use XDG_CACHE_HOME for help file

  required for flatpak

rednotebook/gui/menu.py

@@ -16,6 +16,7 @@
 # 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
 # -----------------------------------------------------------------------
 import os
+import platform
 import webbrowser
 
 from gi.repository import GdkPixbuf, Gtk
@@ -408,7 +409,18 @@ def on_help_menu_item_activate(self, widget):
  headers=[_("RedNotebook Documentation"), info.version, ""],
  options={"toc": 1},
  )
- utils.show_html_in_browser(html, os.path.join(temp_dir, "help.html"))
+
+ # workaround: for flatpak, temp_dir is located at /tmp which is not visible outside sandbox
+ # but XDG_CACHE_HOME is.
+ if platform.system() == "Linux":
+ cache_dir = os.getenv(
+ "XDG_CACHE_HOME", os.path.join(os.path.expanduser("~"), ".cache")
+ )
+ help_file = os.path.join(cache_dir, "help.html")
+ else:
+ help_file = os.path.join(temp_dir, "help.html")
+
+ utils.show_html_in_browser(html, help_file)
 
  def on_online_help(self, widget):
  webbrowser.open(info.answers_url)