#2463 Selection stops when method type-args are flipped (#2487)

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

@@ -248,10 +248,12 @@ public class MethodMatcher {
                 // e.g. <T> String method( List<? extends T> in )
 
                 Type.ResolvedPair resolved = mthdParType.resolveParameterToType( matchingType, aCandidateMethodType );
-                if ( resolved == null ) {
-                    // cannot find a candidate type, but should have since the typeFromCandidateMethod had parameters
-                    // to be resolved
-                    return !hasGenericTypeParameters( aCandidateMethodType );
+                if ( resolved.getMatch() == null ) {
+                    // we should be dealing with something containing a type parameter at this point. This is
+                    // covered with the checks above. Therefore resolved itself cannot be null.
+                    // If there is no match here, continue with the next candidate, perhaps there will a match with
+                    // the next method type parameter
+                    continue;
                 }
 
                 // resolved something at this point, a candidate can be fetched or created
@@ -270,13 +272,10 @@ public class MethodMatcher {
                     // it might be already set, but we just checked if its an equivalent type
                     if ( typeVarCandidate.match == null ) {
                         typeVarCandidate.match = resolved.getMatch();
-                        if ( typeVarCandidate.match == null) {
-                            return false;
-                        }
                         typeVarCandidate.pairs.add( resolved );
                     }
                     else if ( !areEquivalent( resolved.getMatch(), typeVarCandidate.match ) ) {
-                        // type has been resolved twice, but with a different candidate (conflict)
+                        // type has been resolved twice, but with a different candidate (conflict). Stop
                         return false;
                     }
 

processor/src/test/java/org/mapstruct/ap/test/selection/methodgenerics/multiple/MultipleTypeVarTest.java

@@ -50,6 +50,22 @@ public class MultipleTypeVarTest {
         assertThat( target.getProp() ).containsExactly( entry( "test", 5L ) );
     }
 
+    @ProcessorTest
+    @WithClasses( ReturnTypeHasMultipleTypeVarBothArgumentsFlippedGenericMapper.class )
+    public void testGenericReturnTypeVarBothGenericArgumentsFlipped() {
+
+        ReturnTypeHasMultipleTypeVarBothArgumentsFlippedGenericMapper.Pair pair
+            = new ReturnTypeHasMultipleTypeVarBothArgumentsFlippedGenericMapper.Pair( "test", 5L );
+        ReturnTypeHasMultipleTypeVarBothArgumentsFlippedGenericMapper.Source src =
+            new ReturnTypeHasMultipleTypeVarBothArgumentsFlippedGenericMapper.Source( pair );
+        ReturnTypeHasMultipleTypeVarBothArgumentsFlippedGenericMapper.Target target =
+            ReturnTypeHasMultipleTypeVarBothArgumentsFlippedGenericMapper.INSTANCE.toTarget( src );
+
+        assertThat( target ).isNotNull();
+        assertThat( target.getProp() ).isNotNull();
+        assertThat( target.getProp() ).containsExactly( entry( "test", 5L ) );
+    }
+
     @ProcessorTest
     @WithClasses( SourceTypeHasMultipleTypeVarBothGenericMapper.class )
     public void testGenericSourceTypeVarBothGeneric() {

processor/src/test/java/org/mapstruct/ap/test/selection/methodgenerics/multiple/ReturnTypeHasMultipleTypeVarBothArgumentsFlippedGenericMapper.java

@@ -0,0 +1,76 @@
+/*
+ * 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.methodgenerics.multiple;
+
+import java.util.HashMap;
+import java.util.Map;
+
+import org.mapstruct.Mapper;
+import org.mapstruct.factory.Mappers;
+
+/**
+ * @author Sjaak Derksen
+ */
+@Mapper
+public interface ReturnTypeHasMultipleTypeVarBothArgumentsFlippedGenericMapper {
+
+    ReturnTypeHasMultipleTypeVarBothArgumentsFlippedGenericMapper INSTANCE =
+        Mappers.getMapper( ReturnTypeHasMultipleTypeVarBothArgumentsFlippedGenericMapper.class );
+
+    Target toTarget(Source source);
+
+    default <U, T> HashMap<T, U> toMap( Pair<T, U> entry) {
+        HashMap<T, U> result = new HashMap<>(  );
+        result.put( entry.first, entry.second );
+        return result;
+    }
+
+    class Source {
+
+        private Pair<String, Long> prop;
+
+        public Source(Pair<String, Long> prop) {
+            this.prop = prop;
+        }
+
+        public Pair<String, Long> getProp() {
+            return prop;
+        }
+    }
+
+    class Target {
+
+        private Map<String, Long> prop;
+
+        public Map<String, Long> getProp() {
+            return prop;
+        }
+
+        public Target setProp(Map<String, Long> prop) {
+            this.prop = prop;
+            return this;
+        }
+    }
+
+    class Pair<T, U> {
+        private final T first;
+        private final U second;
+
+        public Pair(T first, U second) {
+            this.first = first;
+            this.second = second;
+        }
+
+        public T getFirst() {
+            return first;
+        }
+
+        public U getSecond() {
+            return second;
+        }
+    }
+
+}

processor/src/test/java/org/mapstruct/ap/test/selection/methodgenerics/objectfactory/ObjectFactoryMapper.java

@@ -0,0 +1,61 @@
+/*
+ * Copyright MapStruct Authors.
+ *
+ * Licensed under the Apache License version 2.0, available at http://www.apache.org/licenses/LICENSE-2.0
+ */
+package org.mapstruct.ap.test.selection.methodgenerics.objectfactory;
+
+import org.mapstruct.Mapper;
+import org.mapstruct.ObjectFactory;
+import org.mapstruct.TargetType;
+import org.mapstruct.factory.Mappers;
+
+@Mapper
+public interface ObjectFactoryMapper {
+
+    ObjectFactoryMapper INSTANCE = Mappers.getMapper( ObjectFactoryMapper.class );
+
+    TargetA toTarget(SourceA source);
+
+    @ObjectFactory
+    default <T extends Target, S extends Source> T createTarget(S source, @TargetType Class<T> targetType) {
+        if ( source.isA() ) {
+            return (T) new TargetA();
+        }
+        return (T) new TargetB();
+    }
+
+    abstract class Source {
+        public abstract boolean isA();
+    }
+
+    class SourceA extends Source {
+        @Override
+        public boolean isA() {
+            return true;
+        }
+    }
+
+    class SourceB extends Source {
+        @Override
+        public boolean isA() {
+            return false;
+        }
+    }
+
+    abstract class Target {
+    }
+
+    class TargetA extends Target {
+
+        private TargetA() {
+        }
+    }
+
+    class TargetB extends Target {
+
+        private TargetB() {
+        }
+    }
+
+}

processor/src/test/java/org/mapstruct/ap/test/selection/methodgenerics/objectfactory/ObjectFactoryTest.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.selection.methodgenerics.objectfactory;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import org.mapstruct.ap.testutil.IssueKey;
+import org.mapstruct.ap.testutil.ProcessorTest;
+import org.mapstruct.ap.testutil.WithClasses;
+
+public class ObjectFactoryTest {
+
+    @IssueKey( "2463" )
+    @ProcessorTest
+    @WithClasses(  ObjectFactoryMapper.class )
+    public void testSelectionOfFactoryMethod() {
+
+        ObjectFactoryMapper.SourceA source = new ObjectFactoryMapper.SourceA();
+
+        ObjectFactoryMapper.Target target = ObjectFactoryMapper.INSTANCE.toTarget( source );
+
+        assertThat( target ).isNotNull();
+        assertThat( target ).isInstanceOf( ObjectFactoryMapper.TargetA.class );
+    }
+}