#2937 Fix conditional check for collections with adders

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

@@ -62,6 +62,7 @@
 -->
 <#macro _assignment assignmentToUse>
    <@includeModel object=assignmentToUse
+        presenceCheck=ext.presenceCheck
         targetBeanName=ext.targetBeanName
                existingInstanceMapping=ext.existingInstanceMapping
                targetReadAccessorName=ext.targetReadAccessorName

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

@@ -7,4 +7,5 @@
 -->
 <#-- @ftlvariable name="" type="org.mapstruct.ap.internal.model.MethodReferencePresenceCheck" -->
 <@includeModel object=methodReference
+               presenceCheck=true
                targetType=ext.targetType/>

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

@@ -6,4 +6,4 @@
 
 -->
 <#-- @ftlvariable name="" type="org.mapstruct.ap.internal.model.common.SourceRHS" -->
-<#if sourceLoopVarName??>${sourceLoopVarName}<#elseif sourceLocalVarName??>${sourceLocalVarName}<#else>${sourceReference}</#if>
+<#if sourceLoopVarName?? && !ext.presenceCheck??>${sourceLoopVarName}<#elseif sourceLocalVarName??>${sourceLocalVarName}<#else>${sourceReference}</#if>

processor/src/test/java/org/mapstruct/ap/test/bugs/_2937/Issue2937Mapper.java

@@ -0,0 +1,59 @@
+/*
+ * 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._2937;
+
+import java.util.ArrayList;
+import java.util.Collection;
+
+import org.mapstruct.CollectionMappingStrategy;
+import org.mapstruct.Condition;
+import org.mapstruct.Mapper;
+import org.mapstruct.factory.Mappers;
+
+/**
+ * @author Filip Hrisafov
+ */
+@Mapper(collectionMappingStrategy = CollectionMappingStrategy.ADDER_PREFERRED)
+public interface Issue2937Mapper {
+
+    Issue2937Mapper INSTANCE = Mappers.getMapper( Issue2937Mapper.class );
+
+    Target map(Source source);
+
+    @Condition
+    default boolean isApplicable(Collection<?> collection) {
+        return collection == null || collection.size() > 1;
+    }
+
+    class Source {
+        private final Collection<String> names;
+
+        public Source(Collection<String> names) {
+            this.names = names;
+        }
+
+        public Collection<String> getNames() {
+            return names;
+        }
+
+    }
+
+    class Target {
+        private final Collection<String> names;
+
+        public Target() {
+            this.names = new ArrayList<>();
+        }
+
+        public Collection<String> getNames() {
+            return names;
+        }
+
+        public void addName(String name) {
+            this.names.add( name );
+        }
+    }
+}

processor/src/test/java/org/mapstruct/ap/test/bugs/_2937/Issue2937Test.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._2937;
+
+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 static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * @author Filip Hrisafov
+ */
+@IssueKey("2937")
+@WithClasses({
+    Issue2937Mapper.class,
+})
+class Issue2937Test {
+
+    @ProcessorTest
+    void shouldCorrectlyUseConditionalForAdder() {
+        List<String> sourceNames = new ArrayList<>();
+        sourceNames.add( "Tester 1" );
+        Issue2937Mapper.Source source = new Issue2937Mapper.Source( sourceNames );
+        Issue2937Mapper.Target target = Issue2937Mapper.INSTANCE.map( source );
+
+        assertThat( target.getNames() ).isEmpty();
+
+        sourceNames.add( "Tester 2" );
+
+        target = Issue2937Mapper.INSTANCE.map( source );
+
+        assertThat( target.getNames() )
+            .containsExactly( "Tester 1", "Tester 2" );
+    }
+}