org.eclipse.jgit/src/org/eclipse/jgit/api/DescribeCommand.java - sop/jgit - Git at Google

 /*
  * Copyright (C) 2013, CloudBees, 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.api;

 import static org.eclipse.jgit.lib.Constants.R_TAGS;

 import java.io.IOException;
 import java.text.MessageFormat;
 import java.util.ArrayList;
 import java.util.Collection;
 import java.util.Collections;
 import java.util.Comparator;
 import java.util.List;
 import java.util.Map;
 import java.util.Optional;
 import java.util.stream.Collectors;

 import org.eclipse.jgit.api.errors.GitAPIException;
 import org.eclipse.jgit.api.errors.JGitInternalException;
 import org.eclipse.jgit.api.errors.RefNotFoundException;
 import org.eclipse.jgit.errors.IncorrectObjectTypeException;
 import org.eclipse.jgit.errors.InvalidPatternException;
 import org.eclipse.jgit.errors.MissingObjectException;
 import org.eclipse.jgit.ignore.internal.IMatcher;
 import org.eclipse.jgit.ignore.internal.PathMatcher;
 import org.eclipse.jgit.internal.JGitText;
 import org.eclipse.jgit.lib.Constants;
 import org.eclipse.jgit.lib.ObjectId;
 import org.eclipse.jgit.lib.Ref;
 import org.eclipse.jgit.lib.Repository;
 import org.eclipse.jgit.revwalk.RevCommit;
 import org.eclipse.jgit.revwalk.RevFlag;
 import org.eclipse.jgit.revwalk.RevFlagSet;
 import org.eclipse.jgit.revwalk.RevWalk;

 /**
  * Given a commit, show the most recent tag that is reachable from a commit.
  *
  * @since 3.2
  */
 public class DescribeCommand extends GitCommand<String> {
 	private final RevWalk w;

 	/**
 	 * Commit to describe.
 	 */
 	private RevCommit target;

 	/**
 	 * How many tags we'll consider as candidates.
 	 * This can only go up to the number of flags JGit can support in a walk,
 	 * which is 24.
 	 */
 	private int maxCandidates = 10;

 	/**
 	 * Whether to always use long output format or not.
 	 */
 	private boolean longDesc;

 	/**
 	 * Pattern matchers to be applied to tags under consideration
 	 */
 	private List<IMatcher> matchers = new ArrayList<>();

 	/**
 	 *
 	 * @param repo
 	 */
 	protected DescribeCommand(Repository repo) {
 		super(repo);
 		w = new RevWalk(repo);
 		w.setRetainBody(false);
 	}

 	/**
 	 * Sets the commit to be described.
 	 *
 	 * @param target
 	 * 		A non-null object ID to be described.
 	 * @return {@code this}
 	 * @throws MissingObjectException
 	 *             the supplied commit does not exist.
 	 * @throws IncorrectObjectTypeException
 	 *             the supplied id is not a commit or an annotated tag.
 	 * @throws IOException
 	 *             a pack file or loose object could not be read.
 	 */
 	public DescribeCommand setTarget(ObjectId target) throws IOException {
 		this.target = w.parseCommit(target);
 		return this;
 	}

 	/**
 	 * Sets the commit to be described.
 	 *
 	 * @param rev
 	 * 		Commit ID, tag, branch, ref, etc.
 	 * 		See {@link Repository#resolve(String)} for allowed syntax.
 	 * @return {@code this}
 	 * @throws IncorrectObjectTypeException
 	 *             the supplied id is not a commit or an annotated tag.
 	 * @throws RefNotFoundException
 	 * 				the given rev didn't resolve to any object.
 	 * @throws IOException
 	 *             a pack file or loose object could not be read.
 	 */
 	public DescribeCommand setTarget(String rev) throws IOException,
 			RefNotFoundException {
 		ObjectId id = repo.resolve(rev);
 		if (id == null)
 			throw new RefNotFoundException(MessageFormat.format(JGitText.get().refNotResolved, rev));
 		return setTarget(id);
 	}

 	/**
 	 * Determine whether always to use the long format or not. When set to
 	 * <code>true</code> the long format is used even the commit matches a tag.
 	 *
 	 * @param longDesc
 	 *            <code>true</code> if always the long format should be used.
 	 * @return {@code this}
 	 *
 	 * @see <a
 	 *      href="https://www.kernel.org/pub/software/scm/git/docs/git-describe.html"
 	 *      >Git documentation about describe</a>
 	 * @since 4.0
 	 */
 	public DescribeCommand setLong(boolean longDesc) {
 		this.longDesc = longDesc;
 		return this;
 	}

 	private String longDescription(Ref tag, int depth, ObjectId tip)
 			throws IOException {
 		return String.format(
 				"%s-%d-g%s", tag.getName().substring(R_TAGS.length()), //$NON-NLS-1$
 				Integer.valueOf(depth), w.getObjectReader().abbreviate(tip)
 						.name());
 	}

 	/**
 	 * Sets one or more {@code glob(7)} patterns that tags must match to be considered.
 	 * If multiple patterns are provided, tags only need match one of them.
 	 *
 	 * @param patterns the {@code glob(7)} pattern or patterns
 	 * @return {@code this}
 	 * @throws InvalidPatternException if the pattern passed in was invalid.
 	 *
 	 * @see <a
 	 *      href="https://www.kernel.org/pub/software/scm/git/docs/git-describe.html"
 	 *      >Git documentation about describe</a>
 	 * @since 4.9
 	 */
 	public DescribeCommand setMatch(String... patterns) throws InvalidPatternException {
 		for (String p : patterns) {
 			matchers.add(PathMatcher.createPathMatcher(p, null, false));
 		}
 		return this;
 	}

 	private Optional<Ref> getBestMatch(List<Ref> tags) {
 		if (tags == null || tags.size() == 0) {
 			return Optional.empty();
 		} else if (matchers.size() == 0) {
 			// No matchers, simply return the first tag entry
 			return Optional.of(tags.get(0));
 		} else {
 			// Find the first tag that matches one of the matchers; precedence according to matcher definition order
 			for (IMatcher matcher : matchers) {
 				Optional<Ref> match = tags.stream()
 						.filter(tag -> matcher.matches(tag.getName(), false))
 						.findFirst();
 				if (match.isPresent()) {
 					return match;
 				}
 			}
 			return Optional.empty();
 		}
 	}

 	private ObjectId getObjectIdFromRef(Ref r) {
 		ObjectId key = repo.peel(r).getPeeledObjectId();
 		if (key == null) {
 			key = r.getObjectId();
 		}
 		return key;
 	}

 	/**
 	 * Describes the specified commit. Target defaults to HEAD if no commit was
 	 * set explicitly.
 	 *
 	 * @return if there's a tag that points to the commit being described, this
 	 *         tag name is returned. Otherwise additional suffix is added to the
 	 *         nearest tag, just like git-describe(1).
 	 *         <p>
 	 *         If none of the ancestors of the commit being described has any
 	 *         tags at all, then this method returns null, indicating that
 	 *         there's no way to describe this tag.
 	 */
 	@Override
 	public String call() throws GitAPIException {
 		try {
 			checkCallable();

 			if (target == null)
 				setTarget(Constants.HEAD);

 			Collection<Ref> tagList = repo.getRefDatabase().getRefs(R_TAGS).values();
 			Map<ObjectId, List<Ref>> tags = tagList.stream()
 					.collect(Collectors.groupingBy(this::getObjectIdFromRef));

 			// combined flags of all the candidate instances
 			final RevFlagSet allFlags = new RevFlagSet();

 			/**
 			 * Tracks the depth of each tag as we find them.
 			 */
 			class Candidate {
 				final Ref tag;
 				final RevFlag flag;

 				/**
 				 * This field counts number of commits that are reachable from
 				 * the tip but not reachable from the tag.
 				 */
 				int depth;

 				Candidate(RevCommit commit, Ref tag) {
 					this.tag = tag;
 					this.flag = w.newFlag(tag.getName());
 					// we'll mark all the nodes reachable from this tag accordingly
 					allFlags.add(flag);
 					w.carry(flag);
 					commit.add(flag);
 					// As of this writing, JGit carries a flag from a child to its parents
 					// right before RevWalk.next() returns, so all the flags that are added
 					// must be manually carried to its parents. If that gets fixed,
 					// this will be unnecessary.
 					commit.carry(flag);
 				}

 				/**
 				 * Does this tag contain the given commit?
 				 */
 				boolean reaches(RevCommit c) {
 					return c.has(flag);
 				}

 				String describe(ObjectId tip) throws IOException {
 					return longDescription(tag, depth, tip);
 				}

 			}
 			List<Candidate> candidates = new ArrayList<>();    // all the candidates we find

 			// is the target already pointing to a suitable tag? if so, we are done!
 			Optional<Ref> bestMatch = getBestMatch(tags.get(target));
 			if (bestMatch.isPresent()) {
 				return longDesc ? longDescription(bestMatch.get(), 0, target) :
 						bestMatch.get().getName().substring(R_TAGS.length());
 			}

 			w.markStart(target);

 			int seen = 0;   // commit seen thus far
 			RevCommit c;
 			while ((c = w.next()) != null) {
 				if (!c.hasAny(allFlags)) {
 					// if a tag already dominates this commit,
 					// then there's no point in picking a tag on this commit
 					// since the one that dominates it is always more preferable
 					bestMatch = getBestMatch(tags.get(c));
 					if (bestMatch.isPresent()) {
 						Candidate cd = new Candidate(c, bestMatch.get());
 						candidates.add(cd);
 						cd.depth = seen;
 					}
 				}

 				// if the newly discovered commit isn't reachable from a tag that we've seen
 				// it counts toward the total depth.
 				for (Candidate cd : candidates) {
 					if (!cd.reaches(c))
 						cd.depth++;
 				}

 				// if we have search going for enough tags, we will start
 				// closing down. JGit can only give us a finite number of bits,
 				// so we can't track all tags even if we wanted to.
 				if (candidates.size() >= maxCandidates)
 					break;

 				// TODO: if all the commits in the queue of RevWalk has allFlags
 				// there's no point in continuing search as we'll not discover any more
 				// tags. But RevWalk doesn't expose this.
 				seen++;
 			}

 			// at this point we aren't adding any more tags to our search,
 			// but we still need to count all the depths correctly.
 			while ((c = w.next()) != null) {
 				if (c.hasAll(allFlags)) {
 					// no point in visiting further from here, so cut the search here
 					for (RevCommit p : c.getParents())
 						p.add(RevFlag.SEEN);
 				} else {
 					for (Candidate cd : candidates) {
 						if (!cd.reaches(c))
 							cd.depth++;
 					}
 				}
 			}

 			// if all the nodes are dominated by all the tags, the walk stops
 			if (candidates.isEmpty())
 				return null;

 			Candidate best = Collections.min(candidates, new Comparator<Candidate>() {
 				@Override
 				public int compare(Candidate o1, Candidate o2) {
 					return o1.depth - o2.depth;
 				}
 			});

 			return best.describe(target);
 		} catch (IOException e) {
 			throw new JGitInternalException(e.getMessage(), e);
 		} finally {
 			setCallable(false);
 			w.close();
 		}
 	}
 }
	/*
	* Copyright (C) 2013, CloudBees, 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.api;

	import static org.eclipse.jgit.lib.Constants.R_TAGS;

	import java.io.IOException;
	import java.text.MessageFormat;
	import java.util.ArrayList;
	import java.util.Collection;
	import java.util.Collections;
	import java.util.Comparator;
	import java.util.List;
	import java.util.Map;
	import java.util.Optional;
	import java.util.stream.Collectors;

	import org.eclipse.jgit.api.errors.GitAPIException;
	import org.eclipse.jgit.api.errors.JGitInternalException;
	import org.eclipse.jgit.api.errors.RefNotFoundException;
	import org.eclipse.jgit.errors.IncorrectObjectTypeException;
	import org.eclipse.jgit.errors.InvalidPatternException;
	import org.eclipse.jgit.errors.MissingObjectException;
	import org.eclipse.jgit.ignore.internal.IMatcher;
	import org.eclipse.jgit.ignore.internal.PathMatcher;
	import org.eclipse.jgit.internal.JGitText;
	import org.eclipse.jgit.lib.Constants;
	import org.eclipse.jgit.lib.ObjectId;
	import org.eclipse.jgit.lib.Ref;
	import org.eclipse.jgit.lib.Repository;
	import org.eclipse.jgit.revwalk.RevCommit;
	import org.eclipse.jgit.revwalk.RevFlag;
	import org.eclipse.jgit.revwalk.RevFlagSet;
	import org.eclipse.jgit.revwalk.RevWalk;

	/**
	* Given a commit, show the most recent tag that is reachable from a commit.
	*
	* @since 3.2
	*/
	public class DescribeCommand extends GitCommand<String> {
	private final RevWalk w;

	/**
	* Commit to describe.
	*/
	private RevCommit target;

	/**
	* How many tags we'll consider as candidates.
	* This can only go up to the number of flags JGit can support in a walk,
	* which is 24.
	*/
	private int maxCandidates = 10;

	/**
	* Whether to always use long output format or not.
	*/
	private boolean longDesc;

	/**
	* Pattern matchers to be applied to tags under consideration
	*/
	private List<IMatcher> matchers = new ArrayList<>();

	/**
	*
	* @param repo
	*/
	protected DescribeCommand(Repository repo) {
	super(repo);
	w = new RevWalk(repo);
	w.setRetainBody(false);
	}

	/**
	* Sets the commit to be described.
	*
	* @param target
	* A non-null object ID to be described.
	* @return {@code this}
	* @throws MissingObjectException
	* the supplied commit does not exist.
	* @throws IncorrectObjectTypeException
	* the supplied id is not a commit or an annotated tag.
	* @throws IOException
	* a pack file or loose object could not be read.
	*/
	public DescribeCommand setTarget(ObjectId target) throws IOException {
	this.target = w.parseCommit(target);
	return this;
	}

	/**
	* Sets the commit to be described.
	*
	* @param rev
	* Commit ID, tag, branch, ref, etc.
	* See {@link Repository#resolve(String)} for allowed syntax.
	* @return {@code this}
	* @throws IncorrectObjectTypeException
	* the supplied id is not a commit or an annotated tag.
	* @throws RefNotFoundException
	* the given rev didn't resolve to any object.
	* @throws IOException
	* a pack file or loose object could not be read.
	*/
	public DescribeCommand setTarget(String rev) throws IOException,
	RefNotFoundException {
	ObjectId id = repo.resolve(rev);
	if (id == null)
	throw new RefNotFoundException(MessageFormat.format(JGitText.get().refNotResolved, rev));
	return setTarget(id);
	}

	/**
	* Determine whether always to use the long format or not. When set to
	* <code>true</code> the long format is used even the commit matches a tag.
	*
	* @param longDesc
	* <code>true</code> if always the long format should be used.
	* @return {@code this}
	*
	* @see <a
	* href="https://www.kernel.org/pub/software/scm/git/docs/git-describe.html"
	* >Git documentation about describe</a>
	* @since 4.0
	*/
	public DescribeCommand setLong(boolean longDesc) {
	this.longDesc = longDesc;
	return this;
	}

	private String longDescription(Ref tag, int depth, ObjectId tip)
	throws IOException {
	return String.format(
	"%s-%d-g%s", tag.getName().substring(R_TAGS.length()), //$NON-NLS-1$
	Integer.valueOf(depth), w.getObjectReader().abbreviate(tip)
	.name());
	}

	/**
	* Sets one or more {@code glob(7)} patterns that tags must match to be considered.
	* If multiple patterns are provided, tags only need match one of them.
	*
	* @param patterns the {@code glob(7)} pattern or patterns
	* @return {@code this}
	* @throws InvalidPatternException if the pattern passed in was invalid.
	*
	* @see <a
	* href="https://www.kernel.org/pub/software/scm/git/docs/git-describe.html"
	* >Git documentation about describe</a>
	* @since 4.9
	*/
	public DescribeCommand setMatch(String... patterns) throws InvalidPatternException {
	for (String p : patterns) {
	matchers.add(PathMatcher.createPathMatcher(p, null, false));
	}
	return this;
	}

	private Optional<Ref> getBestMatch(List<Ref> tags) {
	if (tags == null \|\| tags.size() == 0) {
	return Optional.empty();
	} else if (matchers.size() == 0) {
	// No matchers, simply return the first tag entry
	return Optional.of(tags.get(0));
	} else {
	// Find the first tag that matches one of the matchers; precedence according to matcher definition order
	for (IMatcher matcher : matchers) {
	Optional<Ref> match = tags.stream()
	.filter(tag -> matcher.matches(tag.getName(), false))
	.findFirst();
	if (match.isPresent()) {
	return match;
	}
	}
	return Optional.empty();
	}
	}

	private ObjectId getObjectIdFromRef(Ref r) {
	ObjectId key = repo.peel(r).getPeeledObjectId();
	if (key == null) {
	key = r.getObjectId();
	}
	return key;
	}

	/**
	* Describes the specified commit. Target defaults to HEAD if no commit was
	* set explicitly.
	*
	* @return if there's a tag that points to the commit being described, this
	* tag name is returned. Otherwise additional suffix is added to the
	* nearest tag, just like git-describe(1).
	* <p>
	* If none of the ancestors of the commit being described has any
	* tags at all, then this method returns null, indicating that
	* there's no way to describe this tag.
	*/
	@Override
	public String call() throws GitAPIException {
	try {
	checkCallable();

	if (target == null)
	setTarget(Constants.HEAD);

	Collection<Ref> tagList = repo.getRefDatabase().getRefs(R_TAGS).values();
	Map<ObjectId, List<Ref>> tags = tagList.stream()
	.collect(Collectors.groupingBy(this::getObjectIdFromRef));

	// combined flags of all the candidate instances
	final RevFlagSet allFlags = new RevFlagSet();

	/**
	* Tracks the depth of each tag as we find them.
	*/
	class Candidate {
	final Ref tag;
	final RevFlag flag;

	/**
	* This field counts number of commits that are reachable from
	* the tip but not reachable from the tag.
	*/
	int depth;

	Candidate(RevCommit commit, Ref tag) {
	this.tag = tag;
	this.flag = w.newFlag(tag.getName());
	// we'll mark all the nodes reachable from this tag accordingly
	allFlags.add(flag);
	w.carry(flag);
	commit.add(flag);
	// As of this writing, JGit carries a flag from a child to its parents
	// right before RevWalk.next() returns, so all the flags that are added
	// must be manually carried to its parents. If that gets fixed,
	// this will be unnecessary.
	commit.carry(flag);
	}

	/**
	* Does this tag contain the given commit?
	*/
	boolean reaches(RevCommit c) {
	return c.has(flag);
	}

	String describe(ObjectId tip) throws IOException {
	return longDescription(tag, depth, tip);
	}

	}
	List<Candidate> candidates = new ArrayList<>(); // all the candidates we find

	// is the target already pointing to a suitable tag? if so, we are done!
	Optional<Ref> bestMatch = getBestMatch(tags.get(target));
	if (bestMatch.isPresent()) {
	return longDesc ? longDescription(bestMatch.get(), 0, target) :
	bestMatch.get().getName().substring(R_TAGS.length());
	}

	w.markStart(target);

	int seen = 0; // commit seen thus far
	RevCommit c;
	while ((c = w.next()) != null) {
	if (!c.hasAny(allFlags)) {
	// if a tag already dominates this commit,
	// then there's no point in picking a tag on this commit
	// since the one that dominates it is always more preferable
	bestMatch = getBestMatch(tags.get(c));
	if (bestMatch.isPresent()) {
	Candidate cd = new Candidate(c, bestMatch.get());
	candidates.add(cd);
	cd.depth = seen;
	}
	}

	// if the newly discovered commit isn't reachable from a tag that we've seen
	// it counts toward the total depth.
	for (Candidate cd : candidates) {
	if (!cd.reaches(c))
	cd.depth++;
	}

	// if we have search going for enough tags, we will start
	// closing down. JGit can only give us a finite number of bits,
	// so we can't track all tags even if we wanted to.
	if (candidates.size() >= maxCandidates)
	break;

	// TODO: if all the commits in the queue of RevWalk has allFlags
	// there's no point in continuing search as we'll not discover any more
	// tags. But RevWalk doesn't expose this.
	seen++;
	}

	// at this point we aren't adding any more tags to our search,
	// but we still need to count all the depths correctly.
	while ((c = w.next()) != null) {
	if (c.hasAll(allFlags)) {
	// no point in visiting further from here, so cut the search here
	for (RevCommit p : c.getParents())
	p.add(RevFlag.SEEN);
	} else {
	for (Candidate cd : candidates) {
	if (!cd.reaches(c))
	cd.depth++;
	}
	}
	}

	// if all the nodes are dominated by all the tags, the walk stops
	if (candidates.isEmpty())
	return null;

	Candidate best = Collections.min(candidates, new Comparator<Candidate>() {
	@Override
	public int compare(Candidate o1, Candidate o2) {
	return o1.depth - o2.depth;
	}
	});

	return best.describe(target);
	} catch (IOException e) {
	throw new JGitInternalException(e.getMessage(), e);
	} finally {
	setCallable(false);
	w.close();
	}
	}
	}