[vim/vim] can not restore registers content properly (#2345)

[ramele]

Sometimes, there is a need for a mapping to yank something without a trace so it has to save and restore the relevant registers.
The problem is that there is no way to set register " without modifying register 0. So if, for example, we have the following:
:reg 01"
--- Registers ---
"" deleted text^J
"0 yanked text^J
"1 deleted text^J

Now we want to do a yank as part of a mapping, this mapping will have to restore register " with the deleted text. But now the original content of register 0 (the yanked text) is lost.

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[Tony Mechelynck]

Have you tried saving and restoring with the :let command, by means of an auxiliary variable (possibly a script-local variable)? (see :help script-variable, :help let-register and :help expr-register)

Best regards,
Tony.

[ramele]

If you meant :let @"='text', then yes -after this register 0 contains the same text.

[Christian Brabandt]

I think this has been discussed before, but I don't find it. I think I even made a patch back then, but Bram didn't want to change this behaviour, as this might have unexpected results.

[Nikolay Aleksandrovich Pavlov]

2017-11-18 7:37 GMT+03:00 Tony Mechelynck <vim-dev...@256bit.org>:
> Have you tried saving and restoring with the :let command, by means of an
> auxiliary variable (possibly a script-local variable)? (see :help
> script-variable, :help let-register and :help expr-register)

You can’t do that: `:let @x` is not going to work correctly if you
yanked NUL byte, or if you yanked a block selection. For
saving/restoring registers one must use getreg()/setreg(), but this is
only good as long as registers are internal to Vim and you have an
idea of what registers your command have touched: @", @0..@9 and @-
have a habit of being auto-populated under different circumstances.

If register is not internal to Vim (i.e. @* or @+, @" with some
&clipboard values) it is completely impossible to restore it correctly
because of

1. In X11 there is no register contents to restore at all, accessing a
register yields a call to the owner and Vim can only make himself the
owner and not restore the original app as such.
2. System clipboard does not necessary contain only text, but Vim is
completely unable to “restore” anything, but text.

So what you need to save/restore registers correctly is something like

function RExe(s)
let clipboard_save = &clipboard
let &clipboard = ''
let registers_save = []
for r in ['0', '1', '2', '3', '4', '5', '6', '7', '8', '9', '-', '"']
call add(registers_save, [r, getreg(r, 1, 1), getregtype(r)])
endfor
try
execute a:s
finally
for reg in registers_save
call call('setreg', reg)
endfor
let &clipboard = clipboard_save
endtry
endfunction

>
> Best regards,
> Tony.
>
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[Nikolai Aleksandrovich Pavlov]

And getreg() fails to fix the problem as well: whether I have '"' or '0' at the end, the result is the same value in both.

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[Nikolai Aleksandrovich Pavlov]

By the way, I once written a function which may serve as a replacement to normal! gvy followed by getreg('"', 1, 1): https://gist.github.com/fa35a5128886c0ecbca8f7c14fbcdde1. Usage to just yank is

let data = selection#modrange('b', 42, getpos("'<"), getpos("'>"), 0)

You may see there that handling blockwise selection is tricky and you will need to somehow get width, and while just y equivalent which is not using any registers for characterwise selection is easy, handle replacement is not so.

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[lacygoill]

Fixed by 8.2.0924 which provides the getreginfo() function.
The latter outputs a dictionary providing everything you need to save and restore the unnamed register:

• its contents as a list (which allows you to not lose NULs) via the regcontents key
• its type via the regtype key
• the name of the register it points to via the points_to key

---

Before the patch, you could try (and fail because it didn't point back to the same register) to save/restore it like this:

let save = ['"', getreg('"', 1, 1), getregtype('"')]
" do something which alters the unnamed register
call call('setreg', save)

Now, you can do it like this:

let save = getreginfo('"')
" do something which alters the unnamed register
call setreg('"', save)

---

Broken code before the patch:

vim -es -Nu NONE -i NONE -S <(cat <<'EOF'
    call setline(1, ['yanked text', 'deleted text', 'line deleted by mapping'])
    norm! yyjdd
    pu=['registers before mapping'] + [execute('reg \"01')]

    nno cd :call Func()<cr>
    fu Func()
        let save = ['"', getreg('"', 1, 1), getregtype('"')]
        norm! 2Gdd
        call call('setreg', save)
    endfu

    au VimEnter * call feedkeys('cd', 'xt')
        \ | $pu=['', 'registers after mapping'] + [execute('reg \"01')]
        \ | exe 'g/^registers/t.|norm! Vr='
        \ | 2,$p | qa!
EOF
)

registers before mapping
========================

Type Name Content
  l  ""   deleted text^J
  l  "0   yanked text^J
  l  "1   deleted text^J

registers after mapping
=======================

Type Name Content
  l  ""   deleted text^J
  l  "0   deleted text^J
  l  "1   line deleted by mapping^J

Working code after the patch:

vim -es -Nu NONE -i NONE -S <(cat <<'EOF'
    call setline(1, ['yanked text', 'deleted text', 'line deleted by mapping'])
    norm! yyjdd
    pu=['registers before mapping'] + [execute('reg \"01')]

    nno cd :call Func()<cr>
    fu Func()
        let save = getreginfo('"')
        norm! 2Gdd
        call setreg('"', save)
    endfu

    au VimEnter * call feedkeys('cd', 'xt')
        \ | $pu=['', 'registers after mapping'] + [execute('reg \"01')]
        \ | exe 'g/^registers/t.|norm! Vr='
        \ | 2,$p | qa!
EOF
)

registers before mapping
========================

Type Name Content
  l  ""   deleted text^J
  l  "0   yanked text^J
  l  "1   deleted text^J

registers after mapping
=======================

Type Name Content
  l  ""   deleted text^J
  l  "0   yanked text^J
  l  "1   deleted text^J

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[Christian Brabandt]

Closed #2345.

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