direnv: allow configuring extra files to watch from devenv.nix

direnvrc

@@ -123,6 +123,14 @@ use_devenv() {
     fi
   fi
 
+  local extra_files_watchlist="$flake_dir/.devenv/watchfiles.txt"
+  # Watch extra files configured in devenv.nix
+  if [[ -f "$extra_files_watchlist" ]]; then
+    for file in $(cat "$extra_files_watchlist"); do
+      files_to_watch+=("$file")
+    done
+  fi
+
   nix_direnv_watch_file "${files_to_watch[@]}"
 
   local layout_dir profile_rc
@@ -155,4 +163,13 @@ use_devenv() {
     log_status "using cached devenv shell"
     _nix_import_env "$profile_rc"
   fi
+
+  # Watch extra files configured in devenv.nix
+  # This picks up new files and reloads the shell on initial run
+  # TODO: can compare files in files_to_watch with the files we have now
+  if [[ -f "$extra_files_watchlist" ]]; then
+    for file in $(cat "$extra_files_watchlist"); do
+      watch_file "$file"
+    done < "$filename"
+  fi
 }

src/modules/integrations/direnv.nix

@@ -0,0 +1,25 @@
+{ pkgs, config, lib, ... }:
+
+let
+  cfg = config.direnv;
+in
+{
+  options.direnv = {
+    watchFiles = lib.mkOption {
+      description = lib.mdDoc "Extra files to watch for changes and reload the direnv environment";
+      # TODO: best type here? any way to exclude defaults?
+      # TODO: regex support?
+      type = lib.types.listOf lib.types.str;
+      default = [ ];
+    };
+
+    watchfiles = lib.mkOption {
+      internal = true;
+      type = lib.types.package;
+    };
+  };
+
+  config = {
+    direnv.watchfiles = pkgs.writeText "watchfiles.txt" (lib.concatStringsSep "\n" cfg.watchFiles);
+  };
+}

src/modules/top-level.nix

@@ -267,6 +267,8 @@ in
         echo "Please install direnv: https://direnv.net/docs/installation.html"
       fi
 
+      ln -snf ${config.direnv.watchfiles} ${lib.escapeShellArg config.devenv.dotfile}/watchfiles.txt
+
       mkdir -p "$DEVENV_STATE"
       if [ ! -L "$DEVENV_DOTFILE/profile" ] || [ "$(${pkgs.coreutils}/bin/readlink $DEVENV_DOTFILE/profile)" != "${profile}" ]
       then