Pass rc.weekstart to libshared for ISO8601 weeknum parsing if "monday"

src/Context.cpp

@@ -1105,6 +1105,11 @@ void Context::staticInitialization() {
   Task::regex = Variant::searchUsingRegex = config.getBoolean("regex");
   Lexer::dateFormat = Variant::dateFormat = config.get("dateformat");
 
+  auto weekStart = Datetime::dayOfWeek(config.get("weekstart"));
+  if (weekStart != 0 && weekStart != 1)
+    throw std::string(
+        "The 'weekstart' configuration variable may only contain 'Sunday' or 'Monday'.");
+  Datetime::weekstart = weekStart;
   Datetime::isoEnabled = config.getBoolean("date.iso");
   Datetime::standaloneDateEnabled = false;
   Datetime::standaloneTimeEnabled = false;

src/commands/CmdCalendar.cpp

@@ -404,12 +404,7 @@ int CmdCalendar::execute(std::string& output) {
 std::string CmdCalendar::renderMonths(int firstMonth, int firstYear, const Datetime& today,
                                       std::vector<Task>& all, int monthsPerLine) {
   auto& config = Context::getContext().config;
-
-  // What day of the week does the user consider the first?
-  auto weekStart = Datetime::dayOfWeek(config.get("weekstart"));
-  if (weekStart != 0 && weekStart != 1)
-    throw std::string(
-        "The 'weekstart' configuration variable may only contain 'Sunday' or 'Monday'.");
+  auto weekStart = Datetime::weekstart;
 
   // Build table for the number of months to be displayed.
   Table view;