Neovim 0.5+ undo file version bumping script. Fixes "E824: Incompatible undo file"

ufbump

#!/usr/bin/env python3

"""
Neovim undo file version bumping script

This python script backups and converts Vim undo files generated by
vanilla Vim 7.2.444 - 9.0 or Neovim 0.1.0 - 0.4.4 (UF_VERSION=2) to
reuse them on Neovim 0.5.0+ (UF_VERSION=3) without the error message
"E824: Incompatible undo file".

See https://github.com/neovim/neovim/pull/13973 for more information.

Example usage w/ undodir:
    $ ./ufbump ~/.local/share/nvim/undo/*

Alternative form if the shell complains about "too many arguments":
    $ find ~/.local/share/nvim/undo -type f -exec ./ufbump '{}' +

Example usage w/o undodir:
    $ find /code/path -name '*.un~' -type f -exec ./ufbump '{}' +

USE AT YOUR OWN RISK!


The author disclaims copyright to this source code.
In place of a legal notice, here is a blessing:

* May you do good and not evil.
* May you find forgiveness for yourself and forgive others.
* May you share freely, never taking more than you give.

"""

import os
import shutil
import struct
import sys

UF_START_MAGIC = b"Vim\237UnDo\345"
UF_ENTRY_END_MAGIC = b"\x35\x81"

UF_OLD_VERSION = 2
UF_NEW_VERSION = 3


def main(path):
    path_tmp = path + ".tmp"
    path_bak = path + ".bak"

    with open(path, "rb") as src:
        magic = src.read(len(UF_START_MAGIC))
        if magic != UF_START_MAGIC:
            print("%s: not a vim undo file, skipped" % path)
            return

        version, *_ = struct.unpack(">h", src.read(2))
        if version != UF_OLD_VERSION:
            print("%s: undo file version was %d, skipped" % (path, version))
            return

        with open(path_tmp, "wb") as dest:
            dest.write(UF_START_MAGIC)
            dest.write(struct.pack(">h", UF_NEW_VERSION))
            dest.write(src.read().replace(UF_ENTRY_END_MAGIC, UF_ENTRY_END_MAGIC * 2))

    os.rename(path, path_bak)
    os.rename(path_tmp, path)
    print("%s: added empty extmark section" % path)


if __name__ == "__main__":
    script, *argv = sys.argv
    if not argv:
        print(__doc__.strip())
    for path in argv:
        main(path)