hvindex misbehaving with lualatex

Question

While attempting to implement 'hvindex' in a luatex-compiled document, I discovered that the nesting feature provided by hvindex doesn't work. Here a code sample, with the precise preamble that I am using in the actual document; I cannot grasp what the problem is---perhaps some disconnect between hvindex and lualatex ?

\documentclass[10pt, letterpaper,fleqn,leqno]{article}
\usepackage{fontspec}
\usepackage[math]{iwona}
\usepackage{amsmath}
\usepackage{mathtools}
\usepackage{xfrac}
\usepackage{expl3}
\usepackage{fontawesome5}
\usepackage{fontmfizz}
\usepackage{marvosym}
\usepackage{textcomp}
\usepackage{polyglossia}
\usepackage{todo}
\usepackage{marginnote}
\usepackage{multicol}
\usepackage{hycolor}
\usepackage[colorlinks,backref]{hyperref}
\usepackage[includehead=false,bottom=1in,top=1in,inner=.8in,outer=1.5in, heightrounded, marginparsep=4mm, marginparwidth=3cm]{geometry}
\usepackage[usenames,dvipsnames,svgnames,table]{xcolor}
\usepackage{lipsum}
\usepackage{makeidx}
\usepackage[makeidx]{hvindex} % one must also load 'makeidx'
\PassOptionsToPackage{protrusion=true,final}{microtype}
\newfontfeature{Microtype}{protrusion=default;expansion=default;}
\setmainfont[Microtype,Ligatures=TeX]{iwona}
\hypersetup{pdfpagemode=FullScreen, bookmarks=true, bookmarksopen=true,linkcolor=ForestGreen, pdfhighlight =/I urlcolor=BlueViolet, anchorcolor=Maroon}
\makeindex
\begin{document}
What are possible explanations for why \Index{states!Democratic} states appear to have higher homeless rates per capita than \Index{states!Republican} states\\

Here, just to make sure that I don't need a ``states`` indexing entry to kick-off the sub-indexing of (republican and democratic), I will force them with two ``index`` entries: \index{states} \ \ \ \ \ \ and \index{States} \ \ \ \ \ ; neither of which will appear in the printout


\printindex
\end{document}

The printout is like this:

What are possible explanations for why Democratic states appear to have higher homeless rates per capita than Republican states. Here, just to make sure that I didn't / don’t need a states entry to kick off the indexing of (republican and democratic), I will force them with two “index“ entries: and ; neither of which will appear in the printout

here is the Index

Index

Democratic, 1

Republican, 1

States, 1

states, 1

---

The intent of course is that the Index should include nested entries such as:

states,

___Democratic, 1

___Republican, 1

States, 1

Answer 1

It's a bug in hvindex.sty:

\def\IndexXXii#1!#2@#3@#4\IndexNIL{%
  \ifx\relax#3\relax            %               no @ in last arg
    \ifx\hvIDXfont\hvIDXfontDefault\index{#2}#2%
    \else\index{#1!#2@\hvIDXfont{#2}}\hvIDXfont{#2}\fi%
  \else\index{#1!\protect#2@#3}#3\fi}

In the case of \Index{states!Democratic}, just

\index{Democratic}

is passed instead of the intended

\index{states!Democratic}

Indeed, if I fix the bug, the result is as expected.

\documentclass{article}
\usepackage[makeidx]{hvindex} % one must also load 'makeidx'
\def\IndexXXii#1!#2@#3@#4\IndexNIL{%
  \ifx\relax#3\relax            %               no @ in last arg
    \ifx\hvIDXfont\hvIDXfontDefault\index{#1!#2}#2% <----- added #1!
    \else\index{#1!#2@\hvIDXfont{#2}}\hvIDXfont{#2}\fi%
  \else\index{#1!\protect#2@#3}#3\fi}
\begin{document}
What are possible explanations for why \Index{states!Democratic} states 
appear to have higher homeless rates per capita than \Index{states!Republican} states
Here, just to make sure that I don't need a states indexing entry to kick-off 
the sub-indexing of (republican and democratic), I will force them with two index 
entries: \Index{states} and \Index{states}; neither of which will appear in the printout
\printindex
\end{document}

Answer 2

You are using \index so apparently not using hvindex or most of the other packages listed.

\documentclass[10pt, letterpaper,fleqn,leqno]{article}
\usepackage{makeidx}
\makeindex
\begin{document}
What are possible explanations for why \index{states!Democratic}
states appear to have higher homeless rates per capita than
\index{states!Republican} states
Here, just to make sure that I don't need a ``states`` indexing
entry to kick-off the sub-indexing of (republican and democratic),


%    I will force them with two index entries: \index{states} and
%    \index{States}; neither of which will appear in the printout
\printindex
\end{document}

Answer 3

The package user-guide, hvindex , v. 0.04 simplifying indexing ...by Herbert Voß(2017/12/12) indicates that "With the option makeidx the also called package is loaded and the macro \makeindex is executed." I had explicitly added \usepackage{makeidx} to the preamble because 1) the indexing was NOT working as-advertised, and 2), the phrase "the also-called package" was not explicit about whether the user had to add this to the preamble (as I did), or whether the call to 'makeidx' is made from within the package 'hvindex'. My call to the "mother package" having been explained here, I also found this older answer about erroneous code within hvindex; enter link description here wherein an error in the code is detailed. I had, in fact, tried to correct that code, but I still got erroneous nesting in my example. Hence, the posting, yesterday. Also, I had included all the preamble, on the assumption that there may be some conflicts there that someone might spot. In fact, today, I methodically removed each preamble line and discovered that the nesting was not affected (it was still erroneous). Now: Thanks be to Egreg, who identified an error in the code which still exists 9 years after the aforementioned URL's answer (which in itself was "not quite right" !), which answer also pre-dates the latest hvindex user-guide. So apparently Herbert Voß wasn't aware of the bug. I have since corrected hvindex.sty on my computer. And, it works:

\documentclass[10pt]{article}
\usepackage[makeidx]{hvindex}
\usepackage[usenames,dvipsnames,svgnames,table]{xcolor}
\usepackage{hycolor}
\usepackage[colorlinks,backref]{hyperref}
\hypersetup{pdfpagemode=FullScreen, bookmarks=true, bookmarksopen=true,linkcolor=ForestGreen, 
    pdfhighlight =/I urlcolor=BlueViolet, anchorcolor=Maroon}
\makeindex
\begin{document}
    What are possible explanations for why \Index{states!Democratic} states 
    appear to have higher homeless rates per capita than \Index{states!Republican} states
\Index{foo} bar1 baz1\\
\Index{foo!bar2} baz2\\
\Index{foo!bar3!baz3}\\
\Index{foo@\textsc{foo}} bar4 baz4\\
\Index{foo!bar@\texttt{baz5}}\\
\Index{foo! bar! baz@\texttt{baz6}}\\
foo bar4 baz7 \\

\Index{cakes!chocolate} \Index{cakes} made by student bakers\\
%cakes \Index{cakes! made by} student bakers\\
%cakes made by student \Index{cakes!made by!made by@\texttt{bakers}}\\
chocolate cakes made by  \Index{cakes!made by!made by@\texttt{student}} bakers \\
chocolate cakes made by student \Index{cakes!made by!made by@\texttt{bakers}}

\printindex
\end{document}