containsGitModulesFile() should not crash on bare repository

Change-Id: Iba7e4674b3d33c730613a6ac703977f48b015853
Signed-off-by: Andrey Loskutov <loskutov@gmx.de>

org.eclipse.jgit.test/tst/org/eclipse/jgit/submodule/SubmoduleWalkTest.java

@@ -65,6 +65,7 @@ import org.eclipse.jgit.dircache.DirCacheEditor.PathEdit;
 import org.eclipse.jgit.dircache.DirCacheEntry;
 import org.eclipse.jgit.errors.ConfigInvalidException;
 import org.eclipse.jgit.errors.NoWorkTreeException;
+import org.eclipse.jgit.internal.storage.file.FileRepository;
 import org.eclipse.jgit.junit.RepositoryTestCase;
 import org.eclipse.jgit.junit.TestRepository;
 import org.eclipse.jgit.lib.Config;
@@ -100,6 +101,13 @@ public class SubmoduleWalkTest extends RepositoryTestCase {
 		assertEquals(ObjectId.zeroId(), gen.getObjectId());
 	}
 
+	@Test
+	public void bareRepositoryWithNoSubmodules() throws IOException {
+		FileRepository bareRepo = createBareRepository();
+		boolean result = SubmoduleWalk.containsGitModulesFile(bareRepo);
+		assertFalse(result);
+	}
+
 	@Test
 	public void repositoryWithRootLevelSubmodule() throws IOException,
 			ConfigInvalidException, NoWorkTreeException, GitAPIException {

org.eclipse.jgit/src/org/eclipse/jgit/submodule/SubmoduleWalk.java

@@ -451,13 +451,14 @@ public class SubmoduleWalk implements AutoCloseable {
 	}
 
 	/**
-	 * Checks whether the working tree (or the index in case of a bare repo)
+	 * Checks whether the working tree contains a .gitmodules file. That's a
-	 * contains a .gitmodules file. That's a hint that the repo contains
+	 * hint that the repo contains submodules.
-	 * submodules.
 	 *
 	 * @param repository
 	 *            the repository to check
-	 * @return <code>true</code> if the repo contains a .gitmodules file
+	 * @return <code>true</code> if the working tree contains a .gitmodules file,
+	 *         <code>false</code> otherwise. Always returns <code>false</code>
+	 *         for bare repositories.
 	 * @throws IOException
 	 * @throws CorruptObjectException
 	 * @since 3.6
@@ -465,8 +466,7 @@ public class SubmoduleWalk implements AutoCloseable {
 	public static boolean containsGitModulesFile(Repository repository)
 			throws IOException {
 		if (repository.isBare()) {
-			DirCache dc = repository.readDirCache();
+			return false;
-			return (dc.findEntry(Constants.DOT_GIT_MODULES) >= 0);
 		}
 		File modulesFile = new File(repository.getWorkTree(),
 				Constants.DOT_GIT_MODULES);