mapstruct#3747 Do not generate redundant if condition with constructo…

…r mapping and RETURN_DEFAULT null value mapping strategy

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

@@ -116,7 +116,7 @@
                 </#list>
             </#if>
         </#list>
-    <#else>
+    <#elseif !propertyMappingsByParameter(sourceParameters[0]).empty>
         <#if mapNullToDefault>if ( <@includeModel object=getPresenceCheckByParameter(sourceParameters[0]) /> ) {</#if>
         <#list propertyMappingsByParameter(sourceParameters[0]) as propertyMapping>
             <@includeModel object=propertyMapping targetBeanName=resultName existingInstanceMapping=existingInstanceMapping defaultValueAssignment=propertyMapping.defaultValueAssignment/>

processor/src/test/java/org/mapstruct/ap/test/bugs/_3747/Issue3747Mapper.java

@@ -0,0 +1,42 @@
+/*
+ * 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._3747;
+
+import org.mapstruct.Mapper;
+import org.mapstruct.NullValueMappingStrategy;
+
+/**
+ * @author Filip Hrisafov
+ */
+@Mapper(nullValueMappingStrategy = NullValueMappingStrategy.RETURN_DEFAULT)
+public interface Issue3747Mapper {
+
+    Target map(Source source);
+
+    class Source {
+        private final String value;
+
+        public Source(String value) {
+            this.value = value;
+        }
+
+        public String getValue() {
+            return value;
+        }
+    }
+
+    class Target {
+        private final String value;
+
+        public Target(String value) {
+            this.value = value;
+        }
+
+        public String getValue() {
+            return value;
+        }
+    }
+}

processor/src/test/java/org/mapstruct/ap/test/bugs/_3747/Issue3747Test.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.bugs._3747;
+
+import org.junit.jupiter.api.extension.RegisterExtension;
+import org.mapstruct.ap.testutil.IssueKey;
+import org.mapstruct.ap.testutil.ProcessorTest;
+import org.mapstruct.ap.testutil.WithClasses;
+import org.mapstruct.ap.testutil.runner.GeneratedSource;
+
+/**
+ * @author Filip Hrisafov
+ */
+@IssueKey("3747")
+@WithClasses(Issue3747Mapper.class)
+class Issue3747Test {
+
+    @RegisterExtension
+    final GeneratedSource generatedSource = new GeneratedSource();
+
+    @ProcessorTest
+    void shouldNotGenerateObsoleteCode() {
+        generatedSource.addComparisonToFixtureFor( Issue3747Mapper.class );
+    }
+}

processor/src/test/resources/fixtures/org/mapstruct/ap/test/bugs/_3747/Issue3747MapperImpl.java

@@ -0,0 +1,29 @@
+/*
+ * 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._3747;
+
+import javax.annotation.processing.Generated;
+
+@Generated(
+    value = "org.mapstruct.ap.MappingProcessor",
+    date = "2024-11-03T12:50:02+0100",
+    comments = "version: , compiler: javac, environment: Java 21.0.3 (N/A)"
+)
+public class Issue3747MapperImpl implements Issue3747Mapper {
+
+    @Override
+    public Target map(Source source) {
+
+        String value = null;
+        if ( source != null ) {
+            value = source.getValue();
+        }
+
+        Target target = new Target( value );
+
+        return target;
+    }
+}