Allow to replace existing Change-Id

It is useful to be able to replace an existing Change-Id
in the message, for example if the user decides not to
amend the previous commit.

Bug: 321188
Change-Id: I594e7f9efd0c57d794d2bd26d55ec45f4e6a47fd
Signed-off-by: Stefan Lay <stefan.lay@sap.com>
Signed-off-by: Chris Aniszczyk <caniszczyk@gmail.com>

org.eclipse.jgit.test/tst/org/eclipse/jgit/util/ChangeIdUtilTest.java

@@ -123,6 +123,13 @@ public class ChangeIdUtilTest extends TestCase {
 				call("has changeid\n\nBug: 33\nmore text\nSigned-off-by: me@you.too\nChange-Id: I0123456789012345678901234567890123456789\nAnd then some\n"));
 	}
 
+	public void testHasChangeidWithReplacement() throws Exception {
+		assertEquals(
+				"has changeid\n\nBug: 33\nmore text\nSigned-off-by: me@you.too\nChange-Id: I988d2d7a6f2c0578fccabd4ebd3cec0768bc7f9f\nAnd then some\n",
+				call("has changeid\n\nBug: 33\nmore text\nSigned-off-by: me@you.too\nChange-Id: I0123456789012345678901234567890123456789\nAnd then some\n",
+						true));
+	}
+
 	public void testOneliner() throws Exception {
 		assertEquals(
 				"oneliner\n\nChange-Id: I3a98091ce4470de88d52ae317fcd297e2339f063\n",
@@ -236,6 +243,47 @@ public class ChangeIdUtilTest extends TestCase {
 				"Change-Id: I4f4e2e1e8568ddc1509baecb8c1270a1fb4b6da7\n");
 	}
 
+	public void testChangeIdAlreadySetWithReplacement() throws Exception {
+		// If a Change-Id is already present in the footer, the hook
+		// replaces the Change-Id with the new value..
+		//
+		assertEquals("a\n" + //
+				"\n" + //
+				"Change-Id: Ifa324efa85bfb3c8696a46a0f67fa70c35be5f5f\n",
+				call("a\n" + //
+						"\n" + //
+						"Change-Id: Iaeac9b4149291060228ef0154db2985a31111335\n",
+						true));
+		assertEquals("fix: this thing\n" + //
+				"\n" + //
+				"Change-Id: Ib63e4990a06412a3f24bd93bb160e98ac1bd412b\n",
+				call("fix: this thing\n" + //
+						"\n" + //
+						"Change-Id: I388bdaf52ed05b55e62a22d0a20d2c1ae0d33e7e\n",
+						true));
+		assertEquals("fix-a-widget: this thing\n" + //
+				"\n" + //
+				"Change-Id: If0444e4d0cabcf41b3d3b46b7e9a7a64a82117af\n",
+				call("fix-a-widget: this thing\n" + //
+						"\n" + //
+						"Change-Id: Id3bc5359d768a6400450283e12bdfb6cd135ea4b\n",
+						true));
+		assertEquals("FIX: this thing\n" + //
+				"\n" + //
+				"Change-Id: Iba5a3b2d5e5df46448f6daf362b6bfa775c6491d\n",
+				call("FIX: this thing\n" + //
+						"\n" + //
+						"Change-Id: I1b55098b5a2cce0b3f3da783dda50d5f79f873fa\n",
+						true));
+		assertEquals("Fix-A-Widget: this thing\n" + //
+				"\n" + //
+				"Change-Id: I2573d47c62c42429fbe424d70cfba931f8f87848\n",
+				call("Fix-A-Widget: this thing\n" + //
+				"\n" + //
+				"Change-Id: I4f4e2e1e8568ddc1509baecb8c1270a1fb4b6da7\n",
+				true));
+	}
+
 	public void testTimeAltersId() throws Exception {
 		assertEquals("a\n" + //
 				"\n" + //
@@ -513,11 +561,15 @@ public class ChangeIdUtilTest extends TestCase {
 	}
 
 	private String call(final String body) throws Exception {
+		return call(body, false);
+	}
+
+	private String call(final String body, boolean replaceExisting) throws Exception {
 		ObjectId computeChangeId = ChangeIdUtil.computeChangeId(treeId1,
 				parentId1, author, committer, body);
 		if (computeChangeId == null)
 			return body;
-		return ChangeIdUtil.insertId(body, computeChangeId);
+		return ChangeIdUtil.insertId(body, computeChangeId, replaceExisting);
 	}
 
 }

org.eclipse.jgit/src/org/eclipse/jgit/util/ChangeIdUtil.java

@@ -61,6 +61,8 @@ import org.eclipse.jgit.lib.PersonIdent;
  */
 public class ChangeIdUtil {
 
+	static final String CHANGE_ID = "Change-Id:";
+
 	// package-private so the unit test can test this part only
 	static String clean(String msg) {
 		return msg.//
@@ -136,8 +138,39 @@ public class ChangeIdUtil {
 	 * @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 insertId(message, changeId, false);
+	}
+
+	/**
+	 * Find the right place to insert a Change-Id and return it.
+	 * <p>
+	 * If no Change-Id is found the Change-Id is inserted before
+	 * the first footer line but after a Bug line.
+	 *
+	 * If Change-Id is found and replaceExisting is set to false,
+	 * the message is unchanged.
+	 *
+	 * If Change-Id is found and replaceExisting is set to true,
+	 * the Change-Id is replaced with {@code changeId}.
+	 *
+	 * @param message
+	 * @param changeId
+	 * @param replaceExisting
+	 * @return a commit message with an inserted Change-Id line
+	 */
+	public static String insertId(String message, ObjectId changeId,
+			boolean replaceExisting) {
+		if (message.indexOf(CHANGE_ID) > 0) {
+			if (replaceExisting) {
+				int i = message.indexOf(CHANGE_ID) + 10;
+				while (message.charAt(i) == ' ')
+					i++;
+				String oldId = message.length() == (i + 40) ?
+						message.substring(i) : message.substring(i, i + 41);
+				message = message.replace(oldId, "I" + changeId.getName());
+			}
 			return message;
+		}
 
 		String[] lines = message.split("\n");
 		int footerFirstLine = lines.length;
@@ -173,7 +206,8 @@ public class ChangeIdUtil {
 		}
 		if (insertAfter == lines.length && insertAfter == footerFirstLine)
 			ret.append("\n");
-		ret.append("Change-Id: I");
+		ret.append(CHANGE_ID);
+		ret.append(" I");
 		ret.append(ObjectId.toString(changeId));
 		ret.append("\n");
 		for (; i < lines.length; ++i) {