debug-rebuild-ref-tree: Simple program to build a RefTree

This tool scans all references in the repository and writes out a new
reference pointing to a single commit whose root tree is a RefTree
containing the current refs of this repository.

It alway skips storing the reference it will write to, avoiding the
obvious cycle.

Change-Id: I20b1eeb81c55dc49dd600eac3bf8f90297394113

org.eclipse.jgit.pgm/META-INF/MANIFEST.MF

@@ -21,6 +21,7 @@ Import-Package: org.apache.commons.compress.archivers;version="[1.3,2.0)",
  org.eclipse.jgit.gitrepo;version="[4.2.0,4.3.0)",
  org.eclipse.jgit.internal.storage.file;version="[4.2.0,4.3.0)",
  org.eclipse.jgit.internal.storage.pack;version="[4.2.0,4.3.0)",
+ org.eclipse.jgit.internal.storage.reftree;version="[4.2.0,4.3.0)",
  org.eclipse.jgit.lib;version="[4.2.0,4.3.0)",
  org.eclipse.jgit.merge;version="4.2.0",
  org.eclipse.jgit.nls;version="[4.2.0,4.3.0)",

org.eclipse.jgit.pgm/META-INF/services/org.eclipse.jgit.pgm.TextBuiltin

@@ -41,6 +41,7 @@ org.eclipse.jgit.pgm.debug.DiffAlgorithms
 org.eclipse.jgit.pgm.debug.MakeCacheTree
 org.eclipse.jgit.pgm.debug.ReadDirCache
 org.eclipse.jgit.pgm.debug.RebuildCommitGraph
+org.eclipse.jgit.pgm.debug.RebuildRefTree
 org.eclipse.jgit.pgm.debug.ShowCacheTree
 org.eclipse.jgit.pgm.debug.ShowCommands
 org.eclipse.jgit.pgm.debug.ShowDirCache

org.eclipse.jgit.pgm/resources/org/eclipse/jgit/pgm/internal/CLIText.properties

@@ -228,6 +228,7 @@ usage_MergeBase=Find as good common ancestors as possible for a merge
 usage_MergesTwoDevelopmentHistories=Merges two development histories
 usage_ReadDirCache= Read the DirCache 100 times
 usage_RebuildCommitGraph=Recreate a repository from another one's commit graph
+usage_RebuildRefTree=Copy references into a RefTree
 usage_Remote=Manage set of tracked repositories
 usage_RepositoryToReadFrom=Repository to read from
 usage_RepositoryToReceiveInto=Repository to receive into
@@ -359,6 +360,7 @@ usage_tags=fetch all tags
 usage_notags=do not fetch tags
 usage_tagMessage=tag message
 usage_untrackedFilesMode=show untracked files
+usage_updateRef=reference to update
 usage_updateRemoteRefsFromAnotherRepository=Update remote refs from another repository
 usage_useNameInsteadOfOriginToTrackUpstream=use <name> instead of 'origin' to track upstream
 usage_checkoutBranchAfterClone=checkout named branch instead of remotes's HEAD

org.eclipse.jgit.pgm/src/org/eclipse/jgit/pgm/debug/RebuildRefTree.java

@@ -0,0 +1,130 @@
+/*
+ * Copyright (C) 2015, Google Inc.
+ * and other copyright owners as documented in the project's IP log.
+ *
+ * This program and the accompanying materials are made available
+ * under the terms of the Eclipse Distribution License v1.0 which
+ * accompanies this distribution, is reproduced below, and is
+ * available at http://www.eclipse.org/org/documents/edl-v10.php
+ *
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or
+ * without modification, are permitted provided that the following
+ * conditions are met:
+ *
+ * - Redistributions of source code must retain the above copyright
+ *   notice, this list of conditions and the following disclaimer.
+ *
+ * - Redistributions in binary form must reproduce the above
+ *   copyright notice, this list of conditions and the following
+ *   disclaimer in the documentation and/or other materials provided
+ *   with the distribution.
+ *
+ * - Neither the name of the Eclipse Foundation, Inc. nor the
+ *   names of its contributors may be used to endorse or promote
+ *   products derived from this software without specific prior
+ *   written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
+ * CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
+ * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+ * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+ * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+ * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+ * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
+ * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+package org.eclipse.jgit.pgm.debug;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Map;
+
+import org.eclipse.jgit.internal.storage.reftree.RefTree;
+import org.eclipse.jgit.lib.CommitBuilder;
+import org.eclipse.jgit.lib.ObjectId;
+import org.eclipse.jgit.lib.ObjectInserter;
+import org.eclipse.jgit.lib.ObjectReader;
+import org.eclipse.jgit.lib.PersonIdent;
+import org.eclipse.jgit.lib.Ref;
+import org.eclipse.jgit.lib.RefDatabase;
+import org.eclipse.jgit.lib.RefUpdate;
+import org.eclipse.jgit.pgm.Command;
+import org.eclipse.jgit.pgm.TextBuiltin;
+import org.eclipse.jgit.revwalk.RevWalk;
+import org.kohsuke.args4j.Argument;
+
+@Command(usage = "usage_RebuildRefTree")
+class RebuildRefTree extends TextBuiltin {
+	@Argument(index = 0, required = true, metaVar = "metaVar_ref", usage = "usage_updateRef")
+	String refName;
+
+	@Override
+	protected void run() throws Exception {
+		try (ObjectReader reader = db.newObjectReader();
+				RevWalk rw = new RevWalk(reader);
+				ObjectInserter inserter = db.newObjectInserter()) {
+			RefDatabase refDb = db.getRefDatabase();
+
+			CommitBuilder b = new CommitBuilder();
+			Ref ref = db.getRefDatabase().exactRef(refName);
+			RefUpdate update = db.updateRef(refName);
+			ObjectId oldTreeId;
+
+			if (ref != null && ref.getObjectId() != null) {
+				ObjectId oldId = ref.getObjectId();
+				update.setExpectedOldObjectId(oldId);
+				b.setParentId(oldId);
+				oldTreeId = rw.parseCommit(oldId).getTree();
+			} else {
+				update.setExpectedOldObjectId(ObjectId.zeroId());
+				oldTreeId = ObjectId.zeroId();
+			}
+
+			RefTree tree = rebuild(refDb.getRefs(RefDatabase.ALL));
+			b.setTreeId(tree.writeTree(inserter));
+			b.setAuthor(new PersonIdent(db));
+			b.setCommitter(b.getAuthor());
+			if (b.getTreeId().equals(oldTreeId)) {
+				return;
+			}
+
+			update.setNewObjectId(inserter.insert(b));
+			inserter.flush();
+
+			RefUpdate.Result result = update.update(rw);
+			switch (result) {
+			case NEW:
+			case FAST_FORWARD:
+				break;
+			default:
+				throw die(String.format("%s: %s", update.getName(), result)); //$NON-NLS-1$
+			}
+		}
+	}
+
+	private RefTree rebuild(Map<String, Ref> refMap) {
+		RefTree tree = RefTree.newEmptyTree();
+		List<org.eclipse.jgit.internal.storage.reftree.Command> cmds
+			= new ArrayList<>();
+
+		for (Ref r : refMap.values()) {
+			if (refName.equals(r.getName())) {
+				continue;
+			}
+
+			cmds.add(new org.eclipse.jgit.internal.storage.reftree.Command(
+					null,
+					db.peel(r)));
+		}
+		tree.apply(cmds);
+		return tree;
+	}
+}