GoKawiilNeovim overwrote and deleted legacy Vim persistent undo files
Computer scientist David Chisnall reported that installing Neovim caused it to detect existing Vim persistent-undo files, delete their contents, and replace them with a new incompatible format, without renaming or upgrading the originals. He said Vim itself could no longer read the resulting files either. When he raised an issue about the data loss, he was told the persistent undo file format is considered unstable and not guaranteed to preserve data.
GoKawiil's interpretation of the reporting above, not reported fact.
The incident highlights a mismatch between user expectations of a feature named 'persistent undo,' which implies durability, and the maintainers' stated position that its file format is not stable across versions. It suggests users relying on long-term undo history across forks or upgrades should back up such data rather than assume compatibility, since Neovim's silent overwrite behavior could cause irreversible loss for others in similar setups.
- Neovim replaced Vim's undo files with an incompatible format upon first use, deleting original data.
- Vim itself could no longer read the files after Neovim modified them.
- Neovim maintainers reportedly said the persistent undo format is unstable and not guaranteed for data preservation.
Source: unsung.aresluna.org — Marcin Wichary, 2026-09-27
Published there as: “Installing NeoVim caused original Vim undo files to be deleted”
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