A setting to follow XDG Base Directory standard

XDG Base Directory is a standard for locations for storing various
files. Nix has a few files which seem to fit in the standard, but
currently use a custom location directly in the user's ~, polluting
it:

- ~/.nix-profile
- ~/.nix-defexpr
- ~/.nix-channels

This commit adds a config option (use-xdg-base-directories) to follow
the XDG spec and instead use the following locations:

- $XDG_STATE_HOME/nix/profile
- $XDG_STATE_HOME/nix/defexpr
- $XDG_STATE_HOME/nix/channels

If $XDG_STATE_HOME is not set, it is assumed to be ~/.local/state.

Co-authored-by: Théophane Hufschmitt <7226587+thufschmitt@users.noreply.github.com>
Co-authored-by: Tim Fenney <kodekata@gmail.com>
Co-authored-by: pasqui23 <pasqui23@users.noreply.github.com>
Co-authored-by: Artturin <Artturin@artturin.com>
Co-authored-by: John Ericson <Ericson2314@Yahoo.com>

1 files changed, 29 insertions, 2 deletions

diff --git a/scripts/nix-profile-daemon.sh.in b/scripts/nix-profile-daemon.sh.in
index 0a47571ac..235536c65 100644
--- a/scripts/nix-profile-daemon.sh.in
+++ b/scripts/nix-profile-daemon.sh.in
@@ -2,7 +2,33 @@
 if [ -n "${__ETC_PROFILE_NIX_SOURCED:-}" ]; then return; fi
 __ETC_PROFILE_NIX_SOURCED=1
 
-export NIX_PROFILES="@localstatedir@/nix/profiles/default $HOME/.nix-profile"
+NIX_LINK=$HOME/.nix-profile
+if [ -n "$XDG_STATE_HOME" ]; then
+    NIX_LINK_NEW="$XDG_STATE_HOME/nix/profile"
+else
+    NIX_LINK_NEW=$HOME/.local/state/nix/profile
+fi
+if ! [ -e "$NIX_LINK" ]; then
+    NIX_LINK="$NIX_LINK_NEW"
+else
+    if [ -t 2 ] && [ -e "$NIX_LINK_NEW" ]; then
+        warning="\033[1;35mwarning:\033[0m"
+        printf "$warning Both %s and legacy %s exist; using the latter.\n" "$NIX_LINK_NEW" "$NIX_LINK" 1>&2
+        if [ "$(realpath "$NIX_LINK")" = "$(realpath "$NIX_LINK_NEW")" ]; then
+            printf "         Since the profiles match, you can safely delete either of them.\n" 1>&2
+        else
+            # This should be an exceptionally rare occasion: the only way to get it would be to
+            # 1. Update to newer Nix;
+            # 2. Remove .nix-profile;
+            # 3. Set the $NIX_LINK_NEW to something other than the default user profile;
+            # 4. Roll back to older Nix.
+            # If someone did all that, they can probably figure out how to migrate the profile.
+            printf "$warning Profiles do not match. You should manually migrate from %s to %s.\n" "$NIX_LINK" "$NIX_LINK_NEW" 1>&2
+        fi
+    fi
+fi
+
+export NIX_PROFILES="@localstatedir@/nix/profiles/default $NIX_LINK"
 
 # Set $NIX_SSL_CERT_FILE so that Nixpkgs applications like curl work.
 if [ -n "${NIX_SSL_CERT_FILE:-}" ]; then
@@ -34,4 +60,5 @@ else
   unset -f check_nix_profiles
 fi
 
-export PATH="$HOME/.nix-profile/bin:@localstatedir@/nix/profiles/default/bin:$PATH"
+export PATH="$NIX_LINK/bin:@localstatedir@/nix/profiles/default/bin:$PATH"
+unset NIX_LINK