Why does memoir class encode the contents of .idx file and how can it still be used to produce a properly sorted Russian index?

Question

When using the answer I faced the following error message on the 2nd pass (with pdflatex):

Undefined control sequence. \item \T

It originates from the entry in the .ind file:

\item \T2A\CYRD \T2A\cyro \T2A\cyrz , \hyperpage{224}

In turn it is generated by the following entry in the .idx file:

\indexentry{\T2A\CYRD \T2A\cyro \T2A\cyrz |hyperpage}{224}

If I switch memoir to article or book then the index contains the entries defined in the document verbatim, without them being encoded.

The following MWE can be used to validate:

\documentclass{memoir}
\usepackage[utf8]{inputenc}
\usepackage[T1,T2A]{fontenc}
\usepackage[main=russian]{babel}
\usepackage{lipsum}
\usepackage{makeidx}
\makeindex

\newcommand{\rindex}[1]{\expandafter\index\expandafter{\detokenize{#1}}}

\begin{document} 
жзи\rindex{жзи}
\clearpage
где\rindex{где}
\clearpage
абв\rindex{абв}
\clearpage
эюя\rindex{эюя}
\clearpage
шщы\rindex{шщы}
\clearpage
клм\rindex{клм}

\printindex
\end{document}

It passes the 1st pass, then command texindy -L russian -C utf8 "document.idx" generates the .ind file, and the 2nd pass fails.

Answer 1

I found the answer right after posting the question, as it often happens.

For that to work the following package has to be included:

\usepackage[xindy]{imakeidx}

and the

\usepackage{makeindex}

has to be removed.