Show changes since buffer was opened

Question

Is it possible to show all changes made to a buffer since the buffer was opened?

This question https://stackoverflow.com/questions/749297/can-i-see-changes-before-i-save-my-file-in-vim is related, but asks for changes since the last write, which can easily be accomplished by looking at the file on the file system.

I am using persistent undo (set undofile), so I cannot use :earlier <reallylargenumber>.

Answer 1

I played around. Could you try the following (rarely tested):

autocmd BufReadPost * let b:undo_seq_load=changenr()

function! DiffSinceLoad()
    let tmpa = tempname()
    let tmpb = tempname()
    let curchange=changenr()
    exe "undo " . b:undo_seq_load
    exec 'w '.tmpa
    exe "undo " . curchange
    exec 'w '.tmpb
    update
    exec 'tabnew '.tmpa
    diffthis
    vert split
    exec 'edit '.tmpb
    diffthis
endfunction
command! -nargs=0 DiffSinceLoad call DiffSinceLoad()

This is based on this answer.

Second iteration: This is now in my vimrc.

• Use only one temporary file
• If the buffer with the temporary file gets hidden, it is deleted.
• When the buffer with the temporary file is deleted, :diffoff is called via autocmd.

 

" store the changenr at file load
autocmd BufReadPost * let b:changenr_on_load=changenr()
function! DiffSinceLoad()
    let tmpa = tempname()
    let curchange=changenr()
    exe "undo " . b:changenr_on_load
    exe 'w ' . tmpa
    exe 'undo ' . curchange
    "diffthis
    exe 'vertical diffsplit ' . tmpa
    " when buffer gets hidden, delete it and reset diff settings
    setlocal bufhidden=delete
    autocmd BufDelete <buffer> diffoff
    " return to edited file
    wincmd p
endfunction
command! -nargs=0 DiffSinceLoad silent call DiffSinceLoad()

Answer 2

This will do what you're looking for:

:w !diff % -