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>

4 files changed, 62 insertions, 9 deletions

diff --git a/scripts/install-multi-user.sh b/scripts/install-multi-user.sh
index f149ea0d7..7c66538b0 100644
--- a/scripts/install-multi-user.sh
+++ b/scripts/install-multi-user.sh
@@ -136,7 +136,7 @@ EOF
     cat <<EOF
 $step. Delete the files Nix added to your system:
 
-  sudo rm -rf /etc/nix $NIX_ROOT $ROOT_HOME/.nix-profile $ROOT_HOME/.nix-defexpr $ROOT_HOME/.nix-channels $HOME/.nix-profile $HOME/.nix-defexpr $HOME/.nix-channels
+  sudo rm -rf "/etc/nix" "$NIX_ROOT" "$ROOT_HOME/.nix-profile" "$ROOT_HOME/.nix-defexpr" "$ROOT_HOME/.nix-channels" "$ROOT_HOME/.local/state/nix" "$ROOT_HOME/.cache/nix" "$HOME/.nix-profile" "$HOME/.nix-defexpr" "$HOME/.nix-channels" "$HOME/.local/state/nix" "$HOME/.cache/nix"
 
 and that is it.
 
diff --git a/scripts/install-nix-from-closure.sh b/scripts/install-nix-from-closure.sh
index ccd19e1a8..794622530 100644
--- a/scripts/install-nix-from-closure.sh
+++ b/scripts/install-nix-from-closure.sh
@@ -188,6 +188,8 @@ fi
 # shellcheck source=./nix-profile.sh.in
 . "$nix/etc/profile.d/nix.sh"
 
+NIX_LINK="$HOME/.nix-profile"
+
 if ! "$nix/bin/nix-env" -i "$nix"; then
     echo "$0: unable to install Nix into your default profile" >&2
     exit 1
@@ -196,7 +198,7 @@ fi
 # Install an SSL certificate bundle.
 if [ -z "$NIX_SSL_CERT_FILE" ] || ! [ -f "$NIX_SSL_CERT_FILE" ]; then
     "$nix/bin/nix-env" -i "$cacert"
-    export NIX_SSL_CERT_FILE="$HOME/.nix-profile/etc/ssl/certs/ca-bundle.crt"
+    export NIX_SSL_CERT_FILE="$NIX_LINK/etc/ssl/certs/ca-bundle.crt"
 fi
 
 # Subscribe the user to the Nixpkgs channel and fetch it.
@@ -214,8 +216,8 @@ fi
 
 added=
 p=
-p_sh=$HOME/.nix-profile/etc/profile.d/nix.sh
-p_fish=$HOME/.nix-profile/etc/profile.d/nix.fish
+p_sh=$NIX_LINK/etc/profile.d/nix.sh
+p_fish=$NIX_LINK/etc/profile.d/nix.fish
 if [ -z "$NIX_INSTALLER_NO_MODIFY_PROFILE" ]; then
     # Make the shell source nix.sh during login.
     for i in .bash_profile .bash_login .profile; do
diff --git a/scripts/nix-profile-daemon.sh.in b/scripts/nix-profile-daemon.sh.in
index 0a47571ac..235536c65 100644
--- a/scripts/nix-profile-daemon.sh.in
+++ b/scripts/nix-profile-daemon.sh.in
@@ -2,7 +2,33 @@
 if [ -n "${__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
diff --git a/scripts/nix-profile.sh.in b/scripts/nix-profile.sh.in
index 5636085d4..264d9a8e2 100644
--- a/scripts/nix-profile.sh.in
+++ b/scripts/nix-profile.sh.in
@@ -2,11 +2,35 @@ if [ -n "$HOME" ] && [ -n "$USER" ]; then
 
     # Set up the per-user profile.
 
-    NIX_LINK=$HOME/.nix-profile
+    NIX_LINK="$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
 
     # Set up environment.
     # This part should be kept in sync with nixpkgs:nixos/modules/programs/environment.nix
-    export NIX_PROFILES="@localstatedir@/nix/profiles/default $HOME/.nix-profile"
+    export NIX_PROFILES="@localstatedir@/nix/profiles/default $NIX_LINK"
 
     # Set $NIX_SSL_CERT_FILE so that Nixpkgs applications like curl work.
     if [ -e /etc/ssl/certs/ca-certificates.crt ]; then # NixOS, Ubuntu, Debian, Gentoo, Arch
@@ -31,5 +55,5 @@ if [ -n "$HOME" ] && [ -n "$USER" ]; then
     fi
 
     export PATH="$NIX_LINK/bin:$PATH"
-    unset NIX_LINK
+    unset NIX_LINK NIX_LINK_NEW
 fi