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 */
43
44 package org.eclipse.jgit.merge;
45
46 import java.util.ArrayList;
47 import java.util.Iterator;
48 import java.util.List;
49
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;
57
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;
65
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 }
73
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 }
83
84 // An special edit which acts as a sentinel value by marking the end the
85 // list of edits
86 private final static Edittml#Edit">Edit END_EDIT = new Edit(Integer.MAX_VALUE,
87 Integer.MAX_VALUE);
88
89 @SuppressWarnings("ReferenceEquality")
90 private static boolean isEndEdit(Edit edit) {
91 return edit == END_EDIT;
92 }
93
94 /**
95 * Does the three way merge between a common base and two sequences.
96 *
97 * @param cmp comparison method for this execution.
98 * @param base the common base sequence
99 * @param ours the first sequence to be merged
100 * @param theirs the second sequence to be merged
101 * @return the resulting content
102 */
103 public <S extends Sequence> MergeResult<S> merge(
104 SequenceComparator<S> cmp, S base, S ours, S theirs) {
105 List<S> sequences = new ArrayList<>(3);
106 sequences.add(base);
107 sequences.add(ours);
108 sequences.add(theirs);
109 MergeResult<S> result = new MergeResult<>(sequences);
110
111 if (ours.size() == 0) {
112 if (theirs.size() != 0) {
113 EditList theirsEdits = diffAlg.diff(cmp, base, theirs);
114 if (!theirsEdits.isEmpty()) {
115 // we deleted, they modified -> Let their complete content
116 // conflict with empty text
117 result.add(1, 0, 0, ConflictState.FIRST_CONFLICTING_RANGE);
118 result.add(2, 0, theirs.size(),
119 ConflictState.NEXT_CONFLICTING_RANGE);
120 } else
121 // we deleted, they didn't modify -> Let our deletion win
122 result.add(1, 0, 0, ConflictState.NO_CONFLICT);
123 } else
124 // we and they deleted -> return a single chunk of nothing
125 result.add(1, 0, 0, ConflictState.NO_CONFLICT);
126 return result;
127 } else if (theirs.size() == 0) {
128 EditList oursEdits = diffAlg.diff(cmp, base, ours);
129 if (!oursEdits.isEmpty()) {
130 // we modified, they deleted -> Let our complete content
131 // conflict with empty text
132 result.add(1, 0, ours.size(),
133 ConflictState.FIRST_CONFLICTING_RANGE);
134 result.add(2, 0, 0, ConflictState.NEXT_CONFLICTING_RANGE);
135 } else
136 // they deleted, we didn't modify -> Let their deletion win
137 result.add(2, 0, 0, ConflictState.NO_CONFLICT);
138 return result;
139 }
140
141 EditList oursEdits = diffAlg.diff(cmp, base, ours);
142 Iterator<Edit> baseToOurs = oursEdits.iterator();
143 EditList theirsEdits = diffAlg.diff(cmp, base, theirs);
144 Iterator<Edit> baseToTheirs = theirsEdits.iterator();
145 int current = 0; // points to the next line (first line is 0) of base
146 // which was not handled yet
147 Edit oursEdit = nextEdit(baseToOurs);
148 Edit theirsEdit = nextEdit(baseToTheirs);
149
150 // iterate over all edits from base to ours and from base to theirs
151 // leave the loop when there are no edits more for ours or for theirs
152 // (or both)
153 while (!isEndEdit(theirsEdit) || !isEndEdit(oursEdit)) {
154 if (oursEdit.getEndA() < theirsEdit.getBeginA()) {
155 // something was changed in ours not overlapping with any change
156 // from theirs. First add the common part in front of the edit
157 // then the edit.
158 if (current != oursEdit.getBeginA()) {
159 result.add(0, current, oursEdit.getBeginA(),
160 ConflictState.NO_CONFLICT);
161 }
162 result.add(1, oursEdit.getBeginB(), oursEdit.getEndB(),
163 ConflictState.NO_CONFLICT);
164 current = oursEdit.getEndA();
165 oursEdit = nextEdit(baseToOurs);
166 } else if (theirsEdit.getEndA() < oursEdit.getBeginA()) {
167 // something was changed in theirs not overlapping with any
168 // from ours. First add the common part in front of the edit
169 // then the edit.
170 if (current != theirsEdit.getBeginA()) {
171 result.add(0, current, theirsEdit.getBeginA(),
172 ConflictState.NO_CONFLICT);
173 }
174 result.add(2, theirsEdit.getBeginB(), theirsEdit.getEndB(),
175 ConflictState.NO_CONFLICT);
176 current = theirsEdit.getEndA();
177 theirsEdit = nextEdit(baseToTheirs);
178 } else {
179 // here we found a real overlapping modification
180
181 // if there is a common part in front of the conflict add it
182 if (oursEdit.getBeginA() != current
183 && theirsEdit.getBeginA() != current) {
184 result.add(0, current, Math.min(oursEdit.getBeginA(),
185 theirsEdit.getBeginA()), ConflictState.NO_CONFLICT);
186 }
187
188 // set some initial values for the ranges in A and B which we
189 // want to handle
190 int oursBeginB = oursEdit.getBeginB();
191 int theirsBeginB = theirsEdit.getBeginB();
192 // harmonize the start of the ranges in A and B
193 if (oursEdit.getBeginA() < theirsEdit.getBeginA()) {
194 theirsBeginB -= theirsEdit.getBeginA()
195 - oursEdit.getBeginA();
196 } else {
197 oursBeginB -= oursEdit.getBeginA() - theirsEdit.getBeginA();
198 }
199
200 // combine edits:
201 // Maybe an Edit on one side corresponds to multiple Edits on
202 // the other side. Then we have to combine the Edits of the
203 // other side - so in the end we can merge together two single
204 // edits.
205 //
206 // It is important to notice that this combining will extend the
207 // ranges of our conflict always downwards (towards the end of
208 // the content). The starts of the conflicting ranges in ours
209 // and theirs are not touched here.
210 //
211 // This combining is an iterative process: after we have
212 // combined some edits we have to do the check again. The
213 // combined edits could now correspond to multiple edits on the
214 // other side.
215 //
216 // Example: when this combining algorithm works on the following
217 // edits
218 // oursEdits=((0-5,0-5),(6-8,6-8),(10-11,10-11)) and
219 // theirsEdits=((0-1,0-1),(2-3,2-3),(5-7,5-7))
220 // it will merge them into
221 // oursEdits=((0-8,0-8),(10-11,10-11)) and
222 // theirsEdits=((0-7,0-7))
223 //
224 // Since the only interesting thing to us is how in ours and
225 // theirs the end of the conflicting range is changing we let
226 // oursEdit and theirsEdit point to the last conflicting edit
227 Edit nextOursEdit = nextEdit(baseToOurs);
228 Edit nextTheirsEdit = nextEdit(baseToTheirs);
229 for (;;) {
230 if (oursEdit.getEndA() >= nextTheirsEdit.getBeginA()) {
231 theirsEdit = nextTheirsEdit;
232 nextTheirsEdit = nextEdit(baseToTheirs);
233 } else if (theirsEdit.getEndA() >= nextOursEdit.getBeginA()) {
234 oursEdit = nextOursEdit;
235 nextOursEdit = nextEdit(baseToOurs);
236 } else {
237 break;
238 }
239 }
240
241 // harmonize the end of the ranges in A and B
242 int oursEndB = oursEdit.getEndB();
243 int theirsEndB = theirsEdit.getEndB();
244 if (oursEdit.getEndA() < theirsEdit.getEndA()) {
245 oursEndB += theirsEdit.getEndA() - oursEdit.getEndA();
246 } else {
247 theirsEndB += oursEdit.getEndA() - theirsEdit.getEndA();
248 }
249
250 // A conflicting region is found. Strip off common lines in
251 // in the beginning and the end of the conflicting region
252
253 // Determine the minimum length of the conflicting areas in OURS
254 // and THEIRS. Also determine how much bigger the conflicting
255 // area in THEIRS is compared to OURS. All that is needed to
256 // limit the search for common areas at the beginning or end
257 // (the common areas cannot be bigger then the smaller
258 // conflicting area. The delta is needed to know whether the
259 // complete conflicting area is common in OURS and THEIRS.
260 int minBSize = oursEndB - oursBeginB;
261 int BSizeDelta = minBSize - (theirsEndB - theirsBeginB);
262 if (BSizeDelta > 0)
263 minBSize -= BSizeDelta;
264
265 int commonPrefix = 0;
266 while (commonPrefix < minBSize
267 && cmp.equals(ours, oursBeginB + commonPrefix, theirs,
268 theirsBeginB + commonPrefix))
269 commonPrefix++;
270 minBSize -= commonPrefix;
271 int commonSuffix = 0;
272 while (commonSuffix < minBSize
273 && cmp.equals(ours, oursEndB - commonSuffix - 1, theirs,
274 theirsEndB - commonSuffix - 1))
275 commonSuffix++;
276 minBSize -= commonSuffix;
277
278 // Add the common lines at start of conflict
279 if (commonPrefix > 0)
280 result.add(1, oursBeginB, oursBeginB + commonPrefix,
281 ConflictState.NO_CONFLICT);
282
283 // Add the conflict (Only if there is a conflict left to report)
284 if (minBSize > 0 || BSizeDelta != 0) {
285 result.add(1, oursBeginB + commonPrefix, oursEndB
286 - commonSuffix,
287 ConflictState.FIRST_CONFLICTING_RANGE);
288 result.add(2, theirsBeginB + commonPrefix, theirsEndB
289 - commonSuffix,
290 ConflictState.NEXT_CONFLICTING_RANGE);
291 }
292
293 // Add the common lines at end of conflict
294 if (commonSuffix > 0)
295 result.add(1, oursEndB - commonSuffix, oursEndB,
296 ConflictState.NO_CONFLICT);
297
298 current = Math.max(oursEdit.getEndA(), theirsEdit.getEndA());
299 oursEdit = nextOursEdit;
300 theirsEdit = nextTheirsEdit;
301 }
302 }
303 // maybe we have a common part behind the last edit: copy it to the
304 // result
305 if (current < base.size()) {
306 result.add(0, current, base.size(), ConflictState.NO_CONFLICT);
307 }
308 return result;
309 }
310
311 /**
312 * Helper method which returns the next Edit for an Iterator over Edits.
313 * When there are no more edits left this method will return the constant
314 * END_EDIT.
315 *
316 * @param it
317 * the iterator for which the next edit should be returned
318 * @return the next edit from the iterator or END_EDIT if there no more
319 * edits
320 */
321 private static Edit nextEdit(Iterator<Edit> it) {
322 return (it.hasNext() ? it.next() : END_EDIT);
323 }
324 }