jgit/org.eclipse.jgit/src/org/eclipse/jgit/merge/RecursiveMerger.java

/*
 * Copyright (C) 2012, Research In Motion Limited
 * Copyright (C) 2012, Christian Halstrick <christian.halstrick@sap.com>
 * 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.
 */

/*
 * Contributors:
 *    George Young - initial API and implementation
 *    Christian Halstrick - initial API and implementation
 */
package org.eclipse.jgit.merge;

import java.io.IOException;
import java.text.MessageFormat;
import java.util.ArrayList;
import java.util.List;

import org.eclipse.jgit.dircache.DirCache;
import org.eclipse.jgit.dircache.DirCacheBuilder;
import org.eclipse.jgit.dircache.DirCacheEntry;
import org.eclipse.jgit.errors.IncorrectObjectTypeException;
import org.eclipse.jgit.errors.NoMergeBaseException;
import org.eclipse.jgit.internal.JGitText;
import org.eclipse.jgit.lib.CommitBuilder;
import org.eclipse.jgit.lib.ObjectId;
import org.eclipse.jgit.lib.ObjectInserter;
import org.eclipse.jgit.lib.PersonIdent;
import org.eclipse.jgit.lib.Repository;
import org.eclipse.jgit.revwalk.RevCommit;
import org.eclipse.jgit.revwalk.filter.RevFilter;
import org.eclipse.jgit.treewalk.TreeWalk;
import org.eclipse.jgit.treewalk.WorkingTreeIterator;

/**
 * A three-way merger performing a content-merge if necessary across multiple
 * bases using recursion
 *
 * This merger extends the resolve merger and does several things differently:
 *
 * - allow more than one merge base, up to a maximum
 *
 * - uses "Lists" instead of Arrays for chained types
 *
 * - recursively merges the merge bases together to compute a usable base
 * @since 3.0
 */
public class RecursiveMerger extends ResolveMerger {
	/**
	 * The maximum number of merge bases. This merge will stop when the number
	 * of merge bases exceeds this value
	 */
	public final int MAX_BASES = 200;

	private PersonIdent ident = new PersonIdent(db);

	/**
	 * Normal recursive merge when you want a choice of DirCache placement
	 * inCore
	 *
	 * @param local
	 * @param inCore
	 */
	protected RecursiveMerger(Repository local, boolean inCore) {
		super(local, inCore);
	}

	/**
	 * Normal recursive merge, implies not inCore
	 *
	 * @param local
	 */
	protected RecursiveMerger(Repository local) {
		this(local, false);
	}

	/**
	 * Get a single base commit for two given commits. If the two source commits
	 * have more than one base commit recursively merge the base commits
	 * together until you end up with a single base commit.
	 *
	 * @throws IOException
	 * @throws IncorrectObjectTypeException
	 */
	@Override
	protected RevCommit getBaseCommit(RevCommit a, RevCommit b)
			throws IncorrectObjectTypeException, IOException {
		return getBaseCommit(a, b, 0);
	}

	/**
	 * Get a single base commit for two given commits. If the two source commits
	 * have more than one base commit recursively merge the base commits
	 * together until a virtual common base commit has been found.
	 *
	 * @param a
	 *            the first commit to be merged
	 * @param b
	 *            the second commit to be merged
	 * @param callDepth
	 *            the callDepth when this method is called recursively
	 * @return the merge base of two commits
	 * @throws IOException
	 * @throws IncorrectObjectTypeException
	 *             one of the input objects is not a commit.
	 * @throws NoMergeBaseException
	 *             too many merge bases are found or the computation of a common
	 *             merge base failed (e.g. because of a conflict).
	 */
	protected RevCommit getBaseCommit(RevCommit a, RevCommit b, int callDepth)
			throws IOException {
		ArrayList<RevCommit> baseCommits = new ArrayList<RevCommit>();
		walk.reset();
		walk.setRevFilter(RevFilter.MERGE_BASE);
		walk.markStart(a);
		walk.markStart(b);
		RevCommit c;
		while ((c = walk.next()) != null)
			baseCommits.add(c);

		if (baseCommits.isEmpty())
			return null;
		if (baseCommits.size() == 1)
			return baseCommits.get(0);
		if (baseCommits.size() >= MAX_BASES)
			throw new NoMergeBaseException(NoMergeBaseException.MergeBaseFailureReason.TOO_MANY_MERGE_BASES, MessageFormat.format(
					JGitText.get().mergeRecursiveTooManyMergeBasesFor,
					Integer.valueOf(MAX_BASES), a.name(), b.name(),
							Integer.valueOf(baseCommits.size())));

		// We know we have more than one base commit. We have to do merges now
		// to determine a single base commit. We don't want to spoil the current
		// dircache and working tree with the results of this intermediate
		// merges. Therefore set the dircache to a new in-memory dircache and
		// disable that we update the working-tree. We set this back to the
		// original values once a single base commit is created.
		RevCommit currentBase = baseCommits.get(0);
		DirCache oldDircache = dircache;
		boolean oldIncore = inCore;
		WorkingTreeIterator oldWTreeIt = workingTreeIterator;
		workingTreeIterator = null;
		try {
			dircache = dircacheFromTree(currentBase.getTree());
			inCore = true;

			List<RevCommit> parents = new ArrayList<RevCommit>();
			parents.add(currentBase);
			for (int commitIdx = 1; commitIdx < baseCommits.size(); commitIdx++) {
				RevCommit nextBase = baseCommits.get(commitIdx);
				if (commitIdx >= MAX_BASES)
					throw new NoMergeBaseException(
							NoMergeBaseException.MergeBaseFailureReason.TOO_MANY_MERGE_BASES,
							MessageFormat.format(
							JGitText.get().mergeRecursiveTooManyMergeBasesFor,
							Integer.valueOf(MAX_BASES), a.name(), b.name(),
									Integer.valueOf(baseCommits.size())));
				parents.add(nextBase);
				if (mergeTrees(
						openTree(getBaseCommit(currentBase, nextBase,
								callDepth + 1).getTree()),
						currentBase.getTree(),
						nextBase.getTree()))
					currentBase = createCommitForTree(resultTree, parents);
				else
					throw new NoMergeBaseException(
							NoMergeBaseException.MergeBaseFailureReason.CONFLICTS_DURING_MERGE_BASE_CALCULATION,
							MessageFormat.format(
									JGitText.get().mergeRecursiveTooManyMergeBasesFor,
									Integer.valueOf(MAX_BASES), a.name(),
									b.name(),
									Integer.valueOf(baseCommits.size())));
			}
		} finally {
			inCore = oldIncore;
			dircache = oldDircache;
			workingTreeIterator = oldWTreeIt;
		}
		return currentBase;
	}

	/**
	 * Create a new commit by explicitly specifying the content tree and the
	 * parents. The commit message is not set and author/committer are set to
	 * the current user.
	 *
	 * @param tree
	 *            the tree this commit should capture
	 * @param parents
	 *            the list of parent commits
	 * @return a new (persisted) commit
	 * @throws IOException
	 */
	private RevCommit createCommitForTree(ObjectId tree, List<RevCommit> parents)
			throws IOException {
		CommitBuilder c = new CommitBuilder();
		c.setParentIds(parents);
		c.setTreeId(tree);
		c.setAuthor(ident);
		c.setCommitter(ident);
		ObjectInserter odi = db.newObjectInserter();
		ObjectId newCommitId = odi.insert(c);
		odi.flush();
		RevCommit ret = walk.lookupCommit(newCommitId);
		walk.parseHeaders(ret);
		return ret;
	}

	/**
	 * Create a new in memory dircache which has the same content as a given
	 * tree.
	 *
	 * @param treeId
	 *            the tree which should be used to fill the dircache
	 * @return a new in memory dircache
	 * @throws IOException
	 */
	private DirCache dircacheFromTree(ObjectId treeId) throws IOException {
		DirCache ret = DirCache.newInCore();
		DirCacheBuilder builder = ret.builder();
		TreeWalk tw = new TreeWalk(db);
		tw.addTree(treeId);
		tw.setRecursive(true);
		while (tw.next()) {
			DirCacheEntry e = new DirCacheEntry(tw.getRawPath());
			e.setFileMode(tw.getFileMode(0));
			e.setObjectId(tw.getObjectId(0));
			builder.add(e);
		}
		builder.finish();
		return ret;
	}
}