Why is my # mapping behaving oddly in TeX files?

Question

I recently made the following key-map in my .vimrc file:

inoremap # \
inoremap \ #

since I just want to switch those two key on my keyboard, everything works just fine until I notice this:

1. Only in .tex file, when I hit the # key (now map to \), it will show as # for about 1 second, then if I do nothing it will change to \.

2. also only in .tex file, when I hit the # key and immediately hit another key, for most of the key, say x, although it shows # at first, it will change to /x as soon as I hit x. But for some key like b, if I do not wait it to turn to \ (as described in (1)) before I hit b, it will be #b in the end, if I wait it to turn to \, then it will show as \b.

Any solution to this?

The following is my .vimrc file:

call plug#begin()

Plug 'lervag/vimtex'
Plug 'vim-scripts/AutoComplPop'
Plug 'SirVer/ultisnips'
Plug 'honza/vim-snippets'

call plug#end()

set complete+=kspell

let g:tex_flavor='latex'
let g:vimtex_view_method = 'zathura'
let g:vimtex_quickfix_mode=0
" show conceal"
set conceallevel=2
let g:tex_conceal='abdmg'

let g:UltiSnipsExpandTrigger="<tab>"
let g:UltiSnipsJumpForwardTrigger="<tab>"
let g:UltiSnipsJumpBackwardTrigger="<s-tab>"

" :UltiSnipsEdit to split your window."
let g:UltiSnipsEditSplit="vertical"
let g:UltiSnipsSnippetDirectories=["UltiSnips", "mySnips"]

autocmd BufWinLeave *.* mkview
" autocmd BufWinEnter *.* silent loadview"

" keymap, see :help map-modes for reference"
inoremap # \
inoremap \ #

set cursorline
set cursorcolumn
set expandtab
set ts=4 sts=4 sw=4
set colorcolumn=80,120
set rnu
set ruler
syntax on


hi cursorline cterm=NONE ctermbg=237
hi cursorcolumn ctermbg=237
hi cursorlinenr cterm=NONE ctermbg=237
hi Conceal cterm=NONE ctermfg=lightyellow ctermbg=NONE
" to clear conceal highlighting use the command :hi clear Conceal"
hi ColorColumn ctermbg=240

Answer 1

This is probably because there's another multi-key mapping that starts with a #; this is added by the TeX-specific plugin you have and loaded only for those files. You can reproduce it with:

inoremap # \
inoremap \ #
inoremap #x Pressed #x

If you type just # Vim doesn't know if you want trigger the # mapping or the #x mapping, so it needs to wait for a bit to see which one you want, since people aren't infinitely fast typers.

Vim will wait for the second keypress for timeoutlen milliseconds; the default is 1000 (1 second), but you can decrease this with e.g. set timeout=200. This does mean you'll have to type those mapping faster (only if there's a mapping for the single keypress and more than one, e.g. it won't affect g<other>; that will just wait forever since there's no mapping for just g).

Pressing e.g. #y will insert \y as expected; since #y isn't mapped Vim knows you wanted to trigger the # mapping. You don't need to wait for the screen to update, but it does look a bit odd.

---

To see which mappings are set up use :imap #:

i  #x          * Pressed #x
i  #           * \

and add :verbose to see where they're set from:

:verbose imap #
i  #x          * Pressed #x
        Last set from ~/.vim/vimrc line 737
i  #           * \
        Last set from ~/.vim/vimrc line 734

---

You can probably configure your TeX plugin to not map these; I installed that plugin and got:

i  #B          *@vimtex#imaps#wrap_math("#B", vimtex#imaps#style_math("mathbb"))
i  #-          *@vimtex#imaps#wrap_math("#-", vimtex#imaps#style_math("overline"))
i  #c          *@vimtex#imaps#wrap_math("#c", vimtex#imaps#style_math("mathcal"))
i  #f          *@vimtex#imaps#wrap_math("#f", vimtex#imaps#style_math("mathfrak"))
i  #b          *@vimtex#imaps#wrap_math("#b", vimtex#imaps#style_math("mathbf"))
i  #/          *@vimtex#imaps#wrap_math("#/", vimtex#imaps#style_math("slashed"))

Which confirms that this is your issue.

Looking at the plugin documentation, there's a few options to change or disable this; let g:vimtex_imaps_enabled = 0 will disable all insert-mode mappings, but you can also select a different "leader". Note that this disables many other insert mode mappings too (:VimtexImapsList has a list).

See :help vimtex-imaps for the full documentation on it so you can see what works well for you.