#3462 Stream getters should not be treated as alternative setter

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

@@ -821,12 +821,6 @@ public class Type extends ModelElement implements Comparable<Type> {
                     candidate = adderMethod;
                 }
 
-                if ( cmStrategy == CollectionMappingStrategyGem.TARGET_IMMUTABLE
-                    && candidate.getAccessorType() == AccessorType.GETTER ) {
-                    // If the collection mapping strategy is target immutable
-                    // then the getter method cannot be used as a setter
-                    continue;
-                }
             }
             else if ( candidate.getAccessorType() == AccessorType.FIELD  && ( Executables.isFinal( candidate ) ||
                 result.containsKey( targetPropertyName ) ) ) {
@@ -834,6 +828,16 @@ public class Type extends ModelElement implements Comparable<Type> {
                 continue;
             }
 
+            if ( candidate.getAccessorType() == AccessorType.GETTER ) {
+                // When the candidate is a getter then it can't be used in the following cases:
+                // 1. The collection mapping strategy is target immutable
+                // 2. The target type is a stream (streams are immutable)
+                if ( cmStrategy == CollectionMappingStrategyGem.TARGET_IMMUTABLE ||
+                    targetType != null && targetType.isStreamType() ) {
+                    continue;
+                }
+            }
+
             Accessor previousCandidate = result.get( targetPropertyName );
             if ( previousCandidate == null || preferredType == null || ( targetType != null
                 && typeUtils.isAssignable( preferredType.getTypeMirror(), targetType.getTypeMirror() ) ) ) {

processor/src/test/java/org/mapstruct/ap/test/bugs/_3462/Issue3462Mapper.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.bugs._3462;
+
+import java.util.List;
+import java.util.stream.Stream;
+
+import org.mapstruct.Mapper;
+import org.mapstruct.factory.Mappers;
+
+/**
+ * @author Filip Hrisafov
+ */
+@Mapper
+public interface Issue3462Mapper {
+
+    Issue3462Mapper INSTANCE = Mappers.getMapper( Issue3462Mapper.class );
+
+    Target map(Source source);
+
+    class Source {
+        private final List<String> values;
+
+        public Source(List<String> values) {
+            this.values = values;
+        }
+
+        public List<String> getValues() {
+            return values;
+        }
+
+        public Stream<String> getValuesStream() {
+            return values != null ? values.stream() : Stream.empty();
+        }
+    }
+
+    class Target {
+        private List<String> values;
+
+        public List<String> getValues() {
+            return values;
+        }
+
+        public void setValues(List<String> values) {
+            this.values = values;
+        }
+
+        public Stream<String> getValuesStream() {
+            return values != null ? values.stream() : Stream.empty();
+        }
+    }
+
+}

processor/src/test/java/org/mapstruct/ap/test/bugs/_3462/Issue3462Test.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._3462;
+
+import java.util.Arrays;
+
+import org.mapstruct.ap.testutil.IssueKey;
+import org.mapstruct.ap.testutil.ProcessorTest;
+import org.mapstruct.ap.testutil.WithClasses;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * @author Filip Hrisafov
+ */
+@IssueKey("3462")
+@WithClasses(Issue3462Mapper.class)
+class Issue3462Test {
+
+    @ProcessorTest
+    void shouldNotTreatStreamGettersAsAlternativeSetter() {
+
+        Issue3462Mapper.Source source = new Issue3462Mapper.Source( Arrays.asList( "first", "second" ) );
+        Issue3462Mapper.Target target = Issue3462Mapper.INSTANCE.map( source );
+
+        assertThat( target ).isNotNull();
+        assertThat( target.getValues() ).containsExactly( "first", "second" );
+        assertThat( target.getValuesStream() ).containsExactly( "first", "second" );
+
+    }
+}