#2145 fixing 2 step mapping methods (refactoring) (#2146)

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

@@ -482,6 +482,24 @@ public class Type extends ModelElement implements Comparable<Type> {
         return typeUtils.isAssignable( typeMirrorToMatch, other.typeMirror );
     }
 
+    /**
+     * Whether this type is raw assignable to the given other type. We can't make a verdict on typevars,
+     * they need to be resolved first.
+     *
+     * @param other The other type.
+     *
+     * @return {@code true} if and only if this type is assignable to the given other type.
+     */
+    public boolean isRawAssignableTo(Type other) {
+        if ( isTypeVar() || other.isTypeVar() ) {
+            return true;
+        }
+        if ( equals( other ) ) {
+            return true;
+        }
+        return typeUtils.isAssignable( typeUtils.erasure( typeMirror ), typeUtils.erasure( other.typeMirror ) );
+    }
+
     /**
      * getPropertyReadAccessors
      *

processor/src/main/java/org/mapstruct/ap/internal/model/source/Method.java

@@ -187,4 +187,18 @@ public interface Method {
     default boolean isMappingTargetAssignableToReturnType() {
         return isUpdateMethod() && getResultType().isAssignableTo( getReturnType() );
     }
+
+    /**
+     * @return the first source type, intended for mapping methods from single source to target
+     */
+    default Type getMappingSourceType() {
+        return getSourceParameters().get( 0 ).getType();
+    }
+
+    /**
+     * @return the short name for error messages
+     */
+    default String shortName() {
+        return getResultType().getName() + ":" + getName() + "(" + getMappingSourceType().getName() + ")";
+    }
 }

processor/src/main/java/org/mapstruct/ap/internal/model/source/SourceMethod.java

@@ -294,7 +294,7 @@ public class SourceMethod implements Method {
         return method.getDeclaringMapper() == null
             && method.isAbstract()
             && getSourceParameters().size() == 1 && method.getSourceParameters().size() == 1
-            && first( getSourceParameters() ).getType().isAssignableTo( method.getResultType() )
+            && getMappingSourceType().isAssignableTo( method.getResultType() )
             && getResultType().isAssignableTo( first( method.getSourceParameters() ).getType() );
     }
 
@@ -326,7 +326,7 @@ public class SourceMethod implements Method {
     public boolean isIterableMapping() {
         if ( isIterableMapping == null ) {
             isIterableMapping = getSourceParameters().size() == 1
-                && first( getSourceParameters() ).getType().isIterableType()
+                && getMappingSourceType().isIterableType()
                 && getResultType().isIterableType();
         }
         return isIterableMapping;
@@ -335,9 +335,9 @@ public class SourceMethod implements Method {
     public boolean isStreamMapping() {
         if ( isStreamMapping == null ) {
             isStreamMapping = getSourceParameters().size() == 1
-                && ( first( getSourceParameters() ).getType().isIterableType() && getResultType().isStreamType()
+                && ( getMappingSourceType().isIterableType() && getResultType().isStreamType()
-                    || first( getSourceParameters() ).getType().isStreamType() && getResultType().isIterableType()
+                    || getMappingSourceType().isStreamType() && getResultType().isIterableType()
-                    || first( getSourceParameters() ).getType().isStreamType() && getResultType().isStreamType() );
+                    || getMappingSourceType().isStreamType() && getResultType().isStreamType() );
         }
         return isStreamMapping;
     }
@@ -345,7 +345,7 @@ public class SourceMethod implements Method {
     public boolean isMapMapping() {
         if ( isMapMapping == null ) {
             isMapMapping = getSourceParameters().size() == 1
-                && first( getSourceParameters() ).getType().isMapType()
+                && getMappingSourceType().isMapType()
                 && getResultType().isMapType();
         }
         return isMapMapping;

processor/src/main/java/org/mapstruct/ap/internal/model/source/builtin/BuiltInMethod.java

@@ -67,21 +67,13 @@ public abstract class BuiltInMethod implements Method {
 
         Type sourceType = first( sourceTypes );
 
-        if ( getReturnType().isAssignableTo( targetType.erasure() )
+        Type returnType = getReturnType().resolveTypeVarToType( sourceType, getParameter().getType()  );
-            && sourceType.erasure().isAssignableTo( getParameter().getType() ) ) {
+        if ( returnType == null ) {
-            return doTypeVarsMatch( sourceType, targetType );
+            return false;
         }
-        if ( getReturnType().getFullyQualifiedName().equals( "java.lang.Object" )
+
-            && sourceType.erasure().isAssignableTo( getParameter().getType() ) ) {
+        return returnType.isAssignableTo( targetType )
-            // return type could be a type parameter T
+            && sourceType.erasure().isAssignableTo( getParameter().getType() );
-            return doTypeVarsMatch( sourceType, targetType );
-        }
-        if ( getReturnType().isAssignableTo( targetType.erasure() )
-            &&  getParameter().getType().getFullyQualifiedName().equals( "java.lang.Object" ) ) {
-            // parameter type could be a type parameter T
-            return doTypeVarsMatch( sourceType, targetType );
-        }
-        return false;
     }
 
     @Override

processor/src/main/java/org/mapstruct/ap/internal/model/source/builtin/JaxbElemToValue.java

@@ -5,15 +5,16 @@
  */
 package org.mapstruct.ap.internal.model.source.builtin;
 
+import static org.mapstruct.ap.internal.util.Collections.asSet;
+
 import java.util.Set;
+
 import javax.xml.bind.JAXBElement;
 
 import org.mapstruct.ap.internal.model.common.Parameter;
 import org.mapstruct.ap.internal.model.common.Type;
 import org.mapstruct.ap.internal.model.common.TypeFactory;
 
-import static org.mapstruct.ap.internal.util.Collections.asSet;
-
 /**
  * @author Sjaak Derksen
  */
@@ -24,8 +25,9 @@ public class JaxbElemToValue extends BuiltInMethod {
     private final Set<Type> importTypes;
 
     public JaxbElemToValue(TypeFactory typeFactory) {
-        this.parameter = new Parameter( "element", typeFactory.getType( JAXBElement.class ) );
+        Type type = typeFactory.getType(  JAXBElement.class  );
-        this.returnType = typeFactory.getType( Object.class );
+        this.parameter = new Parameter( "element", type );
+        this.returnType = type.getTypeParameters().get( 0 );
         this.importTypes = asSet( parameter.getType() );
     }
 

processor/src/main/java/org/mapstruct/ap/internal/model/source/selector/SelectedMethod.java

@@ -6,6 +6,7 @@
 package org.mapstruct.ap.internal.model.source.selector;
 
 import java.util.List;
+import java.util.Objects;
 
 import org.mapstruct.ap.internal.model.common.ParameterBinding;
 import org.mapstruct.ap.internal.model.source.Method;
@@ -39,4 +40,21 @@ public class SelectedMethod<T extends Method> {
     public String toString() {
         return method.toString();
     }
+
+    @Override
+    public boolean equals(Object o) {
+        if ( this == o ) {
+            return true;
+        }
+        if ( o == null || getClass() != o.getClass() ) {
+            return false;
+        }
+        SelectedMethod<?> that = (SelectedMethod<?>) o;
+        return method.equals( that.method );
+    }
+
+    @Override
+    public int hashCode() {
+        return Objects.hash( method );
+    }
 }

processor/src/main/java/org/mapstruct/ap/internal/model/source/selector/XmlElementDeclSelector.java

@@ -69,7 +69,7 @@ public class XmlElementDeclSelector implements MethodSelector {
             }
 
             String name = xmlElementDecl.name().get();
-            TypeMirror scope = xmlElementDecl.scope().get();
+            TypeMirror scope = xmlElementDecl.scope().getValue();
 
             boolean nameIsSetAndMatches = name != null && name.equals( xmlElementRefInfo.nameValue() );
             boolean scopeIsSetAndMatches =

processor/src/main/java/org/mapstruct/ap/internal/processor/creation/MappingResolverImpl.java

@@ -5,12 +5,23 @@
  */
 package org.mapstruct.ap.internal.processor.creation;
 
+import static java.util.Collections.singletonList;
+import static org.mapstruct.ap.internal.util.Collections.first;
+import static org.mapstruct.ap.internal.util.Collections.firstKey;
+import static org.mapstruct.ap.internal.util.Collections.firstValue;
+
 import java.util.ArrayList;
 import java.util.HashSet;
+import java.util.Iterator;
+import java.util.LinkedHashMap;
 import java.util.List;
+import java.util.Map;
+import java.util.Objects;
 import java.util.Set;
+import java.util.function.Function;
 import java.util.function.Supplier;
 import java.util.stream.Collectors;
+
 import javax.lang.model.element.AnnotationMirror;
 import javax.lang.model.element.Element;
 import javax.lang.model.element.ExecutableElement;
@@ -42,7 +53,6 @@ import org.mapstruct.ap.internal.model.common.SourceRHS;
 import org.mapstruct.ap.internal.model.common.Type;
 import org.mapstruct.ap.internal.model.common.TypeFactory;
 import org.mapstruct.ap.internal.model.source.Method;
-import org.mapstruct.ap.internal.model.source.SourceMethod;
 import org.mapstruct.ap.internal.model.source.builtin.BuiltInMappingMethods;
 import org.mapstruct.ap.internal.model.source.builtin.BuiltInMethod;
 import org.mapstruct.ap.internal.model.source.selector.MethodSelectors;
@@ -55,9 +65,6 @@ import org.mapstruct.ap.internal.util.MessageConstants;
 import org.mapstruct.ap.internal.util.NativeTypes;
 import org.mapstruct.ap.internal.util.Strings;
 
-import static java.util.Collections.singletonList;
-import static org.mapstruct.ap.internal.util.Collections.first;
-
 /**
  * The one and only implementation of {@link MappingResolver}. The class has been split into an interface an
  * implementation for the sake of avoiding package dependencies. Specifically, this implementation refers to classes
@@ -78,6 +85,8 @@ public class MappingResolverImpl implements MappingResolver {
     private final BuiltInMappingMethods builtInMethods;
     private final MethodSelectors methodSelectors;
 
+    private static final String JL_OBJECT_NAME = Object.class.getName();
+
     /**
      * Private methods which are not present in the original mapper interface and are added to map certain property
      * types.
@@ -113,7 +122,9 @@ public class MappingResolverImpl implements MappingResolver {
             sourceRHS,
             criteria,
             positionHint,
-            forger
+            forger,
+            builtInMethods.getBuiltInMethods(),
+            messager
         );
 
         return attempt.getTargetAssignment( sourceRHS.getSourceTypeForMatching(), targetType );
@@ -141,10 +152,11 @@ public class MappingResolverImpl implements MappingResolver {
         private final List<Method> methods;
         private final SelectionCriteria selectionCriteria;
         private final SourceRHS sourceRHS;
-        private final boolean savedPreferUpdateMapping;
         private final FormattingParameters formattingParameters;
         private final AnnotationMirror positionHint;
         private final Supplier<Assignment> forger;
+        private final List<BuiltInMethod> builtIns;
+        private final FormattingMessager messager;
 
         // resolving via 2 steps creates the possibility of wrong matches, first builtin method matches,
         // second doesn't. In that case, the first builtin method should not lead to a supported method
@@ -155,7 +167,9 @@ public class MappingResolverImpl implements MappingResolver {
                                  FormattingParameters formattingParameters, SourceRHS sourceRHS,
                                  SelectionCriteria criteria,
                                  AnnotationMirror positionHint,
-                                 Supplier<Assignment> forger) {
+                                 Supplier<Assignment> forger,
+                                 List<BuiltInMethod> builtIns,
+                                 FormattingMessager messager) {
 
             this.mappingMethod = mappingMethod;
             this.methods = filterPossibleCandidateMethods( sourceModel );
@@ -164,9 +178,10 @@ public class MappingResolverImpl implements MappingResolver {
             this.sourceRHS = sourceRHS;
             this.supportingMethodCandidates = new HashSet<>();
             this.selectionCriteria = criteria;
-            this.savedPreferUpdateMapping = criteria.isPreferUpdateMapping();
             this.positionHint = positionHint;
             this.forger = forger;
+            this.builtIns = builtIns;
+            this.messager = messager;
         }
 
         private <T extends Method> List<T> filterPossibleCandidateMethods(List<T> candidateMethods) {
@@ -182,14 +197,16 @@ public class MappingResolverImpl implements MappingResolver {
 
         private Assignment getTargetAssignment(Type sourceType, Type targetType) {
 
-            Assignment referencedMethod;
+            Assignment assignment;
 
             // first simple mapping method
             if ( allowMappingMethod() ) {
-                referencedMethod = resolveViaMethod( sourceType, targetType, false );
+                List<SelectedMethod<Method>> matches = getBestMatch( methods, sourceType, targetType );
-                if ( referencedMethod != null ) {
+                reportErrorWhenAmbigious( matches, targetType );
-                    referencedMethod.setAssignment( sourceRHS );
+                if ( !matches.isEmpty() ) {
-                    return referencedMethod;
+                    assignment = toMethodRef( first( matches ) );
+                    assignment.setAssignment( sourceRHS );
+                    return assignment;
                 }
             }
 
@@ -228,38 +245,40 @@ public class MappingResolverImpl implements MappingResolver {
 
                 // check for a built-in method
                 if ( !hasQualfiers() ) {
-                    Assignment builtInMethod = resolveViaBuiltInMethod( sourceType, targetType );
+                    List<SelectedMethod<BuiltInMethod>> matches = getBestMatch( builtIns, sourceType, targetType );
-                    if ( builtInMethod != null ) {
+                    reportErrorWhenAmbigious( matches, targetType );
-                        builtInMethod.setAssignment( sourceRHS );
+                    if ( !matches.isEmpty() ) {
+                        assignment = toBuildInRef( first( matches ) );
+                        assignment.setAssignment( sourceRHS );
                         usedSupportedMappings.addAll( supportingMethodCandidates );
-                        return builtInMethod;
+                        return assignment;
                     }
                 }
             }
 
             if ( allow2Steps() ) {
                 // 2 step method, first: method(method(source))
-                referencedMethod = resolveViaMethodAndMethod( sourceType, targetType );
+                assignment = MethodMethod.getBestMatch( this, sourceType, targetType );
-                if ( referencedMethod != null ) {
+                if ( assignment != null ) {
                     usedSupportedMappings.addAll( supportingMethodCandidates );
-                    return referencedMethod;
+                    return assignment;
                 }
 
                 // 2 step method, then: method(conversion(source))
-                referencedMethod = resolveViaConversionAndMethod( sourceType, targetType );
+                assignment = ConversionMethod.getBestMatch( this, sourceType, targetType );
-                if ( referencedMethod != null ) {
+                if ( assignment != null ) {
                     usedSupportedMappings.addAll( supportingMethodCandidates );
-                    return referencedMethod;
+                    return assignment;
                 }
 
                 // stop here when looking for update methods.
                 selectionCriteria.setPreferUpdateMapping( false );
 
                 // 2 step method, finally: conversion(method(source))
-                ConversionAssignment conversion = resolveViaMethodAndConversion( sourceType, targetType );
+                assignment = MethodConversion.getBestMatch( this, sourceType, targetType );
-                if ( conversion != null ) {
+                if ( assignment != null ) {
                     usedSupportedMappings.addAll( supportingMethodCandidates );
-                    return conversion.getAssignment();
+                    return assignment;
                 }
             }
 
@@ -395,232 +414,6 @@ public class MappingResolverImpl implements MappingResolver {
             return null;
         }
 
-        /**
-         * Returns a reference to a method mapping the given source type to the given target type, if such a method
-         * exists.
-         */
-        private Assignment resolveViaMethod(Type sourceType, Type targetType, boolean considerBuiltInMethods) {
-
-            // first try to find a matching source method
-            SelectedMethod<Method> matchingSourceMethod = getBestMatch( methods, sourceType, targetType );
-
-            if ( matchingSourceMethod != null ) {
-                return getMappingMethodReference( matchingSourceMethod );
-            }
-
-            if ( considerBuiltInMethods ) {
-                return resolveViaBuiltInMethod( sourceType, targetType );
-            }
-
-            return null;
-        }
-
-        /**
-         * Applies matching to given method only
-         *
-         * @param sourceType the source type
-         * @param targetType the target type
-         * @param method     the method to match
-         * @return an assignment if a match, given the criteria could be found. When the method is a
-         * buildIn method, all the bookkeeping is applied.
-         */
-        private Assignment applyMatching(Type sourceType, Type targetType, Method method) {
-
-            if ( method instanceof SourceMethod ) {
-                SelectedMethod<Method> selectedMethod =
-                    getBestMatch( java.util.Collections.singletonList( method ), sourceType, targetType );
-                return selectedMethod != null ? getMappingMethodReference( selectedMethod ) : null;
-            }
-            else if ( method instanceof BuiltInMethod ) {
-                return resolveViaBuiltInMethod( sourceType, targetType );
-            }
-            return null;
-        }
-
-        private Assignment resolveViaBuiltInMethod(Type sourceType, Type targetType) {
-            SelectedMethod<BuiltInMethod> matchingBuiltInMethod =
-                getBestMatch( builtInMethods.getBuiltInMethods(), sourceType, targetType );
-
-            if ( matchingBuiltInMethod != null ) {
-                return createFromBuiltInMethod( matchingBuiltInMethod.getMethod() );
-            }
-
-            return null;
-        }
-
-        private Assignment createFromBuiltInMethod(BuiltInMethod method) {
-            Set<Field> allUsedFields = new HashSet<>( mapperReferences );
-            SupportingField.addAllFieldsIn( supportingMethodCandidates, allUsedFields );
-            SupportingMappingMethod supportingMappingMethod = new SupportingMappingMethod( method, allUsedFields );
-            supportingMethodCandidates.add( supportingMappingMethod );
-            ConversionContext ctx = new DefaultConversionContext(
-                typeFactory,
-                messager,
-                method.getSourceParameters().get( 0 ).getType(),
-                method.getResultType(),
-                formattingParameters
-            );
-            Assignment methodReference = MethodReference.forBuiltInMethod( method, ctx );
-            methodReference.setAssignment( sourceRHS );
-            return methodReference;
-        }
-
-        /**
-         * Suppose mapping required from A to C and:
-         * <ul>
-         * <li>no direct referenced mapping method either built-in or referenced is available from A to C</li>
-         * <li>no conversion is available</li>
-         * <li>there is a method from A to B, methodX</li>
-         * <li>there is a method from B to C, methodY</li>
-         * </ul>
-         * then this method tries to resolve this combination and make a mapping methodY( methodX ( parameter ) )
-         */
-        private Assignment resolveViaMethodAndMethod(Type sourceType, Type targetType) {
-
-            List<Method> methodYCandidates = new ArrayList<>( methods );
-            methodYCandidates.addAll( builtInMethods.getBuiltInMethods() );
-
-            Assignment methodRefY = null;
-
-            // Iterate over all source methods. Check if the return type matches with the parameter that we need.
-            // so assume we need a method from A to C we look for a methodX from A to B (all methods in the
-            // list form such a candidate).
-            // For each of the candidates, we need to look if there's a methodY, either
-            // sourceMethod or builtIn that fits the signature B to C. Only then there is a match. If we have a match
-            // a nested method call can be called. so C = methodY( methodX (A) )
-            for ( Method methodYCandidate : methodYCandidates ) {
-                Type ySourceType = methodYCandidate.getSourceParameters().get( 0 ).getType();
-                if ( Object.class.getName().equals( ySourceType.getName() ) ) {
-                    //  java.lang.Object as intermediate result
-                    continue;
-                }
-
-                ySourceType = ySourceType.resolveTypeVarToType( targetType, methodYCandidate.getResultType() );
-
-                if ( ySourceType != null ) {
-                    methodRefY = applyMatching( ySourceType, targetType, methodYCandidate );
-                    if ( methodRefY != null ) {
-
-                        selectionCriteria.setPreferUpdateMapping( false );
-                        Assignment methodRefX = resolveViaMethod( sourceType, ySourceType, true );
-                        selectionCriteria.setPreferUpdateMapping( savedPreferUpdateMapping );
-                        if ( methodRefX != null ) {
-                            methodRefY.setAssignment( methodRefX );
-                            methodRefX.setAssignment( sourceRHS );
-                            break;
-                        }
-                        else {
-                            // both should match;
-                            supportingMethodCandidates.clear();
-                            methodRefY = null;
-                        }
-                    }
-                }
-            }
-            return methodRefY;
-        }
-
-        /**
-         * Suppose mapping required from A to C and:
-         * <ul>
-         * <li>there is a conversion from A to B, conversionX</li>
-         * <li>there is a method from B to C, methodY</li>
-         * </ul>
-         * then this method tries to resolve this combination and make a mapping methodY( conversionX ( parameter ) )
-         *
-         * Instead of directly using a built in method candidate, all the return types as 'B' of all available built-in
-         * methods are used to resolve a mapping (assignment) from result type to 'B'. If  a match is found, an attempt
-         * is done to find a matching type conversion.
-         */
-        private Assignment resolveViaConversionAndMethod(Type sourceType, Type targetType) {
-
-            List<Method> methodYCandidates = new ArrayList<>( methods );
-            methodYCandidates.addAll( builtInMethods.getBuiltInMethods() );
-
-            Assignment methodRefY = null;
-
-            for ( Method methodYCandidate : methodYCandidates ) {
-                Type ySourceType = methodYCandidate.getSourceParameters().get( 0 ).getType();
-                if ( Object.class.getName().equals( ySourceType.getName() ) ) {
-                    //  java.lang.Object as intermediate result
-                    continue;
-                }
-
-                ySourceType = ySourceType.resolveTypeVarToType( targetType, methodYCandidate.getResultType() );
-
-                if ( ySourceType != null ) {
-                    methodRefY = applyMatching( ySourceType, targetType, methodYCandidate );
-                    if ( methodRefY != null ) {
-                        ConversionAssignment conversionXRef = resolveViaConversion( sourceType, ySourceType );
-                        if ( conversionXRef != null ) {
-                            methodRefY.setAssignment( conversionXRef.getAssignment() );
-                            conversionXRef.getAssignment().setAssignment( sourceRHS );
-                            conversionXRef.reportMessageWhenNarrowing( messager, this );
-                            break;
-                        }
-                        else {
-                            // both should match
-                            supportingMethodCandidates.clear();
-                            methodRefY = null;
-                        }
-                    }
-                }
-            }
-            return methodRefY;
-        }
-
-        /**
-         * Suppose mapping required from A to C and:
-         * <ul>
-         * <li>there is a method from A to B, methodX</li>
-         * <li>there is a conversion from B to C, conversionY</li>
-         * </ul>
-         * then this method tries to resolve this combination and make a mapping conversionY( methodX ( parameter ) )
-         *
-         * Instead of directly using a built in method candidate, all the return types as 'B' of all available built-in
-         * methods are used to resolve a mapping (assignment) from source type to 'B'. If a match is found, an attempt
-         * is done to find a matching type conversion.
-         */
-        private ConversionAssignment resolveViaMethodAndConversion(Type sourceType, Type targetType) {
-
-            List<Method> methodXCandidates = new ArrayList<>( methods );
-            methodXCandidates.addAll( builtInMethods.getBuiltInMethods() );
-
-            ConversionAssignment conversionYRef = null;
-
-            // search the other way around
-            for ( Method methodXCandidate : methodXCandidates ) {
-                Type xTargetType = methodXCandidate.getReturnType();
-                if ( methodXCandidate.isUpdateMethod() ||
-                    Object.class.getName().equals( xTargetType.getFullyQualifiedName() ) ) {
-                    // skip update methods || java.lang.Object as intermediate result
-                    continue;
-                }
-
-                xTargetType =
-                    xTargetType.resolveTypeVarToType( sourceType, methodXCandidate.getParameters().get( 0 ).getType() );
-
-                if ( xTargetType != null ) {
-                    Assignment methodRefX = applyMatching( sourceType, xTargetType, methodXCandidate );
-                    if ( methodRefX != null ) {
-                        conversionYRef = resolveViaConversion( xTargetType, targetType );
-                        if ( conversionYRef != null ) {
-                            conversionYRef.getAssignment().setAssignment( methodRefX );
-                            methodRefX.setAssignment( sourceRHS );
-                            conversionYRef.reportMessageWhenNarrowing( messager, this );
-                            break;
-                        }
-                        else {
-                            // both should match;
-                            supportingMethodCandidates.clear();
-                            conversionYRef = null;
-                        }
-                    }
-                }
-            }
-            return conversionYRef;
-        }
-
         private boolean isCandidateForMapping(Method methodCandidate) {
             return isCreateMethodForMapping( methodCandidate ) || isUpdateMethodForMapping( methodCandidate );
         }
@@ -640,15 +433,17 @@ public class MappingResolverImpl implements MappingResolver {
                 && !methodCandidate.isLifecycleCallbackMethod();
         }
 
-        private <T extends Method> SelectedMethod<T> getBestMatch(List<T> methods, Type sourceType, Type returnType) {
+        private <T extends Method> List<SelectedMethod<T>> getBestMatch(List<T> methods, Type source, Type target) {
-
+            return methodSelectors.getMatchingMethods(
-            List<SelectedMethod<T>> candidates = methodSelectors.getMatchingMethods(
                 mappingMethod,
                 methods,
-                singletonList( sourceType ),
+                singletonList( source ),
-                returnType,
+                target,
                 selectionCriteria
             );
+        }
+
+        private <T extends Method> void reportErrorWhenAmbigious(List<SelectedMethod<T>> candidates, Type target) {
 
             // raise an error if more than one mapping method is suitable to map the given source type
             // into the target type
@@ -660,7 +455,7 @@ public class MappingResolverImpl implements MappingResolver {
                         positionHint,
                         Message.GENERAL_AMBIGIOUS_MAPPING_METHOD,
                         sourceRHS.getSourceErrorMessagePart(),
-                        returnType,
+                        target,
                         Strings.join( candidates, ", " )
                     );
                 }
@@ -669,29 +464,41 @@ public class MappingResolverImpl implements MappingResolver {
                         mappingMethod.getExecutable(),
                         positionHint,
                         Message.GENERAL_AMBIGIOUS_FACTORY_METHOD,
-                        returnType,
+                        target,
                         Strings.join( candidates, ", " )
                     );
                 }
             }
-
-            if ( !candidates.isEmpty() ) {
-                return first( candidates );
-            }
-
-            return null;
         }
 
-        private Assignment getMappingMethodReference(SelectedMethod<Method> method) {
+        private Assignment toMethodRef(SelectedMethod<Method> selectedMethod) {
-            MapperReference mapperReference = findMapperReference( method.getMethod() );
+            MapperReference mapperReference = findMapperReference( selectedMethod.getMethod() );
 
             return MethodReference.forMapperReference(
-                method.getMethod(),
+                selectedMethod.getMethod(),
                 mapperReference,
-                method.getParameterBindings()
+                selectedMethod.getParameterBindings()
             );
         }
 
+        private Assignment toBuildInRef(SelectedMethod<BuiltInMethod> selectedMethod) {
+            BuiltInMethod method = selectedMethod.getMethod();
+            Set<Field> allUsedFields = new HashSet<>( mapperReferences );
+            SupportingField.addAllFieldsIn( supportingMethodCandidates, allUsedFields );
+            SupportingMappingMethod supportingMappingMethod = new SupportingMappingMethod( method, allUsedFields );
+            supportingMethodCandidates.add( supportingMappingMethod );
+            ConversionContext ctx = new DefaultConversionContext(
+                typeFactory,
+                messager,
+                method.getMappingSourceType(),
+                method.getResultType(),
+                formattingParameters
+            );
+            Assignment methodReference = MethodReference.forBuiltInMethod( method, ctx );
+            methodReference.setAssignment( sourceRHS );
+            return methodReference;
+        }
+
         /**
          * Whether the given source and target type are both a collection type or both a map type and the source value
          * can be propagated via a copy constructor.
@@ -770,6 +577,7 @@ public class MappingResolverImpl implements MappingResolver {
 
             return false;
         }
+
     }
 
     private static class ConversionAssignment {
@@ -813,5 +621,408 @@ public class MappingResolverImpl implements MappingResolver {
             );
         }
 
+        String shortName() {
+            return sourceType.getName() + "-->" + targetType.getName();
+        }
+
+        @Override
+        public boolean equals(Object o) {
+            if ( this == o ) {
+                return true;
+            }
+            if ( o == null || getClass() != o.getClass() ) {
+                return false;
+            }
+            ConversionAssignment that = (ConversionAssignment) o;
+            return sourceType.equals( that.sourceType ) && targetType.equals( that.targetType );
+        }
+
+        @Override
+        public int hashCode() {
+            return Objects.hash( sourceType, targetType );
+        }
     }
+
+    /**
+     * Suppose mapping required from A to C and:
+     * <ul>
+     * <li>no direct referenced mapping method either built-in or referenced is available from A to C</li>
+     * <li>no conversion is available</li>
+     * <li>there is a method from A to B, methodX</li>
+     * <li>there is a method from B to C, methodY</li>
+     * </ul>
+     * then this method tries to resolve this combination and make a mapping methodY( methodX ( parameter ) )
+     *
+     * NOTE method X cannot be an update method
+     */
+    private static class MethodMethod<T1 extends Method, T2 extends Method> {
+
+        private final ResolvingAttempt attempt;
+        private final List<T1> xMethods;
+        private final List<T2> yMethods;
+        private final Function<SelectedMethod<T1>, Assignment> xCreate;
+        private final Function<SelectedMethod<T2>, Assignment> yCreate;
+
+        // results
+        private boolean hasResult = false;
+        private Assignment result = null;
+
+        static Assignment getBestMatch(ResolvingAttempt att, Type sourceType, Type targetType) {
+            MethodMethod<Method, Method> mmAttempt =
+                new MethodMethod<>( att, att.methods, att.methods, att::toMethodRef, att::toMethodRef )
+                    .getBestMatch( sourceType, targetType );
+            if ( mmAttempt.hasResult ) {
+                return mmAttempt.result;
+            }
+            MethodMethod<Method, BuiltInMethod> mbAttempt =
+                new MethodMethod<>( att, att.methods, att.builtIns, att::toMethodRef, att::toBuildInRef )
+                    .getBestMatch( sourceType, targetType );
+            if ( mbAttempt.hasResult ) {
+                return mbAttempt.result;
+            }
+            MethodMethod<BuiltInMethod, Method> bmAttempt =
+                new MethodMethod<>( att, att.builtIns, att.methods, att::toBuildInRef, att::toMethodRef )
+                    .getBestMatch( sourceType, targetType );
+            if ( bmAttempt.hasResult ) {
+                return bmAttempt.result;
+            }
+            MethodMethod<BuiltInMethod, BuiltInMethod> bbAttempt =
+                new MethodMethod<>( att, att.builtIns, att.builtIns, att::toBuildInRef, att::toBuildInRef )
+                    .getBestMatch( sourceType, targetType );
+            return bbAttempt.result;
+        }
+
+        MethodMethod(ResolvingAttempt attempt, List<T1> xMethods, List<T2> yMethods,
+                            Function<SelectedMethod<T1>, Assignment> xCreate,
+                            Function<SelectedMethod<T2>, Assignment> yCreate) {
+            this.attempt = attempt;
+            this.xMethods = xMethods;
+            this.yMethods = yMethods;
+            this.xCreate = xCreate;
+            this.yCreate = yCreate;
+        }
+
+        private MethodMethod<T1, T2> getBestMatch(Type sourceType, Type targetType) {
+
+            Set<T2> yCandidates = new HashSet<>();
+            Map<SelectedMethod<T1>, List<SelectedMethod<T2>>> xCandidates = new LinkedHashMap<>();
+            Map<SelectedMethod<T1>, Type> typesInTheMiddle = new LinkedHashMap<>();
+
+            // Iterate over all source methods. Check if the return type matches with the parameter that we need.
+            // so assume we need a method from A to C we look for a methodX from A to B (all methods in the
+            // list form such a candidate).
+            // For each of the candidates, we need to look if there's a methodY, either
+            // sourceMethod or builtIn that fits the signature B to C. Only then there is a match. If we have a match
+            // a nested method call can be called. so C = methodY( methodX (A) )
+            attempt.selectionCriteria.setPreferUpdateMapping( false );
+            for ( T2 yCandidate : yMethods ) {
+                Type ySourceType = yCandidate.getMappingSourceType();
+                ySourceType = ySourceType.resolveTypeVarToType( targetType, yCandidate.getResultType() );
+                Type yTargetType = yCandidate.getResultType();
+                if ( ySourceType == null
+                    || !yTargetType.isRawAssignableTo( targetType )
+                    || JL_OBJECT_NAME.equals( ySourceType.getFullyQualifiedName() ) ) {
+                    //  java.lang.Object as intermediate result
+                    continue;
+                }
+                List<SelectedMethod<T1>> xMatches = attempt.getBestMatch( xMethods, sourceType, ySourceType );
+                if ( !xMatches.isEmpty() ) {
+                    xMatches.stream().forEach( x -> xCandidates.put( x, new ArrayList<>() ) );
+                    final Type typeInTheMiddle = ySourceType;
+                    xMatches.stream().forEach( x -> typesInTheMiddle.put( x, typeInTheMiddle ) );
+                    yCandidates.add( yCandidate );
+                }
+            }
+            attempt.selectionCriteria.setPreferUpdateMapping( true );
+
+            // collect all results
+            List<T2> yCandidatesList = new ArrayList<>( yCandidates );
+            Iterator<Map.Entry<SelectedMethod<T1>, List<SelectedMethod<T2>>>> i = xCandidates.entrySet().iterator();
+            while ( i.hasNext() ) {
+                Map.Entry<SelectedMethod<T1>, List<SelectedMethod<T2>>> entry = i.next();
+                Type typeInTheMiddle = typesInTheMiddle.get( entry.getKey() );
+                entry.getValue().addAll( attempt.getBestMatch( yCandidatesList, typeInTheMiddle, targetType ) );
+                if ( entry.getValue().isEmpty() ) {
+                    i.remove();
+                }
+            }
+
+            // no results left
+            if ( xCandidates.isEmpty() ) {
+                return this;
+            }
+            hasResult = true;
+
+            // get result, there should be one entry left with only one value
+            if ( xCandidates.size() == 1 && firstValue( xCandidates ).size() == 1 ) {
+                Assignment methodRefY = yCreate.apply( first( firstValue( xCandidates ) ) );
+                Assignment methodRefX = xCreate.apply( firstKey( xCandidates ) );
+                methodRefY.setAssignment( methodRefX );
+                methodRefX.setAssignment( attempt.sourceRHS );
+                result = methodRefY;
+            }
+            else  {
+                reportAmbigiousError( xCandidates, targetType );
+            }
+            return this;
+
+        }
+
+        void reportAmbigiousError(Map<SelectedMethod<T1>, List<SelectedMethod<T2>>> xCandidates, Type target) {
+            StringBuilder result = new StringBuilder();
+            xCandidates.entrySet()
+                       .stream()
+                       .forEach( e -> result.append( "method(s)Y: " )
+                                            .append( e.getValue()
+                                                      .stream()
+                                                      .map( v -> v.getMethod().shortName() )
+                                                      .collect( Collectors.joining( ", " ) ) )
+                                            .append( ", methodX: " )
+                                            .append( e.getKey().getMethod().shortName() )
+                                            .append( "; " ) );
+            attempt.messager.printMessage(
+                attempt.mappingMethod.getExecutable(),
+                attempt.positionHint,
+                Message.GENERAL_AMBIGIOUS_MAPPING_METHODY_METHODX,
+                attempt.sourceRHS.getSourceType().getName() + " " + attempt.sourceRHS.getSourceParameterName(),
+                target.getName(),
+                result.toString() );
+        }
+    }
+
+    /**
+     * Suppose mapping required from A to C and:
+     * <ul>
+     * <li>there is a conversion from A to B, conversionX</li>
+     * <li>there is a method from B to C, methodY</li>
+     * </ul>
+     * then this method tries to resolve this combination and make a mapping methodY( conversionX ( parameter ) )
+     *
+     * Instead of directly using a built in method candidate, all the return types as 'B' of all available built-in
+     * methods are used to resolve a mapping (assignment) from result type to 'B'. If  a match is found, an attempt
+     * is done to find a matching type conversion.
+     */
+    private static class ConversionMethod<T extends Method> {
+
+        private final ResolvingAttempt attempt;
+        private final List<T> methods;
+        private final Function<SelectedMethod<T>, Assignment> create;
+
+        // results
+        private boolean hasResult = false;
+        private Assignment result = null;
+
+        static Assignment getBestMatch(ResolvingAttempt att, Type sourceType, Type targetType) {
+            ConversionMethod<Method> mAttempt = new ConversionMethod<>( att, att.methods, att::toMethodRef )
+                    .getBestMatch( sourceType, targetType );
+            if ( mAttempt.hasResult ) {
+                return mAttempt.result;
+            }
+            ConversionMethod<BuiltInMethod> bAttempt =
+                new ConversionMethod<>( att, att.builtIns, att::toBuildInRef )
+                    .getBestMatch( sourceType, targetType );
+            return bAttempt.result;
+        }
+
+        ConversionMethod(ResolvingAttempt attempt, List<T> methods, Function<SelectedMethod<T>, Assignment> create) {
+            this.attempt = attempt;
+            this.methods = methods;
+            this.create = create;
+        }
+
+        private ConversionMethod<T> getBestMatch(Type sourceType, Type targetType) {
+
+            List<T> yCandidates = new ArrayList<>();
+            Map<ConversionAssignment, List<SelectedMethod<T>>> xRefCandidates = new LinkedHashMap<>();
+
+            for ( T yCandidate : methods ) {
+                Type ySourceType = yCandidate.getMappingSourceType();
+                ySourceType = ySourceType.resolveTypeVarToType( targetType, yCandidate.getResultType() );
+                Type yTargetType = yCandidate.getResultType();
+                if ( ySourceType == null
+                    || !yTargetType.isRawAssignableTo( targetType )
+                    || JL_OBJECT_NAME.equals( ySourceType.getFullyQualifiedName() ) ) {
+                    //  java.lang.Object as intermediate result
+                    continue;
+                }
+                ConversionAssignment xRefCandidate = attempt.resolveViaConversion( sourceType, ySourceType );
+                if ( xRefCandidate != null ) {
+                    xRefCandidates.put( xRefCandidate, new ArrayList<>() );
+                    yCandidates.add( yCandidate );
+                }
+            }
+
+            // collect all results
+            Iterator<Map.Entry<ConversionAssignment, List<SelectedMethod<T>>>> i = xRefCandidates.entrySet().iterator();
+            while ( i.hasNext() ) {
+                Map.Entry<ConversionAssignment, List<SelectedMethod<T>>> entry = i.next();
+                entry.getValue().addAll( attempt.getBestMatch( yCandidates, entry.getKey().targetType, targetType ) );
+                if ( entry.getValue().isEmpty() ) {
+                    i.remove();
+                }
+            }
+
+            // no results left
+            if ( xRefCandidates.isEmpty() ) {
+                return this;
+            }
+            hasResult = true;
+
+            // get result, there should be one entry left with only one value
+            if ( xRefCandidates.size() == 1 && firstValue( xRefCandidates ).size() == 1 ) {
+                Assignment methodRefY = create.apply( first( firstValue( xRefCandidates ) ) );
+                ConversionAssignment conversionRefX = firstKey( xRefCandidates );
+                conversionRefX.reportMessageWhenNarrowing( attempt.messager, attempt );
+                methodRefY.setAssignment( conversionRefX.assignment );
+                conversionRefX.assignment.setAssignment( attempt.sourceRHS );
+                result = methodRefY;
+            }
+            else  {
+                reportAmbigiousError( xRefCandidates, targetType );
+            }
+            return this;
+
+        }
+
+        void reportAmbigiousError(Map<ConversionAssignment, List<SelectedMethod<T>>> xRefCandidates, Type target) {
+            StringBuilder result = new StringBuilder();
+            xRefCandidates.entrySet()
+                          .stream()
+                          .forEach( e -> result.append( "method(s)Y: " )
+                                               .append( e.getValue()
+                                                         .stream()
+                                                         .map( v -> v.getMethod().shortName() )
+                                                         .collect( Collectors.joining( ", " ) ) )
+                                               .append( ", conversionX: " )
+                                               .append( e.getKey().shortName() )
+                                               .append( "; " ) );
+            attempt.messager.printMessage(
+                attempt.mappingMethod.getExecutable(),
+                attempt.positionHint,
+                Message.GENERAL_AMBIGIOUS_MAPPING_METHODY_CONVERSIONX,
+                attempt.sourceRHS.getSourceType().getName() + " " + attempt.sourceRHS.getSourceParameterName(),
+                target.getName(),
+                result.toString() );
+        }
+    }
+
+    /**
+     * Suppose mapping required from A to C and:
+     * <ul>
+     * <li>there is a method from A to B, methodX</li>
+     * <li>there is a conversion from B to C, conversionY</li>
+     * </ul>
+     * then this method tries to resolve this combination and make a mapping conversionY( methodX ( parameter ) )
+     *
+     * Instead of directly using a built in method candidate, all the return types as 'B' of all available built-in
+     * methods are used to resolve a mapping (assignment) from source type to 'B'. If a match is found, an attempt
+     * is done to find a matching type conversion.
+     *
+     * NOTE methodX cannot be an update method
+     */
+    private static class MethodConversion<T extends Method> {
+
+        private final ResolvingAttempt attempt;
+        private final List<T> methods;
+        private final Function<SelectedMethod<T>, Assignment> create;
+
+        // results
+        private boolean hasResult = false;
+        private Assignment result = null;
+
+        static Assignment getBestMatch(ResolvingAttempt att, Type sourceType, Type targetType) {
+            MethodConversion<Method> mAttempt = new MethodConversion<>( att, att.methods, att::toMethodRef )
+                    .getBestMatch( sourceType, targetType );
+            if ( mAttempt.hasResult ) {
+                return mAttempt.result;
+            }
+            MethodConversion<BuiltInMethod> bAttempt = new MethodConversion<>( att, att.builtIns, att::toBuildInRef )
+                    .getBestMatch( sourceType, targetType );
+            return bAttempt.result;
+        }
+
+        MethodConversion(ResolvingAttempt attempt, List<T> methods, Function<SelectedMethod<T>, Assignment> create) {
+            this.attempt = attempt;
+            this.methods = methods;
+            this.create = create;
+        }
+
+        private MethodConversion<T> getBestMatch(Type sourceType, Type targetType) {
+
+            List<T> xCandidates = new ArrayList<>();
+            Map<ConversionAssignment, List<SelectedMethod<T>>> yRefCandidates = new LinkedHashMap<>();
+
+            // search through methods, and select egible candidates
+            for ( T xCandidate : methods ) {
+                Type xTargetType = xCandidate.getReturnType();
+                Type xSourceType = xCandidate.getMappingSourceType();
+                xTargetType = xTargetType.resolveTypeVarToType( sourceType, xSourceType );
+                if ( xTargetType == null
+                    || xCandidate.isUpdateMethod()
+                    || !sourceType.isRawAssignableTo( xSourceType )
+                    || JL_OBJECT_NAME.equals( xTargetType.getFullyQualifiedName() ) ) {
+                    // skip update methods || java.lang.Object as intermediate result
+                    continue;
+                }
+                ConversionAssignment yRefCandidate = attempt.resolveViaConversion( xTargetType, targetType );
+                if ( yRefCandidate != null ) {
+                    yRefCandidates.put( yRefCandidate, new ArrayList<>() );
+                    xCandidates.add( xCandidate );
+                }
+            }
+
+            // collect all results
+            Iterator<Map.Entry<ConversionAssignment, List<SelectedMethod<T>>>> i = yRefCandidates.entrySet().iterator();
+            while ( i.hasNext() ) {
+                Map.Entry<ConversionAssignment, List<SelectedMethod<T>>> entry = i.next();
+                entry.getValue().addAll( attempt.getBestMatch( xCandidates, sourceType, entry.getKey().sourceType ) );
+                if ( entry.getValue().isEmpty() ) {
+                    i.remove();
+                }
+            }
+
+            // no results left
+            if ( yRefCandidates.isEmpty() ) {
+                return this;
+            }
+            hasResult = true;
+
+            // get result, there should be one entry left with only one value
+            if ( yRefCandidates.size() == 1 && firstValue( yRefCandidates ).size() == 1 ) {
+                Assignment methodRefX = create.apply( first( firstValue( yRefCandidates ) ) );
+                ConversionAssignment conversionRefY = firstKey( yRefCandidates );
+                conversionRefY.reportMessageWhenNarrowing( attempt.messager, attempt );
+                methodRefX.setAssignment( attempt.sourceRHS );
+                conversionRefY.assignment.setAssignment( methodRefX );
+                result = conversionRefY.assignment;
+            }
+            else  {
+                reportAmbigiousError( yRefCandidates, targetType );
+            }
+            return this;
+
+        }
+
+        void reportAmbigiousError(Map<ConversionAssignment, List<SelectedMethod<T>>> yRefCandidates, Type target) {
+            StringBuilder result = new StringBuilder();
+            yRefCandidates.entrySet()
+                          .stream()
+                          .forEach( e -> result.append( "conversionY: " )
+                                               .append( e.getKey().shortName() )
+                                               .append( ", method(s)X: " )
+                                               .append( e.getValue()
+                                                         .stream()
+                                                         .map( v -> v.getMethod().shortName() )
+                                                         .collect( Collectors.joining( ", " ) ) )
+                                               .append( "; " ) );
+            attempt.messager.printMessage(
+                attempt.mappingMethod.getExecutable(),
+                attempt.positionHint,
+                Message.GENERAL_AMBIGIOUS_MAPPING_CONVERSIONY_METHODX,
+                attempt.sourceRHS.getSourceType().getName() + " " + attempt.sourceRHS.getSourceParameterName(),
+                target.getName(),
+                result.toString() );
+        }
+    }
+
 }

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

@@ -9,6 +9,7 @@ import java.util.ArrayList;
 import java.util.Collection;
 import java.util.HashSet;
 import java.util.List;
+import java.util.Map;
 import java.util.Set;
 
 /**
@@ -63,4 +64,16 @@ public class Collections {
         return result;
     }
 
+    public static <K, V> Map.Entry<K, V> first(Map<K, V> map) {
+        return map.entrySet().iterator().next();
+    }
+
+    public static <K, V> V firstValue(Map<K, V> map) {
+        return first( map ).getValue();
+    }
+
+    public static <K, V> K firstKey(Map<K, V> map) {
+        return first( map ).getKey();
+    }
+
 }

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

@@ -125,6 +125,10 @@ public enum Message {
     GENERAL_NO_QUALIFYING_METHOD_NAMED( "Qualifier error. No method found annotated with @Named#value: [ %s ]. See " + FAQ_QUALIFIER_URL + " for more info." ),
     GENERAL_NO_QUALIFYING_METHOD_COMBINED( "Qualifier error. No method found annotated with @Named#value: [ %s ], annotated with [ %s ]. See " + FAQ_QUALIFIER_URL + " for more info." ),
 
+    GENERAL_AMBIGIOUS_MAPPING_METHODY_METHODX( "Ambiguous 2step methods found, mapping %s to %s. Found methodY( methodX ( parameter ) ): %s." ),
+    GENERAL_AMBIGIOUS_MAPPING_CONVERSIONY_METHODX( "Ambiguous 2step methods found, mapping %s to %s. Found conversionY( methodX ( parameter ) ): %s." ),
+    GENERAL_AMBIGIOUS_MAPPING_METHODY_CONVERSIONX( "Ambiguous 2step methods found, mapping %s to %s. Found methodY( conversionX ( parameter ) ): %s." ),
+
     BUILDER_MORE_THAN_ONE_BUILDER_CREATION_METHOD( "More than one builder creation method for \"%s\". Found methods: \"%s\". Builder will not be used. Consider implementing a custom BuilderProvider SPI.", Diagnostic.Kind.WARNING ),
     BUILDER_NO_BUILD_METHOD_FOUND("No build method \"%s\" found in \"%s\" for \"%s\". Found methods: \"%s\".", Diagnostic.Kind.ERROR ),
     BUILDER_NO_BUILD_METHOD_FOUND_DEFAULT("No build method \"%s\" found in \"%s\" for \"%s\". Found methods: \"%s\". Consider to add @Builder in order to select the correct build method.", Diagnostic.Kind.ERROR ),

processor/src/test/java/org/mapstruct/ap/test/bugs/_2145/Issue2145Mapper.java

@@ -0,0 +1,85 @@
+/*
+ * 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._2145;
+
+import javax.xml.bind.JAXBElement;
+import javax.xml.bind.annotation.XmlElementDecl;
+import javax.xml.namespace.QName;
+
+import org.mapstruct.Mapper;
+import org.mapstruct.Mapping;
+import org.mapstruct.factory.Mappers;
+
+@Mapper( uses = Issue2145Mapper.ObjectFactory.class )
+public interface Issue2145Mapper {
+
+    Issue2145Mapper INSTANCE = Mappers.getMapper( Issue2145Mapper.class );
+
+    @Mapping(target = "nested", source = "value")
+    Target map(Source source);
+
+    default Nested map(String in) {
+        Nested nested = new Nested();
+        nested.setValue( in );
+        return nested;
+    }
+
+    class Target {
+
+        private JAXBElement<Nested> nested;
+
+        public JAXBElement<Nested> getNested() {
+            return nested;
+        }
+
+        public void setNested(JAXBElement<Nested> nested) {
+            this.nested = nested;
+        }
+    }
+
+    class Nested {
+
+        private String value;
+
+        public String getValue() {
+            return value;
+        }
+
+        public void setValue(String value) {
+            this.value = value;
+        }
+    }
+
+    class Source {
+
+        private String value;
+
+        public String getValue() {
+            return value;
+        }
+
+        public void setValue(String value) {
+            this.value = value;
+        }
+    }
+
+    class ObjectFactory {
+
+        private static final QName Q_NAME = new QName( "http://www.test.com/test", "" );
+        private static final QName Q_NAME_NESTED = new QName( "http://www.test.com/test", "nested" );
+
+        @XmlElementDecl(namespace = "http://www.test.com/test", name = "Nested")
+        public JAXBElement<Nested> createNested(Nested value) {
+            return new JAXBElement<Nested>( Q_NAME, Nested.class, null, value );
+        }
+
+        @XmlElementDecl(namespace = "http://www.test.com/test", name = "nested", scope = Nested.class)
+        public JAXBElement<Nested> createNestedInNestedTarget(Nested value) {
+            return new JAXBElement<Nested>( Q_NAME_NESTED, Nested.class, Target.class, value );
+        }
+
+    }
+}

processor/src/test/java/org/mapstruct/ap/test/bugs/_2145/Issue2145Test.java

@@ -0,0 +1,34 @@
+/*
+ * 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._2145;
+
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.mapstruct.ap.testutil.IssueKey;
+import org.mapstruct.ap.testutil.WithClasses;
+import org.mapstruct.ap.testutil.runner.AnnotationProcessorTestRunner;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+@IssueKey("2145")
+@WithClasses(Issue2145Mapper.class)
+@RunWith(AnnotationProcessorTestRunner.class)
+public class Issue2145Test {
+
+    @Test
+    public void test() {
+        Issue2145Mapper.Source source = new Issue2145Mapper.Source();
+        source.setValue( "test" );
+
+        Issue2145Mapper.Target target = Issue2145Mapper.INSTANCE.map( source );
+
+        assertThat( target ).isNotNull();
+        assertThat( target.getNested() ).isNotNull();
+        assertThat( target.getNested().getScope() ).isEqualTo( Issue2145Mapper.Target.class );
+        assertThat( target.getNested().getValue() ).isNotNull();
+        assertThat( target.getNested().getValue().getValue() ).isEqualTo( "test" );
+    }
+}

processor/src/test/java/org/mapstruct/ap/test/selection/twosteperror/ErroneousMapperCM.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.test.selection.twosteperror;
+
+import java.math.BigDecimal;
+
+import org.mapstruct.Mapper;
+import org.mapstruct.factory.Mappers;
+
+@Mapper
+public interface ErroneousMapperCM {
+
+    ErroneousMapperCM INSTANCE = Mappers.getMapper( ErroneousMapperCM.class );
+
+    Target map(Source s);
+
+    default TargetType methodY1(String s) {
+        return new TargetType( s );
+    }
+
+    default TargetType methodY2(Double d) {
+        return new TargetType( d.toString() );
+    }
+
+    // CHECKSTYLE:OFF
+    class Target {
+        public TargetType t1;
+    }
+
+    class Source {
+        public BigDecimal t1;
+    }
+
+    class TargetType {
+        public String t1;
+
+        public TargetType(String test) {
+            this.t1 = test;
+        }
+    }
+
+    class TypeInTheMiddleA {
+
+        TypeInTheMiddleA(String t1) {
+            this.test = t1;
+        }
+
+        public String test;
+    }
+
+    // CHECKSTYLE:ON
+
+}

processor/src/test/java/org/mapstruct/ap/test/selection/twosteperror/ErroneousMapperMC.java

@@ -0,0 +1,52 @@
+/*
+ * 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.selection.twosteperror;
+
+import java.math.BigDecimal;
+
+import org.mapstruct.Mapper;
+import org.mapstruct.factory.Mappers;
+
+@Mapper
+public interface ErroneousMapperMC {
+
+    ErroneousMapperMC INSTANCE = Mappers.getMapper( ErroneousMapperMC.class );
+
+    Target map(Source s);
+
+    default BigDecimal methodX1(SourceType s) {
+        return new BigDecimal( s.t1 );
+    }
+
+    default Double methodX2(SourceType s) {
+        return new Double( s.t1 );
+    }
+
+    // CHECKSTYLE:OFF
+    class Target {
+        public String t1;
+    }
+
+    class Source {
+        public SourceType t1;
+    }
+
+    class SourceType {
+        public String t1;
+    }
+
+    class TargetType {
+        public String t1;
+
+        public TargetType(String test) {
+            this.t1 = test;
+        }
+    }
+
+
+    // CHECKSTYLE:ON
+
+}

processor/src/test/java/org/mapstruct/ap/test/selection/twosteperror/ErroneousMapperMM.java

@@ -0,0 +1,74 @@
+/*
+ * 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.selection.twosteperror;
+
+import org.mapstruct.Mapper;
+import org.mapstruct.factory.Mappers;
+
+@Mapper
+public interface ErroneousMapperMM {
+
+    ErroneousMapperMM INSTANCE = Mappers.getMapper( ErroneousMapperMM.class );
+
+    Target map( Source s );
+
+    default TargetType methodY1(TypeInTheMiddleA s) {
+        return new TargetType( s.test );
+    }
+
+    default TypeInTheMiddleA methodX1(SourceType s) {
+        return new TypeInTheMiddleA( s.t1 );
+    }
+
+    default TargetType methodY2(TypeInTheMiddleB s) {
+        return new TargetType( s.test );
+    }
+
+    default TypeInTheMiddleB methodX2(SourceType s) {
+        return new TypeInTheMiddleB( s.t1 );
+    }
+
+    // CHECKSTYLE:OFF
+    class Target {
+        public TargetType t1;
+    }
+
+    class Source {
+        public SourceType t1;
+    }
+
+    class SourceType {
+        public String t1;
+    }
+
+    class TargetType {
+        public String t1;
+
+        public TargetType(String test) {
+            this.t1 = test;
+        }
+    }
+
+    class TypeInTheMiddleA {
+
+        TypeInTheMiddleA(String t1) {
+            this.test = t1;
+        }
+
+        public String test;
+    }
+
+    class TypeInTheMiddleB {
+
+        TypeInTheMiddleB(String t1) {
+            this.test = t1;
+        }
+
+        public String test;
+    }
+    // CHECKSTYLE:ON
+
+}

processor/src/test/java/org/mapstruct/ap/test/selection/twosteperror/TwoStepMappingTest.java

@@ -0,0 +1,79 @@
+/*
+ * 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.selection.twosteperror;
+
+import org.junit.Test;
+import org.junit.runner.RunWith;
+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.ap.testutil.runner.AnnotationProcessorTestRunner;
+
+@RunWith( AnnotationProcessorTestRunner.class )
+public class TwoStepMappingTest {
+
+    @Test
+    @WithClasses( ErroneousMapperMM.class )
+    @ExpectedCompilationOutcome( value = CompilationResult.FAILED,
+        diagnostics = @Diagnostic(
+            kind = javax.tools.Diagnostic.Kind.ERROR,
+            type = ErroneousMapperMM.class,
+            line = 16,
+            message = "Ambiguous 2step methods found, mapping SourceType s to TargetType. "
+                + "Found methodY( methodX ( parameter ) ): "
+                + "method(s)Y: TargetType:methodY1(TypeInTheMiddleA), methodX: TypeInTheMiddleA:methodX1(SourceType); "
+                + "method(s)Y: TargetType:methodY2(TypeInTheMiddleB), methodX: TypeInTheMiddleB:methodX2(SourceType); ."
+        ) )
+    public void methodAndMethodTest() {
+    }
+
+    @Test
+    @WithClasses( ErroneousMapperCM.class )
+    @ExpectedCompilationOutcome( value = CompilationResult.FAILED,
+        diagnostics = {
+            @Diagnostic(
+                kind = javax.tools.Diagnostic.Kind.ERROR,
+                type = ErroneousMapperCM.class,
+                line = 18,
+                message = "Ambiguous 2step methods found, mapping BigDecimal s to TargetType. "
+                    + "Found methodY( conversionX ( parameter ) ): "
+                    + "method(s)Y: TargetType:methodY1(String), conversionX: BigDecimal-->String; "
+                    + "method(s)Y: TargetType:methodY2(Double), conversionX: BigDecimal-->Double; ."
+            ),
+            @Diagnostic(
+                kind = javax.tools.Diagnostic.Kind.ERROR,
+                type = ErroneousMapperCM.class,
+                line = 18,
+                messageRegExp = "Can't map property.*"
+            )
+        } )
+    public void conversionAndMethodTest() {
+    }
+
+    @Test
+    @WithClasses( ErroneousMapperMC.class )
+    @ExpectedCompilationOutcome( value = CompilationResult.FAILED,
+        diagnostics = {
+            @Diagnostic(
+                kind = javax.tools.Diagnostic.Kind.ERROR,
+                type = ErroneousMapperMC.class,
+                line = 18,
+                message = "Ambiguous 2step methods found, mapping SourceType s to String. "
+                    + "Found conversionY( methodX ( parameter ) ): "
+                    + "conversionY: BigDecimal-->String, method(s)X: BigDecimal:methodX1(SourceType); "
+                    + "conversionY: Double-->String, method(s)X: Double:methodX2(SourceType); ."
+            ),
+            @Diagnostic(
+                kind = javax.tools.Diagnostic.Kind.ERROR,
+                type = ErroneousMapperMC.class,
+                line = 18,
+                messageRegExp = "Can't map property.*"
+            )
+        } )
+    public void methodAndConversionTest() {
+    }
+}