with this patch :idx: can be used for the index generation for LaTeX (#18946)

config/nimdoc.tex.cfg

@@ -3,7 +3,7 @@
 # (c) 2012 Andreas Rumpf
 # Feel free to edit the templates as you need.
 
-split.item.toc = "20"  
+split.item.toc = "20"
 # too long entries in the table of contents wrap around
 # after this number of characters
 
@@ -97,12 +97,14 @@ doc.file = """
 \usepackage{parskip}  % paragraphs delimited by vertical space, no indent
 \usepackage{graphicx}
 
+\newcommand{\nimindexterm}[2]{#2\label{#1}}
+
 \usepackage{dingbat} % for \carriagereturn, etc
 \usepackage{fvextra}  % for code blocks (works better than original fancyvrb)
 \fvset{
   breaklines,
   breakafter={=}:|\_\{\}[](){,}.;+-*/'",
-  breaksymbolleft=\color{red}{\ensuremath{\hookrightarrow}}, 
+  breaksymbolleft=\color{red}{\ensuremath{\hookrightarrow}},
   breaksymbolright=\color{red}{\small\carriagereturn}
 }
 \fvinlineset{%