Handle unexpected merge results

It is possible that a git work tree is dirty directly after the clone
of a repository, eg. when files are not changed correctly due to bogous
.gitattribute files (though this is just a guess). In these cases a
merge might fail due to these dirty files and not due to merge
conflicts. Without this change such results lead to null pointer
exceptions, because result.getConflicts() is null.

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

@@ -113,5 +113,4 @@ public class AbstractGitCommandTestBase extends ZippedRepositoryTestBase
 
   /** Field description */
   private GitContext context;
-  private ScmTransportProtocol scmTransportProtocol;
 }

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

@@ -12,16 +12,23 @@ import org.eclipse.jgit.lib.Repository;
 import org.eclipse.jgit.revwalk.RevCommit;
 import org.junit.Rule;
 import org.junit.Test;
+import org.junit.jupiter.api.Assertions;
 import sonia.scm.NoChangesMadeException;
 import sonia.scm.NotFoundException;
+import sonia.scm.repository.GitWorkdirFactory;
 import sonia.scm.repository.Person;
 import sonia.scm.repository.api.MergeCommandResult;
 import sonia.scm.repository.api.MergeStrategy;
 import sonia.scm.repository.util.WorkdirProvider;
 import sonia.scm.user.User;
 
+import java.io.BufferedWriter;
+import java.io.File;
+import java.io.FileWriter;
 import java.io.IOException;
 import java.util.List;
+import java.util.function.Consumer;
+import java.util.function.Function;
 
 import static org.assertj.core.api.Assertions.assertThat;
 
@@ -163,11 +170,35 @@ public class GitMergeCommandTest extends AbstractGitCommandTestBase {
     assertThat(mergeCommandResult.getFilesWithConflict()).containsExactly("a.txt");
   }
 
+  @Test
+  public void shouldHandleUnexpectedMergeResults() {
+    GitMergeCommand command = createCommand(git -> {
+      FileWriter fw = null;
+      try {
+        fw = new FileWriter(new File(git.getRepository().getWorkTree(), "b.txt"), true);
+        BufferedWriter bw = new BufferedWriter(fw);
+        bw.write("change");
+        bw.newLine();
+        bw.close();
+      } catch (IOException e) {
+        e.printStackTrace();
+      }
+    });
+    MergeCommandRequest request = new MergeCommandRequest();
+    request.setBranchToMerge("mergeable");
+    request.setTargetBranch("master");
+    request.setMergeStrategy(MergeStrategy.MERGE_COMMIT);
+    request.setAuthor(new Person("Dirk Gently", "dirk@holistic.det"));
+    request.setMessageTemplate("simple");
+
+    Assertions.assertThrows(UnexpectedMergeResultException.class, () -> command.merge(request));
+  }
+
   @Test
   public void shouldTakeAuthorFromSubjectIfNotSet() throws IOException, GitAPIException {
     SimplePrincipalCollection principals = new SimplePrincipalCollection();
     principals.add("admin", REALM);
-    principals.add( new User("dirk", "Dirk Gently", "dirk@holistic.det"), REALM);
+    principals.add(new User("dirk", "Dirk Gently", "dirk@holistic.det"), REALM);
     shiro.setSubject(
       new Subject.Builder()
         .principals(principals)
@@ -364,6 +395,20 @@ public class GitMergeCommandTest extends AbstractGitCommandTestBase {
   }
 
   private GitMergeCommand createCommand() {
-    return new GitMergeCommand(createContext(), repository, new SimpleGitWorkdirFactory(new WorkdirProvider()));
+    return createCommand(git -> {
+    });
+  }
+
+  private GitMergeCommand createCommand(Consumer<Git> interceptor) {
+    return new GitMergeCommand(createContext(), repository, new SimpleGitWorkdirFactory(new WorkdirProvider())) {
+      @Override
+      <R, W extends GitCloneWorker<R>> R inClone(Function<Git, W> workerSupplier, GitWorkdirFactory workdirFactory, String initialBranch) {
+        Function<Git, W> interceptedWorkerSupplier = git -> {
+          interceptor.accept(git);
+          return workerSupplier.apply(git);
+        };
+        return super.inClone(interceptedWorkerSupplier, workdirFactory, initialBranch);
+      }
+    };
   }
 }