Ref: Add constant for undefined update index

Code that creates references and wants to support ref dbs with and
without update indexes needs to set this value. This leds to a
proliferation of "-1" in the code base.

Make the "undefined" value a constant in the ref interface.

Change-Id: I2622a37536a84b4a4036dd55792e185486fa0628
Signed-off-by: Ivan Frade <ifrade@google.com>

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

@@ -67,7 +67,7 @@ public abstract class ObjectIdRef implements Ref {
 		 */
 		public Unpeeled(@NonNull Storage st, @NonNull String name,
 				@Nullable ObjectId id) {
-			super(st, name, id, -1);
+			super(st, name, id, UNDEFINED_UPDATE_INDEX);
 		}
 
 		/**
@@ -119,7 +119,7 @@ public abstract class ObjectIdRef implements Ref {
 		 */
 		public PeeledTag(@NonNull Storage st, @NonNull String name,
 				@Nullable ObjectId id, @NonNull ObjectId p) {
-			super(st, name, id, -1);
+			super(st, name, id, UNDEFINED_UPDATE_INDEX);
 			peeledObjectId = p;
 		}
 
@@ -172,7 +172,7 @@ public abstract class ObjectIdRef implements Ref {
 		 */
 		public PeeledNonTag(@NonNull Storage st, @NonNull String name,
 				@Nullable ObjectId id) {
-			super(st, name, id, -1);
+			super(st, name, id, UNDEFINED_UPDATE_INDEX);
 		}
 
 		/**
@@ -284,7 +284,7 @@ public abstract class ObjectIdRef implements Ref {
 	 */
 	@Override
 	public long getUpdateIndex() {
-		if (updateIndex == -1) {
+		if (updateIndex == UNDEFINED_UPDATE_INDEX) {
 			throw new UnsupportedOperationException();
 		}
 		return updateIndex;

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

@@ -125,6 +125,13 @@ public interface Ref {
 		}
 	}
 
+	/**
+	 * Update index value when a reference doesn't have one
+	 *
+	 * @since 5.4
+	 */
+	long UNDEFINED_UPDATE_INDEX = -1L;
+
 	/**
 	 * What this ref is called within the repository.
 	 *

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

@@ -71,7 +71,7 @@ public class SymbolicRef implements Ref {
 	public SymbolicRef(@NonNull String refName, @NonNull Ref target) {
 		this.name = refName;
 		this.target = target;
-		this.updateIndex = -1;
+		this.updateIndex = UNDEFINED_UPDATE_INDEX;
 	}
 
 	/**
@@ -155,7 +155,7 @@ public class SymbolicRef implements Ref {
 	 */
 	@Override
 	public long getUpdateIndex() {
-		if (updateIndex == -1) {
+		if (updateIndex == UNDEFINED_UPDATE_INDEX) {
 			throw new UnsupportedOperationException();
 		}
 		return updateIndex;