Package org.eclipse.jgit.merge

Source Code of org.eclipse.jgit.merge.ResolveMerger

/*
* 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.JGitText;
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.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())
              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())
        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())
        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())
            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)
        && !(tw.idEqual(T_INDEX, T_OURS) && modeO == modeI);
    if (isDirty)
      failingPaths
          .put(tw.getPathString(), MergeFailureReason.DIRTY_INDEX);
    return isDirty;
  }

  private boolean isWorktreeDirty() {
    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 = nonTree(modeF)
        && !(tw.idEqual(T_FILE, T_OURS) && modeO == modeF);
    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;
  }
}
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