implement fast forward if possible

scm-core/src/main/java/sonia/scm/repository/api/MergeCommandResult.java

@@ -13,6 +13,7 @@ import static java.util.Collections.unmodifiableCollection;
  */
 public class MergeCommandResult {
   private final Collection<String> filesWithConflict;
+  private boolean aborted = false;
 
   private MergeCommandResult(Collection<String> filesWithConflict) {
     this.filesWithConflict = filesWithConflict;
@@ -41,4 +42,12 @@ public class MergeCommandResult {
   public Collection<String> getFilesWithConflict() {
     return unmodifiableCollection(filesWithConflict);
   }
+
+  public boolean isAborted() {
+    return aborted;
+  }
+
+  public void setAborted(boolean aborted) {
+    this.aborted = aborted;
+  }
 }

scm-plugins/scm-git-plugin/src/main/java/sonia/scm/repository/spi/GitMergeCommand.java

@@ -3,7 +3,6 @@ package sonia.scm.repository.spi;
 import com.google.common.base.Strings;
 import com.google.common.collect.ImmutableSet;
 import org.eclipse.jgit.api.Git;
-import org.eclipse.jgit.api.MergeCommand.FastForwardMode;
 import org.eclipse.jgit.api.MergeResult;
 import org.eclipse.jgit.api.errors.GitAPIException;
 import org.eclipse.jgit.lib.ObjectId;
@@ -20,6 +19,7 @@ import sonia.scm.repository.api.MergeStrategy;
 
 import java.io.IOException;
 import java.text.MessageFormat;
+import java.util.Collections;
 import java.util.Set;
 
 public class GitMergeCommand extends AbstractGitCommand implements MergeCommand {
@@ -93,10 +93,17 @@ public class GitMergeCommand extends AbstractGitCommand implements MergeCommand
     @Override
     MergeCommandResult run() throws IOException {
       MergeResult result = doMergeInClone();
+
       if (result.getMergeStatus().isSuccessful()) {
+        if (mergeStrategy != MergeStrategy.FAST_FORWARD_IF_POSSIBLE) {
           doCommit();
+        }
         push();
         return MergeCommandResult.success();
+      } else if (mergeStrategy == MergeStrategy.FAST_FORWARD_IF_POSSIBLE) {
+        MergeCommandResult failure = MergeCommandResult.failure(Collections.emptyList());
+        failure.setAborted(true);
+        return failure;
       } else {
         return analyseFailure(result);
       }
@@ -113,8 +120,10 @@ public class GitMergeCommand extends AbstractGitCommand implements MergeCommand
 
         if (mergeStrategy == MergeStrategy.SQUASH) {
           mergeCommand.setSquash(true);
+        } else if (mergeStrategy == MergeStrategy.FAST_FORWARD_IF_POSSIBLE) {
+          mergeCommand.setFastForward(org.eclipse.jgit.api.MergeCommand.FastForwardMode.FF_ONLY);
         } else {
-          mergeCommand.setFastForward(FastForwardMode.NO_FF);
+          mergeCommand.setFastForward(org.eclipse.jgit.api.MergeCommand.FastForwardMode.NO_FF);
         }
 
         result = mergeCommand.call();

scm-plugins/scm-git-plugin/src/test/java/sonia/scm/repository/spi/GitMergeCommandTest.java

@@ -262,6 +262,31 @@ public class GitMergeCommandTest extends AbstractGitCommandTestBase {
     assertThat(changes.size()).isEqualTo(3);
   }
 
+
+  @Test
+  public void shouldMergeWithFastForward() throws IOException, GitAPIException {
+    Repository repository = createContext().open();
+
+    ObjectId featureBranchHead = new Git(repository).log().add(repository.resolve("squash")).setMaxCount(1).call().iterator().next().getId();
+
+    GitMergeCommand command = createCommand();
+    MergeCommandRequest request = new MergeCommandRequest();
+    request.setBranchToMerge("squash");
+    request.setTargetBranch("master");
+    request.setMergeStrategy(MergeStrategy.FAST_FORWARD_IF_POSSIBLE);
+    request.setAuthor(new Person("Dirk Gently", "dirk@holistic.det"));
+
+    MergeCommandResult mergeCommandResult = command.merge(request);
+
+    assertThat(mergeCommandResult.isSuccess()).isTrue();
+
+    Iterable<RevCommit> commits = new Git(repository).log().add(repository.resolve("master")).setMaxCount(1).call();
+    RevCommit mergeCommit = commits.iterator().next();
+    PersonIdent mergeAuthor = mergeCommit.getAuthorIdent();
+    assertThat(mergeAuthor.getName()).isEqualTo("Philip J Fry");
+    assertThat(mergeCommit.getId()).isEqualTo(featureBranchHead);
+  }
+
   @Test(expected = NotFoundException.class)
   public void shouldHandleNotExistingSourceBranchInMerge() {
     GitMergeCommand command = createCommand();