Add support for special symref FETCH_HEAD and MERGE_HEAD

The RefDirectory class was not returning FETCH_HEAD and
MERGE_HEAD when trying to get all refs via getRefs(RefDatabase.ALL).
This fix adds constants for FETCH_HEAD and ORIG_HEAD and adds a
new getter getAdditionalRefs() to get these additional refs.
To be compatible with c git the getRefs(ALL) method will not return
FETCH_HEAD, MERGE_HEAD and ORIG_HEAD.

Change-Id: Ie114ca92e9d5e7d61d892f4413ade65acdc08c32
Signed-off-by: Christian Halstrick <christian.halstrick@sap.com>

org.eclipse.jgit/src/org/eclipse/jgit/lib/Constants.java

@@ -79,6 +79,9 @@ public final class Constants {
 	/** Special name for the "HEAD" symbolic-ref. */
 	public static final String HEAD = "HEAD";
 
+	/** Special name for the "FETCH_HEAD" symbolic-ref. */
+	public static final String FETCH_HEAD = "FETCH_HEAD";
+
 	/**
 	 * Text string that identifies an object as a commit.
 	 * <p>
@@ -527,6 +530,12 @@ public final class Constants {
 	/** name of the file containing the IDs of the parents of a merge commit */
 	public static final String MERGE_HEAD = "MERGE_HEAD";
 
+	/**
+	 * name of the ref ORIG_HEAD used by certain commands to store the original
+	 * value of HEAD
+	 */
+	public static final String ORIG_HEAD = "ORIG_HEAD";
+
 	/** objectid for the empty blob */
 	public static final ObjectId EMPTY_BLOB_ID = ObjectId
 			.fromString("e69de29bb2d1d6434b8b29ae775ad8c2e48c5391");

org.eclipse.jgit/src/org/eclipse/jgit/lib/RefDatabase.java

@@ -44,6 +44,7 @@
 package org.eclipse.jgit.lib;
 
 import java.io.IOException;
+import java.util.List;
 import java.util.Map;
 
 /**
@@ -176,6 +177,19 @@ public abstract class RefDatabase {
 	 */
 	public abstract Map<String, Ref> getRefs(String prefix) throws IOException;
 
+	/**
+	 * Get the additional reference-like entities from the repository.
+	 * <p>
+	 * The result list includes non-ref items such as MERGE_HEAD and
+	 * FETCH_RESULT cast to be refs. The names of these refs are not returned by
+	 * <code>getRefs(ALL)</code> but are accepted by {@link #getRef(String)}
+	 *
+	 * @return a list of additional refs
+	 * @throws IOException
+	 *             the reference space cannot be accessed.
+	 */
+	public abstract List<Ref> getAdditionalRefs() throws IOException;
+
 	/**
 	 * Peel a possibly unpeeled reference by traversing the annotated tags.
 	 * <p>

org.eclipse.jgit/src/org/eclipse/jgit/storage/file/RefDirectory.java

@@ -69,6 +69,8 @@ import java.io.IOException;
 import java.io.InputStreamReader;
 import java.text.MessageFormat;
 import java.util.Arrays;
+import java.util.LinkedList;
+import java.util.List;
 import java.util.Map;
 import java.util.concurrent.atomic.AtomicInteger;
 import java.util.concurrent.atomic.AtomicReference;
@@ -123,6 +125,10 @@ public class RefDirectory extends RefDatabase {
 	/** If in the header, denotes the file has peeled data. */
 	public static final String PACKED_REFS_PEELED = " peeled"; //$NON-NLS-1$
 
+	/** The names of the additional refs supported by this class */
+	private static final String[] additionalRefsNames = new String[] {
+			Constants.MERGE_HEAD, Constants.FETCH_HEAD, Constants.ORIG_HEAD };
+
 	private final FileRepository parent;
 
 	private final File gitDir;
@@ -297,6 +303,17 @@ public class RefDirectory extends RefDatabase {
 		return new RefMap(prefix, packed, upcast(loose), symbolic.toRefList());
 	}
 
+	@Override
+	public List<Ref> getAdditionalRefs() throws IOException {
+		List<Ref> ret = new LinkedList<Ref>();
+		for (String name : additionalRefsNames) {
+			Ref r = getRef(name);
+			if (r != null)
+				ret.add(r);
+		}
+		return ret;
+	}
+
 	@SuppressWarnings("unchecked")
 	private RefList<Ref> upcast(RefList<? extends Ref> loose) {
 		return (RefList<Ref>) loose;