#2437 Do not visit the same type element twice when retrieving methods

When using the diamond inheritance a TypeElement might be visited twice.
This is however, incorrect. We need to visit a TypeElement exactly once.

processor/src/main/java/org/mapstruct/ap/internal/util/AbstractElementUtilsDecorator.java

@@ -7,6 +7,8 @@ package org.mapstruct.ap.internal.util;
 
 import java.io.Writer;
 import java.util.ArrayList;
+import java.util.Collection;
+import java.util.HashSet;
 import java.util.List;
 import java.util.ListIterator;
 import java.util.Map;
@@ -118,7 +120,7 @@ public abstract class AbstractElementUtilsDecorator implements ElementUtils {
     public List<ExecutableElement> getAllEnclosedExecutableElements(TypeElement element) {
         List<ExecutableElement> enclosedElements = new ArrayList<>();
         element = replaceTypeElementIfNecessary( element );
-        addEnclosedMethodsInHierarchy( enclosedElements, element, element );
+        addEnclosedMethodsInHierarchy( enclosedElements, new HashSet<>(), element, element );
 
         return enclosedElements;
     }
@@ -132,7 +134,9 @@ public abstract class AbstractElementUtilsDecorator implements ElementUtils {
         return enclosedElements;
     }
 
-    private void addEnclosedMethodsInHierarchy(List<ExecutableElement> alreadyAdded, TypeElement element,
+    private void addEnclosedMethodsInHierarchy(List<ExecutableElement> alreadyAdded,
+                                               Collection<String> alreadyVisitedElements,
+                                               TypeElement element,
                                                TypeElement parentType) {
         if ( element != parentType ) { // otherwise the element was already checked for replacement
             element = replaceTypeElementIfNecessary( element );
@@ -142,11 +146,17 @@ public abstract class AbstractElementUtilsDecorator implements ElementUtils {
             throw new TypeHierarchyErroneousException( element );
         }
 
+        if ( !alreadyVisitedElements.add( element.getQualifiedName().toString() ) ) {
+            // If we already visited the element we should not go into it again.
+            // This can happen when diamond inheritance is used with interfaces
+            return;
+        }
         addMethodNotYetOverridden( alreadyAdded, methodsIn( element.getEnclosedElements() ), parentType );
 
         if ( hasNonObjectSuperclass( element ) ) {
             addEnclosedMethodsInHierarchy(
                 alreadyAdded,
+                alreadyVisitedElements,
                 asTypeElement( element.getSuperclass() ),
                 parentType
             );
@@ -155,6 +165,7 @@ public abstract class AbstractElementUtilsDecorator implements ElementUtils {
         for ( TypeMirror interfaceType : element.getInterfaces() ) {
             addEnclosedMethodsInHierarchy(
                 alreadyAdded,
+                alreadyVisitedElements,
                 asTypeElement( interfaceType ),
                 parentType
             );

processor/src/test/java/org/mapstruct/ap/test/bugs/_2437/Issue2437Test.java

@@ -0,0 +1,30 @@
+/*
+ * 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._2437;
+
+import org.mapstruct.ap.testutil.IssueKey;
+import org.mapstruct.ap.testutil.ProcessorTest;
+import org.mapstruct.ap.testutil.WithClasses;
+
+/**
+ * @author Filip Hrisafov
+ */
+@IssueKey("2437")
+@WithClasses({
+    Phone.class,
+    PhoneDto.class,
+    PhoneMapper.class,
+    PhoneParent1Mapper.class,
+    PhoneParent2Mapper.class,
+    PhoneSuperMapper.class,
+})
+class Issue2437Test {
+
+    @ProcessorTest
+    void shouldGenerateValidCode() {
+
+    }
+}

processor/src/test/java/org/mapstruct/ap/test/bugs/_2437/Phone.java

@@ -0,0 +1,22 @@
+/*
+ * 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._2437;
+
+/**
+ * @author Filip Hrisafov
+ */
+public class Phone {
+
+    private final String number;
+
+    public Phone(String number) {
+        this.number = number;
+    }
+
+    public String getNumber() {
+        return number;
+    }
+}

processor/src/test/java/org/mapstruct/ap/test/bugs/_2437/PhoneDto.java

@@ -0,0 +1,22 @@
+/*
+ * 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._2437;
+
+/**
+ * @author Filip Hrisafov
+ */
+public class PhoneDto {
+
+    private final String number;
+
+    public PhoneDto(String number) {
+        this.number = number;
+    }
+
+    public String getNumber() {
+        return number;
+    }
+}

processor/src/test/java/org/mapstruct/ap/test/bugs/_2437/PhoneMapper.java

@@ -0,0 +1,15 @@
+/*
+ * 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._2437;
+
+import org.mapstruct.Mapper;
+
+/**
+ * @author Filip Hrisafov
+ */
+@Mapper
+public interface PhoneMapper extends PhoneParent1Mapper, PhoneParent2Mapper {
+}

processor/src/test/java/org/mapstruct/ap/test/bugs/_2437/PhoneParent1Mapper.java

@@ -0,0 +1,12 @@
+/*
+ * 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._2437;
+
+/**
+ * @author Filip Hrisafov
+ */
+public interface PhoneParent1Mapper extends PhoneSuperMapper {
+}

processor/src/test/java/org/mapstruct/ap/test/bugs/_2437/PhoneParent2Mapper.java

@@ -0,0 +1,12 @@
+/*
+ * 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._2437;
+
+/**
+ * @author Filip Hrisafov
+ */
+public interface PhoneParent2Mapper extends PhoneSuperMapper {
+}

processor/src/test/java/org/mapstruct/ap/test/bugs/_2437/PhoneSuperMapper.java

@@ -0,0 +1,14 @@
+/*
+ * 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._2437;
+
+/**
+ * @author Filip Hrisafov
+ */
+public interface PhoneSuperMapper {
+
+    Phone map(PhoneDto dto);
+}