Add ignoreRemoteFailures option to RepoCommand

With ignoreRemoteFailures set to true, we can ignore remote failures
(e.g. the branch of a project described in the manifest file does not
exist), skip that project and continue to the next one, instead of fail
the whole operation.

Change-Id: I8b3765713599e34f1411f9bbc7f575ec7c2384e0
Signed-off-by: Yuxuan 'fishy' Wang <fishywang@google.com>

org.eclipse.jgit/src/org/eclipse/jgit/gitrepo/RepoCommand.java

 import java.util.List;
 import java.util.Map;
 
+import org.eclipse.jgit.annotations.Nullable;
 import org.eclipse.jgit.api.Git;
 import org.eclipse.jgit.api.GitCommand;
 import org.eclipse.jgit.api.SubmoduleAddCommand;
  * @since 3.4
  */
 public class RepoCommand extends GitCommand<RevCommit> {
-
 	private String path;
 	private String uri;
 	private String groups;
 	private RemoteReader callback;
 	private InputStream inputStream;
 	private IncludedFileReader includedReader;
+	private boolean ignoreRemoteFailures = false;
 
 	private List<RepoProject> bareProjects;
 	private Git git;
 		 *            The URI of the remote repository
 		 * @param ref
 		 *            The ref (branch/tag/etc.) to read
-		 * @return the sha1 of the remote repository
+		 * @return the sha1 of the remote repository, or null if the ref does
+		 *		   not exist.
 		 * @throws GitAPIException
 		 */
+		@Nullable
 		public ObjectId sha1(String uri, String ref) throws GitAPIException;
 
 		/**
 	}
 
 	/**
-	 * Set whether the branch name should be recorded in .gitmodules
+	 * Set whether the branch name should be recorded in .gitmodules.
 	 * <p>
 	 * Submodule entries in .gitmodules can include a "branch" field
 	 * to indicate what remote branch each submodule tracks.
 		return this;
 	}
 
+	/**
+	 * Set whether to skip projects whose commits don't exist remotely.
+	 * <p>
+	 * When set to true, we'll just skip the manifest entry and continue
+	 * on to the next one.
+	 * <p>
+	 * When set to false (default), we'll throw an error when remote
+	 * failures occur.
+	 * <p>
+	 * Not implemented for non-bare repositories.
+	 *
+	 * @param ignore Whether to ignore the remote failures.
+	 * @return this command
+	 * @since 4.3
+	 */
+	public RepoCommand setIgnoreRemoteFailures(boolean ignore) {
+		this.ignoreRemoteFailures = ignore;
+		return this;
+	}
+
 	/**
 	 * Set the author/committer for the bare repository commit.
 	 * <p>
 				for (RepoProject proj : bareProjects) {
 					String name = proj.getPath();
 					String nameUri = proj.getName();
-					cfg.setString("submodule", name, "path", name); //$NON-NLS-1$ //$NON-NLS-2$
-					cfg.setString("submodule", name, "url", nameUri); //$NON-NLS-1$ //$NON-NLS-2$
-					// create gitlink
-					DirCacheEntry dcEntry = new DirCacheEntry(name);
 					ObjectId objectId;
-					if (ObjectId.isId(proj.getRevision())) {
+					if (ObjectId.isId(proj.getRevision())
+							&& !ignoreRemoteFailures) {
 						objectId = ObjectId.fromString(proj.getRevision());
 					} else {
 						objectId = callback.sha1(nameUri, proj.getRevision());
-						if (recordRemoteBranch)
+						if (objectId == null) {
+							if (ignoreRemoteFailures) {
+								continue;
+							}
+							throw new RemoteUnavailableException(nameUri);
+						}
+						if (recordRemoteBranch) {
 							// can be branch or tag
 							cfg.setString("submodule", name, "branch", //$NON-NLS-1$ //$NON-NLS-2$
 									proj.getRevision());
+						}
 					}
-					if (objectId == null)
-						throw new RemoteUnavailableException(nameUri);
+					cfg.setString("submodule", name, "path", name); //$NON-NLS-1$ //$NON-NLS-2$
+					cfg.setString("submodule", name, "url", nameUri); //$NON-NLS-1$ //$NON-NLS-2$
+
+					// create gitlink
+					DirCacheEntry dcEntry = new DirCacheEntry(name);
 					dcEntry.setObjectId(objectId);
 					dcEntry.setFileMode(FileMode.GITLINK);
 					builder.add(dcEntry);