#3310 Make sure that adders work properly when they are in a generic class

processor/src/main/java/org/mapstruct/ap/internal/model/common/Type.java

@@ -958,9 +958,8 @@ public class Type extends ModelElement implements Comparable<Type> {
         List<Accessor> adderList = getAdders();
         List<Accessor> candidateList = new ArrayList<>();
         for ( Accessor adder : adderList ) {
-            ExecutableElement executable = (ExecutableElement) adder.getElement();
+            TypeMirror adderParameterType = determineTargetType( adder ).getTypeMirror();
-            VariableElement arg = executable.getParameters().get( 0 );
+            if ( typeUtils.isSameType( boxed( adderParameterType ), boxed( typeArg ) ) ) {
-            if ( typeUtils.isSameType( boxed( arg.asType() ), boxed( typeArg ) ) ) {
                 candidateList.add( adder );
             }
         }

processor/src/test/java/org/mapstruct/ap/test/bugs/_3310/Issue3310Mapper.java

@@ -0,0 +1,61 @@
+/*
+ * Copyright MapStruct Authors.
+ *
+ * Licensed under the Apache License version 2.0, available at http://www.apache.org/licenses/LICENSE-2.0
+ */
+package org.mapstruct.ap.test.bugs._3310;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import org.mapstruct.CollectionMappingStrategy;
+import org.mapstruct.Mapper;
+import org.mapstruct.factory.Mappers;
+
+/**
+ * @author Filip Hrisafov
+ */
+@Mapper(collectionMappingStrategy = CollectionMappingStrategy.ADDER_PREFERRED)
+public interface Issue3310Mapper {
+
+    Issue3310Mapper INSTANCE = Mappers.getMapper( Issue3310Mapper.class );
+
+    Target map(Source source);
+
+    abstract class BaseClass<T> {
+
+        private List<T> items;
+
+        public List<T> getItems() {
+            return items;
+        }
+
+        public void setItems(List<T> items) {
+            throw new UnsupportedOperationException( "adder should be used instead" );
+        }
+
+        public void addItem(T item) {
+            if ( items == null ) {
+                items = new ArrayList<>();
+            }
+            items.add( item );
+        }
+    }
+
+    class Target extends BaseClass<String> {
+
+    }
+
+    class Source {
+
+        private final List<String> items;
+
+        public Source(List<String> items) {
+            this.items = items;
+        }
+
+        public List<String> getItems() {
+            return items;
+        }
+    }
+}

processor/src/test/java/org/mapstruct/ap/test/bugs/_3310/Issue3310Test.java

@@ -0,0 +1,31 @@
+/*
+ * Copyright MapStruct Authors.
+ *
+ * Licensed under the Apache License version 2.0, available at http://www.apache.org/licenses/LICENSE-2.0
+ */
+package org.mapstruct.ap.test.bugs._3310;
+
+import java.util.Collections;
+
+import org.mapstruct.ap.testutil.IssueKey;
+import org.mapstruct.ap.testutil.ProcessorTest;
+import org.mapstruct.ap.testutil.WithClasses;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * @author Filip Hrisafov
+ */
+@IssueKey("3310")
+@WithClasses(Issue3310Mapper.class)
+class Issue3310Test {
+
+    @ProcessorTest
+    void shouldUseAdderWithGenericBaseClass() {
+        Issue3310Mapper.Source source = new Issue3310Mapper.Source( Collections.singletonList( "test" ) );
+        Issue3310Mapper.Target target = Issue3310Mapper.INSTANCE.map( source );
+
+        assertThat( target ).isNotNull();
+        assertThat( target.getItems() ).containsExactly( "test" );
+    }
+}