Add support for computing a Change-Id à la Gerrit

A Change-Id helps tools like Gerrit Code Review to keeps different
versions of a patch together. The Change-Id is computed as a SHA-1
hash of some of the same basic information as a commit id on the first
commit intended to solve a particular problem and then reused for
updated solutions.

Change-Id: I04334f84e76e83a4185283cb72ea0308b1cb4182
Signed-off-by: Robin Rosenberg <robin.rosenberg@dewire.com>

2 files changed, 208 insertions, 0 deletions

diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/lib/ObjectWriter.java b/org.eclipse.jgit/src/org/eclipse/jgit/lib/ObjectWriter.java
index ea57a0215e..20147ed6ce 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/lib/ObjectWriter.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/lib/ObjectWriter.java
@@ -300,6 +300,24 @@ public class ObjectWriter {
 		return writeObject(Constants.OBJ_BLOB, len, is, false);
 	}
 
+	/**
+	 * Compute the SHA-1 of an object without actually creating an object in the
+	 * database
+	 *
+	 * @param type
+	 *            kind of object
+	 * @param len
+	 *            number of bytes to consume
+	 * @param is
+	 *            stream for read data from
+	 * @return SHA-1 of data combined with type information
+	 * @throws IOException
+	 */
+	public ObjectId computeObjectSha1(final int type, final long len, final InputStream is)
+			throws IOException {
+		return writeObject(type, len, is, false);
+	}
+
 	ObjectId writeObject(final int type, long len, final InputStream is,
 			boolean store) throws IOException {
 		final File t;
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/util/ChangeIdUtil.java b/org.eclipse.jgit/src/org/eclipse/jgit/util/ChangeIdUtil.java
new file mode 100644
index 0000000000..6c146f79f0
--- /dev/null
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/util/ChangeIdUtil.java
@@ -0,0 +1,190 @@
+/*
+ * Copyright (C) 2010, Robin Rosenberg
+ * 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.util;
+
+import java.io.ByteArrayInputStream;
+import java.io.IOException;
+import java.util.regex.Pattern;
+
+import org.eclipse.jgit.lib.Constants;
+import org.eclipse.jgit.lib.ObjectId;
+import org.eclipse.jgit.lib.ObjectWriter;
+import org.eclipse.jgit.lib.PersonIdent;
+
+/**
+ * Utilities for creating and working with Change-Id's, like the one used by
+ * Gerrit Code Review.
+ * <p>
+ * A Change-Id is a SHA-1 computed from the content of a commit, in a similar
+ * fashion to how the commit id is computed. Unlike the commit id a Change-Id is
+ * retained in the commit and subsequent revised commits in the footer of the
+ * commit text.
+ */
+public class ChangeIdUtil {
+
+	// package-private so the unit test can test this part only
+	static String clean(String msg) {
+		return msg.//
+				replaceAll("(?i)(?m)^Signed-off-by:.*$\n?", "").//
+				replaceAll("(?m)^#.*$\n?", "").//
+				replaceAll("(?m)\n\n\n+", "\\\n").//
+				replaceAll("\\n*$", "").//
+				replaceAll("(?s)\ndiff --git.*", "").//
+				trim();
+	}
+
+	/**
+	 * Compute a Change-Id.
+	 *
+	 * @param treeId
+	 *            The id of the tree that would be committed
+	 * @param firstParentId
+	 *            parent id of previous commit or null
+	 * @param author
+	 *            the {@link PersonIdent} for the presumed author and time
+	 * @param committer
+	 *            the {@link PersonIdent} for the presumed committer and time
+	 * @param message
+	 *            The commit message
+	 * @return the change id SHA1 string (without the 'I') or null if the
+	 *         message is not complete enough
+	 * @throws IOException
+	 */
+	public static ObjectId computeChangeId(final ObjectId treeId,
+			final ObjectId firstParentId, final PersonIdent author,
+			final PersonIdent committer, final String message)
+			throws IOException {
+		String cleanMessage = clean(message);
+		if (cleanMessage.length() == 0)
+			return null;
+		StringBuilder b = new StringBuilder();
+		b.append("tree ");
+		b.append(ObjectId.toString(treeId));
+		b.append("\n");
+		if (firstParentId != null) {
+			b.append("parent ");
+			b.append(ObjectId.toString(firstParentId));
+			b.append("\n");
+		}
+		b.append("author ");
+		b.append(author.toExternalString());
+		b.append("\n");
+		b.append("committer ");
+		b.append(committer.toExternalString());
+		b.append("\n\n");
+		b.append(cleanMessage);
+		ObjectWriter w = new ObjectWriter(null);
+		byte[] bytes = b.toString().getBytes(Constants.CHARACTER_ENCODING);
+		ByteArrayInputStream is = new ByteArrayInputStream(bytes);
+		ObjectId sha1 = w.computeObjectSha1(Constants.OBJ_COMMIT, bytes.length,
+				is);
+		return sha1;
+	}
+
+	private static final Pattern issuePattern = Pattern
+			.compile("^(Bug|Issue)[a-zA-Z0-9-]*:.*$");
+
+	private static final Pattern footerPattern = Pattern
+			.compile("(^[a-zA-Z0-9-]+:(?!//).*$)");
+
+	private static final Pattern includeInFooterPattern = Pattern
+			.compile("^[ \\[].*$");
+
+	/**
+	 * Find the right place to insert a Change-Id and return it.
+	 * <p>
+	 * The Change-Id is inserted before the first footer line but after a Bug
+	 * line.
+	 *
+	 * @param message
+	 * @param changeId
+	 * @return a commit message with an inserted Change-Id line
+	 */
+	public static String insertId(String message, ObjectId changeId) {
+		if (message.indexOf("\nChange-Id:") > 0)
+			return message;
+
+		String[] lines = message.split("\n");
+		int footerFirstLine = lines.length;
+		for (int i = lines.length - 1; i > 1; --i) {
+			if (footerPattern.matcher(lines[i]).matches()) {
+				footerFirstLine = i;
+				continue;
+			}
+			if (footerFirstLine != lines.length && lines[i].length() == 0) {
+				break;
+			}
+			if (footerFirstLine != lines.length
+					&& includeInFooterPattern.matcher(lines[i]).matches()) {
+				footerFirstLine = i + 1;
+				continue;
+			}
+			footerFirstLine = lines.length;
+			break;
+		}
+		int insertAfter = footerFirstLine;
+		for (int i = footerFirstLine; i < lines.length; ++i) {
+			if (issuePattern.matcher(lines[i]).matches()) {
+				insertAfter = i + 1;
+				continue;
+			}
+			break;
+		}
+		StringBuilder ret = new StringBuilder();
+		int i = 0;
+		for (; i < insertAfter; ++i) {
+			ret.append(lines[i]);
+			ret.append("\n");
+		}
+		if (insertAfter == lines.length && insertAfter == footerFirstLine)
+			ret.append("\n");
+		ret.append("Change-Id: I");
+		ret.append(ObjectId.toString(changeId));
+		ret.append("\n");
+		for (; i < lines.length; ++i) {
+			ret.append(lines[i]);
+			ret.append("\n");
+		}
+		return ret.toString();
+	}
+}