Add semantic check for empty unit name

src/parser/nmodl.yy

@@ -618,7 +618,6 @@ units           :   {
 
 unit            :   "(" { scanner.scan_unit(); } ")"
                     {
-                        // @todo Empty units should be handled in semantic analysis
                         auto unit = scanner.get_unit();
                         auto text = unit->eval();
                         $$ = new ast::Unit(unit);

src/visitors/semantic_analysis_visitor.cpp

@@ -2,8 +2,10 @@
 #include "ast/function_block.hpp"
 #include "ast/procedure_block.hpp"
 #include "ast/program.hpp"
+#include "ast/string.hpp"
 #include "ast/suffix.hpp"
 #include "ast/table_statement.hpp"
+#include "ast/unit.hpp"
 #include "utils/logger.hpp"
 #include "visitors/visitor_utils.hpp"
 
@@ -66,5 +68,14 @@ void SemanticAnalysisVisitor::visit_destructor_block(const ast::DestructorBlock&
     /// -->
 }
 
+void SemanticAnalysisVisitor::visit_unit(const ast::Unit& node) {
+    /// <-- This code is for check 3
+    if (node.get_name()->get_value().empty()) {
+        logger->warn("SemanticAnalysisVisitor:: An unit cannot be created without name.");
+        check_fail = true;
+    }
+    /// -->
+}
+
 }  // namespace visitor
 }  // namespace nmodl

src/visitors/semantic_analysis_visitor.hpp

@@ -26,6 +26,7 @@
  * 1. Check that a function or a procedure containing a TABLE statement contains only one argument
  * (mandatory in mod2c).
  * 2. Check that destructor blocks are only inside mod file that are point_process
+ * 3. Check that unit always have a name
  */
 #include "ast/ast.hpp"
 #include "visitors/ast_visitor.hpp"
@@ -56,6 +57,9 @@ class SemanticAnalysisVisitor: public ConstAstVisitor {
     /// Visit destructor and check that the file is of type POINT_PROCESS or ARTIFICIAL_CELL
     void visit_destructor_block(const ast::DestructorBlock& node) override;
 
+    /// Visit an unit and check that name is not empty
+    void visit_unit(const ast::Unit& node) override;
+
   public:
     SemanticAnalysisVisitor() = default;