YouCompleteMe considers underscore as word character

Question

YouCompleteMe considers underscores _ as word characters, which is desirable in most programming languages. But in TeX and LaTeX, this is not the case, especially where the underscore has a reserved marker for subscripts.

What I want is to remove underscores as word characters, so that it does not recognise constructions like alpha_ or sum_ as words.

How can a disable _ as a word character?

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A MWE (I use Neovim wiht vim-plug):

" ~/.config/nvim/init.vim file
call plug#begin('~/.local/share/nvim/plugged')
  Plug 'sirver/ultisnips'
  Plug 'ycm-core/YouCompleteMe'
call plug#end()

# custom snippet file
snippet _ "subscript" iA
_{$1}
endsnippet

% main `main.tex` file
\documentclass{article}

\begin{document}
  $\sum_{n}$
  $\sum_}$  % <- Here is the problem.
\end{document}

In the above problem line, if I type \sum, YCM suggests me the word sum_ for autocompletion. Ignoring that and continue typing _, the snippet is not expanded correctly as _{}, but _}, where the cursor lies just before }. Notice that this happens only for the second and subsequent \sums.

Edit: This happens for any word followed by an underscore, if that word previously appeared in the code and YMC parsed it. So this produces the same problem:

Hi
Hi_}  % <- Same problem

Answer 1

As @statox mentioned in the comments, setting iskeyword solves the problem.

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For those who want a specific solution:

It is a good practice to write filetype plugins for every filetype you use (in this case, .tex files), it keeps your init.vim file clean and tidy. Add the following line into your ~/.config/nvim/ftplugin/tex.vim file:

setlocal iskeyword=@,48-57,192-255