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
This commit is contained in:
Robert Helgesson 2017-05-06 00:44:00 +02:00
parent 7e58b6bb35
commit 88ec7145ba
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GPG key ID: C3DB11069E65DC86
2 changed files with 81 additions and 21 deletions

View file

@ -9,32 +9,23 @@ read the warning below.
Words of warning
----------------
This project is in early development! I personally use it to manage
This project is under development. I personally use it to manage
several user configurations but it may fail catastrophically for you.
So beware!
To configure programs and services the Home Manager must write various
things to your home directory and possibly overwrite files you have
previously created. For example, if you use Home Manager to install
and configure Git then your `~/.gitconfig` will be replaced by a link
to a configuration generated by Home Manager:
In some cases Home Manager cannot detect whether it will overwrite a
previous manual configuration. For example, the Gnome Terminal module
will write to your dconf store and cannot tell whether a configuration
that it is about to be overwrite was from a previous Home Manager
generation or from manual configuration.
```
$ ls -gG ~/.gitconfig
lrwxrwxrwx 1 73 Jan 8 21:59 /home/rycee/.gitconfig -> /nix/store/pk7g12816avnxyhnkbdhqhnlzrw7fsga-home-manager-files/.gitconfig
```
Home Manager targets [NixOS][] version 17.03 (the current stable
version), it may or may not work on other Linux distributions and
NixOS versions.
So, if you already have a wonderful, painstakingly created
`~/.gitconfig` it will be gone. Home Manager will _not_ attempt to
backup the previous `~/.gitconfig` file.
Further, Home Manager targets [NixOS][] version 17.03 (the current
stable version), it may or may not work on other Linux distributions
and NixOS versions.
Finally, the `home-manager` tool does not explicitly support rollbacks
at the moment so if your home directory gets messed up you'll have to
fix it yourself (you can attempt to run the activation script for the
Also, the `home-manager` tool does not explicitly support rollbacks at
the moment so if your home directory gets messed up you'll have to fix
it yourself (you can attempt to run the activation script for the
desired generation).
Now when your expectations have been built up and you are eager to try
@ -132,6 +123,44 @@ $ home-manager build
which will create a `result` link to a directory containing an
activation script and the generated home directory files.
File safety
-----------
To configure programs and services the Home Manager must write various
things to your home directory. To prevent overwriting any existing
files when switching to a new generation, Home Manager will attempt to
detect collisions between existing files and generated files. If any
such collision is detected the activation will terminate before
changing anything on your computer.
For example, suppose you have a wonderful, painstakingly created
`~/.gitconfig` and add
```nix
{
# …
programs.git = {
enable = true;
userName = "Jane Doe";
userEmail = "jane.doe@example.org";
};
# …
}
```
to your configuration. Attempting to switch to the generation will
then result in
```
$ home-manager switch
Activating checkLinkTargets
Existing file '/home/jdoe/.gitconfig' is in the way
Please move the above files and try again
```
[Nix]: https://nixos.org/nix/
[NixOS]: https://nixos.org/
[Nixpkgs]: https://nixos.org/nixpkgs/

View file

@ -246,6 +246,37 @@ in
# script's "check" and the "write" phases.
home.activation.writeBoundary = dagEntryAnywhere "";
# This verifies that the links we are about to create will not
# overwrite an existing file.
home.activation.checkLinkTargets = dagEntryBefore ["writeBoundary"] (
let
pattern = "-home-manager-files/";
check = pkgs.writeText "check" ''
newGenFiles="$1"
shift
for sourcePath in "$@" ; do
relativePath="''${sourcePath#$newGenFiles/}"
targetPath="$HOME/$relativePath"
if [[ -e "$targetPath" \
&& ! "$(readlink -e "$targetPath")" =~ "${pattern}" ]] ; then
echo -e "Existing file '$targetPath' is in the way"
collision=1
fi
done
if [[ -v collision ]] ; then
echo -e "Please move the above files and try again"
exit 1
fi
'';
in
''
newGenFiles="$(readlink -e "$newGenPath/home-files")"
find "$newGenFiles" -type f -print0 -or -type l -print0 \
| xargs -0 bash ${check} "$newGenFiles"
''
);
home.activation.linkGeneration = dagEntryAfter ["writeBoundary"] (
let
link = pkgs.writeText "link" ''