Check that a struct field name of a struct declaration does not shadow an enum or a struct definition.

src/main/java/de/hsrm/compiler/Klang/ContextAnalysis.java

@@ -799,6 +799,16 @@ public class ContextAnalysis extends KlangBaseVisitor<Node> {
       throw new RuntimeException(Helper.getErrorPrefix(line, col) + error);
     }
 
+    if (structDefs.containsKey(structFieldName)) {
+      var error = "Struct field name " + structFieldName + " shadows a struct of the same name.";
+      throw new RuntimeException(Helper.getErrorPrefix(line, col) + error);
+    }
+
+    if (enumDefs.containsKey(structFieldName)) {
+      var error = "Struct field name " + structFieldName + " shadows an enum of the same name.";
+      throw new RuntimeException(Helper.getErrorPrefix(line, col) + error);
+    }
+
     var structField = new StructField(structFieldName);
     structField.type = structFieldType;
     structField.line = line;