Fix #8442: missing index entries in pdf output with memoir + xindy

CHANGES

@@ -100,6 +100,8 @@ Bugs fixed
   specified
 * #8735: LaTeX: wrong internal links in pdf to captioned code-blocks when
   :confval:`numfig` is not True
+* #8442: LaTeX: some indexed terms are ignored when using xelatex engine
+  (or pdflatex and :confval:`latex_use_xindy` set to True) with memoir class
 
 Testing
 --------

sphinx/templates/latex/latex.tex_t

@@ -17,6 +17,9 @@
 %% turn off hyperref patch of \index as sphinx.xdy xindy module takes care of
 %% suitable \hyperpage mark-up, working around hyperref-xindy incompatibility
 \PassOptionsToPackage{hyperindex=false}{hyperref}
+%% memoir class requires extra handling
+\makeatletter\@ifclassloaded{memoir}
+{\ifdefined\memhyperindexfalse\memhyperindexfalse\fi}{}\makeatother
 <% endif -%>
 <%= passoptionstopackages %>
 \PassOptionsToPackage{warn}{textcomp}