Refresh cached GC root

This helps with tools that delete gcroots based on access time.

direnvrc

@@ -189,6 +189,15 @@ _nix_add_gcroot() {
   _nix build --out-link "$symlink" "$storepath"
 }
 
+_nix_refresh_gcroots() {
+  # Use touch to update all symlinks' timestamps to prevent nh
+  # from garbage collecting the frequently used direnv environment.
+  local layout_dir
+  layout_dir=$(direnv_layout_dir)
+
+  touch -h "${layout_dir}"/flake-profile-* "${layout_dir}"/flake-inputs/* "${layout_dir}"/nix-profile-*
+}
+
 _nix_clean_old_gcroots() {
   local layout_dir=$1
 
@@ -354,6 +363,7 @@ use_flake() {
     if [[ -e ${profile_rc} ]]; then
       # Our cache is valid, use that
       _nix_direnv_info "Using cached dev shell"
+      _nix_refresh_gcroots
     else
       # We don't have a profile_rc to use!
       _nix_direnv_error "use_flake failed - Is your flake's devShell working?"
@@ -515,6 +525,7 @@ use_nix() {
   else
     if [[ -e ${profile_rc} ]]; then
       _nix_direnv_info "Using cached dev shell"
+      _nix_refresh_gcroots
     else
       _nix_direnv_error "use_nix failed - Is your nix shell working?"
       unset IN_NIX_SHELL