RevWalkUtils: add progress callback to findBranchesReachableFrom

Offer a version of findBranchesReachableFrom method with progress
monitor callback. This is required to allow UI clients to cancel long
running operations and show progress.

Bug: 547642
Change-Id: I31d1de54dbaa6ffb11e03da4c447963e8defa1d0
Signed-off-by: Andrey Loskutov <loskutov@gmx.de>

org.eclipse.jgit/resources/org/eclipse/jgit/internal/JGitText.properties

@@ -625,6 +625,7 @@ rewinding=Rewinding to commit {0}
 s3ActionDeletion=Deletion
 s3ActionReading=Reading
 s3ActionWriting=Writing
+searchForReachableBranches=Finding reachable branches
 searchForReuse=Finding sources
 searchForSizes=Getting sizes
 secondsAgo={0} seconds ago

org.eclipse.jgit/src/org/eclipse/jgit/internal/JGitText.java

@@ -686,6 +686,7 @@ public class JGitText extends TranslationBundle {
 	/***/ public String s3ActionDeletion;
 	/***/ public String s3ActionReading;
 	/***/ public String s3ActionWriting;
+	/***/ public String searchForReachableBranches;
 	/***/ public String searchForReuse;
 	/***/ public String searchForSizes;
 	/***/ public String secondsAgo;

org.eclipse.jgit/src/org/eclipse/jgit/revwalk/RevWalkUtils.java

@@ -50,6 +50,9 @@ import java.util.List;
 
 import org.eclipse.jgit.errors.IncorrectObjectTypeException;
 import org.eclipse.jgit.errors.MissingObjectException;
+import org.eclipse.jgit.internal.JGitText;
+import org.eclipse.jgit.lib.NullProgressMonitor;
+import org.eclipse.jgit.lib.ProgressMonitor;
 import org.eclipse.jgit.lib.Ref;
 
 /**
@@ -153,15 +156,51 @@ public final class RevWalkUtils {
 			RevWalk revWalk, Collection<Ref> refs)
 			throws MissingObjectException, IncorrectObjectTypeException,
 			IOException {
+		return findBranchesReachableFrom(commit, revWalk, refs,
+				NullProgressMonitor.INSTANCE);
+	}
+
+	/**
+	 * Find the list of branches a given commit is reachable from when following
+	 * parents.
+	 * <p>
+	 * Note that this method calls
+	 * {@link org.eclipse.jgit.revwalk.RevWalk#reset()} at the beginning.
+	 * <p>
+	 * In order to improve performance this method assumes clock skew among
+	 * committers is never larger than 24 hours.
+	 *
+	 * @param commit
+	 *            the commit we are looking at
+	 * @param revWalk
+	 *            The RevWalk to be used.
+	 * @param refs
+	 *            the set of branches we want to see reachability from
+	 * @param monitor
+	 *            the callback for progress and cancellation
+	 * @return the list of branches a given commit is reachable from
+	 * @throws org.eclipse.jgit.errors.MissingObjectException
+	 * @throws org.eclipse.jgit.errors.IncorrectObjectTypeException
+	 * @throws java.io.IOException
+	 * @since 5.4
+	 */
+	public static List<Ref> findBranchesReachableFrom(RevCommit commit,
+			RevWalk revWalk, Collection<Ref> refs, ProgressMonitor monitor)
+			throws MissingObjectException, IncorrectObjectTypeException,
+			IOException {
 
 		// Make sure commit is from the same RevWalk
 		commit = revWalk.parseCommit(commit.getId());
 		revWalk.reset();
 		List<Ref> result = new ArrayList<>();
-
+		monitor.beginTask(JGitText.get().searchForReachableBranches,
+				refs.size());
 		final int SKEW = 24*3600; // one day clock skew
 
 		for (Ref ref : refs) {
+			if (monitor.isCancelled())
+				return result;
+			monitor.update(1);
 			RevObject maybehead = revWalk.parseAny(ref.getObjectId());
 			if (!(maybehead instanceof RevCommit))
 				continue;
@@ -176,6 +215,7 @@ public final class RevWalkUtils {
 			if (revWalk.isMergedInto(commit, headCommit))
 				result.add(ref);
 		}
+		monitor.endTask();
 		return result;
 	}