined\DeclareFontFamilySubstitution
+  \def\substitutefont{\DeclareFontFamilySubstitution}
+\else
+  \usepackage{substitutefont}
+\fi
+
+\endinput