Adapt ProtobbufAccessorNamingStrategy to work properly with builders

When the adder method is part of the protobuf builder then it's superclass it not the generated message
Add list prefix to the element name when the enclosing element of the adder is assignable to protobuf MessageOrBuilder

Author: filiphr

mapstruct-protobuf3/spi-impl/src/main/java/org/mapstruct/example/protobuf/ProtobufAccessorNamingStrategy.java

@@ -1,32 +1,41 @@
 package org.mapstruct.example.protobuf;
 
-import org.mapstruct.ap.spi.DefaultAccessorNamingStrategy;
-
 import javax.lang.model.element.Element;
-import javax.lang.model.element.ElementKind;
 import javax.lang.model.element.ExecutableElement;
 import javax.lang.model.element.TypeElement;
 import javax.lang.model.type.TypeMirror;
 
+import org.mapstruct.ap.spi.DefaultAccessorNamingStrategy;
+import org.mapstruct.ap.spi.MapStructProcessingEnvironment;
+
 /**
  * @author Thomas Kratz
+ * @author Filip Hrisafov
  */
 public class ProtobufAccessorNamingStrategy extends DefaultAccessorNamingStrategy {
 
-    public static final String PROTOBUF_GENERATED_MESSAGE_V3 = "com.google.protobuf.GeneratedMessageV3";
+    public static final String PROTOBUF_MESSAGE_OR_BUILDER = "com.google.protobuf.MessageOrBuilder";
     public static final String LIST_SUFFIX = "List";
 
+    protected TypeMirror protobufMesageOrBuilderType;
+
+    @Override
+    public void init(MapStructProcessingEnvironment processingEnvironment) {
+        super.init(processingEnvironment);
+
+        TypeElement typeElement = elementUtils.getTypeElement(PROTOBUF_MESSAGE_OR_BUILDER);
+        if (typeElement != null) {
+            protobufMesageOrBuilderType = typeElement.asType();
+        }
+    }
+
     @Override
     public String getElementName(ExecutableElement adderMethod) {
 
         String methodName = super.getElementName(adderMethod);
         Element receiver = adderMethod.getEnclosingElement();
-        if (receiver != null && receiver.getKind() == ElementKind.CLASS) {
-            TypeElement type = (TypeElement) receiver;
-            TypeMirror superType = type.getSuperclass();
-            if (superType != null && PROTOBUF_GENERATED_MESSAGE_V3.equals(superType.toString())) {
-                methodName += LIST_SUFFIX;
-            }
+        if (receiver != null && protobufMesageOrBuilderType != null && typeUtils.isAssignable(receiver.asType(), protobufMesageOrBuilderType)) {
+            methodName += LIST_SUFFIX;
         }
         return methodName;
     }