MergeAlgorithm.java

  1. /*
  2.  * Copyright (C) 2009, Christian Halstrick <christian.halstrick@sap.com> and others
  3.  *
  4.  * This program and the accompanying materials are made available under the
  5.  * terms of the Eclipse Distribution License v. 1.0 which is available at
  6.  * https://www.eclipse.org/org/documents/edl-v10.php.
  7.  *
  8.  * SPDX-License-Identifier: BSD-3-Clause
  9.  */

  11. package org.eclipse.jgit.merge;

  13. import java.util.ArrayList;
  14. import java.util.Iterator;
  15. import java.util.List;

  17. import org.eclipse.jgit.annotations.NonNull;
  18. import org.eclipse.jgit.diff.DiffAlgorithm;
  19. import org.eclipse.jgit.diff.Edit;
  20. import org.eclipse.jgit.diff.EditList;
  21. import org.eclipse.jgit.diff.HistogramDiff;
  22. import org.eclipse.jgit.diff.Sequence;
  23. import org.eclipse.jgit.diff.SequenceComparator;
  24. import org.eclipse.jgit.merge.MergeChunk.ConflictState;

  26. /**
  27.  * Provides the merge algorithm which does a three-way merge on content provided
  28.  * as RawText. By default {@link org.eclipse.jgit.diff.HistogramDiff} is used as
  29.  * diff algorithm.
  30.  */
  31. public final class MergeAlgorithm {

  33.     private final DiffAlgorithm diffAlg;

  35.     @NonNull
  36.     private ContentMergeStrategy strategy = ContentMergeStrategy.CONFLICT;

  38.     /**
  39.      * Creates a new MergeAlgorithm which uses
  40.      * {@link org.eclipse.jgit.diff.HistogramDiff} as diff algorithm
  41.      */
  42.     public MergeAlgorithm() {
  43.         this(new HistogramDiff());
  44.     }

  46.     /**
  47.      * Creates a new MergeAlgorithm
  48.      *
  49.      * @param diff
  50.      *            the diff algorithm used by this merge
  51.      */
  52.     public MergeAlgorithm(DiffAlgorithm diff) {
  53.         this.diffAlg = diff;
  54.     }

  56.     /**
  57.      * Retrieves the {@link ContentMergeStrategy}.
  58.      *
  59.      * @return the {@link ContentMergeStrategy} in effect
  60.      * @since 5.12
  61.      */
  62.     @NonNull
  63.     public ContentMergeStrategy getContentMergeStrategy() {
  64.         return strategy;
  65.     }

  67.     /**
  68.      * Sets the {@link ContentMergeStrategy}.
  69.      *
  70.      * @param strategy
  71.      *            {@link ContentMergeStrategy} to set; if {@code null}, set
  72.      *            {@link ContentMergeStrategy#CONFLICT}
  73.      * @since 5.12
  74.      */
  75.     public void setContentMergeStrategy(ContentMergeStrategy strategy) {
  76.         this.strategy = strategy == null ? ContentMergeStrategy.CONFLICT
  77.                 : strategy;
  78.     }

  80.     // An special edit which acts as a sentinel value by marking the end the
  81.     // list of edits
  82.     private static final Edit END_EDIT = new Edit(Integer.MAX_VALUE,
  83.             Integer.MAX_VALUE);

  85.     @SuppressWarnings("ReferenceEquality")
  86.     private static boolean isEndEdit(Edit edit) {
  87.         return edit == END_EDIT;
  88.     }

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

  107.         if (ours.size() == 0) {
  108.             if (theirs.size() != 0) {
  109.                 EditList theirsEdits = diffAlg.diff(cmp, base, theirs);
  110.                 if (!theirsEdits.isEmpty()) {
  111.                     // we deleted, they modified
  112.                     switch (strategy) {
  113.                     case OURS:
  114.                         result.add(1, 0, 0, ConflictState.NO_CONFLICT);
  115.                         break;
  116.                     case THEIRS:
  117.                         result.add(2, 0, theirs.size(),
  118.                                 ConflictState.NO_CONFLICT);
  119.                         break;
  120.                     default:
  121.                         // Let their complete content conflict with empty text
  122.                         result.add(1, 0, 0,
  123.                                 ConflictState.FIRST_CONFLICTING_RANGE);
  124.                         result.add(2, 0, theirs.size(),
  125.                                 ConflictState.NEXT_CONFLICTING_RANGE);
  126.                         break;
  127.                     }
  128.                 } else {
  129.                     // we deleted, they didn't modify -> Let our deletion win
  130.                     result.add(1, 0, 0, ConflictState.NO_CONFLICT);
  131.                 }
  132.             } else {
  133.                 // we and they deleted -> return a single chunk of nothing
  134.                 result.add(1, 0, 0, ConflictState.NO_CONFLICT);
  135.             }
  136.             return result;
  137.         } else if (theirs.size() == 0) {
  138.             EditList oursEdits = diffAlg.diff(cmp, base, ours);
  139.             if (!oursEdits.isEmpty()) {
  140.                 // we modified, they deleted
  141.                 switch (strategy) {
  142.                 case OURS:
  143.                     result.add(1, 0, ours.size(), ConflictState.NO_CONFLICT);
  144.                     break;
  145.                 case THEIRS:
  146.                     result.add(2, 0, 0, ConflictState.NO_CONFLICT);
  147.                     break;
  148.                 default:
  149.                     // Let our complete content conflict with empty text
  150.                     result.add(1, 0, ours.size(),
  151.                             ConflictState.FIRST_CONFLICTING_RANGE);
  152.                     result.add(2, 0, 0, ConflictState.NEXT_CONFLICTING_RANGE);
  153.                     break;
  154.                 }
  155.             } else {
  156.                 // they deleted, we didn't modify -> Let their deletion win
  157.                 result.add(2, 0, 0, ConflictState.NO_CONFLICT);
  158.             }
  159.             return result;
  160.         }

  162.         EditList oursEdits = diffAlg.diff(cmp, base, ours);
  163.         Iterator<Edit> baseToOurs = oursEdits.iterator();
  164.         EditList theirsEdits = diffAlg.diff(cmp, base, theirs);
  165.         Iterator<Edit> baseToTheirs = theirsEdits.iterator();
  166.         int current = 0; // points to the next line (first line is 0) of base
  167.                          // which was not handled yet
  168.         Edit oursEdit = nextEdit(baseToOurs);
  169.         Edit theirsEdit = nextEdit(baseToTheirs);

  171.         // iterate over all edits from base to ours and from base to theirs
  172.         // leave the loop when there are no edits more for ours or for theirs
  173.         // (or both)
  174.         while (!isEndEdit(theirsEdit) || !isEndEdit(oursEdit)) {
  175.             if (oursEdit.getEndA() < theirsEdit.getBeginA()) {
  176.                 // something was changed in ours not overlapping with any change
  177.                 // from theirs. First add the common part in front of the edit
  178.                 // then the edit.
  179.                 if (current != oursEdit.getBeginA()) {
  180.                     result.add(0, current, oursEdit.getBeginA(),
  181.                             ConflictState.NO_CONFLICT);
  182.                 }
  183.                 result.add(1, oursEdit.getBeginB(), oursEdit.getEndB(),
  184.                         ConflictState.NO_CONFLICT);
  185.                 current = oursEdit.getEndA();
  186.                 oursEdit = nextEdit(baseToOurs);
  187.             } else if (theirsEdit.getEndA() < oursEdit.getBeginA()) {
  188.                 // something was changed in theirs not overlapping with any
  189.                 // from ours. First add the common part in front of the edit
  190.                 // then the edit.
  191.                 if (current != theirsEdit.getBeginA()) {
  192.                     result.add(0, current, theirsEdit.getBeginA(),
  193.                             ConflictState.NO_CONFLICT);
  194.                 }
  195.                 result.add(2, theirsEdit.getBeginB(), theirsEdit.getEndB(),
  196.                         ConflictState.NO_CONFLICT);
  197.                 current = theirsEdit.getEndA();
  198.                 theirsEdit = nextEdit(baseToTheirs);
  199.             } else {
  200.                 // here we found a real overlapping modification

  202.                 // if there is a common part in front of the conflict add it
  203.                 if (oursEdit.getBeginA() != current
  204.                         && theirsEdit.getBeginA() != current) {
  205.                     result.add(0, current, Math.min(oursEdit.getBeginA(),
  206.                             theirsEdit.getBeginA()), ConflictState.NO_CONFLICT);
  207.                 }

  209.                 // set some initial values for the ranges in A and B which we
  210.                 // want to handle
  211.                 int oursBeginB = oursEdit.getBeginB();
  212.                 int theirsBeginB = theirsEdit.getBeginB();
  213.                 // harmonize the start of the ranges in A and B
  214.                 if (oursEdit.getBeginA() < theirsEdit.getBeginA()) {
  215.                     theirsBeginB -= theirsEdit.getBeginA()
  216.                             - oursEdit.getBeginA();
  217.                 } else {
  218.                     oursBeginB -= oursEdit.getBeginA() - theirsEdit.getBeginA();
  219.                 }

  221.                 // combine edits:
  222.                 // Maybe an Edit on one side corresponds to multiple Edits on
  223.                 // the other side. Then we have to combine the Edits of the
  224.                 // other side - so in the end we can merge together two single
  225.                 // edits.
  226.                 //
  227.                 // It is important to notice that this combining will extend the
  228.                 // ranges of our conflict always downwards (towards the end of
  229.                 // the content). The starts of the conflicting ranges in ours
  230.                 // and theirs are not touched here.
  231.                 //
  232.                 // This combining is an iterative process: after we have
  233.                 // combined some edits we have to do the check again. The
  234.                 // combined edits could now correspond to multiple edits on the
  235.                 // other side.
  236.                 //
  237.                 // Example: when this combining algorithm works on the following
  238.                 // edits
  239.                 // oursEdits=((0-5,0-5),(6-8,6-8),(10-11,10-11)) and
  240.                 // theirsEdits=((0-1,0-1),(2-3,2-3),(5-7,5-7))
  241.                 // it will merge them into
  242.                 // oursEdits=((0-8,0-8),(10-11,10-11)) and
  243.                 // theirsEdits=((0-7,0-7))
  244.                 //
  245.                 // Since the only interesting thing to us is how in ours and
  246.                 // theirs the end of the conflicting range is changing we let
  247.                 // oursEdit and theirsEdit point to the last conflicting edit
  248.                 Edit nextOursEdit = nextEdit(baseToOurs);
  249.                 Edit nextTheirsEdit = nextEdit(baseToTheirs);
  250.                 for (;;) {
  251.                     if (oursEdit.getEndA() >= nextTheirsEdit.getBeginA()) {
  252.                         theirsEdit = nextTheirsEdit;
  253.                         nextTheirsEdit = nextEdit(baseToTheirs);
  254.                     } else if (theirsEdit.getEndA() >= nextOursEdit.getBeginA()) {
  255.                         oursEdit = nextOursEdit;
  256.                         nextOursEdit = nextEdit(baseToOurs);
  257.                     } else {
  258.                         break;
  259.                     }
  260.                 }

  262.                 // harmonize the end of the ranges in A and B
  263.                 int oursEndB = oursEdit.getEndB();
  264.                 int theirsEndB = theirsEdit.getEndB();
  265.                 if (oursEdit.getEndA() < theirsEdit.getEndA()) {
  266.                     oursEndB += theirsEdit.getEndA() - oursEdit.getEndA();
  267.                 } else {
  268.                     theirsEndB += oursEdit.getEndA() - theirsEdit.getEndA();
  269.                 }

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

  274.                 // Determine the minimum length of the conflicting areas in OURS
  275.                 // and THEIRS. Also determine how much bigger the conflicting
  276.                 // area in THEIRS is compared to OURS. All that is needed to
  277.                 // limit the search for common areas at the beginning or end
  278.                 // (the common areas cannot be bigger then the smaller
  279.                 // conflicting area. The delta is needed to know whether the
  280.                 // complete conflicting area is common in OURS and THEIRS.
  281.                 int minBSize = oursEndB - oursBeginB;
  282.                 int BSizeDelta = minBSize - (theirsEndB - theirsBeginB);
  283.                 if (BSizeDelta > 0)
  284.                     minBSize -= BSizeDelta;

  286.                 int commonPrefix = 0;
  287.                 while (commonPrefix < minBSize
  288.                         && cmp.equals(ours, oursBeginB + commonPrefix, theirs,
  289.                                 theirsBeginB + commonPrefix))
  290.                     commonPrefix++;
  291.                 minBSize -= commonPrefix;
  292.                 int commonSuffix = 0;
  293.                 while (commonSuffix < minBSize
  294.                         && cmp.equals(ours, oursEndB - commonSuffix - 1, theirs,
  295.                                 theirsEndB - commonSuffix - 1))
  296.                     commonSuffix++;
  297.                 minBSize -= commonSuffix;

  299.                 // Add the common lines at start of conflict
  300.                 if (commonPrefix > 0)
  301.                     result.add(1, oursBeginB, oursBeginB + commonPrefix,
  302.                             ConflictState.NO_CONFLICT);

  304.                 // Add the conflict (Only if there is a conflict left to report)
  305.                 if (minBSize > 0 || BSizeDelta != 0) {
  306.                     switch (strategy) {
  307.                     case OURS:
  308.                         result.add(1, oursBeginB + commonPrefix,
  309.                                 oursEndB - commonSuffix,
  310.                                 ConflictState.NO_CONFLICT);
  311.                         break;
  312.                     case THEIRS:
  313.                         result.add(2, theirsBeginB + commonPrefix,
  314.                                 theirsEndB - commonSuffix,
  315.                                 ConflictState.NO_CONFLICT);
  316.                         break;
  317.                     default:
  318.                         result.add(1, oursBeginB + commonPrefix,
  319.                                 oursEndB - commonSuffix,
  320.                                 ConflictState.FIRST_CONFLICTING_RANGE);
  321.                         result.add(2, theirsBeginB + commonPrefix,
  322.                                 theirsEndB - commonSuffix,
  323.                                 ConflictState.NEXT_CONFLICTING_RANGE);
  324.                         break;
  325.                     }
  326.                 }

  328.                 // Add the common lines at end of conflict
  329.                 if (commonSuffix > 0)
  330.                     result.add(1, oursEndB - commonSuffix, oursEndB,
  331.                             ConflictState.NO_CONFLICT);

  333.                 current = Math.max(oursEdit.getEndA(), theirsEdit.getEndA());
  334.                 oursEdit = nextOursEdit;
  335.                 theirsEdit = nextTheirsEdit;
  336.             }
  337.         }
  338.         // maybe we have a common part behind the last edit: copy it to the
  339.         // result
  340.         if (current < base.size()) {
  341.             result.add(0, current, base.size(), ConflictState.NO_CONFLICT);
  342.         }
  343.         return result;
  344.     }

  346.     /**
  347.      * Helper method which returns the next Edit for an Iterator over Edits.
  348.      * When there are no more edits left this method will return the constant
  349.      * END_EDIT.
  350.      *
  351.      * @param it
  352.      *            the iterator for which the next edit should be returned
  353.      * @return the next edit from the iterator or END_EDIT if there no more
  354.      *         edits
  355.      */
  356.     private static Edit nextEdit(Iterator<Edit> it) {
  357.         return (it.hasNext() ? it.next() : END_EDIT);
  358.     }
  359. }
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