| /* |
| * Copyright (C) 2010, Google Inc. |
| * 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.diff; |
| |
| /** |
| * Compares two {@link Sequence}s to create an {@link EditList} of changes. |
| * <p> |
| * An algorithm's {@code diff} method must be callable from concurrent threads |
| * without data collisions. This permits some algorithms to use a singleton |
| * pattern, with concurrent invocations using the same singleton. Other |
| * algorithms may support parameterization, in which case the caller can create |
| * a unique instance per thread. |
| */ |
| public abstract class DiffAlgorithm { |
| /** |
| * Supported diff algorithm |
| */ |
| public enum SupportedAlgorithm { |
| /** |
| * Myers diff algorithm |
| */ |
| MYERS, |
| |
| /** |
| * Histogram diff algorithm |
| */ |
| HISTOGRAM |
| } |
| |
| /** |
| * @param alg |
| * the diff algorithm for which an implementation should be |
| * returned |
| * @return an implementation of the specified diff algorithm |
| */ |
| public static DiffAlgorithm getAlgorithm(SupportedAlgorithm alg) { |
| switch (alg) { |
| case MYERS: |
| return MyersDiff.INSTANCE; |
| case HISTOGRAM: |
| return new HistogramDiff(); |
| default: |
| throw new IllegalArgumentException(); |
| } |
| } |
| |
| /** |
| * Compare two sequences and identify a list of edits between them. |
| * |
| * @param <S> |
| * type of sequence being compared. |
| * @param cmp |
| * the comparator supplying the element equivalence function. |
| * @param a |
| * the first (also known as old or pre-image) sequence. Edits |
| * returned by this algorithm will reference indexes using the |
| * 'A' side: {@link Edit#getBeginA()}, {@link Edit#getEndA()}. |
| * @param b |
| * the second (also known as new or post-image) sequence. Edits |
| * returned by this algorithm will reference indexes using the |
| * 'B' side: {@link Edit#getBeginB()}, {@link Edit#getEndB()}. |
| * @return a modifiable edit list comparing the two sequences. If empty, the |
| * sequences are identical according to {@code cmp}'s rules. The |
| * result list is never null. |
| */ |
| public <S extends Sequence> EditList diff( |
| SequenceComparator<? super S> cmp, S a, S b) { |
| Edit region = cmp.reduceCommonStartEnd(a, b, coverEdit(a, b)); |
| |
| switch (region.getType()) { |
| case INSERT: |
| case DELETE: |
| return EditList.singleton(region); |
| |
| case REPLACE: { |
| if (region.getLengthA() == 1 && region.getLengthB() == 1) |
| return EditList.singleton(region); |
| |
| SubsequenceComparator<S> cs = new SubsequenceComparator<>(cmp); |
| Subsequence<S> as = Subsequence.a(a, region); |
| Subsequence<S> bs = Subsequence.b(b, region); |
| EditList e = Subsequence.toBase(diffNonCommon(cs, as, bs), as, bs); |
| return normalize(cmp, e, a, b); |
| } |
| |
| case EMPTY: |
| return new EditList(0); |
| |
| default: |
| throw new IllegalStateException(); |
| } |
| } |
| |
| private static <S extends Sequence> Edit coverEdit(S a, S b) { |
| return new Edit(0, a.size(), 0, b.size()); |
| } |
| |
| /** |
| * Reorganize an {@link EditList} for better diff consistency. |
| * <p> |
| * {@code DiffAlgorithms} may return {@link Edit.Type#INSERT} or |
| * {@link Edit.Type#DELETE} edits that can be "shifted". For |
| * example, the deleted section |
| * <pre> |
| * -a |
| * -b |
| * -c |
| * a |
| * b |
| * c |
| * </pre> |
| * can be shifted down by 1, 2 or 3 locations. |
| * <p> |
| * To avoid later merge issues, we shift such edits to a |
| * consistent location. {@code normalize} uses a simple strategy of |
| * shifting such edits to their latest possible location. |
| * <p> |
| * This strategy may not always produce an aesthetically pleasing |
| * diff. For instance, it works well with |
| * <pre> |
| * function1 { |
| * ... |
| * } |
| * |
| * +function2 { |
| * + ... |
| * +} |
| * + |
| * function3 { |
| * ... |
| * } |
| * </pre> |
| * but less so for |
| * <pre> |
| * # |
| * # comment1 |
| * # |
| * function1() { |
| * } |
| * |
| * # |
| * +# comment3 |
| * +# |
| * +function3() { |
| * +} |
| * + |
| * +# |
| * # comment2 |
| * # |
| * function2() { |
| * } |
| * </pre> |
| * <a href="https://github.com/mhagger/diff-slider-tools">More |
| * sophisticated strategies</a> are possible, say by calculating a |
| * suitable "aesthetic cost" for each possible position and using |
| * the lowest cost, but {@code normalize} just shifts edits |
| * to the end as much as possible. |
| * |
| * @param <S> |
| * type of sequence being compared. |
| * @param cmp |
| * the comparator supplying the element equivalence function. |
| * @param e |
| * a modifiable edit list comparing the provided sequences. |
| * @param a |
| * the first (also known as old or pre-image) sequence. |
| * @param b |
| * the second (also known as new or post-image) sequence. |
| * @return a modifiable edit list with edit regions shifted to their |
| * latest possible location. The result list is never null. |
| * @since 4.7 |
| */ |
| private static <S extends Sequence> EditList normalize( |
| SequenceComparator<? super S> cmp, EditList e, S a, S b) { |
| Edit prev = null; |
| for (int i = e.size() - 1; i >= 0; i--) { |
| Edit cur = e.get(i); |
| Edit.Type curType = cur.getType(); |
| |
| int maxA = (prev == null) ? a.size() : prev.beginA; |
| int maxB = (prev == null) ? b.size() : prev.beginB; |
| |
| if (curType == Edit.Type.INSERT) { |
| while (cur.endA < maxA && cur.endB < maxB |
| && cmp.equals(b, cur.beginB, b, cur.endB)) { |
| cur.shift(1); |
| } |
| } else if (curType == Edit.Type.DELETE) { |
| while (cur.endA < maxA && cur.endB < maxB |
| && cmp.equals(a, cur.beginA, a, cur.endA)) { |
| cur.shift(1); |
| } |
| } |
| prev = cur; |
| } |
| return e; |
| } |
| |
| /** |
| * Compare two sequences and identify a list of edits between them. |
| * |
| * This method should be invoked only after the two sequences have been |
| * proven to have no common starting or ending elements. The expected |
| * elimination of common starting and ending elements is automatically |
| * performed by the {@link #diff(SequenceComparator, Sequence, Sequence)} |
| * method, which invokes this method using {@link Subsequence}s. |
| * |
| * @param <S> |
| * type of sequence being compared. |
| * @param cmp |
| * the comparator supplying the element equivalence function. |
| * @param a |
| * the first (also known as old or pre-image) sequence. Edits |
| * returned by this algorithm will reference indexes using the |
| * 'A' side: {@link Edit#getBeginA()}, {@link Edit#getEndA()}. |
| * @param b |
| * the second (also known as new or post-image) sequence. Edits |
| * returned by this algorithm will reference indexes using the |
| * 'B' side: {@link Edit#getBeginB()}, {@link Edit#getEndB()}. |
| * @return a modifiable edit list comparing the two sequences. |
| */ |
| public abstract <S extends Sequence> EditList diffNonCommon( |
| SequenceComparator<? super S> cmp, S a, S b); |
| } |
