MergeAlgorithm.java

  1. /*
  2.  * Copyright (C) 2009, Christian Halstrick <christian.halstrick@sap.com>
  3.  * and other copyright owners as documented in the project's IP log.
  4.  *
  5.  * This program and the accompanying materials are made available
  6.  * under the terms of the Eclipse Distribution License v1.0 which
  7.  * accompanies this distribution, is reproduced below, and is
  8.  * available at http://www.eclipse.org/org/documents/edl-v10.php
  9.  *
  10.  * All rights reserved.
  11.  *
  12.  * Redistribution and use in source and binary forms, with or
  13.  * without modification, are permitted provided that the following
  14.  * conditions are met:
  15.  *
  16.  * - Redistributions of source code must retain the above copyright
  17.  *   notice, this list of conditions and the following disclaimer.
  18.  *
  19.  * - Redistributions in binary form must reproduce the above
  20.  *   copyright notice, this list of conditions and the following
  21.  *   disclaimer in the documentation and/or other materials provided
  22.  *   with the distribution.
  23.  *
  24.  * - Neither the name of the Eclipse Foundation, Inc. nor the
  25.  *   names of its contributors may be used to endorse or promote
  26.  *   products derived from this software without specific prior
  27.  *   written permission.
  28.  *
  29.  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
  30.  * CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
  31.  * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
  32.  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  33.  * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
  34.  * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  35.  * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
  36.  * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
  37.  * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
  38.  * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
  39.  * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
  40.  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
  41.  * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  42.  */

  44. package org.eclipse.jgit.merge;

  46. import java.util.ArrayList;
  47. import java.util.Iterator;
  48. import java.util.List;

  50. import org.eclipse.jgit.diff.DiffAlgorithm;
  51. import org.eclipse.jgit.diff.Edit;
  52. import org.eclipse.jgit.diff.EditList;
  53. import org.eclipse.jgit.diff.HistogramDiff;
  54. import org.eclipse.jgit.diff.Sequence;
  55. import org.eclipse.jgit.diff.SequenceComparator;
  56. import org.eclipse.jgit.merge.MergeChunk.ConflictState;

  58. /**
  59.  * Provides the merge algorithm which does a three-way merge on content provided
  60.  * as RawText. By default {@link org.eclipse.jgit.diff.HistogramDiff} is used as
  61.  * diff algorithm.
  62.  */
  63. public final class MergeAlgorithm {
  64.     private final DiffAlgorithm diffAlg;

  66.     /**
  67.      * Creates a new MergeAlgorithm which uses
  68.      * {@link org.eclipse.jgit.diff.HistogramDiff} as diff algorithm
  69.      */
  70.     public MergeAlgorithm() {
  71.         this(new HistogramDiff());
  72.     }

  74.     /**
  75.      * Creates a new MergeAlgorithm
  76.      *
  77.      * @param diff
  78.      *            the diff algorithm used by this merge
  79.      */
  80.     public MergeAlgorithm(DiffAlgorithm diff) {
  81.         this.diffAlg = diff;
  82.     }

  84.     // An special edit which acts as a sentinel value by marking the end the
  85.     // list of edits
  86.     private final static Edit END_EDIT = new Edit(Integer.MAX_VALUE,
  87.             Integer.MAX_VALUE);

  89.     /**
  90.      * Does the three way merge between a common base and two sequences.
  91.      *
  92.      * @param cmp comparison method for this execution.
  93.      * @param base the common base sequence
  94.      * @param ours the first sequence to be merged
  95.      * @param theirs the second sequence to be merged
  96.      * @return the resulting content
  97.      */
  98.     public <S extends Sequence> MergeResult<S> merge(
  99.             SequenceComparator<S> cmp, S base, S ours, S theirs) {
  100.         List<S> sequences = new ArrayList<>(3);
  101.         sequences.add(base);
  102.         sequences.add(ours);
  103.         sequences.add(theirs);
  104.         MergeResult<S> result = new MergeResult<>(sequences);

  106.         if (ours.size() == 0) {
  107.             if (theirs.size() != 0) {
  108.                 EditList theirsEdits = diffAlg.diff(cmp, base, theirs);
  109.                 if (!theirsEdits.isEmpty()) {
  110.                     // we deleted, they modified -> Let their complete content
  111.                     // conflict with empty text
  112.                     result.add(1, 0, 0, ConflictState.FIRST_CONFLICTING_RANGE);
  113.                     result.add(2, 0, theirs.size(),
  114.                             ConflictState.NEXT_CONFLICTING_RANGE);
  115.                 } else
  116.                     // we deleted, they didn't modify -> Let our deletion win
  117.                     result.add(1, 0, 0, ConflictState.NO_CONFLICT);
  118.             } else
  119.                 // we and they deleted -> return a single chunk of nothing
  120.                 result.add(1, 0, 0, ConflictState.NO_CONFLICT);
  121.             return result;
  122.         } else if (theirs.size() == 0) {
  123.             EditList oursEdits = diffAlg.diff(cmp, base, ours);
  124.             if (!oursEdits.isEmpty()) {
  125.                 // we modified, they deleted -> Let our complete content
  126.                 // conflict with empty text
  127.                 result.add(1, 0, ours.size(),
  128.                         ConflictState.FIRST_CONFLICTING_RANGE);
  129.                 result.add(2, 0, 0, ConflictState.NEXT_CONFLICTING_RANGE);
  130.             } else
  131.                 // they deleted, we didn't modify -> Let their deletion win
  132.                 result.add(2, 0, 0, ConflictState.NO_CONFLICT);
  133.             return result;
  134.         }

  136.         EditList oursEdits = diffAlg.diff(cmp, base, ours);
  137.         Iterator<Edit> baseToOurs = oursEdits.iterator();
  138.         EditList theirsEdits = diffAlg.diff(cmp, base, theirs);
  139.         Iterator<Edit> baseToTheirs = theirsEdits.iterator();
  140.         int current = 0; // points to the next line (first line is 0) of base
  141.                          // which was not handled yet
  142.         Edit oursEdit = nextEdit(baseToOurs);
  143.         Edit theirsEdit = nextEdit(baseToTheirs);

  145.         // iterate over all edits from base to ours and from base to theirs
  146.         // leave the loop when there are no edits more for ours or for theirs
  147.         // (or both)
  148.         while (theirsEdit != END_EDIT || oursEdit != END_EDIT) {
  149.             if (oursEdit.getEndA() < theirsEdit.getBeginA()) {
  150.                 // something was changed in ours not overlapping with any change
  151.                 // from theirs. First add the common part in front of the edit
  152.                 // then the edit.
  153.                 if (current != oursEdit.getBeginA()) {
  154.                     result.add(0, current, oursEdit.getBeginA(),
  155.                             ConflictState.NO_CONFLICT);
  156.                 }
  157.                 result.add(1, oursEdit.getBeginB(), oursEdit.getEndB(),
  158.                         ConflictState.NO_CONFLICT);
  159.                 current = oursEdit.getEndA();
  160.                 oursEdit = nextEdit(baseToOurs);
  161.             } else if (theirsEdit.getEndA() < oursEdit.getBeginA()) {
  162.                 // something was changed in theirs not overlapping with any
  163.                 // from ours. First add the common part in front of the edit
  164.                 // then the edit.
  165.                 if (current != theirsEdit.getBeginA()) {
  166.                     result.add(0, current, theirsEdit.getBeginA(),
  167.                             ConflictState.NO_CONFLICT);
  168.                 }
  169.                 result.add(2, theirsEdit.getBeginB(), theirsEdit.getEndB(),
  170.                         ConflictState.NO_CONFLICT);
  171.                 current = theirsEdit.getEndA();
  172.                 theirsEdit = nextEdit(baseToTheirs);
  173.             } else {
  174.                 // here we found a real overlapping modification

  176.                 // if there is a common part in front of the conflict add it
  177.                 if (oursEdit.getBeginA() != current
  178.                         && theirsEdit.getBeginA() != current) {
  179.                     result.add(0, current, Math.min(oursEdit.getBeginA(),
  180.                             theirsEdit.getBeginA()), ConflictState.NO_CONFLICT);
  181.                 }

  183.                 // set some initial values for the ranges in A and B which we
  184.                 // want to handle
  185.                 int oursBeginB = oursEdit.getBeginB();
  186.                 int theirsBeginB = theirsEdit.getBeginB();
  187.                 // harmonize the start of the ranges in A and B
  188.                 if (oursEdit.getBeginA() < theirsEdit.getBeginA()) {
  189.                     theirsBeginB -= theirsEdit.getBeginA()
  190.                             - oursEdit.getBeginA();
  191.                 } else {
  192.                     oursBeginB -= oursEdit.getBeginA() - theirsEdit.getBeginA();
  193.                 }

  195.                 // combine edits:
  196.                 // Maybe an Edit on one side corresponds to multiple Edits on
  197.                 // the other side. Then we have to combine the Edits of the
  198.                 // other side - so in the end we can merge together two single
  199.                 // edits.
  200.                 //
  201.                 // It is important to notice that this combining will extend the
  202.                 // ranges of our conflict always downwards (towards the end of
  203.                 // the content). The starts of the conflicting ranges in ours
  204.                 // and theirs are not touched here.
  205.                 //
  206.                 // This combining is an iterative process: after we have
  207.                 // combined some edits we have to do the check again. The
  208.                 // combined edits could now correspond to multiple edits on the
  209.                 // other side.
  210.                 //
  211.                 // Example: when this combining algorithm works on the following
  212.                 // edits
  213.                 // oursEdits=((0-5,0-5),(6-8,6-8),(10-11,10-11)) and
  214.                 // theirsEdits=((0-1,0-1),(2-3,2-3),(5-7,5-7))
  215.                 // it will merge them into
  216.                 // oursEdits=((0-8,0-8),(10-11,10-11)) and
  217.                 // theirsEdits=((0-7,0-7))
  218.                 //
  219.                 // Since the only interesting thing to us is how in ours and
  220.                 // theirs the end of the conflicting range is changing we let
  221.                 // oursEdit and theirsEdit point to the last conflicting edit
  222.                 Edit nextOursEdit = nextEdit(baseToOurs);
  223.                 Edit nextTheirsEdit = nextEdit(baseToTheirs);
  224.                 for (;;) {
  225.                     if (oursEdit.getEndA() >= nextTheirsEdit.getBeginA()) {
  226.                         theirsEdit = nextTheirsEdit;
  227.                         nextTheirsEdit = nextEdit(baseToTheirs);
  228.                     } else if (theirsEdit.getEndA() >= nextOursEdit.getBeginA()) {
  229.                         oursEdit = nextOursEdit;
  230.                         nextOursEdit = nextEdit(baseToOurs);
  231.                     } else {
  232.                         break;
  233.                     }
  234.                 }

  236.                 // harmonize the end of the ranges in A and B
  237.                 int oursEndB = oursEdit.getEndB();
  238.                 int theirsEndB = theirsEdit.getEndB();
  239.                 if (oursEdit.getEndA() < theirsEdit.getEndA()) {
  240.                     oursEndB += theirsEdit.getEndA() - oursEdit.getEndA();
  241.                 } else {
  242.                     theirsEndB += oursEdit.getEndA() - theirsEdit.getEndA();
  243.                 }

  245.                 // A conflicting region is found. Strip off common lines in
  246.                 // in the beginning and the end of the conflicting region

  248.                 // Determine the minimum length of the conflicting areas in OURS
  249.                 // and THEIRS. Also determine how much bigger the conflicting
  250.                 // area in THEIRS is compared to OURS. All that is needed to
  251.                 // limit the search for common areas at the beginning or end
  252.                 // (the common areas cannot be bigger then the smaller
  253.                 // conflicting area. The delta is needed to know whether the
  254.                 // complete conflicting area is common in OURS and THEIRS.
  255.                 int minBSize = oursEndB - oursBeginB;
  256.                 int BSizeDelta = minBSize - (theirsEndB - theirsBeginB);
  257.                 if (BSizeDelta > 0)
  258.                     minBSize -= BSizeDelta;

  260.                 int commonPrefix = 0;
  261.                 while (commonPrefix < minBSize
  262.                         && cmp.equals(ours, oursBeginB + commonPrefix, theirs,
  263.                                 theirsBeginB + commonPrefix))
  264.                     commonPrefix++;
  265.                 minBSize -= commonPrefix;
  266.                 int commonSuffix = 0;
  267.                 while (commonSuffix < minBSize
  268.                         && cmp.equals(ours, oursEndB - commonSuffix - 1, theirs,
  269.                                 theirsEndB - commonSuffix - 1))
  270.                     commonSuffix++;
  271.                 minBSize -= commonSuffix;

  273.                 // Add the common lines at start of conflict
  274.                 if (commonPrefix > 0)
  275.                     result.add(1, oursBeginB, oursBeginB + commonPrefix,
  276.                             ConflictState.NO_CONFLICT);

  278.                 // Add the conflict (Only if there is a conflict left to report)
  279.                 if (minBSize > 0 || BSizeDelta != 0) {
  280.                     result.add(1, oursBeginB + commonPrefix, oursEndB
  281.                             - commonSuffix,
  282.                             ConflictState.FIRST_CONFLICTING_RANGE);
  283.                     result.add(2, theirsBeginB + commonPrefix, theirsEndB
  284.                             - commonSuffix,
  285.                             ConflictState.NEXT_CONFLICTING_RANGE);
  286.                 }

  288.                 // Add the common lines at end of conflict
  289.                 if (commonSuffix > 0)
  290.                     result.add(1, oursEndB - commonSuffix, oursEndB,
  291.                             ConflictState.NO_CONFLICT);

  293.                 current = Math.max(oursEdit.getEndA(), theirsEdit.getEndA());
  294.                 oursEdit = nextOursEdit;
  295.                 theirsEdit = nextTheirsEdit;
  296.             }
  297.         }
  298.         // maybe we have a common part behind the last edit: copy it to the
  299.         // result
  300.         if (current < base.size()) {
  301.             result.add(0, current, base.size(), ConflictState.NO_CONFLICT);
  302.         }
  303.         return result;
  304.     }

  306.     /**
  307.      * Helper method which returns the next Edit for an Iterator over Edits.
  308.      * When there are no more edits left this method will return the constant
  309.      * END_EDIT.
  310.      *
  311.      * @param it
  312.      *            the iterator for which the next edit should be returned
  313.      * @return the next edit from the iterator or END_EDIT if there no more
  314.      *         edits
  315.      */
  316.     private static Edit nextEdit(Iterator<Edit> it) {
  317.         return (it.hasNext() ? it.next() : END_EDIT);
  318.     }
  319. }
Created with JaCoCo 0.8.4.201905082037