RefTree: Store references in a Git tree

A group of updates can be applied by updating the tree in one step,
writing out a new root tree, and storing its SHA-1. If references
are stored in RefTrees, comparing two repositories is a matter of
checking if two SHA-1s are identical. Without RefTrees comparing two
repositories requires listing all references and comparing the sets.

Track the "refs/" directory as a root tree by storing references
that point directly at an object as a GITLINK entry in the tree.
For example "refs/heads/master" is written as "heads/master".

Annotated tags also store their peeled value with ^{} suffix, using
"tags/v1.0" and "tags/v1.0^{}" GITLINK entries.

Symbolic references are written as SYMLINK entries with the blob of
the symlink carrying the name of the symbolic reference target.

HEAD is outside of "refs/" namespace so it is stored as a special
"..HEAD" entry. This name is chosen because ".." is not valid in
a reference name and it almost looks like "../HEAD" which names
HEAD if the reader was inside of the "refs/" directory.

A new Command type is required to handle symbolic references and
peeled references.

Change-Id: Id47e5d4d32149a9e500854147edd7d93c1041a39

1 files changed, 17 insertions, 0 deletions

diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/dircache/DirCacheEntry.java b/org.eclipse.jgit/src/org/eclipse/jgit/dircache/DirCacheEntry.java
index 5df9e0b4df..4ebf2e0d71 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/dircache/DirCacheEntry.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/dircache/DirCacheEntry.java
@@ -294,6 +294,23 @@ public class DirCacheEntry {
 		NB.encodeInt16(info, infoOffset + P_FLAGS, flags);
 	}
 
+	/**
+	 * Duplicate DirCacheEntry with same path and copied info.
+	 * <p>
+	 * The same path buffer is reused (avoiding copying), however a new info
+	 * buffer is created and its contents are copied.
+	 *
+	 * @param src
+	 *            entry to clone.
+	 * @since 4.2
+	 */
+	public DirCacheEntry(DirCacheEntry src) {
+		path = src.path;
+		info = new byte[INFO_LEN];
+		infoOffset = 0;
+		System.arraycopy(src.info, src.infoOffset, info, 0, INFO_LEN);
+	}
+
 	void write(final OutputStream os) throws IOException {
 		final int len = isExtended() ? INFO_LEN_EXTENDED : INFO_LEN;
 		final int pathLen = path.length;