#410 do not instantiate a field (referenced mapper) when not used, e.g. only static referenced

processor/src/main/java/org/mapstruct/ap/model/AnnotationMapperReference.java

@@ -33,8 +33,8 @@ public class AnnotationMapperReference extends MapperReference {
 
     private final Annotation annotation;
 
-    public AnnotationMapperReference(Type type, String variableName, Annotation annotation) {
+    public AnnotationMapperReference(Type type, String variableName, Annotation annotation, boolean isUsed) {
-        super( type, variableName );
+        super( type, variableName, isUsed );
         this.annotation = annotation;
     }
 

processor/src/main/java/org/mapstruct/ap/model/AssignmentFactory.java

@@ -96,6 +96,7 @@ public class AssignmentFactory {
     private static MapperReference findMapperReference( List<MapperReference> mapperReferences, SourceMethod method ) {
         for ( MapperReference ref : mapperReferences ) {
             if ( ref.getType().equals( method.getDeclaringMapper() ) ) {
+                ref.setUsed( !method.isStatic() );
                 return ref;
             }
         }

processor/src/main/java/org/mapstruct/ap/model/Decorator.java

@@ -70,7 +70,7 @@ public class Decorator extends GeneratedType {
             mapperElement.getKind() == ElementKind.INTERFACE ? mapperElement.getSimpleName().toString() : null,
             methods,
             Arrays.asList(
-                new Field( typeFactory.getType( mapperElement ), "delegate" ),
+                new Field( typeFactory.getType( mapperElement ), "delegate", true ),
                 new DecoratorConstructor(
                     mapperElement.getSimpleName().toString() + IMPLEMENTATION_SUFFIX,
                     mapperElement.getSimpleName().toString() + "Impl_",

processor/src/main/java/org/mapstruct/ap/model/Field.java

@@ -33,10 +33,17 @@ public class Field extends ModelElement {
 
     private final Type type;
     private final String variableName;
+    private boolean used;
 
+    public Field(Type type, String variableName, boolean used) {
+        this.type = type;
+        this.variableName = variableName;
+        this.used = used;
+    }
     public Field(Type type, String variableName) {
         this.type = type;
         this.variableName = variableName;
+        this.used = false;
     }
 
     /**
@@ -51,7 +58,7 @@ public class Field extends ModelElement {
     /**
      * Returns the variable name of this field.
      *
-     * @return the variable name of this referfieldence
+     * @return the variable name of this reference
      */
     public String getVariableName() {
         return variableName;
@@ -61,4 +68,21 @@ public class Field extends ModelElement {
     public Set<Type> getImportTypes() {
         return Collections.emptySet();
     }
+
+    /**
+     * indicates whether the field is indeed used
+     * @return true when field is used
+     */
+    public boolean isUsed() {
+        return used;
+    }
+
+    /**
+     * sets the field as being used
+     * @param isUsed must be true when being used.
+     */
+    public void setUsed(boolean isUsed) {
+        this.used = isUsed;
+    }
+
 }

processor/src/main/java/org/mapstruct/ap/model/MapperReference.java

@@ -30,4 +30,8 @@ public abstract class MapperReference extends Field {
     public MapperReference(Type type, String variableName) {
         super( type, variableName );
     }
+
+    public MapperReference(Type type, String variableName, boolean isUsed) {
+        super( type, variableName, isUsed );
+    }
 }

processor/src/main/java/org/mapstruct/ap/processor/AnnotationBasedComponentModelProcessor.java

@@ -76,7 +76,8 @@ public abstract class AnnotationBasedComponentModelProcessor implements ModelEle
         return new AnnotationMapperReference(
             originalReference.getType(),
             originalReference.getVariableName(),
-            getMapperReferenceAnnotation()
+            getMapperReferenceAnnotation(),
+            originalReference.isUsed()
         );
     }
 

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

@@ -459,6 +459,7 @@ public class MappingResolverImpl implements MappingResolver {
         private MapperReference findMapperReference(SourceMethod method) {
             for ( MapperReference ref : mapperReferences ) {
                 if ( ref.getType().equals( method.getDeclaringMapper() ) ) {
+                    ref.setUsed( !method.isStatic() );
                     return ref;
                 }
             }

processor/src/main/resources/org.mapstruct.ap.model.AnnotationMapperReference.ftl

@@ -18,5 +18,5 @@
      limitations under the License.
 
 -->
-<#nt><@includeModel object=annotation/>
+<#if used><#nt><@includeModel object=annotation/>
-private <@includeModel object=type/> ${variableName};
+private <@includeModel object=type/> ${variableName};</#if>

processor/src/main/resources/org.mapstruct.ap.model.DefaultMapperReference.ftl

@@ -18,4 +18,4 @@
      limitations under the License.
 
 -->
-private final <@includeModel object=type/> ${variableName} = <#if annotatedMapper>Mappers.getMapper( <@includeModel object=type/>.class );<#else>new <@includeModel object=type/>();</#if>
+<#if used>private final <@includeModel object=type/> ${variableName} = <#if annotatedMapper>Mappers.getMapper( <@includeModel object=type/>.class );<#else>new <@includeModel object=type/>();</#if></#if>

processor/src/main/resources/org.mapstruct.ap.model.Field.ftl

@@ -18,4 +18,4 @@
      limitations under the License.
 
 -->
-private final <@includeModel object=type/> ${variableName};
+<#if used>private final <@includeModel object=type/> ${variableName};</#if>

processor/src/test/java/org/mapstruct/ap/test/references/statics/CustomMapper.java

@@ -22,9 +22,11 @@ package org.mapstruct.ap.test.references.statics;
  *
  * @author Sjaak Derksen
  */
-//@CHECKSTYLE:OFF
 public class CustomMapper {
 
+    private CustomMapper() {
+    }
+
     public static Category toCategory(float in) {
 
         if ( in < 2.5 ) {