Vim not setting `tex` filetype on startup

Question

I noticed that if I open a non-existent HTML file with Vim, the filetype is set automatically to html:

$ vim foobar.html
:set filetype # --> filetype=html

On the other hand, the same does not happen with TeX. If I create a non-existent file the filetype is plaintext, and I have to save the file and reopen it to have it correctly set:

$ vim blabla.tex
:set filetype # --> filetype=plaintext

I also tried with Python, C, VimL, Javascript files and the filetype is always set right away. I don't know why this does not happen with TeX files.

The only thing I can think might interfere is vim-latex. Could that be possible? If so, how do I fix this problem?

If it might be of help, here is my not so long .vimrc file.

Answer 1

Vim uses a giant heuristic to determine plaintex vs other variations of tex.

If you look in $VIMRUNTIME/filetype.vim you will find the following function

" Choose context, plaintex, or tex (LaTeX) based on these rules:
" 1. Check the first line of the file for "%&<format>".
" 2. Check the first 1000 non-comment lines for LaTeX or ConTeXt keywords.
" 3. Default to "latex" or to g:tex_flavor, can be set in user's vimrc.
func! s:FTtex()
  let firstline = getline(1)
  if firstline =~ '^%&\s*\a\+'
    let format = tolower(matchstr(firstline, '\a\+'))
    let format = substitute(format, 'pdf', '', '')
    if format == 'tex'
      let format = 'plain'
    endif
  else
    " Default value, may be changed later:
    let format = exists("g:tex_flavor") ? g:tex_flavor : 'plain'
    " Save position, go to the top of the file, find first non-comment line.
    let save_cursor = getpos('.')
    call cursor(1,1)
    let firstNC = search('^\s*[^[:space:]%]', 'c', 1000)
    if firstNC " Check the next thousand lines for a LaTeX or ConTeXt keyword.
      let lpat = 'documentclass\>\|usepackage\>\|begin{\|newcommand\>\|renewcommand\>'
      let cpat = 'start\a\+\|setup\a\+\|usemodule\|enablemode\|enableregime\|setvariables\|useencoding\|usesymbols\|stelle\a\+\|verwende\a\+\|stel\a\+\|gebruik\a\+\|usa\a\+\|imposta\a\+\|regle\a\+\|utilisemodule\>'
      let kwline = search('^\s*\\\%(' . lpat . '\)\|^\s*\\\(' . cpat . '\)',
                              \ 'cnp', firstNC + 1000)
      if kwline == 1    " lpat matched
        let format = 'latex'
      elseif kwline == 2    " cpat matched
        let format = 'context'
      endif     " If neither matched, keep default set above.
      " let lline = search('^\s*\\\%(' . lpat . '\)', 'cn', firstNC + 1000)
      " let cline = search('^\s*\\\%(' . cpat . '\)', 'cn', firstNC + 1000)
      " if cline > 0
      "   let format = 'context'
      " endif
      " if lline > 0 && (cline == 0 || cline > lline)
      "   let format = 'tex'
      " endif
    endif " firstNC
    call setpos('.', save_cursor)
  endif " firstline =~ '^%&\s*\a\+'

  " Translation from formats to file types.  TODO:  add AMSTeX, RevTex, others?
  if format == 'plain'
    setf plaintex
  elseif format == 'context'
    setf context
  else " probably LaTeX
    setf tex
  endif
  return
endfunc

This function determines which flavor of tex to use. If you look at it you can see that default value is taken from g:tex_flavor (if it exists, defaults to plain). If you set this variable to tex (in you vimrc), vim will default to the tex filetype.

let g:tex_flavor = 'tex'

Answer 2

There is a way to automate the process you're doing manually.

Adding autocmd BufRead,BufNewFile *.tex set filetype=tex to your .vimrc file will set tex filetype for each tex file, once you open them in vim.