Let merges without effect throw an exception

scm-core/src/main/java/sonia/scm/repository/spi/MergeCommand.java

@@ -7,6 +7,12 @@ import sonia.scm.repository.api.MergeStrategy;
 import java.util.Set;
 
 public interface MergeCommand {
+  /**
+   * Executes the merge.
+   * @param request The parameters specifying the merge.
+   * @return Result holding either the new revision or a list of conflicting files.
+   * @throws sonia.scm.NoChangesMadeException If the merge neither had a conflict nor made any change.
+   */
   MergeCommandResult merge(MergeCommandRequest request);
 
   MergeDryRunCommandResult dryRun(MergeCommandRequest request);

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

@@ -186,6 +186,10 @@ class AbstractGitCommand
       return context;
     }
 
+    sonia.scm.repository.Repository getRepository() {
+      return repository;
+    }
+
     void checkOutBranch(String branchName) throws IOException {
       try {
         clone.checkout().setName(branchName).call();

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

@@ -4,6 +4,7 @@ import org.eclipse.jgit.api.Git;
 import org.eclipse.jgit.api.MergeCommand;
 import org.eclipse.jgit.api.MergeResult;
 import org.eclipse.jgit.revwalk.RevCommit;
+import sonia.scm.NoChangesMadeException;
 import sonia.scm.repository.Repository;
 import sonia.scm.repository.api.MergeCommandResult;
 
@@ -26,7 +27,7 @@ class GitMergeCommit extends GitMergeStrategy {
     MergeResult result = doMergeInClone(mergeCommand);
 
     if (result.getMergeStatus().isSuccessful()) {
-      Optional<RevCommit> revCommit = doCommit();
+      RevCommit revCommit = doCommit().orElseThrow(() -> new NoChangesMadeException(getRepository()));
       push();
       return MergeCommandResult.success(extractRevisionFromRevCommit(revCommit));
     } else {

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

@@ -4,6 +4,7 @@ import org.eclipse.jgit.api.Git;
 import org.eclipse.jgit.api.MergeCommand;
 import org.eclipse.jgit.api.MergeResult;
 import org.eclipse.jgit.revwalk.RevCommit;
+import sonia.scm.NoChangesMadeException;
 import sonia.scm.repository.Repository;
 import sonia.scm.repository.api.MergeCommandResult;
 
@@ -26,7 +27,7 @@ class GitMergeWithSquash extends GitMergeStrategy {
     MergeResult result = doMergeInClone(mergeCommand);
 
     if (result.getMergeStatus().isSuccessful()) {
-      Optional<RevCommit> revCommit = doCommit();
+      RevCommit revCommit = doCommit().orElseThrow(() -> new NoChangesMadeException(getRepository()));
       push();
       return MergeCommandResult.success(extractRevisionFromRevCommit(revCommit));
     } else {

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

@@ -6,10 +6,7 @@ import java.util.Optional;
 
 public class GitRevisionExtractor {
 
-  static String extractRevisionFromRevCommit(Optional<RevCommit> revCommit) {
+  static String extractRevisionFromRevCommit(RevCommit revCommit) {
-    if (revCommit.isPresent()) {
+    return revCommit.toString().split(" ")[1];
-      return revCommit.get().toString().split(" ")[1];
-    }
-    return "";
   }
 }

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

@@ -12,6 +12,7 @@ import org.eclipse.jgit.lib.Repository;
 import org.eclipse.jgit.revwalk.RevCommit;
 import org.junit.Rule;
 import org.junit.Test;
+import sonia.scm.NoChangesMadeException;
 import sonia.scm.NotFoundException;
 import sonia.scm.repository.Person;
 import sonia.scm.repository.api.MergeCommandResult;
@@ -106,7 +107,7 @@ public class GitMergeCommandTest extends AbstractGitCommandTestBase {
     assertThat(mergeCommit.getParent(1).name()).isEqualTo("d81ad6c63d7e2162308d69637b339dedd1d9201c");
   }
 
-  @Test
+  @Test(expected = NoChangesMadeException.class)
   public void shouldNotMergeTwice() throws IOException, GitAPIException {
     GitMergeCommand command = createCommand();
     MergeCommandRequest request = new MergeCommandRequest();
@@ -120,15 +121,9 @@ public class GitMergeCommandTest extends AbstractGitCommandTestBase {
     assertThat(mergeCommandResult.isSuccess()).isTrue();
 
     Repository repository = createContext().open();
-    ObjectId firstMergeCommit = new Git(repository).log().add(repository.resolve("master")).setMaxCount(1).call().iterator().next().getId();
+    new Git(repository).log().add(repository.resolve("master")).setMaxCount(1).call().iterator().next().getId();
 
-    MergeCommandResult secondMergeCommandResult = command.merge(request);
+    command.merge(request);
-
-    assertThat(secondMergeCommandResult.isSuccess()).isTrue();
-
-    ObjectId secondMergeCommit = new Git(repository).log().add(repository.resolve("master")).setMaxCount(1).call().iterator().next().getId();
-
-    assertThat(secondMergeCommit).isEqualTo(firstMergeCommit);
   }
 
   @Test

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

@@ -14,17 +14,8 @@ public class GitRevisionExtractorTest {
   @Test
   void shouldReturnRevisionFromRevCommit() {
     RevCommit revCommit = mock(RevCommit.class);
-    Optional<RevCommit> optionalRevCommit = Optional.of(revCommit);
     when(revCommit.toString()).thenReturn("commit 123456abcdef -t 4561");
-    String revision = GitRevisionExtractor.extractRevisionFromRevCommit(optionalRevCommit);
+    String revision = GitRevisionExtractor.extractRevisionFromRevCommit(revCommit);
     assertThat(revision).isEqualTo("123456abcdef");
   }
-
-  @Test
-  void shouldReturnEmptyStringIfRevCommitNotAvailable() {
-    Optional<RevCommit> optionalRevCommit = Optional.empty();
-    String revision = GitRevisionExtractor.extractRevisionFromRevCommit(optionalRevCommit);
-    assertThat(revision).isEqualTo("");
-  }
-
 }