Format merge commit messages like C Git

The automatically generated commit message of a merge should have the
same structure as in C Git for consistency (as per git fmt-merge-msg).

Before this change:

  merging refs/heads/a into refs/heads/master

After:

  Merge branch 'a'

Plurals, "into" and joining by "," and "and" also work.

Change-Id: I9658ce2817adc90d2df1060e8ac508d7bd0571cb

3 files changed, 181 insertions, 3 deletions

diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/api/MergeCommand.java b/org.eclipse.jgit/src/org/eclipse/jgit/api/MergeCommand.java
index 9e31c47c37..1528e799ae 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/api/MergeCommand.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/api/MergeCommand.java
@@ -69,6 +69,7 @@ import org.eclipse.jgit.lib.Ref.Storage;
 import org.eclipse.jgit.lib.RefUpdate;
 import org.eclipse.jgit.lib.RefUpdate.Result;
 import org.eclipse.jgit.lib.Repository;
+import org.eclipse.jgit.merge.MergeMessageFormatter;
 import org.eclipse.jgit.merge.MergeStrategy;
 import org.eclipse.jgit.merge.ResolveMerger;
 import org.eclipse.jgit.merge.ResolveMerger.MergeFailureReason;
@@ -132,7 +133,7 @@ public class MergeCommand extends GitCommand<MergeResult> {
 			revWalk = new RevWalk(repo);
 			RevCommit headCommit = revWalk.lookupCommit(head.getObjectId());
 
-			// we know for know there is only one commit
+			// we know for now there is only one commit
 			Ref ref = commits.get(0);
 
 			refLogMessage.append(ref.getName());
@@ -164,8 +165,9 @@ public class MergeCommand extends GitCommand<MergeResult> {
 						headCommit, srcCommit }, MergeStatus.FAST_FORWARD,
 						mergeStrategy, null, null);
 			} else {
-				repo.writeMergeCommitMsg("merging " + ref.getName() + " into "
-						+ head.getName());
+
+				repo.writeMergeCommitMsg(new MergeMessageFormatter().format(
+						commits, head));
 				repo.writeMergeHeads(Arrays.asList(ref.getObjectId()));
 				ThreeWayMerger merger = (ThreeWayMerger) mergeStrategy
 						.newMerger(repo);
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/merge/MergeMessageFormatter.java b/org.eclipse.jgit/src/org/eclipse/jgit/merge/MergeMessageFormatter.java
new file mode 100644
index 0000000000..cb2f8a522c
--- /dev/null
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/merge/MergeMessageFormatter.java
@@ -0,0 +1,132 @@
+/*
+ * Copyright (C) 2010, Robin Stocker <robin@nibor.org>
+ * 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.List;
+
+import org.eclipse.jgit.lib.Constants;
+import org.eclipse.jgit.lib.Ref;
+import org.eclipse.jgit.lib.Repository;
+import org.eclipse.jgit.util.StringUtils;
+
+/**
+ * Formatter for constructing the commit message for a merge commit.
+ * <p>
+ * The format should be the same as C Git does it, for compatibility.
+ */
+public class MergeMessageFormatter {
+	/**
+	 * Construct the merge commit message.
+	 *
+	 * @param refsToMerge
+	 *            the refs which will be merged
+	 * @param target
+	 *            the branch ref which will be merged into
+	 * @return merge commit message
+	 */
+	public String format(List<Ref> refsToMerge, Ref target) {
+		StringBuilder sb = new StringBuilder();
+		sb.append("Merge ");
+
+		List<String> branches = new ArrayList<String>();
+		List<String> remoteBranches = new ArrayList<String>();
+		List<String> tags = new ArrayList<String>();
+		List<String> commits = new ArrayList<String>();
+		List<String> others = new ArrayList<String>();
+		for (Ref ref : refsToMerge) {
+			if (ref.getName().startsWith(Constants.R_HEADS))
+				branches.add("'" + Repository.shortenRefName(ref.getName())
+						+ "'");
+
+			else if (ref.getName().startsWith(Constants.R_REMOTES))
+				remoteBranches.add("'"
+						+ Repository.shortenRefName(ref.getName()) + "'");
+
+			else if (ref.getName().startsWith(Constants.R_TAGS))
+				tags.add("'" + Repository.shortenRefName(ref.getName()) + "'");
+
+			else if (ref.getName().equals(ref.getObjectId().getName()))
+				commits.add("'" + ref.getName() + "'");
+
+			else
+				others.add(ref.getName());
+		}
+
+		List<String> listings = new ArrayList<String>();
+
+		if (!branches.isEmpty())
+			listings.add(joinNames(branches, "branch", "branches"));
+
+		if (!remoteBranches.isEmpty())
+			listings.add(joinNames(remoteBranches, "remote branch",
+					"remote branches"));
+
+		if (!tags.isEmpty())
+			listings.add(joinNames(tags, "tag", "tags"));
+
+		if (!commits.isEmpty())
+			listings.add(joinNames(commits, "commit", "commits"));
+
+		if (!others.isEmpty())
+			listings.add(StringUtils.join(others, ", ", " and "));
+
+		sb.append(StringUtils.join(listings, ", "));
+
+		if (!target.getName().equals(Constants.R_HEADS + Constants.MASTER)) {
+			String targetShortName = Repository
+					.shortenRefName(target.getName());
+			sb.append(" into " + targetShortName);
+		}
+
+		return sb.toString();
+	}
+
+	private static String joinNames(List<String> names, String singular,
+			String plural) {
+		if (names.size() == 1)
+			return singular + " " + names.get(0);
+		else
+			return plural + " " + StringUtils.join(names, ", ", " and ");
+	}
+}
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/util/StringUtils.java b/org.eclipse.jgit/src/org/eclipse/jgit/util/StringUtils.java
index 119c041570..3759a12820 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/util/StringUtils.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/util/StringUtils.java
@@ -44,6 +44,7 @@
 package org.eclipse.jgit.util;
 
 import java.text.MessageFormat;
+import java.util.Collection;
 
 import org.eclipse.jgit.JGitText;
 
@@ -158,6 +159,49 @@ public final class StringUtils {
 		}
 	}
 
+	/**
+	 * Join a collection of Strings together using the specified separator.
+	 *
+	 * @param parts
+	 *            Strings to join
+	 * @param separator
+	 *            used to join
+	 * @return a String with all the joined parts
+	 */
+	public static String join(Collection<String> parts, String separator) {
+		return StringUtils.join(parts, separator, separator);
+	}
+
+	/**
+	 * Join a collection of Strings together using the specified separator and a
+	 * lastSeparator which is used for joining the second last and the last
+	 * part.
+	 *
+	 * @param parts
+	 *            Strings to join
+	 * @param separator
+	 *            separator used to join all but the two last elements
+	 * @param lastSeparator
+	 *            separator to use for joining the last two elements
+	 * @return a String with all the joined parts
+	 */
+	public static String join(Collection<String> parts, String separator,
+			String lastSeparator) {
+		StringBuilder sb = new StringBuilder();
+		int i = 0;
+		int lastIndex = parts.size() - 1;
+		for (String part : parts) {
+			sb.append(part);
+			if (i == lastIndex - 1) {
+				sb.append(lastSeparator);
+			} else if (i != lastIndex) {
+				sb.append(separator);
+			}
+			i++;
+		}
+		return sb.toString();
+	}
+
 	private StringUtils() {
 		// Do not create instances
 	}