Forbid exogenous deterministic variables with a lead or lag

Ref. dynare#1765

src/ParsingDriver.cc

 /*
- * Copyright © 2003-2020 Dynare Team
+ * Copyright © 2003-2021 Dynare Team
  *
  * This file is part of Dynare.
  *
@@ -398,6 +398,10 @@ ParsingDriver::add_model_variable(int symb_id, int lag)
     error("Symbol " + mod_file->symbol_table.getName(symb_id)
           +" is a function name external to Dynare. It cannot be used like a variable without input argument inside model.");
 
+  // See dynare#1765
+  if (type == SymbolType::exogenousDet && lag != 0)
+    error("Exogenous deterministic variable " + mod_file->symbol_table.getName(symb_id) + " cannot be given a lead or a lag.");
+
   if (type == SymbolType::modelLocalVariable && lag != 0)
     error("Model local variable " + mod_file->symbol_table.getName(symb_id) + " cannot be given a lead or a lag.");