Fix edge cases in mirror command (#1812)

- The clone of the repository failed, if no master branch had
  been mirrored, because this was what the HEAD was set to, and
  jgit fails with an exception if the HEAD branch does not exist.
- The HEAD branch had to be corrected to an existing branch,
  because otherwise a rejected 'master' branch could not be
  deleted and was synchronized in a second sync if the working
  directory had been cached.

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

@@ -30,10 +30,13 @@ import org.eclipse.jgit.api.Git;
 import org.eclipse.jgit.api.errors.GitAPIException;
 import org.eclipse.jgit.junit.http.AppServer;
 import org.eclipse.jgit.junit.http.SimpleHttpServer;
+import org.eclipse.jgit.lib.Constants;
 import org.eclipse.jgit.lib.ObjectId;
 import org.eclipse.jgit.lib.Ref;
+import org.eclipse.jgit.lib.Repository;
 import org.eclipse.jgit.revwalk.RevObject;
 import org.eclipse.jgit.revwalk.RevWalk;
+import org.junit.After;
 import org.junit.Before;
 import org.junit.Rule;
 import org.junit.Test;
@@ -43,13 +46,17 @@ import sonia.scm.net.GlobalProxyConfiguration;
 import sonia.scm.net.HttpURLConnectionFactory;
 import sonia.scm.repository.GitChangesetConverterFactory;
 import sonia.scm.repository.GitConfig;
+import sonia.scm.repository.GitHeadModifier;
+import sonia.scm.repository.GitUtil;
 import sonia.scm.repository.api.MirrorCommandResult;
 import sonia.scm.repository.api.MirrorFilter;
 import sonia.scm.repository.api.SimpleUsernamePasswordCredential;
 import sonia.scm.repository.work.NoneCachingWorkingCopyPool;
+import sonia.scm.repository.work.SimpleWorkingCopyFactory;
 import sonia.scm.repository.work.WorkdirProvider;
 import sonia.scm.security.GPG;
 import sonia.scm.store.InMemoryConfigurationStoreFactory;
+import sonia.scm.util.IOUtil;
 
 import javax.net.ssl.TrustManager;
 import java.io.File;
@@ -80,9 +87,10 @@ public class GitMirrorCommandTest extends AbstractGitCommandTestBase {
   private final GitTagConverter gitTagConverter = new GitTagConverter(gpg);
 
   private File clone;
+  private File workdirAfterClose;
   private GitMirrorCommand command;
 
-
+  private final GitHeadModifier gitHeadModifier = mock(GitHeadModifier.class);
 
   @Before
   public void bendContextToNewRepository() throws IOException, GitAPIException {
@@ -92,7 +100,9 @@ public class GitMirrorCommandTest extends AbstractGitCommandTestBase {
     GitContext emptyContext = createMirrorContext(clone);
     SimpleGitWorkingCopyFactory workingCopyFactory =
       new SimpleGitWorkingCopyFactory(
-        new NoneCachingWorkingCopyPool(new WorkdirProvider(repositoryLocationResolver)), new SimpleMeterRegistry());
+        new KeepingWorkingCopyPool(new WorkdirProvider(repositoryLocationResolver)),
+        new SimpleMeterRegistry()
+      );
 
     MirrorHttpConnectionProvider mirrorHttpConnectionProvider = new MirrorHttpConnectionProvider(
       new HttpURLConnectionFactory(
@@ -106,7 +116,15 @@ public class GitMirrorCommandTest extends AbstractGitCommandTestBase {
       mirrorHttpConnectionProvider,
       gitChangesetConverterFactory,
       gitTagConverter,
-      workingCopyFactory);
+      workingCopyFactory,
+      gitHeadModifier);
+  }
+
+  @After
+  public void cleanupWorkdir() {
+    if (workdirAfterClose != null) {
+      IOUtil.deleteSilently(workdirAfterClose);
+    }
   }
 
   @Test
@@ -154,6 +172,10 @@ public class GitMirrorCommandTest extends AbstractGitCommandTestBase {
       assertThat(createdMirror.branchList().call().stream().filter(r -> r.getName().contains("master")).findAny())
         .isEmpty();
     }
+    try (Repository workdirRepository = GitUtil.open(workdirAfterClose)) {
+      assertThat(workdirRepository.findRef(Constants.HEAD).getTarget().getName()).isEqualTo("refs/heads/test-branch");
+    }
+    verify(gitHeadModifier).ensure(repository, "test-branch");
   }
 
   @Test
@@ -840,4 +862,16 @@ public class GitMirrorCommandTest extends AbstractGitCommandTestBase {
   private interface InvocationCheck {
     void invoked();
   }
+
+  private class KeepingWorkingCopyPool extends NoneCachingWorkingCopyPool {
+
+    public KeepingWorkingCopyPool(WorkdirProvider workdirProvider) {
+      super(workdirProvider);
+    }
+
+    @Override
+    public void contextClosed(SimpleWorkingCopyFactory<?, ?, ?>.WorkingCopyContext workingCopyContext, File workdir) {
+      workdirAfterClose = workdir;
+    }
+  }
 }