How can I warn when a large chunk of data is about to be (unknowingly) deleted?

Question

I would like a warning when a large chunk of data is to be deleted.

I tend to use the mouse along with vim to highlight text (to copy or delete).

I also use the mouse to scroll notes when I want to look around after searching a keyword.

Sometimes the mouse accidentally goes into visual mode—when I scroll up and down, this will causes all the text along the scrolling path to be selected or deselected.

I often don't realize this at the time and end up deleting (somehow) a large chunk of data without even realizing it.

Is there some kind of script I can install that will warn me when deleting in conjunction with visual-mode and/or scrolling?

I believe most of the issue is related to these:

1. highlighting (be it v or V or mouse left button accidentally dragged when scrolling),
2. scrolling (be it Ctrl-e, Ctrl-y, or mouse wheel)
3. text manipulating (be it delete or yank, etc.)

Answer 1

Here's a small script that does what you want:

function CheckBeforeDelete(cmd)
    let delta = line("'>") - line("'<")
    if delta > 10
        echo "You're about to delete ".delta." lines of data. Continue? (y/n) > "

        let char = ''
        while char != 'n' && char != 'y' && char != "\<ESC>"
            let char = nr2char(getchar())
        endwhile

        norm! :

        if char != 'y'
            return
        endif
    endif

    exe 'norm!gv'.a:cmd
    if index(['c'], tolower(a:cmd)) >= 0
        startinsert
    endif
endfunction

vnoremap d :<C-u>call CheckBeforeDelete('d')<CR>
vnoremap D :<C-u>call CheckBeforeDelete('D')<CR>
vnoremap c :<C-u>call CheckBeforeDelete('c')<CR>
vnoremap C :<C-u>call CheckBeforeDelete('C')<CR>
vnoremap <DEL> :<C-u>call CheckBeforeDelete("\< <BS>DEL>")<CR>
vnoremap x :<C-u>call CheckBeforeDelete('x')<CR>

autocmd WinScrolled * if tolower(mode()[0]) == 'v' | echohl WarningMsg | echo "You are scrolling and selecting text at the same time!" | echohl None | endif

This will prompt you for confirmation before you try to delete more than 10 lines, using visual mode, and the keys d, D, c, C, <del> or x.

It will also display a warning message when you're scrolling and selecting text at the same time.

Answer 2

I would like a warning when a large chunk of data is to be deleted

By default Vim should echo the number of lines deleted once you get past 2 full lines. This should help you do you quick sanity check. Also 'showcmd' (on by default) will show you the size of your current selection. Add set showcmd to your vimrc if need be.

Example:

Sometimes the mouse accidentally goes into visual mode—when I scroll up and down, this will causes all the text along the scrolling path to be selected or deselected.

Selected text should look different than normal text. You may want to check your colorscheme and/or terminal to make sure the colors stand out better

I often don't realize this at the time and end up deleting (somehow) a large chunk of data without even realizing it.

If you are using visual mode to delete then you may want to get in the habit of using o to toggle between the start and end of the visual selection. This will help you verify the size of the selection

Ultimately, it sounds like you have developed some troublesome habits. It might be worth it to improve your habits. e.g. avoid relying on the mouse so much, exit visual mode when looking around, set your colorscheme to have more contrast, looking at 'showcmd' to see the size of the your selection

With all that said you can use TextYankPost autocommand event to give yourself a warning. e.g.

augroup DeleteMsg
  autocmd!
  autocmd TextYankPost *
        \ if v:event.operator is# 'd' && v:event.visual && len(v:event.regcontents) > 3 |
        \   echoerr "Big delete!" |
        \ endif
augroup END