hm-switch: also aggressively manage nix.conf for non-nixos installs

scripts/hm-switch.sh

@@ -7,6 +7,16 @@ echo "SCRIPT_DIR: ${SCRIPT_DIR}"
 
 HOME_MANAGER_DIR="${SCRIPT_DIR}/../nix-conf/home-manager"
 
+# Manage nix.conf. Ideally, this should be done with snapshot-based version
+# and with preview on-the-spot, with some timeout
+if [ -f /etc/nix/nix.conf ]; then
+    # managed nix.conf
+    BACKUP_FILE="/etc/nix/nix.conf.backup"
+    echo "overwriting /etc/nix/nix.conf. Please find latest backup in ${BACKUP_FILE}"
+    sudo cp /etc/nix/nix.conf ${BACKUP_FILE}
+    sudo cp "${HOME_MANAGER_DIR}/hwtr/nix.conf" /etc/nix/
+fi
+
 # Mason is bad: it puts binaries onto xdg.data
 # let's make mason starts fresh, just in case we introduce RPATH hacks 
 # that injects binary for Mason to use.
@@ -15,7 +25,6 @@ rm -rf ~/.local/share/nvim/mason
 # test if we have home-manager, if not, attempt to use nix to put home-manager to
 # our environment
 if [ $(home-manager >/dev/null 2>&1) ]; then
-    # highly likely we don't even have nix support to start with, so let's fix that
     nix-shell -p home-manager --run "home-manager switch --flake $HOME_MANAGER_DIR $@"
 else
     home-manager switch -b backup --flake "$HOME_MANAGER_DIR" $@