Arnie97 · August 29, 2022 08:19 · Aug 26, 2022
diff --git a/ufbump b/ufbump
@@ -0,0 +1,76 @@
+#!/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)
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