Add support for creating detached heads

An extra flag when creating a RefUpdate object allows the
caller to destroy the symref and replace it with an object
ref, a.k.a. detached HEAD.

Change-Id: Ia88d48eab1eb4861ebfa39e3be9258c3824a19db
Signed-off-by: Robin Rosenberg <robin.rosenberg@dewire.com>
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

2 files changed, 38 insertions, 0 deletions

diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/lib/RefDatabase.java b/org.eclipse.jgit/src/org/eclipse/jgit/lib/RefDatabase.java
index 67358c8084..fb6a27db30 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/lib/RefDatabase.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/lib/RefDatabase.java
@@ -137,10 +137,30 @@ class RefDatabase {
 	 *             to the base ref, as the symbolic ref could not be read.
 	 */
 	RefUpdate newUpdate(final String name) throws IOException {
+		return newUpdate(name, false);
+	}
+
+	/**
+	 * Create a command to update, create or delete a ref in this repository.
+	 *
+	 * @param name
+	 *            name of the ref the caller wants to modify.
+	 * @param detach
+	 *            true to detach the ref, i.e. replace symref with object ref
+	 * @return an update command. The caller must finish populating this command
+	 *         and then invoke one of the update methods to actually make a
+	 *         change.
+	 * @throws IOException
+	 *             a symbolic ref was passed in and could not be resolved back
+	 *             to the base ref, as the symbolic ref could not be read.
+	 */
+	RefUpdate newUpdate(final String name, boolean detach) throws IOException {
 		refreshPackedRefs();
 		Ref r = readRefBasic(name, 0);
 		if (r == null)
 			r = new Ref(Ref.Storage.NEW, name, null);
+		else if (detach)
+			r = new Ref(Ref.Storage.NEW, name, r.getObjectId());
 		return new RefUpdate(this, r, fileForRef(r.getName()));
 	}
 
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/lib/Repository.java b/org.eclipse.jgit/src/org/eclipse/jgit/lib/Repository.java
index 5b8b34fa6a..f576b057ca 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/lib/Repository.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/lib/Repository.java
@@ -502,6 +502,24 @@ public class Repository {
 	}
 
 	/**
+	 * Create a command to update, create or delete a ref in this repository.
+	 *
+	 * @param ref
+	 *            name of the ref the caller wants to modify.
+	 * @param detach
+	 *            true to create a detached head
+	 * @return an update command. The caller must finish populating this command
+	 *         and then invoke one of the update methods to actually make a
+	 *         change.
+	 * @throws IOException
+	 *             a symbolic ref was passed in and could not be resolved back
+	 *             to the base ref, as the symbolic ref could not be read.
+	 */
+	public RefUpdate updateRef(final String ref, final boolean detach) throws IOException {
+		return refs.newUpdate(ref, detach);
+	}
+
+	/**
 	 * Create a command to rename a ref in this repository
 	 *
 	 * @param fromRef