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

/*
 * Copyright (C) 2010, Christian Halstrick <christian.halstrick@sap.com>,
 * Copyright (C) 2010, Matthias Sohn <matthias.sohn@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.
 */
package org.eclipse.jgit.merge;

import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.HashMap;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.List;
import java.util.Map;

import org.eclipse.jgit.diff.DiffAlgorithm;
import org.eclipse.jgit.diff.DiffAlgorithm.SupportedAlgorithm;
import org.eclipse.jgit.diff.RawText;
import org.eclipse.jgit.diff.RawTextComparator;
import org.eclipse.jgit.diff.Sequence;
import org.eclipse.jgit.dircache.DirCache;
import org.eclipse.jgit.dircache.DirCacheBuildIterator;
import org.eclipse.jgit.dircache.DirCacheBuilder;
import org.eclipse.jgit.dircache.DirCacheCheckout;
import org.eclipse.jgit.dircache.DirCacheEntry;
import org.eclipse.jgit.errors.CorruptObjectException;
import org.eclipse.jgit.errors.IncorrectObjectTypeException;
import org.eclipse.jgit.errors.IndexWriteException;
import org.eclipse.jgit.errors.MissingObjectException;
import org.eclipse.jgit.errors.NoWorkTreeException;
import org.eclipse.jgit.internal.JGitText;
import org.eclipse.jgit.lib.ConfigConstants;
import org.eclipse.jgit.lib.Constants;
import org.eclipse.jgit.lib.FileMode;
import org.eclipse.jgit.lib.ObjectId;
import org.eclipse.jgit.lib.ObjectInserter;
import org.eclipse.jgit.lib.ObjectReader;
import org.eclipse.jgit.lib.Repository;
import org.eclipse.jgit.treewalk.CanonicalTreeParser;
import org.eclipse.jgit.treewalk.NameConflictTreeWalk;
import org.eclipse.jgit.treewalk.WorkingTreeIterator;
import org.eclipse.jgit.util.FileUtils;

/**
 * A three-way merger performing a content-merge if necessary
 */
public class ResolveMerger extends ThreeWayMerger {
	/**
	 * If the merge fails (means: not stopped because of unresolved conflicts)
	 * this enum is used to explain why it failed
	 */
	public enum MergeFailureReason {
		/** the merge failed because of a dirty index */
		DIRTY_INDEX,
		/** the merge failed because of a dirty workingtree */
		DIRTY_WORKTREE,
		/** the merge failed because of a file could not be deleted */
		COULD_NOT_DELETE
	}

	private NameConflictTreeWalk tw;

	private String commitNames[];

	private static final int T_BASE = 0;

	private static final int T_OURS = 1;

	private static final int T_THEIRS = 2;

	private static final int T_INDEX = 3;

	private static final int T_FILE = 4;

	private DirCacheBuilder builder;

	private ObjectId resultTree;

	private List<String> unmergedPaths = new ArrayList<String>();

	private List<String> modifiedFiles = new LinkedList<String>();

	private Map<String, DirCacheEntry> toBeCheckedOut = new HashMap<String, DirCacheEntry>();

	private Map<String, MergeResult<? extends Sequence>> mergeResults = new HashMap<String, MergeResult<? extends Sequence>>();

	private Map<String, MergeFailureReason> failingPaths = new HashMap<String, MergeFailureReason>();

	private ObjectInserter oi;

	private boolean enterSubtree;

	private boolean inCore;

	private DirCache dircache;

	private WorkingTreeIterator workingTreeIterator;

	private MergeAlgorithm mergeAlgorithm;

	/**
	 * @param local
	 * @param inCore
	 */
	protected ResolveMerger(Repository local, boolean inCore) {
		super(local);
		SupportedAlgorithm diffAlg = local.getConfig().getEnum(
				ConfigConstants.CONFIG_DIFF_SECTION, null,
				ConfigConstants.CONFIG_KEY_ALGORITHM,
				SupportedAlgorithm.HISTOGRAM);
		mergeAlgorithm = new MergeAlgorithm(DiffAlgorithm.getAlgorithm(diffAlg));
		commitNames = new String[] { "BASE", "OURS", "THEIRS" };
		oi = getObjectInserter();
		this.inCore = inCore;

		if (inCore) {
			dircache = DirCache.newInCore();
		}
	}

	/**
	 * @param local
	 */
	protected ResolveMerger(Repository local) {
		this(local, false);
	}

	@Override
	protected boolean mergeImpl() throws IOException {
		boolean implicitDirCache = false;

		if (dircache == null) {
			dircache = getRepository().lockDirCache();
			implicitDirCache = true;
		}

		try {
			builder = dircache.builder();
			DirCacheBuildIterator buildIt = new DirCacheBuildIterator(builder);

			tw = new NameConflictTreeWalk(db);
			tw.addTree(mergeBase());
			tw.addTree(sourceTrees[0]);
			tw.addTree(sourceTrees[1]);
			tw.addTree(buildIt);
			if (workingTreeIterator != null)
				tw.addTree(workingTreeIterator);

			while (tw.next()) {
				if (!processEntry(
						tw.getTree(T_BASE, CanonicalTreeParser.class),
						tw.getTree(T_OURS, CanonicalTreeParser.class),
						tw.getTree(T_THEIRS, CanonicalTreeParser.class),
						tw.getTree(T_INDEX, DirCacheBuildIterator.class),
						(workingTreeIterator == null) ? null : tw.getTree(T_FILE, WorkingTreeIterator.class))) {
					cleanUp();
					return false;
				}
				if (tw.isSubtree() && enterSubtree)
					tw.enterSubtree();
			}

			if (!inCore) {
				// All content-merges are successfully done. If we can now write the
				// new index we are on quite safe ground. Even if the checkout of
				// files coming from "theirs" fails the user can work around such
				// failures by checking out the index again.
				if (!builder.commit()) {
					cleanUp();
					throw new IndexWriteException();
				}
				builder = null;

				// No problem found. The only thing left to be done is to checkout
				// all files from "theirs" which have been selected to go into the
				// new index.
				checkout();
			} else {
				builder.finish();
				builder = null;
			}

			if (getUnmergedPaths().isEmpty()) {
				resultTree = dircache.writeTree(oi);
				return true;
			} else {
				resultTree = null;
				return false;
			}
		} finally {
			if (implicitDirCache)
				dircache.unlock();
		}
	}

	private void checkout() throws NoWorkTreeException, IOException {
		ObjectReader r = db.getObjectDatabase().newReader();
		try {
			for (Map.Entry<String, DirCacheEntry> entry : toBeCheckedOut
					.entrySet()) {
				File f = new File(db.getWorkTree(), entry.getKey());
				if (entry.getValue() != null) {
					createDir(f.getParentFile());
					DirCacheCheckout.checkoutEntry(db, f, entry.getValue(), r);
				} else {
					if (!f.delete())
						failingPaths.put(entry.getKey(),
								MergeFailureReason.COULD_NOT_DELETE);
				}
				modifiedFiles.add(entry.getKey());
			}
		} finally {
			r.release();
		}
	}

	private void createDir(File f) throws IOException {
		if (!f.isDirectory() && !f.mkdirs()) {
			File p = f;
			while (p != null && !p.exists())
				p = p.getParentFile();
			if (p == null || p.isDirectory())
				throw new IOException(JGitText.get().cannotCreateDirectory);
			FileUtils.delete(p);
			if (!f.mkdirs())
				throw new IOException(JGitText.get().cannotCreateDirectory);
		}
	}

	/**
	 * Reverts the worktree after an unsuccessful merge. We know that for all
	 * modified files the old content was in the old index and the index
	 * contained only stage 0. In case if inCore operation just clear
	 * the history of modified files.
	 *
	 * @throws IOException
	 * @throws CorruptObjectException
	 * @throws NoWorkTreeException
	 */
	private void cleanUp() throws NoWorkTreeException, CorruptObjectException, IOException {
		if (inCore) {
			modifiedFiles.clear();
			return;
		}

		DirCache dc = db.readDirCache();
		ObjectReader or = db.getObjectDatabase().newReader();
		Iterator<String> mpathsIt=modifiedFiles.iterator();
		while(mpathsIt.hasNext()) {
			String mpath=mpathsIt.next();
			DirCacheEntry entry = dc.getEntry(mpath);
			FileOutputStream fos = new FileOutputStream(new File(db.getWorkTree(), mpath));
			try {
				or.open(entry.getObjectId()).copyTo(fos);
			} finally {
				fos.close();
			}
			mpathsIt.remove();
		}
	}

	/**
	 * adds a new path with the specified stage to the index builder
	 *
	 * @param path
	 * @param p
	 * @param stage
	 * @return the entry which was added to the index
	 */
	private DirCacheEntry add(byte[] path, CanonicalTreeParser p, int stage) {
		if (p != null && !p.getEntryFileMode().equals(FileMode.TREE)) {
			DirCacheEntry e = new DirCacheEntry(path, stage);
			e.setFileMode(p.getEntryFileMode());
			e.setObjectId(p.getEntryObjectId());
			builder.add(e);
			return e;
		}
		return null;
	}

	/**
	 * Processes one path and tries to merge. This method will do all do all
	 * trivial (not content) merges and will also detect if a merge will fail.
	 * The merge will fail when one of the following is true
	 * <ul>
	 * <li>the index entry does not match the entry in ours. When merging one
	 * branch into the current HEAD, ours will point to HEAD and theirs will
	 * point to the other branch. It is assumed that the index matches the HEAD
	 * because it will only not match HEAD if it was populated before the merge
	 * operation. But the merge commit should not accidentally contain
	 * modifications done before the merge. Check the <a href=
	 * "http://www.kernel.org/pub/software/scm/git/docs/git-read-tree.html#_3_way_merge"
	 * >git read-tree</a> documentation for further explanations.</li>
	 * <li>A conflict was detected and the working-tree file is dirty. When a
	 * conflict is detected the content-merge algorithm will try to write a
	 * merged version into the working-tree. If the file is dirty we would
	 * override unsaved data.</li>
	 *
	 * @param base
	 *            the common base for ours and theirs
	 * @param ours
	 *            the ours side of the merge. When merging a branch into the
	 *            HEAD ours will point to HEAD
	 * @param theirs
	 *            the theirs side of the merge. When merging a branch into the
	 *            current HEAD theirs will point to the branch which is merged
	 *            into HEAD.
	 * @param index
	 *            the index entry
	 * @param work
	 *            the file in the working tree
	 * @return <code>false</code> if the merge will fail because the index entry
	 *         didn't match ours or the working-dir file was dirty and a
	 *         conflict occurred
	 * @throws MissingObjectException
	 * @throws IncorrectObjectTypeException
	 * @throws CorruptObjectException
	 * @throws IOException
	 */
	private boolean processEntry(CanonicalTreeParser base,
			CanonicalTreeParser ours, CanonicalTreeParser theirs,
			DirCacheBuildIterator index, WorkingTreeIterator work)
			throws MissingObjectException, IncorrectObjectTypeException,
			CorruptObjectException, IOException {
		enterSubtree = true;
		final int modeO = tw.getRawMode(T_OURS);
		final int modeT = tw.getRawMode(T_THEIRS);
		final int modeB = tw.getRawMode(T_BASE);

		if (modeO == 0 && modeT == 0 && modeB == 0)
			// File is either untracked or new, staged but uncommitted
			return true;

		if (isIndexDirty())
			return false;

		if (nonTree(modeO) && nonTree(modeT) && tw.idEqual(T_OURS, T_THEIRS)) {
			// OURS and THEIRS have equal content. Check the file mode
			if (modeO == modeT) {
				// content and mode of OURS and THEIRS are equal: it doesn't
				// matter which one we choose. OURS is chosen.
				add(tw.getRawPath(), ours, DirCacheEntry.STAGE_0);
				// no checkout needed!
				return true;
			} else {
				// same content but different mode on OURS and THEIRS.
				// Try to merge the mode and report an error if this is
				// not possible.
				int newMode = mergeFileModes(modeB, modeO, modeT);
				if (newMode != FileMode.MISSING.getBits()) {
					if (newMode == modeO)
						// ours version is preferred
						add(tw.getRawPath(), ours, DirCacheEntry.STAGE_0);
					else {
						// the preferred version THEIRS has a different mode
						// than ours. Check it out!
						if (isWorktreeDirty(work))
							return false;
						DirCacheEntry e = add(tw.getRawPath(), theirs,
								DirCacheEntry.STAGE_0);
						toBeCheckedOut.put(tw.getPathString(), e);
					}
					return true;
				} else {
					// FileModes are not mergeable. We found a conflict on modes
					add(tw.getRawPath(), base, DirCacheEntry.STAGE_1);
					add(tw.getRawPath(), ours, DirCacheEntry.STAGE_2);
					add(tw.getRawPath(), theirs, DirCacheEntry.STAGE_3);
					unmergedPaths.add(tw.getPathString());
					mergeResults.put(
							tw.getPathString(),
							new MergeResult<RawText>(Collections
									.<RawText> emptyList()));
				}
				return true;
			}
		}

		if (nonTree(modeO) && modeB == modeT && tw.idEqual(T_BASE, T_THEIRS)) {
			// THEIRS was not changed compared to BASE. All changes must be in
			// OURS. OURS is chosen.
			add(tw.getRawPath(), ours, DirCacheEntry.STAGE_0);
			// no checkout needed!
			return true;
		}

		if (modeB == modeO && tw.idEqual(T_BASE, T_OURS)) {
			// OURS was not changed compared to BASE. All changes must be in
			// THEIRS. THEIRS is chosen.

			// Check worktree before checking out THEIRS
			if (isWorktreeDirty(work))
				return false;
			if (nonTree(modeT)) {
				DirCacheEntry e = add(tw.getRawPath(), theirs,
						DirCacheEntry.STAGE_0);
				if (e != null)
					toBeCheckedOut.put(tw.getPathString(), e);
				return true;
			} else if (modeT == 0 && modeB != 0) {
				// we want THEIRS ... but THEIRS contains the deletion of the
				// file
				toBeCheckedOut.put(tw.getPathString(), null);
				return true;
			}
		}

		if (tw.isSubtree()) {
			// file/folder conflicts: here I want to detect only file/folder
			// conflict between ours and theirs. file/folder conflicts between
			// base/index/workingTree and something else are not relevant or
			// detected later
			if (nonTree(modeO) && !nonTree(modeT)) {
				if (nonTree(modeB))
					add(tw.getRawPath(), base, DirCacheEntry.STAGE_1);
				add(tw.getRawPath(), ours, DirCacheEntry.STAGE_2);
				unmergedPaths.add(tw.getPathString());
				enterSubtree = false;
				return true;
			}
			if (nonTree(modeT) && !nonTree(modeO)) {
				if (nonTree(modeB))
					add(tw.getRawPath(), base, DirCacheEntry.STAGE_1);
				add(tw.getRawPath(), theirs, DirCacheEntry.STAGE_3);
				unmergedPaths.add(tw.getPathString());
				enterSubtree = false;
				return true;
			}

			// ours and theirs are both folders or both files (and treewalk
			// tells us we are in a subtree because of index or working-dir).
			// If they are both folders no content-merge is required - we can
			// return here.
			if (!nonTree(modeO))
				return true;

			// ours and theirs are both files, just fall out of the if block
			// and do the content merge
		}

		if (nonTree(modeO) && nonTree(modeT)) {
			// Check worktree before modifying files
			if (isWorktreeDirty(work))
				return false;

			MergeResult<RawText> result = contentMerge(base, ours, theirs);
			File of = writeMergedFile(result);
			updateIndex(base, ours, theirs, result, of);
			if (result.containsConflicts())
				unmergedPaths.add(tw.getPathString());
			modifiedFiles.add(tw.getPathString());
		} else if (modeO != modeT) {
			// OURS or THEIRS has been deleted
			if (((modeO != 0 && !tw.idEqual(T_BASE, T_OURS)) || (modeT != 0 && !tw
					.idEqual(T_BASE, T_THEIRS)))) {

				add(tw.getRawPath(), base, DirCacheEntry.STAGE_1);
				add(tw.getRawPath(), ours, DirCacheEntry.STAGE_2);
				DirCacheEntry e = add(tw.getRawPath(), theirs,
						DirCacheEntry.STAGE_3);

				// OURS was deleted checkout THEIRS
				if (modeO == 0) {
					// Check worktree before checking out THEIRS
					if (isWorktreeDirty(work))
						return false;
					if (nonTree(modeT)) {
						if (e != null)
							toBeCheckedOut.put(tw.getPathString(), e);
					}
				}

				unmergedPaths.add(tw.getPathString());

				// generate a MergeResult for the deleted file
				mergeResults.put(tw.getPathString(),
						contentMerge(base, ours, theirs));
			}
		}
		return true;
	}

	/**
	 * Does the content merge. The three texts base, ours and theirs are
	 * specified with {@link CanonicalTreeParser}. If any of the parsers is
	 * specified as <code>null</code> then an empty text will be used instead.
	 *
	 * @param base
	 * @param ours
	 * @param theirs
	 *
	 * @return the result of the content merge
	 * @throws IOException
	 */
	private MergeResult<RawText> contentMerge(CanonicalTreeParser base,
			CanonicalTreeParser ours, CanonicalTreeParser theirs)
			throws IOException {
		RawText baseText = base == null ? RawText.EMPTY_TEXT : getRawText(
				base.getEntryObjectId(), db);
		RawText ourText = ours == null ? RawText.EMPTY_TEXT : getRawText(
				ours.getEntryObjectId(), db);
		RawText theirsText = theirs == null ? RawText.EMPTY_TEXT : getRawText(
				theirs.getEntryObjectId(), db);
		return (mergeAlgorithm.merge(RawTextComparator.DEFAULT, baseText,
				ourText, theirsText));
	}

	private boolean isIndexDirty() {
		final int modeI = tw.getRawMode(T_INDEX);
		final int modeO = tw.getRawMode(T_OURS);

		// Index entry has to match ours to be considered clean
		final boolean isDirty = nonTree(modeI)
				&& !(modeO == modeI && tw.idEqual(T_INDEX, T_OURS));
		if (isDirty)
			failingPaths
					.put(tw.getPathString(), MergeFailureReason.DIRTY_INDEX);
		return isDirty;
	}

	private boolean isWorktreeDirty(WorkingTreeIterator work) {
		if (inCore)
			return false;

		final int modeF = tw.getRawMode(T_FILE);
		final int modeO = tw.getRawMode(T_OURS);

		// Worktree entry has to match ours to be considered clean
		final boolean isDirty;
		if (nonTree(modeF))
			isDirty = work.isModeDifferent(modeO)
					|| !tw.idEqual(T_FILE, T_OURS);
		else
			isDirty = false;

		if (isDirty)
			failingPaths.put(tw.getPathString(),
					MergeFailureReason.DIRTY_WORKTREE);
		return isDirty;
	}

	/**
	 * Updates the index after a content merge has happened. If no conflict has
	 * occurred this includes persisting the merged content to the object
	 * database. In case of conflicts this method takes care to write the
	 * correct stages to the index.
	 *
	 * @param base
	 * @param ours
	 * @param theirs
	 * @param result
	 * @param of
	 * @throws FileNotFoundException
	 * @throws IOException
	 */
	private void updateIndex(CanonicalTreeParser base,
			CanonicalTreeParser ours, CanonicalTreeParser theirs,
			MergeResult<RawText> result, File of) throws FileNotFoundException,
			IOException {
		if (result.containsConflicts()) {
			// a conflict occurred, the file will contain conflict markers
			// the index will be populated with the three stages and only the
			// workdir (if used) contains the halfways merged content
			add(tw.getRawPath(), base, DirCacheEntry.STAGE_1);
			add(tw.getRawPath(), ours, DirCacheEntry.STAGE_2);
			add(tw.getRawPath(), theirs, DirCacheEntry.STAGE_3);
			mergeResults.put(tw.getPathString(), result);
		} else {
			// no conflict occurred, the file will contain fully merged content.
			// the index will be populated with the new merged version
			DirCacheEntry dce = new DirCacheEntry(tw.getPathString());
			int newMode = mergeFileModes(tw.getRawMode(0), tw.getRawMode(1),
					tw.getRawMode(2));
			// set the mode for the new content. Fall back to REGULAR_FILE if
			// you can't merge modes of OURS and THEIRS
			dce.setFileMode((newMode == FileMode.MISSING.getBits()) ? FileMode.REGULAR_FILE
					: FileMode.fromBits(newMode));
			dce.setLastModified(of.lastModified());
			dce.setLength((int) of.length());
			InputStream is = new FileInputStream(of);
			try {
				dce.setObjectId(oi.insert(Constants.OBJ_BLOB, of.length(), is));
			} finally {
				is.close();
				if (inCore)
					FileUtils.delete(of);
			}
			builder.add(dce);
		}
	}

	/**
	 * Writes merged file content to the working tree. In case {@link #inCore}
	 * is set and we don't have a working tree the content is written to a
	 * temporary file
	 *
	 * @param result
	 *            the result of the content merge
	 * @return the file to which the merged content was written
	 * @throws FileNotFoundException
	 * @throws IOException
	 */
	private File writeMergedFile(MergeResult<RawText> result)
			throws FileNotFoundException, IOException {
		MergeFormatter fmt = new MergeFormatter();
		File of = null;
		FileOutputStream fos;
		if (!inCore) {
			File workTree = db.getWorkTree();
			if (workTree == null)
				// TODO: This should be handled by WorkingTreeIterators which
				// support write operations
				throw new UnsupportedOperationException();

			of = new File(workTree, tw.getPathString());
			fos = new FileOutputStream(of);
			try {
				fmt.formatMerge(fos, result, Arrays.asList(commitNames),
						Constants.CHARACTER_ENCODING);
			} finally {
				fos.close();
			}
		}
		else if (!result.containsConflicts()) {
			// When working inCore, only trivial merges can be handled,
			// so we generate objects only in conflict free cases
			of = File.createTempFile("merge_", "_temp", null);
			fos = new FileOutputStream(of);
			try {
				fmt.formatMerge(fos, result, Arrays.asList(commitNames),
						Constants.CHARACTER_ENCODING);
			} finally {
				fos.close();
			}
		}
		return of;
	}

	/**
	 * Try to merge filemodes. If only ours or theirs have changed the mode
	 * (compared to base) we choose that one. If ours and theirs have equal
	 * modes return that one. If also that is not the case the modes are not
	 * mergeable. Return {@link FileMode#MISSING} int that case.
	 *
	 * @param modeB
	 *            filemode found in BASE
	 * @param modeO
	 *            filemode found in OURS
	 * @param modeT
	 *            filemode found in THEIRS
	 *
	 * @return the merged filemode or {@link FileMode#MISSING} in case of a
	 *         conflict
	 */
	private int mergeFileModes(int modeB, int modeO, int modeT) {
		if (modeO == modeT)
			return modeO;
		if (modeB == modeO)
			// Base equal to Ours -> chooses Theirs if that is not missing
			return (modeT == FileMode.MISSING.getBits()) ? modeO : modeT;
		if (modeB == modeT)
			// Base equal to Theirs -> chooses Ours if that is not missing
			return (modeO == FileMode.MISSING.getBits()) ? modeT : modeO;
		return FileMode.MISSING.getBits();
	}

	private static RawText getRawText(ObjectId id, Repository db)
			throws IOException {
		if (id.equals(ObjectId.zeroId()))
			return new RawText(new byte[] {});
		return new RawText(db.open(id, Constants.OBJ_BLOB).getCachedBytes());
	}

	private static boolean nonTree(final int mode) {
		return mode != 0 && !FileMode.TREE.equals(mode);
	}

	@Override
	public ObjectId getResultTreeId() {
		return (resultTree == null) ? null : resultTree.toObjectId();
	}

	/**
	 * @param commitNames
	 *            the names of the commits as they would appear in conflict
	 *            markers
	 */
	public void setCommitNames(String[] commitNames) {
		this.commitNames = commitNames;
	}

	/**
	 * @return the names of the commits as they would appear in conflict
	 *         markers.
	 */
	public String[] getCommitNames() {
		return commitNames;
	}

	/**
	 * @return the paths with conflicts. This is a subset of the files listed
	 *         by {@link #getModifiedFiles()}
	 */
	public List<String> getUnmergedPaths() {
		return unmergedPaths;
	}

	/**
	 * @return the paths of files which have been modified by this merge. A
	 *         file will be modified if a content-merge works on this path or if
	 *         the merge algorithm decides to take the theirs-version. This is a
	 *         superset of the files listed by {@link #getUnmergedPaths()}.
	 */
	public List<String> getModifiedFiles() {
		return modifiedFiles;
	}

	/**
	 * @return a map which maps the paths of files which have to be checked out
	 *         because the merge created new fully-merged content for this file
	 *         into the index. This means: the merge wrote a new stage 0 entry
	 *         for this path.
	 */
	public Map<String, DirCacheEntry> getToBeCheckedOut() {
		return toBeCheckedOut;
	}

	/**
	 * @return the mergeResults
	 */
	public Map<String, MergeResult<? extends Sequence>> getMergeResults() {
		return mergeResults;
	}

	/**
	 * @return lists paths causing this merge to fail (not stopped because of a
	 *         conflict). <code>null</code> is returned if this merge didn't
	 *         fail.
	 */
	public Map<String, MergeFailureReason> getFailingPaths() {
		return (failingPaths.size() == 0) ? null : failingPaths;
	}

	/**
	 * Returns whether this merge failed (i.e. not stopped because of a
	 * conflict)
	 *
	 * @return <code>true</code> if a failure occurred, <code>false</code>
	 *         otherwise
	 */
	public boolean failed() {
		return failingPaths.size() > 0;
	}

	/**
	 * Sets the DirCache which shall be used by this merger. If the DirCache is
	 * not set explicitly this merger will implicitly get and lock a default
	 * DirCache. If the DirCache is explicitly set the caller is responsible to
	 * lock it in advance. Finally the merger will call
	 * {@link DirCache#commit()} which requires that the DirCache is locked. If
	 * the {@link #mergeImpl()} returns without throwing an exception the lock
	 * will be released. In case of exceptions the caller is responsible to
	 * release the lock.
	 *
	 * @param dc
	 *            the DirCache to set
	 */
	public void setDirCache(DirCache dc) {
		this.dircache = dc;
	}

	/**
	 * Sets the WorkingTreeIterator to be used by this merger. If no
	 * WorkingTreeIterator is set this merger will ignore the working tree and
	 * fail if a content merge is necessary.
	 * <p>
	 * TODO: enhance WorkingTreeIterator to support write operations. Then this
	 * merger will be able to merge with a different working tree abstraction.
	 *
	 * @param workingTreeIterator
	 *            the workingTreeIt to set
	 */
	public void setWorkingTreeIterator(WorkingTreeIterator workingTreeIterator) {
		this.workingTreeIterator = workingTreeIterator;
	}
}