What the 'detailed action name' format is defined by g_action_parse_detailed_name() to be one of "action" (no parameter), "action::string" (parameter type "s") or "action(target)" for arbitrary parameter types.

However, in gtk+' gtk_actionable_set_detailed_action_name(), the only allowed formats are the first two. This creates an unexpected API inconsistency and and inability to use this API for non-"s" actions (which *is* documented there, but still unexpected). IMO this should be fixed to make this function accept the full format as defined by gio; patch attached.