listings interfering with babel

Question

Consider this script:

\documentclass{article}                                                                                                                                                                            
%\usepackage[latvian]{babel}
\usepackage{listings}
\begin{document}                                                                                                                                                                                          
\end{document}

I get an error

(/usr/local/texlive/2018/texmf-dist/tex/latex/listings/listings.cfg))
(./latvianpres.aux)

! LaTeX Error: No counter 'chapter' defined.

if I uncomment the line

%\usepackage[latvian]{babel}

What is the problem and how to solve it?

Answer 1

It looks like a bug in Latvian babel (as Ulrike Fischer said). The file latvian.ldf (loaded by babel) defines \thechapter:

\def\thechapter{%
  \ifx\chapter\undefined\relax\else
  \arabic{chapter}.\fi}

independently if you are using a class with or without \chapters. Later on, \AtBeginDocument listings defines the lstlisting counter conditionally if \thechapter is defined:

\newcounter{lstlisting}[chapter]

or if not:

\newcounter{lstlisting}

When \thechapter exist (it does, when latvian.ldf is loaded), listings tries to hook the lstlisting counter to the chapter counter, which does not exist and you get the error.

You can work around it with this:

\documentclass{article}
\usepackage[latvian]{babel}
\usepackage{listings}

\let\THEchapter\thechapter
\let\thechapter\relax
\begin{document}
\let\thechapter\THEchapter

\end{document}