#1338 Always determine collection argument type when searching for adder

If the Collection type is not actually generic it has no type parameters.
However, it's type argument can be determined.
One such list exists in protobuf (ProtocolStringList)

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

@@ -51,6 +51,8 @@ import org.mapstruct.ap.internal.util.accessor.Accessor;
 import org.mapstruct.ap.internal.util.accessor.ExecutableElementAccessor;
 import org.mapstruct.ap.spi.BuilderInfo;
 
+import static org.mapstruct.ap.internal.util.Collections.first;
+
 /**
  * Represents (a reference to) the type of a bean property, parameter etc. Types are managed per generated source file.
  * Each type corresponds to a {@link TypeMirror}, i.e. there are different instances for e.g. {@code Set<String>} and
@@ -578,23 +580,21 @@ public class Type extends ModelElement implements Comparable<Type> {
         if ( collectionProperty.isCollectionType ) {
 
             // this is a collection, so this can be done always
-            if ( !collectionProperty.getTypeParameters().isEmpty() ) {
-                // there's only one type arg to a collection
-                TypeMirror typeArg = collectionProperty.getTypeParameters().get( 0 ).getTypeBound().getTypeMirror();
-                // now, look for a method that
-                // 1) starts with add,
-                // 2) and has typeArg as one and only arg
-                List<Accessor> adderList = getAdders();
-                for ( Accessor adder : adderList ) {
-                    ExecutableElement executable = adder.getExecutable();
-                    if ( executable == null ) {
-                        // it should not be null, but to be safe
-                        continue;
-                    }
-                    VariableElement arg = executable.getParameters().get( 0 );
-                    if ( typeUtils.isSameType( arg.asType(), typeArg ) ) {
-                        candidates.add( adder );
-                    }
+            TypeMirror typeArg = first( collectionProperty.determineTypeArguments( Iterable.class ) ).getTypeBound()
+                .getTypeMirror();
+            // now, look for a method that
+            // 1) starts with add,
+            // 2) and has typeArg as one and only arg
+            List<Accessor> adderList = getAdders();
+            for ( Accessor adder : adderList ) {
+                ExecutableElement executable = adder.getExecutable();
+                if ( executable == null ) {
+                    // it should not be null, but to be safe
+                    continue;
+                }
+                VariableElement arg = executable.getParameters().get( 0 );
+                if ( typeUtils.isSameType( arg.asType(), typeArg ) ) {
+                    candidates.add( adder );
                 }
             }
         }

processor/src/test/java/org/mapstruct/ap/test/bugs/_1338/Issue1338Mapper.java

@@ -0,0 +1,34 @@
+/**
+ *  Copyright 2012-2017 Gunnar Morling (http://www.gunnarmorling.de/)
+ *  and/or other contributors as indicated by the @authors tag. See the
+ *  copyright.txt file in the distribution for a full listing of all
+ *  contributors.
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License");
+ *  you may not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS,
+ *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ */
+package org.mapstruct.ap.test.bugs._1338;
+
+import org.mapstruct.CollectionMappingStrategy;
+import org.mapstruct.Mapper;
+import org.mapstruct.factory.Mappers;
+
+/**
+ * @author Filip Hrisafov
+ */
+@Mapper(collectionMappingStrategy = CollectionMappingStrategy.ADDER_PREFERRED)
+public interface Issue1338Mapper {
+
+    Issue1338Mapper INSTANCE = Mappers.getMapper( Issue1338Mapper.class );
+
+    Target map(Source source);
+}

processor/src/test/java/org/mapstruct/ap/test/bugs/_1338/Issue1338Test.java

@@ -0,0 +1,53 @@
+/**
+ *  Copyright 2012-2017 Gunnar Morling (http://www.gunnarmorling.de/)
+ *  and/or other contributors as indicated by the @authors tag. See the
+ *  copyright.txt file in the distribution for a full listing of all
+ *  contributors.
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License");
+ *  you may not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS,
+ *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ */
+package org.mapstruct.ap.test.bugs._1338;
+
+import java.util.Arrays;
+
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.mapstruct.ap.testutil.IssueKey;
+import org.mapstruct.ap.testutil.WithClasses;
+import org.mapstruct.ap.testutil.runner.AnnotationProcessorTestRunner;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.atIndex;
+
+/**
+ * @author Filip Hrisafov
+ */
+@RunWith(AnnotationProcessorTestRunner.class)
+@IssueKey("1338")
+@WithClasses({
+    Issue1338Mapper.class,
+    Source.class,
+    Target.class
+})
+public class Issue1338Test {
+
+    @Test
+    public void shouldCorrectlyUseAdder() {
+        Target target = Issue1338Mapper.INSTANCE.map( new Source( Arrays.asList( "first", "second" ) ) );
+
+        assertThat( target )
+            .extracting( "properties" )
+            .contains( Arrays.asList( "first", "second" ), atIndex( 0 ) );
+
+    }
+}

processor/src/test/java/org/mapstruct/ap/test/bugs/_1338/Source.java

@@ -0,0 +1,37 @@
+/**
+ *  Copyright 2012-2017 Gunnar Morling (http://www.gunnarmorling.de/)
+ *  and/or other contributors as indicated by the @authors tag. See the
+ *  copyright.txt file in the distribution for a full listing of all
+ *  contributors.
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License");
+ *  you may not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS,
+ *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ */
+package org.mapstruct.ap.test.bugs._1338;
+
+import java.util.List;
+
+/**
+ * @author Filip Hrisafov
+ */
+public class Source {
+
+    private final List<String> properties;
+
+    public Source(List<String> properties) {
+        this.properties = properties;
+    }
+
+    public List<String> getProperties() {
+        return properties;
+    }
+}

processor/src/test/java/org/mapstruct/ap/test/bugs/_1338/Target.java

@@ -0,0 +1,44 @@
+/**
+ *  Copyright 2012-2017 Gunnar Morling (http://www.gunnarmorling.de/)
+ *  and/or other contributors as indicated by the @authors tag. See the
+ *  copyright.txt file in the distribution for a full listing of all
+ *  contributors.
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License");
+ *  you may not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS,
+ *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ */
+package org.mapstruct.ap.test.bugs._1338;
+
+import java.util.ArrayList;
+
+/**
+ * @author Filip Hrisafov
+ */
+public class Target {
+
+    private StringList properties = new StringList();
+
+    public void addProperty(String property) {
+        properties.add( property );
+    }
+
+    public void setProperties(StringList properties) {
+        throw new IllegalStateException( "Setter is there just as a marker it should not be used" );
+    }
+
+    public static class StringList extends ArrayList<String> {
+
+        private StringList() {
+            // Constructor is private so we get a compile error if we try to instantiate it
+        }
+    }
+}