#1321 Support index for list properties

processor/src/main/java/org/mapstruct/ap/internal/model/NestedTargetPropertyMappingHolder.java

@@ -21,13 +21,13 @@ import org.mapstruct.ap.internal.model.beanmapping.PropertyEntry;
 import org.mapstruct.ap.internal.model.beanmapping.SourceReference;
 import org.mapstruct.ap.internal.model.beanmapping.TargetReference;
 import org.mapstruct.ap.internal.model.common.Parameter;
-import org.mapstruct.ap.internal.util.accessor.ReadAccessor;
 import org.mapstruct.ap.internal.model.common.Type;
 import org.mapstruct.ap.internal.model.source.MappingOptions;
 import org.mapstruct.ap.internal.model.source.Method;
 import org.mapstruct.ap.internal.util.Message;
 import org.mapstruct.ap.internal.util.Strings;
 import org.mapstruct.ap.internal.util.accessor.Accessor;
+import org.mapstruct.ap.internal.util.accessor.ReadAccessor;
 
 import static org.mapstruct.ap.internal.util.Collections.first;
 
@@ -665,6 +665,15 @@ public class NestedTargetPropertyMappingHolder {
                         pathProperties.set( pathProperties.size() - 1, mostSimilarProperty );
                     }
 
+                    boolean reverseInheritedListElementAccessor = mapping.getInheritContext() != null
+                        && mapping.getInheritContext().isReversed()
+                        && targetPropertyName.contains( "[" );
+                    if ( reverseInheritedListElementAccessor ) {
+                        // ignore reverse inherited source properties with index accessor like "names[0]"
+                        errorOccurred = false;
+                        return null;
+                    }
+
                     mappingContext.getMessager()
                         .printMessage(
                             mapping.getElement(),

processor/src/main/java/org/mapstruct/ap/internal/model/beanmapping/SourceReference.java

@@ -23,6 +23,7 @@ import org.mapstruct.ap.internal.model.source.Method;
 import org.mapstruct.ap.internal.util.FormattingMessager;
 import org.mapstruct.ap.internal.util.Message;
 import org.mapstruct.ap.internal.util.Strings;
+import org.mapstruct.ap.internal.util.accessor.ListElementAccessor;
 import org.mapstruct.ap.internal.util.accessor.PresenceCheckAccessor;
 import org.mapstruct.ap.internal.util.accessor.ReadAccessor;
 
@@ -322,12 +323,51 @@ public class SourceReference extends AbstractReference {
                                                                  boolean allowedMapToBean) {
             List<PropertyEntry> sourceEntries = new ArrayList<>();
             Type newType = type;
-            for ( int i = 0; i < entryNames.length; i++ ) {
+            for (int i = 0; i < entryNames.length; i++) {
                 boolean matchFound = false;
+
+                String entryName = entryNames[i];
+                int bracketIndex = entryName.indexOf( '[' );
+                boolean containsIndex = bracketIndex != -1 && entryName.endsWith( "]" );
+                if ( containsIndex ) {
+                    String baseName = entryName.substring( 0, bracketIndex );
+                    String rawIndex = entryName.substring( bracketIndex + 1, entryName.length() - 1 );
+
+                    ReadAccessor listAccessor = newType.withoutBounds()
+                        .getReadAccessor( baseName, i > 0 || allowedMapToBean );
+                    if ( listAccessor != null ) {
+
+                        newType = typeFactory.getReturnType(
+                            (DeclaredType) newType.withoutBounds().getTypeMirror(),
+                            listAccessor
+                        );
+
+                        if ( !newType.isListType() ) {
+                            reportMappingError( Message.PROPERTYMAPPING_INDEX_ACCESSORS_ONLY_ON_LIST, baseName );
+                            continue;
+                        }
+
+                        Type elementType = newType.getTypeParameters().get( 0 );
+                        int index = tryParseIndex( rawIndex );
+                        ReadAccessor listElementAccessor =
+                            new ListElementAccessor( listAccessor, elementType.getTypeMirror(), index );
+
+                        sourceEntries.add( forSourceReference(
+                            Arrays.copyOf( entryNames, i + 1 ),
+                            listElementAccessor,
+                            PresenceCheckAccessor.listSizeGreaterThan( listAccessor, index ),
+                            elementType
+                        ) );
+                        newType = elementType;
+                        matchFound = true;
+                    }
+
+                }
+                else {
                     Type noBoundsType = newType.withoutBounds();
-                ReadAccessor readAccessor = noBoundsType.getReadAccessor( entryNames[i], i > 0 || allowedMapToBean );
+                    ReadAccessor readAccessor = noBoundsType.getReadAccessor( entryName, i > 0 || allowedMapToBean );
-                if ( readAccessor != null ) {
+                    if (readAccessor != null) {
-                    PresenceCheckAccessor presenceChecker = noBoundsType.getPresenceChecker( entryNames[i] );
+                        PresenceCheckAccessor presenceChecker = noBoundsType.getPresenceChecker( entryName );
                         newType = typeFactory.getReturnType(
                             (DeclaredType) noBoundsType.getTypeMirror(),
                             readAccessor
@@ -340,6 +380,7 @@ public class SourceReference extends AbstractReference {
                         ) );
                         matchFound = true;
                     }
+                }
                 if ( !matchFound ) {
                     break;
                 }
@@ -347,6 +388,17 @@ public class SourceReference extends AbstractReference {
             return sourceEntries;
         }
 
+        private int tryParseIndex(String rawIndex) {
+
+            try {
+                return Integer.parseInt( rawIndex );
+            }
+            catch ( NumberFormatException e ) {
+                reportMappingError( Message.PROPERTYMAPPING_INDEX_NOT_A_NUMBER, rawIndex );
+                return 0;
+            }
+        }
+
         private void reportMappingError(Message msg, Object... objects) {
             messager.printMessage( method.getExecutable(), annotationMirror, sourceAnnotationValue, msg, objects );
         }

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

@@ -105,6 +105,7 @@ public class Type extends ModelElement implements Comparable<Type> {
     private final boolean isEnumType;
     private final boolean isIterableType;
     private final boolean isCollectionType;
+    private final boolean isListType;
     private final boolean isMapType;
     private final boolean isVoid;
     private final boolean isStream;
@@ -145,7 +146,7 @@ public class Type extends ModelElement implements Comparable<Type> {
                 List<Type> typeParameters, ImplementationType implementationType, Type componentType,
                 String packageName, String name, String qualifiedName,
                 boolean isInterface, boolean isEnumType, boolean isIterableType,
-                boolean isCollectionType, boolean isMapType, boolean isStreamType,
+                boolean isCollectionType, boolean isListType, boolean isMapType, boolean isStreamType,
                 Map<String, String> toBeImportedTypes,
                 Map<String, String> notToBeImportedTypes,
                 Boolean isToBeImported,
@@ -170,6 +171,7 @@ public class Type extends ModelElement implements Comparable<Type> {
         this.isEnumType = isEnumType;
         this.isIterableType = isIterableType;
         this.isCollectionType = isCollectionType;
+        this.isListType = isListType;
         this.isMapType = isMapType;
         this.isStream = isStreamType;
         this.isVoid = typeMirror.getKind() == TypeKind.VOID;
@@ -344,6 +346,10 @@ public class Type extends ModelElement implements Comparable<Type> {
         return isCollectionType;
     }
 
+    public boolean isListType() {
+        return isListType;
+    }
+
     public boolean isMapType() {
         return isMapType;
     }
@@ -552,6 +558,7 @@ public class Type extends ModelElement implements Comparable<Type> {
             isEnumType,
             isIterableType,
             isCollectionType,
+            isListType,
             isMapType,
             isStream,
             toBeImportedTypes,
@@ -595,6 +602,7 @@ public class Type extends ModelElement implements Comparable<Type> {
             isEnumType,
             isIterableType,
             isCollectionType,
+            isListType,
             isMapType,
             isStream,
             toBeImportedTypes,

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

@@ -94,6 +94,7 @@ public class TypeFactory {
 
     private final TypeMirror iterableType;
     private final TypeMirror collectionType;
+    private final TypeMirror listType;
     private final TypeMirror mapType;
     private final TypeMirror streamType;
 
@@ -115,6 +116,8 @@ public class TypeFactory {
         iterableType = typeUtils.erasure( elementUtils.getTypeElement( Iterable.class.getCanonicalName() ).asType() );
         collectionType =
             typeUtils.erasure( elementUtils.getTypeElement( Collection.class.getCanonicalName() ).asType() );
+        listType =
+            typeUtils.erasure( elementUtils.getTypeElement( List.class.getCanonicalName() ).asType() );
         mapType = typeUtils.erasure( elementUtils.getTypeElement( Map.class.getCanonicalName() ).asType() );
         TypeElement streamTypeElement = elementUtils.getTypeElement( JavaStreamConstants.STREAM_FQN );
         streamType = streamTypeElement == null ? null : typeUtils.erasure( streamTypeElement.asType() );
@@ -235,6 +238,7 @@ public class TypeFactory {
 
         boolean isIterableType = typeUtils.isSubtypeErased( mirror, iterableType );
         boolean isCollectionType = typeUtils.isSubtypeErased( mirror, collectionType );
+        boolean isListType = typeUtils.isSubtypeErased( mirror, listType );
         boolean isMapType = typeUtils.isSubtypeErased( mirror, mapType );
         boolean isStreamType = streamType != null && typeUtils.isSubtypeErased( mirror, streamType );
 
@@ -344,6 +348,7 @@ public class TypeFactory {
             isEnumType,
             isIterableType,
             isCollectionType,
+            isListType,
             isMapType,
             isStreamType,
             toBeImportedTypes,
@@ -574,6 +579,7 @@ public class TypeFactory {
                 implementationType.isEnumType(),
                 implementationType.isIterableType(),
                 implementationType.isCollectionType(),
+                implementationType.isListType(),
                 implementationType.isMapType(),
                 implementationType.isStreamType(),
                 toBeImportedTypes,

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

@@ -92,6 +92,8 @@ public enum Message {
     PROPERTYMAPPING_CANNOT_DETERMINE_SOURCE_PARAMETER_FROM_TARGET("No property named \"%s\" exists in source parameter(s). Please define the source explicitly."),
     PROPERTYMAPPING_NO_SUITABLE_COLLECTION_OR_MAP_CONSTRUCTOR( "%s does not have an accessible copy or no-args constructor." ),
     PROPERTYMAPPING_EXPRESSION_AND_CONDITION_QUALIFIED_BY_NAME_BOTH_DEFINED( "Expression and condition qualified by name are both defined in @Mapping, either define an expression or a condition qualified by name." ),
+    PROPERTYMAPPING_INDEX_ACCESSORS_ONLY_ON_LIST( "Can't access element with index because \"%s\" is not of type List." ),
+    PROPERTYMAPPING_INDEX_NOT_A_NUMBER( "Index accessor must be an integer but was: \"%s\"." ),
 
     CONVERSION_LOSSY_WARNING( "%s has a possibly lossy conversion from %s to %s.", Diagnostic.Kind.WARNING ),
     CONVERSION_LOSSY_ERROR( "Can't map %s. It has a possibly lossy conversion from %s to %s." ),
@@ -185,8 +187,8 @@ public enum Message {
     RETRIEVAL_MAPPER_USES_CYCLE( "The mapper %s is referenced itself in Mapper#uses.", Diagnostic.Kind.WARNING ),
     RETRIEVAL_AFTER_METHOD_NOT_IMPLEMENTED( "@AfterMapping can only be applied to an implemented method." ),
     RETRIEVAL_BEFORE_METHOD_NOT_IMPLEMENTED( "@BeforeMapping can only be applied to an implemented method." ),
-    RETRIEVAL_SOURCE_PROPERTY_NAME_WRONG_TYPE( "@SourcePropertyName can only by applied to a String parameter." ),
+    RETRIEVAL_SOURCE_PROPERTY_NAME_WRONG_TYPE( "@SourcePropertyName can only be applied to a String parameter." ),
-    RETRIEVAL_TARGET_PROPERTY_NAME_WRONG_TYPE( "@TargetPropertyName can only by applied to a String parameter." ),
+    RETRIEVAL_TARGET_PROPERTY_NAME_WRONG_TYPE( "@TargetPropertyName can only be applied to a String parameter." ),
 
     INHERITINVERSECONFIGURATION_DUPLICATES( "Several matching inverse methods exist: %s(). Specify a name explicitly." ),
     INHERITINVERSECONFIGURATION_INVALID_NAME( "None of the candidates %s() matches given name: \"%s\"." ),

processor/src/main/java/org/mapstruct/ap/internal/util/accessor/ListElementAccessor.java

@@ -0,0 +1,56 @@
+/*
+ * 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.internal.util.accessor;
+
+import java.util.Collections;
+import java.util.Set;
+import javax.lang.model.element.Element;
+import javax.lang.model.element.Modifier;
+import javax.lang.model.type.TypeMirror;
+
+public class ListElementAccessor implements ReadAccessor {
+
+    private final ReadAccessor listAccessor;
+    private final TypeMirror elementTypeMirror;
+    private final int index;
+
+    public ListElementAccessor(ReadAccessor listAccessor, TypeMirror elementTypeMirror, int index) {
+        this.listAccessor = listAccessor;
+        this.elementTypeMirror = elementTypeMirror;
+        this.index = index;
+    }
+
+    @Override
+    public TypeMirror getAccessedType() {
+        return elementTypeMirror;
+    }
+
+    @Override
+    public String getSimpleName() {
+        return listAccessor.getSimpleName() + "[" + index + "]";
+    }
+
+    @Override
+    public Set<Modifier> getModifiers() {
+        return Collections.emptySet();
+    }
+
+    @Override
+    public Element getElement() {
+        return listAccessor.getElement();
+    }
+
+    @Override
+    public AccessorType getAccessorType() {
+        return AccessorType.GETTER;
+    }
+
+    @Override
+    public String getReadValueSource() {
+        return listAccessor.getReadValueSource() + ".get( " + index + " )";
+    }
+
+}

processor/src/main/java/org/mapstruct/ap/internal/util/accessor/PresenceCheckAccessor.java

@@ -22,6 +22,10 @@ public interface PresenceCheckAccessor {
         return suffix( ".containsKey( \"" + propertyName + "\" )" );
     }
 
+    static PresenceCheckAccessor listSizeGreaterThan(ReadAccessor listAccessor, int index) {
+        return suffix( "." + listAccessor.getSimpleName() + "().size() > " + index );
+    }
+
     static PresenceCheckAccessor suffix(String suffix) {
         return () -> suffix;
     }

processor/src/main/resources/org/mapstruct/ap/internal/model/NestedPropertyMappingMethod.ftl

@@ -9,7 +9,7 @@
 <#lt>private <@includeModel object=returnType.typeBound/> ${name}(<#list parameters as param><@includeModel object=param/><#if param_has_next>, </#if></#list>)<@throws/> {
 <#list propertyEntries as entry>
     <#if entry.presenceChecker?? >
-    if ( <#if entry_index != 0>${entry.previousPropertyName} == null || </#if>!<@includeModel object=entry.presenceChecker /> ) {
+    if ( <#if entry_index != 0>${entry.previousPropertyName} == null || </#if><@includeModel object=entry.presenceChecker.negate() /> ) {
         return ${returnType.null};
     }
     </#if>

processor/src/test/java/org/mapstruct/ap/internal/model/common/DateFormatValidatorFactoryTest.java

@@ -5,8 +5,6 @@
  */
 package org.mapstruct.ap.internal.model.common;
 
-import static org.assertj.core.api.Assertions.assertThat;
-
 import java.lang.annotation.Annotation;
 import java.time.LocalDate;
 import java.time.LocalDateTime;
@@ -14,7 +12,6 @@ import java.time.LocalTime;
 import java.time.ZonedDateTime;
 import java.util.HashMap;
 import java.util.List;
-
 import javax.lang.model.element.AnnotationMirror;
 import javax.lang.model.type.TypeKind;
 import javax.lang.model.type.TypeMirror;
@@ -24,6 +21,8 @@ import org.junit.jupiter.api.Test;
 import org.mapstruct.ap.internal.util.JodaTimeConstants;
 import org.mapstruct.ap.testutil.IssueKey;
 
+import static org.assertj.core.api.Assertions.assertThat;
+
 /**
  * Tests for {@link org.mapstruct.ap.internal.model.common.DateFormatValidatorFactory}.
  *
@@ -174,6 +173,7 @@ public class DateFormatValidatorFactoryTest {
                         false,
                         false,
                         false,
+                        false,
             new HashMap<>(  ),
             new HashMap<>(  ),
                         false,

processor/src/test/java/org/mapstruct/ap/internal/model/common/DefaultConversionContextTest.java

@@ -5,13 +5,10 @@
  */
 package org.mapstruct.ap.internal.model.common;
 
-import static org.assertj.core.api.Assertions.assertThat;
-
 import java.lang.annotation.Annotation;
 import java.time.ZonedDateTime;
 import java.util.HashMap;
 import java.util.List;
-
 import javax.lang.model.element.AnnotationMirror;
 import javax.lang.model.element.AnnotationValue;
 import javax.lang.model.element.Element;
@@ -25,6 +22,8 @@ import org.mapstruct.ap.internal.util.FormattingMessager;
 import org.mapstruct.ap.internal.util.Message;
 import org.mapstruct.ap.testutil.IssueKey;
 
+import static org.assertj.core.api.Assertions.assertThat;
+
 /**
  * Testing DefaultConversionContext for dateFormat
  *
@@ -122,6 +121,7 @@ public class DefaultConversionContextTest {
                         false,
                         false,
                         false,
+                        false,
             new HashMap<>(  ),
             new HashMap<>(  ),
                         false,

processor/src/test/java/org/mapstruct/ap/test/collection/index/Car.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.collection.index;
+
+import java.util.List;
+
+public class Car {
+
+    String make;
+    List<Person> personList;
+
+    public String getMake() {
+        return make;
+    }
+
+    public void setMake(String make) {
+        this.make = make;
+    }
+
+    public List<Person> getPersonList() {
+        return personList;
+    }
+
+    public void setPersonList(List<Person> personList) {
+        this.personList = personList;
+    }
+}

processor/src/test/java/org/mapstruct/ap/test/collection/index/CarDto.java

@@ -0,0 +1,28 @@
+/*
+ * 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.collection.index;
+
+public class CarDto {
+
+    Person driver;
+    String manufacturer;
+
+    public Person getDriver() {
+        return driver;
+    }
+
+    public void setDriver(Person driver) {
+        this.driver = driver;
+    }
+
+    public String getManufacturer() {
+        return manufacturer;
+    }
+
+    public void setManufacturer(String manufacturer) {
+        this.manufacturer = manufacturer;
+    }
+}

processor/src/test/java/org/mapstruct/ap/test/collection/index/CarWithArrayList.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.collection.index;
+
+import java.util.ArrayList;
+
+public class CarWithArrayList {
+
+    String make;
+    ArrayList<Person> personList;
+
+    public String getMake() {
+        return make;
+    }
+
+    public void setMake(String make) {
+        this.make = make;
+    }
+
+    public ArrayList<Person> getPersonList() {
+        return personList;
+    }
+
+    public void setPersonList(ArrayList<Person> personList) {
+        this.personList = personList;
+    }
+}

processor/src/test/java/org/mapstruct/ap/test/collection/index/CarWithDriverNameDto.java

@@ -0,0 +1,37 @@
+/*
+ * 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.collection.index;
+
+public class CarWithDriverNameDto {
+
+    String driverName;
+    Person driver;
+    String manufacturer;
+
+    public String getDriverName() {
+        return driverName;
+    }
+
+    public void setDriverName(String driverName) {
+        this.driverName = driverName;
+    }
+
+    public Person getDriver() {
+        return driver;
+    }
+
+    public void setDriver(Person driver) {
+        this.driver = driver;
+    }
+
+    public String getManufacturer() {
+        return manufacturer;
+    }
+
+    public void setManufacturer(String manufacturer) {
+        this.manufacturer = manufacturer;
+    }
+}

processor/src/test/java/org/mapstruct/ap/test/collection/index/DriverList.java

@@ -0,0 +1,21 @@
+/*
+ * 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.collection.index;
+
+import java.util.Set;
+
+public class DriverList {
+
+    Set<Person> drivers;
+
+    public Set<Person> getDrivers() {
+        return drivers;
+    }
+
+    public void setDrivers(Set<Person> drivers) {
+        this.drivers = drivers;
+    }
+}

processor/src/test/java/org/mapstruct/ap/test/collection/index/ErroneousListIndexIsNoNumberMapper.java

@@ -0,0 +1,18 @@
+/*
+ * 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.collection.index;
+
+import org.mapstruct.Mapper;
+import org.mapstruct.Mapping;
+
+@Mapper
+public interface ErroneousListIndexIsNoNumberMapper {
+
+    @Mapping(target = "manufacturer", source = "make")
+    @Mapping(target = "driver", source = "personList[x]")
+    CarDto mapList(Car source);
+
+}

processor/src/test/java/org/mapstruct/ap/test/collection/index/ErroneousListIndexOnSetMapper.java

@@ -0,0 +1,17 @@
+/*
+ * 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.collection.index;
+
+import org.mapstruct.Mapper;
+import org.mapstruct.Mapping;
+
+@Mapper
+public interface ErroneousListIndexOnSetMapper {
+
+    @Mapping(target = "name", source = "drivers[0].name")
+    PersonDto sourceToTarget(DriverList source);
+
+}

processor/src/test/java/org/mapstruct/ap/test/collection/index/ErroneousListIndexOnStringMapper.java

@@ -0,0 +1,17 @@
+/*
+ * 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.collection.index;
+
+import org.mapstruct.Mapper;
+import org.mapstruct.Mapping;
+
+@Mapper
+public interface ErroneousListIndexOnStringMapper {
+
+    @Mapping(target = "name", source = "name[0]")
+    PersonDto sourceToTarget(Person source);
+
+}

processor/src/test/java/org/mapstruct/ap/test/collection/index/ListIndexInheritInverseMapper.java

@@ -0,0 +1,23 @@
+/*
+ * 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.collection.index;
+
+import org.mapstruct.InheritInverseConfiguration;
+import org.mapstruct.Mapper;
+import org.mapstruct.Mapping;
+
+@Mapper
+public interface ListIndexInheritInverseMapper {
+
+    @Mapping(target = "manufacturer", source = "make")
+    @Mapping(target = "driver", source = "personList[0]")
+    CarDto mapList(Car source);
+
+    @InheritInverseConfiguration
+    @Mapping(target = "personList", ignore = true)
+    Car mapListInverseInherited(CarDto source);
+
+}

processor/src/test/java/org/mapstruct/ap/test/collection/index/ListIndexMapper.java

@@ -0,0 +1,27 @@
+/*
+ * 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.collection.index;
+
+import org.mapstruct.Mapper;
+import org.mapstruct.Mapping;
+import org.mapstruct.MappingTarget;
+
+@Mapper
+public interface ListIndexMapper {
+
+    @Mapping(target = "manufacturer", source = "make")
+    @Mapping(target = "driver", source = "personList[0]")
+    CarDto mapList(Car source);
+
+    @Mapping(target = "manufacturer", source = "make")
+    @Mapping(target = "driver", source = "personList[0]")
+    void updateList(Car source, @MappingTarget CarDto target);
+
+    @Mapping(target = "manufacturer", source = "make")
+    @Mapping(target = "driver", source = "personList[0]")
+    CarDto mapArrayList(CarWithArrayList source);
+
+}

processor/src/test/java/org/mapstruct/ap/test/collection/index/ListIndexMappingTest.java

@@ -0,0 +1,163 @@
+/*
+ * 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.collection.index;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import org.mapstruct.ap.testutil.IssueKey;
+import org.mapstruct.ap.testutil.ProcessorTest;
+import org.mapstruct.ap.testutil.WithClasses;
+import org.mapstruct.ap.testutil.compilation.annotation.CompilationResult;
+import org.mapstruct.ap.testutil.compilation.annotation.Diagnostic;
+import org.mapstruct.ap.testutil.compilation.annotation.ExpectedCompilationOutcome;
+import org.mapstruct.factory.Mappers;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * @author Oliver Erhart
+ */
+@WithClasses({
+    Car.class,
+    CarDto.class,
+    CarWithArrayList.class,
+    CarWithDriverNameDto.class,
+    Person.class,
+    PersonDto.class,
+    ListIndexMapper.class,
+    ListIndexNestedPropertyMapper.class
+})
+@IssueKey("1321")
+public class ListIndexMappingTest {
+
+    @ProcessorTest
+    public void shouldMapWithDirectAssignment() {
+
+        Car source = new Car();
+        List<Person> personList = new ArrayList<>();
+        personList.add( new Person( "First" ) );
+        personList.add( new Person( "Second" ) );
+        source.setPersonList( personList );
+
+        CarDto target = Mappers.getMapper( ListIndexMapper.class ).mapList( source );
+
+        assertThat( target.getDriver().getName() ).isEqualTo( "First" );
+    }
+
+    @ProcessorTest
+    public void shouldMapWithDirectArrayListAssignment() {
+
+        CarWithArrayList source = new CarWithArrayList();
+        ArrayList<Person> personList = new ArrayList<>();
+        personList.add( new Person( "First" ) );
+        personList.add( new Person( "Second" ) );
+        source.setPersonList( personList );
+
+        CarDto target = Mappers.getMapper( ListIndexMapper.class ).mapArrayList( source );
+
+        assertThat( target.getDriver().getName() ).isEqualTo( "First" );
+    }
+
+    @ProcessorTest
+    public void shouldBeNullWhenDirectAssignmentIndexOutOfBounds() {
+
+        Car source = new Car();
+        source.setPersonList( new ArrayList<>() );
+
+        CarDto target = Mappers.getMapper( ListIndexMapper.class ).mapList( source );
+
+        assertThat( target.getDriver() ).isNull();
+    }
+
+    @ProcessorTest
+    public void shouldMapWithNestedPropertyAssignment() {
+
+        Car source = new Car();
+        List<Person> personList = new ArrayList<>();
+        personList.add( new Person( "First" ) );
+        personList.add( new Person( "Second" ) );
+        source.setPersonList( personList );
+
+        CarWithDriverNameDto target = Mappers.getMapper( ListIndexNestedPropertyMapper.class ).sourceToTarget( source );
+
+        assertThat( target.getDriver().getName() ).isEqualTo( "First" );
+        assertThat( target.getDriverName() ).isEqualTo( "First" );
+    }
+
+    @ProcessorTest
+    public void shouldBeNullWhenNestedPropertyAssignmentIndexOutOfBounds() {
+
+        Car source = new Car();
+        source.setPersonList( new ArrayList<>() );
+
+        CarWithDriverNameDto target = Mappers.getMapper( ListIndexNestedPropertyMapper.class ).sourceToTarget( source );
+
+        assertThat( target.getDriver() ).isNull();
+        assertThat( target.getDriverName() ).isNull();
+    }
+
+    @ProcessorTest
+    @WithClasses(ErroneousListIndexOnStringMapper.class)
+    @ExpectedCompilationOutcome(
+        value = CompilationResult.FAILED,
+        diagnostics = {
+            @Diagnostic(
+                kind = javax.tools.Diagnostic.Kind.ERROR,
+                type = ErroneousListIndexOnStringMapper.class,
+                line = 14,
+                message = "Can't access element with index because \"name\" is not of type List."
+            ),
+            @Diagnostic(
+                kind = javax.tools.Diagnostic.Kind.ERROR,
+                type = ErroneousListIndexOnStringMapper.class,
+                line = 14,
+                message = "No property named \"name[0]\" exists in source parameter(s). Did you mean \"name\"?"
+            )
+        }
+    )
+    public void errorWhenSourceIsStringInsteadOfList() { }
+
+    @ProcessorTest
+    @WithClasses(ErroneousListIndexIsNoNumberMapper.class)
+    @ExpectedCompilationOutcome(
+        value = CompilationResult.FAILED,
+        diagnostics = {
+            @Diagnostic(
+                kind = javax.tools.Diagnostic.Kind.ERROR,
+                type = ErroneousListIndexIsNoNumberMapper.class,
+                message = "Index accessor must be an integer but was: \"x\"."
+            )
+        }
+    )
+    public void errorWhenIndexIsNoNumber() { }
+
+    @ProcessorTest
+    @WithClasses({
+        ErroneousListIndexOnSetMapper.class,
+        DriverList.class
+    })
+    @ExpectedCompilationOutcome(
+        value = CompilationResult.FAILED,
+        diagnostics = {
+            @Diagnostic(
+                kind = javax.tools.Diagnostic.Kind.ERROR,
+                type = ErroneousListIndexOnSetMapper.class,
+                line = 14,
+                message = "Can't access element with index because \"drivers\" is not of type List."
+            ),
+            @Diagnostic(
+                kind = javax.tools.Diagnostic.Kind.ERROR,
+                type = ErroneousListIndexOnSetMapper.class,
+                line = 14,
+                message = "No property named \"drivers[0].name\" exists in source parameter(s)." +
+                    " Did you mean \"drivers\"?"
+            )
+        }
+    )
+    public void errorWhenSourceIsSetInsteadOfList() { }
+
+}

processor/src/test/java/org/mapstruct/ap/test/collection/index/ListIndexNestedPropertyMapper.java

@@ -0,0 +1,24 @@
+/*
+ * 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.collection.index;
+
+import org.mapstruct.InheritInverseConfiguration;
+import org.mapstruct.Mapper;
+import org.mapstruct.Mapping;
+
+@Mapper
+public interface ListIndexNestedPropertyMapper {
+
+    @Mapping(target = "manufacturer", source = "make")
+    @Mapping(target = "driver", source = "personList[0]")
+    @Mapping(target = "driverName", source = "source.personList[0].name")
+    CarWithDriverNameDto sourceToTarget(Car source);
+
+    @Mapping(target = "personList", ignore = true)
+    @InheritInverseConfiguration
+    Car inverseInherited(CarWithDriverNameDto source);
+
+}

processor/src/test/java/org/mapstruct/ap/test/collection/index/Person.java

@@ -0,0 +1,23 @@
+/*
+ * 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.collection.index;
+
+public class Person {
+
+    private String name;
+
+    public Person(String name) {
+        this.name = name;
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    public void setName(String name) {
+        this.name = name;
+    }
+}

processor/src/test/java/org/mapstruct/ap/test/collection/index/PersonDto.java

@@ -0,0 +1,19 @@
+/*
+ * 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.collection.index;
+
+public class PersonDto {
+
+    private String name;
+
+    public String getName() {
+        return name;
+    }
+
+    public void setName(String name) {
+        this.name = name;
+    }
+}

processor/src/test/java/org/mapstruct/ap/test/conditional/propertyname/sourcepropertyname/SourcePropertyNameTest.java

@@ -302,7 +302,7 @@ public class SourcePropertyNameTest {
                 kind = javax.tools.Diagnostic.Kind.ERROR,
                 type = ErroneousNonStringSourcePropertyNameParameter.class,
                 line = 23,
-                message = "@SourcePropertyName can only by applied to a String parameter."
+                message = "@SourcePropertyName can only be applied to a String parameter."
             )
         }
     )

processor/src/test/java/org/mapstruct/ap/test/conditional/propertyname/targetpropertyname/TargetPropertyNameTest.java

@@ -301,7 +301,7 @@ public class TargetPropertyNameTest {
                 kind = javax.tools.Diagnostic.Kind.ERROR,
                 type = ErroneousNonStringTargetPropertyNameParameter.class,
                 line = 23,
-                message = "@TargetPropertyName can only by applied to a String parameter."
+                message = "@TargetPropertyName can only be applied to a String parameter."
             )
         }
     )