org.eclipse.jgit/src/org/eclipse/jgit/merge/MergeAlgorithm.java - jgit - Git at Google

 /*
  * Copyright (C) 2009, Christian Halstrick <christian.halstrick@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.util.ArrayList;
 import java.util.Iterator;
 import java.util.List;

 import org.eclipse.jgit.diff.Edit;
 import org.eclipse.jgit.diff.EditList;
 import org.eclipse.jgit.diff.MyersDiff;
 import org.eclipse.jgit.diff.Sequence;
 import org.eclipse.jgit.merge.MergeChunk.ConflictState;

 /**
  * Provides the merge algorithm which does a three-way merge on content provided
  * as RawText. Makes use of {@link MyersDiff} to compute the diffs.
  */
 public final class MergeAlgorithm {

 	/**
 	 * Since this class provides only static methods I add a private default
 	 * constructor to prevent instantiation.
 	 */
 	private MergeAlgorithm() {
 	}

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

 	/**
 	 * Does the three way merge between a common base and two sequences.
 	 *
 	 * @param base the common base sequence
 	 * @param ours the first sequence to be merged
 	 * @param theirs the second sequence to be merged
 	 * @return the resulting content
 	 */
 	public static MergeResult merge(Sequence base, Sequence ours,
 			Sequence theirs) {
 		List<Sequence> sequences = new ArrayList<Sequence>(3);
 		sequences.add(base);
 		sequences.add(ours);
 		sequences.add(theirs);
 		MergeResult result = new MergeResult(sequences);
 		EditList oursEdits = new MyersDiff(base, ours).getEdits();
 		Iterator<Edit> baseToOurs = oursEdits.iterator();
 		EditList theirsEdits = new MyersDiff(base, theirs).getEdits();
 		Iterator<Edit> baseToTheirs = theirsEdits.iterator();
 		int current = 0; // points to the next line (first line is 0) of base
 		                 // which was not handled yet
 		Edit oursEdit = nextEdit(baseToOurs);
 		Edit theirsEdit = nextEdit(baseToTheirs);

 		// iterate over all edits from base to ours and from base to theirs
 		// leave the loop when there are no edits more for ours or for theirs
 		// (or both)
 		while (theirsEdit != END_EDIT || oursEdit != END_EDIT) {
 			if (oursEdit.getEndA() <= theirsEdit.getBeginA()) {
 				// something was changed in ours not overlapping with any change
 				// from theirs. First add the common part in front of the edit
 				// then the edit.
 				if (current != oursEdit.getBeginA()) {
 					result.add(0, current, oursEdit.getBeginA(),
 							ConflictState.NO_CONFLICT);
 				}
 				result.add(1, oursEdit.getBeginB(), oursEdit.getEndB(),
 						ConflictState.NO_CONFLICT);
 				current = oursEdit.getEndA();
 				oursEdit = nextEdit(baseToOurs);
 			} else if (theirsEdit.getEndA() <= oursEdit.getBeginA()) {
 				// something was changed in theirs not overlapping with any
 				// from ours. First add the common part in front of the edit
 				// then the edit.
 				if (current != theirsEdit.getBeginA()) {
 					result.add(0, current, theirsEdit.getBeginA(),
 							ConflictState.NO_CONFLICT);
 				}
 				result.add(2, theirsEdit.getBeginB(), theirsEdit.getEndB(),
 						ConflictState.NO_CONFLICT);
 				current = theirsEdit.getEndA();
 				theirsEdit = nextEdit(baseToTheirs);
 			} else {
 				// here we found a real overlapping modification

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

 				// set some initial values for the ranges in A and B which we
 				// want to handle
 				int oursBeginB = oursEdit.getBeginB();
 				int theirsBeginB = theirsEdit.getBeginB();
 				// harmonize the start of the ranges in A and B
 				if (oursEdit.getBeginA() < theirsEdit.getBeginA()) {
 					theirsBeginB -= theirsEdit.getBeginA()
 							- oursEdit.getBeginA();
 				} else {
 					oursBeginB -= oursEdit.getBeginA() - theirsEdit.getBeginA();
 				}

 				// combine edits:
 				// Maybe an Edit on one side corresponds to multiple Edits on
 				// the other side. Then we have to combine the Edits of the
 				// other side - so in the end we can merge together two single
 				// edits.
 				//
 				// It is important to notice that this combining will extend the
 				// ranges of our conflict always downwards (towards the end of
 				// the content). The starts of the conflicting ranges in ours
 				// and theirs are not touched here.
 				//
 				// This combining is an iterative process: after we have
 				// combined some edits we have to do the check again. The
 				// combined edits could now correspond to multiple edits on the
 				// other side.
 				//
 				// Example: when this combining algorithm works on the following
 				// edits
 				// oursEdits=((0-5,0-5),(6-8,6-8),(10-11,10-11)) and
 				// theirsEdits=((0-1,0-1),(2-3,2-3),(5-7,5-7))
 				// it will merge them into
 				// oursEdits=((0-8,0-8),(10-11,10-11)) and
 				// theirsEdits=((0-7,0-7))
 				//
 				// Since the only interesting thing to us is how in ours and
 				// theirs the end of the conflicting range is changing we let
 				// oursEdit and theirsEdit point to the last conflicting edit
 				Edit nextOursEdit = nextEdit(baseToOurs);
 				Edit nextTheirsEdit = nextEdit(baseToTheirs);
 				for (;;) {
 					if (oursEdit.getEndA() > nextTheirsEdit.getBeginA()) {
 						theirsEdit = nextTheirsEdit;
 						nextTheirsEdit = nextEdit(baseToTheirs);
 					} else if (theirsEdit.getEndA() > nextOursEdit.getBeginA()) {
 						oursEdit = nextOursEdit;
 						nextOursEdit = nextEdit(baseToOurs);
 					} else {
 						break;
 					}
 				}

 				// harmonize the end of the ranges in A and B
 				int oursEndB = oursEdit.getEndB();
 				int theirsEndB = theirsEdit.getEndB();
 				if (oursEdit.getEndA() < theirsEdit.getEndA()) {
 					oursEndB += theirsEdit.getEndA() - oursEdit.getEndA();
 				} else {
 					theirsEndB += oursEdit.getEndA() - theirsEdit.getEndA();
 				}

 				// Add the conflict
 				result.add(1, oursBeginB, oursEndB,
 						ConflictState.FIRST_CONFLICTING_RANGE);
 				result.add(2, theirsBeginB, theirsEndB,
 						ConflictState.NEXT_CONFLICTING_RANGE);

 				current = Math.max(oursEdit.getEndA(), theirsEdit.getEndA());
 				oursEdit = nextOursEdit;
 				theirsEdit = nextTheirsEdit;
 			}
 		}
 		// maybe we have a common part behind the last edit: copy it to the
 		// result
 		if (current < base.size()) {
 			result.add(0, current, base.size(), ConflictState.NO_CONFLICT);
 		}
 		return result;
 	}

 	/**
 	 * Helper method which returns the next Edit for an Iterator over Edits.
 	 * When there are no more edits left this method will return the constant
 	 * END_EDIT.
 	 *
 	 * @param it
 	 *            the iterator for which the next edit should be returned
 	 * @return the next edit from the iterator or END_EDIT if there no more
 	 *         edits
 	 */
 	private static Edit nextEdit(Iterator<Edit> it) {
 		return (it.hasNext() ? it.next() : END_EDIT);
 	}
 }
	/*
	* Copyright (C) 2009, Christian Halstrick <christian.halstrick@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.util.ArrayList;
	import java.util.Iterator;
	import java.util.List;

	import org.eclipse.jgit.diff.Edit;
	import org.eclipse.jgit.diff.EditList;
	import org.eclipse.jgit.diff.MyersDiff;
	import org.eclipse.jgit.diff.Sequence;
	import org.eclipse.jgit.merge.MergeChunk.ConflictState;

	/**
	* Provides the merge algorithm which does a three-way merge on content provided
	* as RawText. Makes use of {@link MyersDiff} to compute the diffs.
	*/
	public final class MergeAlgorithm {

	/**
	* Since this class provides only static methods I add a private default
	* constructor to prevent instantiation.
	*/
	private MergeAlgorithm() {
	}

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

	/**
	* Does the three way merge between a common base and two sequences.
	*
	* @param base the common base sequence
	* @param ours the first sequence to be merged
	* @param theirs the second sequence to be merged
	* @return the resulting content
	*/
	public static MergeResult merge(Sequence base, Sequence ours,
	Sequence theirs) {
	List<Sequence> sequences = new ArrayList<Sequence>(3);
	sequences.add(base);
	sequences.add(ours);
	sequences.add(theirs);
	MergeResult result = new MergeResult(sequences);
	EditList oursEdits = new MyersDiff(base, ours).getEdits();
	Iterator<Edit> baseToOurs = oursEdits.iterator();
	EditList theirsEdits = new MyersDiff(base, theirs).getEdits();
	Iterator<Edit> baseToTheirs = theirsEdits.iterator();
	int current = 0; // points to the next line (first line is 0) of base
	// which was not handled yet
	Edit oursEdit = nextEdit(baseToOurs);
	Edit theirsEdit = nextEdit(baseToTheirs);

	// iterate over all edits from base to ours and from base to theirs
	// leave the loop when there are no edits more for ours or for theirs
	// (or both)
	while (theirsEdit != END_EDIT \|\| oursEdit != END_EDIT) {
	if (oursEdit.getEndA() <= theirsEdit.getBeginA()) {
	// something was changed in ours not overlapping with any change
	// from theirs. First add the common part in front of the edit
	// then the edit.
	if (current != oursEdit.getBeginA()) {
	result.add(0, current, oursEdit.getBeginA(),
	ConflictState.NO_CONFLICT);
	}
	result.add(1, oursEdit.getBeginB(), oursEdit.getEndB(),
	ConflictState.NO_CONFLICT);
	current = oursEdit.getEndA();
	oursEdit = nextEdit(baseToOurs);
	} else if (theirsEdit.getEndA() <= oursEdit.getBeginA()) {
	// something was changed in theirs not overlapping with any
	// from ours. First add the common part in front of the edit
	// then the edit.
	if (current != theirsEdit.getBeginA()) {
	result.add(0, current, theirsEdit.getBeginA(),
	ConflictState.NO_CONFLICT);
	}
	result.add(2, theirsEdit.getBeginB(), theirsEdit.getEndB(),
	ConflictState.NO_CONFLICT);
	current = theirsEdit.getEndA();
	theirsEdit = nextEdit(baseToTheirs);
	} else {
	// here we found a real overlapping modification

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

	// set some initial values for the ranges in A and B which we
	// want to handle
	int oursBeginB = oursEdit.getBeginB();
	int theirsBeginB = theirsEdit.getBeginB();
	// harmonize the start of the ranges in A and B
	if (oursEdit.getBeginA() < theirsEdit.getBeginA()) {
	theirsBeginB -= theirsEdit.getBeginA()
	- oursEdit.getBeginA();
	} else {
	oursBeginB -= oursEdit.getBeginA() - theirsEdit.getBeginA();
	}

	// combine edits:
	// Maybe an Edit on one side corresponds to multiple Edits on
	// the other side. Then we have to combine the Edits of the
	// other side - so in the end we can merge together two single
	// edits.
	//
	// It is important to notice that this combining will extend the
	// ranges of our conflict always downwards (towards the end of
	// the content). The starts of the conflicting ranges in ours
	// and theirs are not touched here.
	//
	// This combining is an iterative process: after we have
	// combined some edits we have to do the check again. The
	// combined edits could now correspond to multiple edits on the
	// other side.
	//
	// Example: when this combining algorithm works on the following
	// edits
	// oursEdits=((0-5,0-5),(6-8,6-8),(10-11,10-11)) and
	// theirsEdits=((0-1,0-1),(2-3,2-3),(5-7,5-7))
	// it will merge them into
	// oursEdits=((0-8,0-8),(10-11,10-11)) and
	// theirsEdits=((0-7,0-7))
	//
	// Since the only interesting thing to us is how in ours and
	// theirs the end of the conflicting range is changing we let
	// oursEdit and theirsEdit point to the last conflicting edit
	Edit nextOursEdit = nextEdit(baseToOurs);
	Edit nextTheirsEdit = nextEdit(baseToTheirs);
	for (;;) {
	if (oursEdit.getEndA() > nextTheirsEdit.getBeginA()) {
	theirsEdit = nextTheirsEdit;
	nextTheirsEdit = nextEdit(baseToTheirs);
	} else if (theirsEdit.getEndA() > nextOursEdit.getBeginA()) {
	oursEdit = nextOursEdit;
	nextOursEdit = nextEdit(baseToOurs);
	} else {
	break;
	}
	}

	// harmonize the end of the ranges in A and B
	int oursEndB = oursEdit.getEndB();
	int theirsEndB = theirsEdit.getEndB();
	if (oursEdit.getEndA() < theirsEdit.getEndA()) {
	oursEndB += theirsEdit.getEndA() - oursEdit.getEndA();
	} else {
	theirsEndB += oursEdit.getEndA() - theirsEdit.getEndA();
	}

	// Add the conflict
	result.add(1, oursBeginB, oursEndB,
	ConflictState.FIRST_CONFLICTING_RANGE);
	result.add(2, theirsBeginB, theirsEndB,
	ConflictState.NEXT_CONFLICTING_RANGE);

	current = Math.max(oursEdit.getEndA(), theirsEdit.getEndA());
	oursEdit = nextOursEdit;
	theirsEdit = nextTheirsEdit;
	}
	}
	// maybe we have a common part behind the last edit: copy it to the
	// result
	if (current < base.size()) {
	result.add(0, current, base.size(), ConflictState.NO_CONFLICT);
	}
	return result;
	}

	/**
	* Helper method which returns the next Edit for an Iterator over Edits.
	* When there are no more edits left this method will return the constant
	* END_EDIT.
	*
	* @param it
	* the iterator for which the next edit should be returned
	* @return the next edit from the iterator or END_EDIT if there no more
	* edits
	*/
	private static Edit nextEdit(Iterator<Edit> it) {
	return (it.hasNext() ? it.next() : END_EDIT);
	}
	}