implement context analysis for struct field access expressions

src/main/java/de/hsrm/compiler/Klang/helper/Helper.java

@@ -1,7 +1,44 @@
 package de.hsrm.compiler.Klang.helper;
 
+import java.util.Map;
+
+import de.hsrm.compiler.Klang.nodes.StructDefinition;
+import de.hsrm.compiler.Klang.types.Type;
+
 public class Helper {
-    public static String getErrorPrefix(int line, int col) {
-        return "Error in line " + line + ":" + col + " ";
+  public static String getErrorPrefix(int line, int col) {
+    return "Error in line " + line + ":" + col + " ";
+  }
+
+  public static Type drillType(Map<String, StructDefinition> structs, String name, String[] path, int pathIndex) {
+    // Search for the referenced field
+    var structDef = structs.get(name);
+    for (var field : structDef.fields) {
+      if (field.name.equals(path[pathIndex])) {
+        if (!field.type.isPrimitiveType()) {
+          // this references a struct!
+
+          // if we exhausted the path, this field type is our type
+          if (pathIndex == path.length - 1) {
+            return field.type;
+          }
+
+          // we did not exhaust the path, go on
+          return drillType(structs, field.type.getName(), path, pathIndex + 1);
+        } else {
+          // this references a primitive, we hit bedrock!
+
+          // make sure we exhausted the complete path
+          if (pathIndex < path.length - 1) {
+            throw new RuntimeException(field.name + " must be a struct but is of type " + field.type.getName() + ":");
+          }
+
+          // hooray, we exhausted the path, this field type is our type
+          return field.type;
+        }
+      }
     }
+
+    throw new RuntimeException("Struct " + structDef.name + " does not contain field " + path[pathIndex]);
+  }
 }