Change " to `` or '' depending on whether it's typed after a space or non-space

Question

The usecase is LaTeX, which I write using VimTeX.

To make double quoted words one would write ``words''.

However, I'm much more used, from many other contexts (both prose and code), to type " for both opening and closing double quotes, and I often forget I have to press `` and ''.

So I'd like a way to change " to `` or '' depending on whether it's preceded by a space (or tab) or not.

So far I've come up with the solution I propose in the self answer, but I'd like to know whether there's something better.

Answer 1

This is the solution I've come up with,

inoremap <buffer> <expr> " <sid>expand_double_quote()
fun! s:expand_double_quote()
  if col('.') < 2 || getline('.')[col('.') - 2 ] == ' '
    return "``"
  else
    return "''"
  endif
endf

which I've put in $HOME/.vim/after/ftplugin/tex.vim.