.ist file has no effect on printed index

Question

I am trying to modify an index with a style .ist file. I create the .ist file, I place it in the same directory as the main file, and pass the option. However, the index remains the same.

Here there is a MWE of my .tex file:

\documentclass[a4paper]{report}
\usepackage{amsmath, mathtools, amsthm}
\let\proof\relax
\let\endproof\relax
\usepackage{thmtools}
\declaretheoremstyle[headfont=\normalfont\bfseries, notefont=\bfseries, bodyfont=\normalfont, shaded={rulecolor=black,rulewidth=0.5pt,bgcolor={rgb}{1,1,1},margin=5pt,textwidth=11.8cm}, notebraces={}{:}, headpunct={}, postheadspace=1em]{mystyle}
\declaretheorem[style=mystyle]{proposition}
\declaretheoremstyle[headfont=\normalfont\bfseries, numbered=no, notefont=\bfseries, bodyfont=\footnotesize, shaded={rulecolor=gray,rulewidth=0.5pt,bgcolor={rgb}{1,1,1},margin=5pt,textwidth=11.8cm}, qed=\qedsymbol, notebraces={--- }{:}, headpunct={}, postheadspace=1em]{mystyle5}
\declaretheorem[style=mystyle5]{proof}
\declaretheoremstyle[headfont=\normalfont\bfseries, shaded={rulecolor=black,rulewidth=0.5pt,margin=5pt,textwidth=11.8cm}, notebraces={}{:}, headpunct={}, postheadspace=1em]{mystyle3}
\declaretheorem[style=mystyle3]{definition}

\numberwithin{proposition}{section}
\numberwithin{definition}{section}
\numberwithin{figure}{section}
\numberwithin{table}{section}
\numberwithin{equation}{section}

\usepackage[splitindex,nonewpage]{imakeidx}
\makeindex[name=proposition,title=Index of Propositions, options={-s index.ist}]
\makeindex[name=definition,title=Index of Definitions, options={-s index.ist}]
\makeindex[name=figure,title=Index of Figures, options={-s index.ist}]

\renewcommand{\thefigure}{\arabic{chapter}.\arabic{section}.\Roman{figure}.}
\renewcommand{\thedefinition}{\arabic{chapter}.\arabic{section}.\Alph{definition}.}
\renewcommand{\theproposition}{\arabic{chapter}.\arabic{section}.\arabic{proposition}.}

\begin{document}

\begin{proposition}[\textbf{WHATEVER1}]\index[proposition]{prop1}
    BLABLABLA   
\end{proposition}

\begin{proposition}[\textbf{WHATEVER2}]\index[proposition]{prop6}
    BLABLABLA   
\end{proposition}

\begin{definition}[\textbf{LOL1}]\index[definition]{def1}
    LOREM IPSUM 
\end{definition}

\begin{proposition}[\textbf{WHATEVER3}]\index[proposition]{prop5}
    BLABLABLA   
\end{proposition}

\begin{proposition}[\textbf{WHATEVER4}]\index[proposition]{prop4}
    BLABLABLA   
\end{proposition}

\begin{definition}[\textbf{LOL2}]\index[definition]{def4}
    LOREM IPSUM 
\end{definition}

\begin{definition}[\textbf{LOL3}]\index[definition]{def3}
    LOREM IPSUM 
\end{definition}

\begin{proposition}[\textbf{WHATEVER5}]\index[proposition]{prop3}
    BLABLABLA   
\end{proposition}

\begin{proposition}[\textbf{WHATEVER6}]\index[proposition]{prop2}
    BLABLABLA   
\end{proposition}

\begin{definition}[\textbf{LOL4}]\index[definition]{def2}
    LOREM IPSUM 
\end{definition}

\printindex[proposition]
\printindex[definition]

\end{document}

Here goes my .ist file:

headings_flag 1

heading_prefix "\n\\centering\\large\\sffamily\\bfseries%
\\noindent\\textbf{"heading_suffix "}\\par\\nopagebreak\n"

item_0 "\n \\item \\small "

delim_0 " \\hfill "
delim_1 " \\hfill "
delim_2 " \\hfill "

See here how the output is the default one, which means that my .ist file is not having any effect:

Why is NOT the .ist file affecting the output? What am I doing wrong?

Thank you all!

Answer 1

The options key can only be honored without the splitindex option, because the production of the indices is handed over to that program and there's no way to pass options to it automatically.

You can do

splitindex -m "makeindex -s index" <filename>

when you do the call. The obvious limitation is that just one style can be passed to each index.

Just remove the splitindex option and imakeidx will honor the chosen style.