Let a merge return the number of merge conflicts.

src/de/uni_passau/fim/gitwrapper/DefaultMergeStrategy.java

 package de.uni_passau.fim.gitwrapper;
 
-import java.util.Optional;
-
 import de.uni_passau.fim.processexecutor.ProcessExecutor;
 
+import java.util.Optional;
+
 /**
  * A {@link MergeStrategy} representing the default 'git merge' merge implementation.
  */
@@ -23,9 +23,9 @@ public class DefaultMergeStrategy implements MergeStrategy {
     }
 
     @Override
-    public Optional<Status> merge(Reference left, Reference right) {
+    public Optional<Integer> merge(Reference left, Reference right) {
         Optional<ProcessExecutor.ExecRes> mergeBase = repo.getGit().exec(repo.getDir(), "merge", "-n", "-q", right.getId());
-        return mergeBase.flatMap(res -> repo.getStatus());
+        return mergeBase.flatMap(res -> repo.getStatus().map(stat -> stat.unmerged.size()));
     }
 
     @Override

src/de/uni_passau/fim/gitwrapper/MergeStrategy.java

@@ -12,7 +12,7 @@ public interface MergeStrategy {
      *         the left parent of the merge
      * @param right
      *         the right parent of the merge
-     * @return optionally the {@link Status} of the working directory after the merge, if the merge was successful
+     * @return optionally the number of merge conflicts after the merge, if the merge was successful
      */
-    Optional<Status> merge(Reference left, Reference right);
+    Optional<Integer> merge(Reference left, Reference right);
 }

src/de/uni_passau/fim/gitwrapper/Reference.java

 package de.uni_passau.fim.gitwrapper;
 
+import de.uni_passau.fim.processexecutor.ProcessExecutor;
+
 import java.util.Arrays;
 import java.util.List;
 import java.util.Objects;
@@ -8,8 +10,6 @@ import java.util.function.Function;
 import java.util.logging.Logger;
 import java.util.stream.Collectors;
 
-import de.uni_passau.fim.processexecutor.ProcessExecutor;
-
 /**
  * A git object referencing a tree-ish object.
  *
@@ -92,9 +92,9 @@ public abstract class Reference {
      *         the {@link Reference} to merge
      * @param strategy
      *         the {@link MergeStrategy} to use for merging
-     * @return the {@link Status} of the working directory after the merge
+     * @return optionally the number of merge conflicts after the merge, if the merge was successful
      */
-    public Optional<Status> merge(Reference other, MergeStrategy strategy) {
+    public Optional<Integer> merge(Reference other, MergeStrategy strategy) {
         if (!repo.checkout(this)) {
             return Optional.empty();
         }