\index in \pagenote with splitindex option (for multiple index)

Question

How does \expandafter works here? The following code needs to be completed. I assume that some of you might do this with ease, hopefully.

The intention is: to propagate the letter n (or any other, for Notes of pagenote into the index) with the pagenotenumber for \index[]{} within \pagenote{}.

The code is derived from \index inside footnote: How to propagate the footnote number correctly with index package?

\documentclass{report}
\usepackage{index}
\usepackage[texindy,splitindex]{imakeidx}
\usepackage[hidelinks]{hyperref}
\usepackage[page]{pagenote}
\newcommand\pn[2]{\hyperpage{#2}n#1}
\makeatletter
\let\if@nopnote\iffalse % just for the example
\newcommand{\is}[2]{%
    \if@nopnote
    \index[#1]{#2}%
    \else
    \expandafter\pagenoteindex\expandafter{\tempnumber}{#2}%
    \fi
}
\renewcommand{\notenuminnotes}[1]{%
    \edef\tempnumber{#1}%
    {\normalfont #1.} }
\makeatother
\newcommand{\pagenoteindex}[3]{\index[#1]{#3|pn{#2}}}
\makeindex[program=texindy,name=Names,title=Names]
\makeindex[program=texindy,name=Something,title=Something]
\makepagenote
\begin{document}
First index.\index[Something]{First index}
Sentence.\pagenote{First pagenote without index.}
\clearpage
Emph index.\index[Something]{Emph index@\emph{Emph index}}
pagenote and index.\pagenote{Second pagenote with index.\is[Something]{Index inside second pagenote}}
\clearpage
Third pagenote.\pagenote{\emph{Emph index word}.\is[Something]{Emph index@\emph{Emph index}}}
Namenindex\index[Names]{Namenindex}
\printnotes
\printindex[Something]
\printindex[Names]
\end{document}

This functionality seems a standard function for indexing in modern book typesetting but not yet recognized with LaTeX. It would be great if someone can support this and present a solution.

Answer 1

Not altogether sure what you want. (I vaguely remember from earlier questions, but there's not much to refresh my memory in this one.)

The following generates note and page numbers in the indices without altering the contents of the document environment. Whether that's the target behaviour, I'm not sure.

The initial problem with your code is that you have defined \pagenoteindex to require 3 arguments, but are passing it only 2. I'm guessing you want an optional argument here, because you're passing one to \is, so we need 4 cases rather than 2:

1. we're inside a page note and have an optional argument;
2. we're inside a page note without one;
3. we're outside with one;
4. we're outside without one.

expl3 makes expansion (relatively) straightforward. It is, at least, a lot less unwieldy than juggling chains of \expandafters which threaten to regress to infinity. We define 2 functions for cases (1) and (2):

\cs_new_protected:Nn \thomkrates_pagenoteindex:nnnn
{
  \index [#1] { #3 | pn {#2}{#4} }
}
\cs_new_protected:Nn \thomkrates_pagenoteindex:nnn
{
  \index  { #2 | pn {#1}{#3} }
}

If using this code, do note this is not the correct way to do this. As explained below, we're bypassing the standard mechanisms here.

Then we tell LaTeX we'd like variants which should receive a pre-expanded argument in second or first place:

\cs_generate_variant:Nn \thomkrates_pagenoteindex:nnnn { nene }
\cs_generate_variant:Nn \thomkrates_pagenoteindex:nnn { ene }

This means LaTeX will expand those arguments before passing them to our base functions, so we don't have to. So now we can define a version of \is to handle our 4 cases:

\NewDocumentCommand {\is} { om }{%
  \if@nopnote
    \IfValueTF { #1 } {
      \index[#1]{#2}
    }{
      \index{#2}
    }
  \else
    \hypertarget{pn:\tempnumber}{}%
    \IfValueTF { #1 } {
      \thomkrates_pagenoteindex:nene { #1 } { \tempnumber } { #2 } { \temppgnumber }
    }{
      \thomkrates_pagenoteindex:ene { \tempnumber } { #2 } { \temppgnumber }
    }
  \fi
}

Because I don't understand the format xindy wants (as opposed to makeindex) and couldn't find the relevant documentation (which I assume exists somewhere), I gave up trying to figure out how to get the page number to show up when \hyperindexformat is used in the .idx rather than \hyperpage.

So at this point we use a brute-force-and-ignorance approach, simply adding the page number directly and bypassing the usual mechanisms:

\renewcommand{\notenuminnotes}[1]{%
  \edef\tempnumber{#1}%
  \edef\temppgnumber{\thepage}%
  {\normalfont #1.} }

We also modify our definition \pn to utilise the target we added in \is:

\newcommand\pn[2]{\hyperpage{#2}\hyperlink{pn:#1}{n#1}}

Complete code:

\documentclass{report}
% ateb: https://tex.stackexchange.com/a/705581/ addaswyd o gwestiwn Thomkrates: https://tex.stackexchange.com/q/705565/
\usepackage{index}
\usepackage[texindy,splitindex]{imakeidx}
\usepackage[hidelinks]{hyperref}
\usepackage[page]{pagenote}
\newcommand\pn[2]{\hyperpage{#2}\hyperlink{pn:#1}{n#1}}
\makeatletter
\let\if@nopnote\iffalse % just for the example
\renewcommand{\notenuminnotes}[1]{%
  \edef\tempnumber{#1}%
  \edef\temppgnumber{\thepage}%
  {\normalfont #1.} }
\ExplSyntaxOn
\NewDocumentCommand {\is} { om }{%
  \if@nopnote
    \IfValueTF { #1 } {
      \index[#1]{#2}
    }{
      \index{#2}
    }
  \else
    \hypertarget{pn:\tempnumber}{}%
    \IfValueTF { #1 } {
      \thomkrates_pagenoteindex:nene { #1 } { \tempnumber } { #2 } { \temppgnumber }
    }{
      \thomkrates_pagenoteindex:ene { \tempnumber } { #2 } { \temppgnumber }
    }
  \fi
}
\cs_new_protected:Nn \thomkrates_pagenoteindex:nnnn
{
  \index [#1] { #3 | pn {#2}{#4} }
}
\cs_generate_variant:Nn \thomkrates_pagenoteindex:nnnn { nene }
\cs_new_protected:Nn \thomkrates_pagenoteindex:nnn
{
  \index  { #2 | pn {#1}{#3} }
}
\cs_generate_variant:Nn \thomkrates_pagenoteindex:nnn { ene }
\ExplSyntaxOff
\makeatother
\makeindex[program=texindy,name=Names,title=Names]
\makeindex[program=texindy,name=Something,title=Something]
\makepagenote
\begin{document}
First index.\index[Something]{First index}
Sentence.\pagenote{First pagenote without index.}
\clearpage
Emph index.\index[Something]{Emph index@\emph{Emph index}}
pagenote and index.\pagenote{Second pagenote with index.\is[Something]{Index inside second pagenote}}
\clearpage
Third pagenote.\pagenote{\emph{Emph index word}.\is[Something]{Emph index@\emph{Emph index}}}
Namenindex\index[Names]{Namenindex}
\printnotes
\printindex[Something]
\printindex[Names]
\end{document}