bug: file.old would be clobbered by backing up file

[viperML]

Are you following the right branch?

• [X] My Nixpkgs and Home Manager versions are in sync

Is there an existing issue for this?

• [X] I have searched the existing issues

Issue description

The automatic backup setting doesn't handle having a backup already in place.

Steps to reproduce:

1. Have some file be backed up by HM into file.old
2. Replace file again with something else.
3. HM won't be able to backup file into file.old.

This behaviour is located here: https://github.com/nix-community/home-manager/blob/d4a5076ea8c2c063c45e0165f9f75f69ef583e20/modules/files.nix#L116-L119

My suggestion: add a new option, that will force the backup, removing the old backup.

Maintainer CC

No response

System information

$ nix-shell -p nix-info --run "nix-info -m"
 - system: `"x86_64-linux"`
 - host os: `Linux 6.5.5, NixOS, 23.11 (Tapir), 23.11.20231006.87828a0`
 - multi-user?: `yes`
 - sandbox: `yes`
 - version: `nix-env (Nix) 2.17.0`
 - nixpkgs: `/nix/store/g68f5abh3xhcz8xsdlfw7wkgkkcx3nwy-source`

[viperML]

CC the git blame: @nyarly

[nyarly]

The backup flag takes an option for what to backup to. I generally just change it to e.g. old2

[viperML]

I am using it through the NixOS module and the backupFileExtension option. So changing it every now and then is not an option.

[stale[bot]]

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[viperML]

Still an issue, everytime I boot NixOS the HM systemd service fails with this.

[stale[bot]]

Thank you for your contribution! I marked this issue as stale due to inactivity. Please be considerate of people watching this issue and receiving notifications before commenting 'I have this issue too'. We welcome additional information that will help resolve this issue. Please read the relevant sections below before commenting.

If you are the original author of the issue

• If this is resolved, please consider closing it so that the maintainers know not to focus on this.
• If this might still be an issue, but you are not interested in promoting its resolution, please consider closing it while encouraging others to take over and reopen an issue if they care enough.
• If you know how to solve the issue, please consider submitting a Pull Request that addresses this issue.

If you are not the original author of the issue

• If you are also experiencing this issue, please add details of your situation to help with the debugging process.
• If you know how to solve the issue, please consider submitting a Pull Request that addresses this issue.

Memorandum on closing issues

Don't be afraid to manually close an issue, even if it holds valuable information. Closed issues stay in the system for people to search, read, cross-reference, or even reopen – nothing is lost! Closing obsolete issues is an important way to help maintainers focus their time and effort.