home-environment: prevent overwriting existing files
This should reduce the risk of overwriting an existing file in the user's home directory. A file will only be replaced if it is a link pointing to a home-manager tree inside the Nix store. If an existing file is detected an error is written indicating the file's path and the activation will terminate before any mutation occurs. Fixes #6
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Robert Helgesson
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README.md
71
README.md
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@ -9,32 +9,23 @@ read the warning below.
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Words of warning
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----------------
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This project is in early development! I personally use it to manage
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This project is under development. I personally use it to manage
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several user configurations but it may fail catastrophically for you.
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So beware!
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To configure programs and services the Home Manager must write various
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things to your home directory and possibly overwrite files you have
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previously created. For example, if you use Home Manager to install
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and configure Git then your `~/.gitconfig` will be replaced by a link
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to a configuration generated by Home Manager:
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In some cases Home Manager cannot detect whether it will overwrite a
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previous manual configuration. For example, the Gnome Terminal module
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will write to your dconf store and cannot tell whether a configuration
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that it is about to be overwrite was from a previous Home Manager
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generation or from manual configuration.
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```
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$ ls -gG ~/.gitconfig
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lrwxrwxrwx 1 73 Jan 8 21:59 /home/rycee/.gitconfig -> /nix/store/pk7g12816avnxyhnkbdhqhnlzrw7fsga-home-manager-files/.gitconfig
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```
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Home Manager targets [NixOS][] version 17.03 (the current stable
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version), it may or may not work on other Linux distributions and
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NixOS versions.
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So, if you already have a wonderful, painstakingly created
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`~/.gitconfig` it will be gone. Home Manager will _not_ attempt to
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backup the previous `~/.gitconfig` file.
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Further, Home Manager targets [NixOS][] version 17.03 (the current
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stable version), it may or may not work on other Linux distributions
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and NixOS versions.
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Finally, the `home-manager` tool does not explicitly support rollbacks
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at the moment so if your home directory gets messed up you'll have to
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fix it yourself (you can attempt to run the activation script for the
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Also, the `home-manager` tool does not explicitly support rollbacks at
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the moment so if your home directory gets messed up you'll have to fix
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it yourself (you can attempt to run the activation script for the
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desired generation).
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Now when your expectations have been built up and you are eager to try
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@ -132,6 +123,44 @@ $ home-manager build
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which will create a `result` link to a directory containing an
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activation script and the generated home directory files.
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File safety
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-----------
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To configure programs and services the Home Manager must write various
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things to your home directory. To prevent overwriting any existing
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files when switching to a new generation, Home Manager will attempt to
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detect collisions between existing files and generated files. If any
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such collision is detected the activation will terminate before
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changing anything on your computer.
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For example, suppose you have a wonderful, painstakingly created
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`~/.gitconfig` and add
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```nix
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{
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# …
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programs.git = {
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enable = true;
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userName = "Jane Doe";
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userEmail = "jane.doe@example.org";
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};
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# …
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}
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```
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to your configuration. Attempting to switch to the generation will
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then result in
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```
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$ home-manager switch
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…
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Activating checkLinkTargets
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Existing file '/home/jdoe/.gitconfig' is in the way
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Please move the above files and try again
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```
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[Nix]: https://nixos.org/nix/
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[NixOS]: https://nixos.org/
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[Nixpkgs]: https://nixos.org/nixpkgs/
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@ -246,6 +246,37 @@ in
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# script's "check" and the "write" phases.
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home.activation.writeBoundary = dagEntryAnywhere "";
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# This verifies that the links we are about to create will not
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# overwrite an existing file.
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home.activation.checkLinkTargets = dagEntryBefore ["writeBoundary"] (
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let
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pattern = "-home-manager-files/";
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check = pkgs.writeText "check" ''
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newGenFiles="$1"
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shift
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for sourcePath in "$@" ; do
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relativePath="''${sourcePath#$newGenFiles/}"
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targetPath="$HOME/$relativePath"
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if [[ -e "$targetPath" \
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&& ! "$(readlink -e "$targetPath")" =~ "${pattern}" ]] ; then
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echo -e "Existing file '$targetPath' is in the way"
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collision=1
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fi
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done
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if [[ -v collision ]] ; then
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echo -e "Please move the above files and try again"
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exit 1
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fi
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'';
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in
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''
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newGenFiles="$(readlink -e "$newGenPath/home-files")"
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find "$newGenFiles" -type f -print0 -or -type l -print0 \
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| xargs -0 bash ${check} "$newGenFiles"
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''
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);
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home.activation.linkGeneration = dagEntryAfter ["writeBoundary"] (
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let
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link = pkgs.writeText "link" ''
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