Forbid redefenition of builtin types

include/elna/boot/semantic.h

@@ -51,11 +51,13 @@ namespace boot
     class declaration_visitor final : public empty_visitor, public error_container
     {
         type current_type;
-        symbol_table symbols;
-
-    public:
+        std::shared_ptr<symbol_table> symbols;
         std::unordered_map<std::string, std::shared_ptr<alias_type>> unresolved;
 
+        bool build_composite_type(const std::vector<field_declaration>& declarations,
+                std::vector<type_field>& fields);
+
+    public:
         explicit declaration_visitor(const char *path, std::shared_ptr<symbol_table> symbols);
 
         void visit(primitive_type_expression *type_expression) override;

include/elna/boot/symbol.h

@@ -85,7 +85,10 @@ namespace boot
 
     struct alias_type
     {
+        const std::string name;
         type reference;
+
+        explicit alias_type(const std::string& name);
     };
 
     struct pointer_type
@@ -173,22 +176,30 @@ namespace boot
 
         iterator begin()
         {
-            return entries.begin();
+            return this->entries.begin();
         }
 
         iterator end()
         {
-            return entries.end();
+            return this->entries.end();
         }
 
         const_iterator cbegin() const
         {
-            return entries.cbegin();
+            return this->entries.cbegin();
         }
 
         const_iterator cend() const
         {
-            return entries.cend();
+            return this->entries.cend();
+        }
+
+        /**
+         * \return Symbol count in the current scope.
+         */
+        std::size_t size() const
+        {
+            return this->entries.size();
         }
 
         /**
@@ -213,6 +224,15 @@ namespace boot
             return nothing;
         }
 
+        /**
+         * \param name Symbol name.
+         * \return Whether the table contains a symbol with the given name.
+         */
+        bool contains(const std::string& name)
+        {
+            return lookup(name) != nothing;
+        }
+
         /**
          * Registers new symbol.
          *