CherryPick: add ability to customise cherry-picked commit message

Originally I wanted to support a feature similar to `-x` options from
https://git-scm.com/docs/git-cherry-pick#_options.
The idea was to append original commit hash in this format:
```
my original commit message

(cherry picked from commit 75355897dc28e9975afed028c1a6d8c6b97b2a3c)
```
This can be useful information in some integrations.
I decided to make it in a more generic way
and pass custom `CherryPickCommitMessageProvider` implementation.
One of the two default implementations can append original commit hash

Change-Id: Id664e8438b0b76c5cb9b58113887eec04aa6f611

5 files changed, 309 insertions, 1 deletions

diff --git a/org.eclipse.jgit.test/tst/org/eclipse/jgit/api/CherryPickCommandTest.java b/org.eclipse.jgit.test/tst/org/eclipse/jgit/api/CherryPickCommandTest.java
index 301d6be662..be3b33a9c5 100644
--- a/org.eclipse.jgit.test/tst/org/eclipse/jgit/api/CherryPickCommandTest.java
+++ b/org.eclipse.jgit.test/tst/org/eclipse/jgit/api/CherryPickCommandTest.java
@@ -9,6 +9,8 @@
  */
 package org.eclipse.jgit.api;
 
+import static org.eclipse.jgit.api.CherryPickCommitMessageProvider.ORIGINAL;
+import static org.eclipse.jgit.api.CherryPickCommitMessageProvider.ORIGINAL_WITH_REFERENCE;
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertNotNull;
@@ -590,4 +592,187 @@ public class CherryPickCommandTest extends RepositoryTestCase {
 			checkFile(new File(db.getWorkTree(), "file"), "a\n2\n3\n");
 		}
 	}
+
+	private void doCherryPickWithCustomProviderBaseTest(Git git,
+			CherryPickCommitMessageProvider commitMessageProvider)
+			throws Exception {
+		writeTrashFile("fileA", "line 1\nline 2\nline 3\n");
+		git.add().addFilepattern("fileA").call();
+		RevCommit commitFirst = git.commit().setMessage("create fileA").call();
+
+		writeTrashFile("fileB", "content from file B\n");
+		git.add().addFilepattern("fileB").call();
+		RevCommit commitCreateFileB = git.commit()
+				.setMessage("create fileB\n\nsome commit details").call();
+
+		writeTrashFile("fileA", "line 1\nline 2\nline 3\nline 4\n");
+		git.add().addFilepattern("fileA").call();
+		RevCommit commitEditFileA1 = git.commit().setMessage("patch fileA 1")
+				.call();
+
+		writeTrashFile("fileA", "line 1\nline 2\nline 3\nline 4\nline 5\n");
+		git.add().addFilepattern("fileA").call();
+		RevCommit commitEditFileA2 = git.commit().setMessage("patch fileA 2")
+				.call();
+
+		git.branchCreate().setName("side").setStartPoint(commitFirst).call();
+		checkoutBranch("refs/heads/side");
+
+		CherryPickResult pickResult = git.cherryPick()
+				.setCherryPickCommitMessageProvider(commitMessageProvider)
+				.include(commitCreateFileB).include(commitEditFileA1)
+				.include(commitEditFileA2).call();
+
+		assertEquals(CherryPickStatus.OK, pickResult.getStatus());
+
+		assertTrue(new File(db.getWorkTree(), "fileA").exists());
+		assertTrue(new File(db.getWorkTree(), "fileB").exists());
+
+		checkFile(new File(db.getWorkTree(), "fileA"),
+				"line 1\nline 2\nline 3\nline 4\nline 5\n");
+		checkFile(new File(db.getWorkTree(), "fileB"), "content from file B\n");
+	}
+
+	@Test
+	public void testCherryPickWithCustomCommitMessageProvider()
+			throws Exception {
+		try (Git git = new Git(db)) {
+			@SuppressWarnings("boxing")
+			CherryPickCommitMessageProvider messageProvider = srcCommit -> {
+				String message = srcCommit.getFullMessage();
+				return String.format("%s (message length: %d)", message,
+						message.length());
+			};
+			doCherryPickWithCustomProviderBaseTest(git, messageProvider);
+
+			Iterator<RevCommit> history = git.log().call().iterator();
+			assertEquals("patch fileA 2 (message length: 13)",
+					history.next().getFullMessage());
+			assertEquals("patch fileA 1 (message length: 13)",
+					history.next().getFullMessage());
+			assertEquals(
+					"create fileB\n\nsome commit details (message length: 33)",
+					history.next().getFullMessage());
+			assertEquals("create fileA", history.next().getFullMessage());
+			assertFalse(history.hasNext());
+		}
+	}
+
+	@Test
+	public void testCherryPickWithCustomCommitMessageProvider_ORIGINAL()
+			throws Exception {
+		try (Git git = new Git(db)) {
+			doCherryPickWithCustomProviderBaseTest(git, ORIGINAL);
+
+			Iterator<RevCommit> history = git.log().call().iterator();
+			assertEquals("patch fileA 2", history.next().getFullMessage());
+			assertEquals("patch fileA 1", history.next().getFullMessage());
+			assertEquals("create fileB\n\nsome commit details",
+					history.next().getFullMessage());
+			assertEquals("create fileA", history.next().getFullMessage());
+			assertFalse(history.hasNext());
+		}
+	}
+
+	@Test
+	public void testCherryPickWithCustomCommitMessageProvider_ORIGINAL_WITH_REFERENCE()
+			throws Exception {
+		try (Git git = new Git(db)) {
+			doCherryPickWithCustomProviderBaseTest(git,
+					ORIGINAL_WITH_REFERENCE);
+
+			Iterator<RevCommit> history = git.log().call().iterator();
+			assertEquals("patch fileA 2\n\n(cherry picked from commit 1ac121e90b0fb6fb18bbb4307e3e9731ceeba9e1)", history.next().getFullMessage());
+			assertEquals("patch fileA 1\n\n(cherry picked from commit 71475239df59076e18564fa360e3a74280926c2a)", history.next().getFullMessage());
+			assertEquals("create fileB\n\nsome commit details\n\n(cherry picked from commit 29b4501297ccf8de9de9f451e7beb384b51f5378)",
+					history.next().getFullMessage());
+			assertEquals("create fileA", history.next().getFullMessage());
+			assertFalse(history.hasNext());
+		}
+	}
+
+	@Test
+	public void testCherryPickWithCustomCommitMessageProvider_ORIGINAL_WITH_REFERENCE_DonNotAddNewLineAfterFooter()
+			throws Exception {
+		try (Git git = new Git(db)) {
+			CherryPickCommitMessageProvider commitMessageProvider = CherryPickCommitMessageProvider.ORIGINAL_WITH_REFERENCE;
+
+			RevCommit commit1 = addFileAndCommit(git, "file1", "content 1",
+					"commit1: no footer line");
+			RevCommit commit2 = addFileAndCommit(git, "file2", "content 2",
+					"commit2: simple single footer line"
+							+ "\n\nSigned-off-by: Alice <alice@example.com>");
+			RevCommit commit3 = addFileAndCommit(git, "file3", "content 3",
+					"commit3: multiple footer lines\n\n"
+							+ "Signed-off-by: Alice <alice@example.com>\n"
+							+ "Signed-off-by: Bob <bob@example.com>");
+			RevCommit commit4 = addFileAndCommit(git, "file4", "content 4",
+					"commit4: extra commit text before footer line\n\n"
+							+ "Commit message details\n\n"
+							+ "Signed-off-by: Alice <alice@example.com>\n"
+							+ "Signed-off-by: Bob <bob@example.com>");
+			RevCommit commit5 = addFileAndCommit(git, "file5", "content 5",
+					"commit5: extra commit text after footer line\n\n"
+							+ "Signed-off-by: Alice <alice@example.com>\n"
+							+ "Signed-off-by: Bob <bob@example.com>\n\n"
+							+ "some extra description after footer");
+
+			git.branchCreate().setName("side").setStartPoint(commit1).call();
+			checkoutBranch("refs/heads/side");
+
+			CherryPickResult pickResult = git.cherryPick()
+					.setCherryPickCommitMessageProvider(commitMessageProvider)
+					.include(commit2).include(commit3).include(commit4)
+					.include(commit5).call();
+
+			assertEquals(CherryPickStatus.OK, pickResult.getStatus());
+
+			assertTrue(new File(db.getWorkTree(), "file1").exists());
+			assertTrue(new File(db.getWorkTree(), "file2").exists());
+			assertTrue(new File(db.getWorkTree(), "file3").exists());
+			assertTrue(new File(db.getWorkTree(), "file4").exists());
+			assertTrue(new File(db.getWorkTree(), "file5").exists());
+
+			Iterator<RevCommit> history = git.log().call().iterator();
+			RevCommit cpCommit1 = history.next();
+			RevCommit cpCommit2 = history.next();
+			RevCommit cpCommit3 = history.next();
+			RevCommit cpCommit4 = history.next();
+			RevCommit cpCommitInit = history.next();
+			assertFalse(history.hasNext());
+
+			assertEquals("commit5: extra commit text after footer line\n\n"
+					+ "Signed-off-by: Alice <alice@example.com>\n"
+					+ "Signed-off-by: Bob <bob@example.com>\n\n"
+					+ "some extra description after footer\n\n"
+					+ "(cherry picked from commit c3c9959207dc7ae7c83da5d36dc14ef2ca42d572)",
+					cpCommit1.getFullMessage());
+			assertEquals("commit4: extra commit text before footer line\n\n"
+					+ "Commit message details\n\n"
+					+ "Signed-off-by: Alice <alice@example.com>\n"
+					+ "Signed-off-by: Bob <bob@example.com>\n"
+					+ "(cherry picked from commit af3e8106c12cb946a37b403ddb2dd6c11a883698)",
+					cpCommit2.getFullMessage());
+			assertEquals("commit3: multiple footer lines\n\n"
+					+ "Signed-off-by: Alice <alice@example.com>\n"
+					+ "Signed-off-by: Bob <bob@example.com>\n"
+					+ "(cherry picked from commit 6d60f1a70a11a32dff4402c157c4ac328c32ce6c)",
+					cpCommit3.getFullMessage());
+			assertEquals("commit2: simple single footer line\n\n"
+					+ "Signed-off-by: Alice <alice@example.com>\n"
+					+ "(cherry picked from commit 92bf0ec458814ecc73da8e050e60547d2ea6cce5)",
+					cpCommit4.getFullMessage());
+
+			assertEquals("commit1: no footer line",
+					cpCommitInit.getFullMessage());
+		}
+	}
+
+	private RevCommit addFileAndCommit(Git git, String fileName,
+			String fileText, String commitMessage)
+			throws IOException, GitAPIException {
+		writeTrashFile(fileName, fileText);
+		git.add().addFilepattern(fileName).call();
+		return git.commit().setMessage(commitMessage).call();
+	}
 }
diff --git a/org.eclipse.jgit.test/tst/org/eclipse/jgit/revwalk/FooterLineTest.java b/org.eclipse.jgit.test/tst/org/eclipse/jgit/revwalk/FooterLineTest.java
index cac0743d68..657c3d242f 100644
--- a/org.eclipse.jgit.test/tst/org/eclipse/jgit/revwalk/FooterLineTest.java
+++ b/org.eclipse.jgit.test/tst/org/eclipse/jgit/revwalk/FooterLineTest.java
@@ -291,18 +291,26 @@ public class FooterLineTest extends RepositoryTestCase {
 		f = footers.get(0);
 		assertEquals("Signed-off-by", f.getKey());
 		assertEquals("A. U. Thor <a@example.com>", f.getValue());
+		assertEquals(217, f.getStartOffset());
+		assertEquals(258, f.getEndOffset());
 
 		f = footers.get(1);
 		assertEquals("CC", f.getKey());
 		assertEquals("<some.mailing.list@example.com>", f.getValue());
+		assertEquals(259, f.getStartOffset());
+		assertEquals(305, f.getEndOffset());
 
 		f = footers.get(2);
 		assertEquals("Acked-by", f.getKey());
 		assertEquals("Some Reviewer <sr@example.com>", f.getValue());
+		assertEquals(356, f.getStartOffset());
+		assertEquals(396, f.getEndOffset());
 
 		f = footers.get(3);
 		assertEquals("Signed-off-by", f.getKey());
 		assertEquals("Main Tain Er <mte@example.com>", f.getValue());
+		assertEquals(397, f.getStartOffset());
+		assertEquals(442, f.getEndOffset());
 	}
 
 	@Test
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/api/CherryPickCommand.java b/org.eclipse.jgit/src/org/eclipse/jgit/api/CherryPickCommand.java
index 38e795b0eb..a1c64788bd 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/api/CherryPickCommand.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/api/CherryPickCommand.java
@@ -9,6 +9,7 @@
  */
 package org.eclipse.jgit.api;
 
+import static org.eclipse.jgit.api.CherryPickCommitMessageProvider.ORIGINAL;
 import static org.eclipse.jgit.lib.Constants.OBJECT_ID_ABBREV_STRING_LENGTH;
 
 import java.io.IOException;
@@ -66,6 +67,8 @@ public class CherryPickCommand extends GitCommand<CherryPickResult> {
 
 	private String ourCommitName = null;
 
+	private CherryPickCommitMessageProvider messageProvider = ORIGINAL;
+
 	private MergeStrategy strategy = MergeStrategy.RECURSIVE;
 
 	private ContentMergeStrategy contentStrategy;
@@ -168,8 +171,10 @@ public class CherryPickCommand extends GitCommand<CherryPickResult> {
 					dco.checkout();
 					if (!noCommit) {
 						try (Git git = new Git(getRepository())) {
+							String commitMessage = messageProvider
+									.getCherryPickedCommitMessage(srcCommit);
 							newHead = git.commit()
-									.setMessage(srcCommit.getFullMessage())
+									.setMessage(commitMessage)
 									.setReflogComment(reflogPrefix + " " //$NON-NLS-1$
 											+ srcCommit.getShortMessage())
 									.setAuthor(srcCommit.getAuthorIdent())
@@ -297,6 +302,22 @@ public class CherryPickCommand extends GitCommand<CherryPickResult> {
 	}
 
 	/**
+	 * Set a message provider for a target cherry-picked commit<br>
+	 * By default original commit message is used (see
+	 * {@link CherryPickCommitMessageProvider#ORIGINAL})
+	 *
+	 * @param messageProvider
+	 *            the commit message provider
+	 * @return {@code this}
+	 * @since 6.9
+	 */
+	public CherryPickCommand setCherryPickCommitMessageProvider(
+			CherryPickCommitMessageProvider messageProvider) {
+		this.messageProvider = messageProvider;
+		return this;
+	}
+
+	/**
 	 * Set the prefix to use in the reflog.
 	 * <p>
 	 * This is primarily needed for implementing rebase in terms of
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/api/CherryPickCommitMessageProvider.java b/org.eclipse.jgit/src/org/eclipse/jgit/api/CherryPickCommitMessageProvider.java
new file mode 100644
index 0000000000..50d65b6fa8
--- /dev/null
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/api/CherryPickCommitMessageProvider.java
@@ -0,0 +1,72 @@
+/*
+ * Copyright (c) 2023 Dmitrii Naumenko <dmitrii.naumenko@jetbrains.com>
+ *
+ * This program and the accompanying materials are made available under the
+ * terms of the Eclipse Distribution License v. 1.0 which is aailable at
+ * https://www.eclipse.org/org/documents/edl-v10.php.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+package org.eclipse.jgit.api;
+
+import java.util.List;
+
+import org.eclipse.jgit.revwalk.FooterLine;
+import org.eclipse.jgit.revwalk.RevCommit;
+
+/**
+ * The interface is used to construct a cherry-picked commit message based on
+ * the original commit
+ *
+ * @see #ORIGINAL
+ * @see #ORIGINAL_WITH_REFERENCE
+ * @since 6.9
+ */
+public interface CherryPickCommitMessageProvider {
+
+	/**
+	 * This provider returns the original commit message
+	 */
+	static final CherryPickCommitMessageProvider ORIGINAL = RevCommit::getFullMessage;
+
+	/**
+	 * This provider returns the original commit message with original commit
+	 * hash in SHA-1 form.<br>
+	 * Example:
+	 *
+	 * <pre>
+	 * <code>my original commit message
+	 *
+	 * (cherry picked from commit 75355897dc28e9975afed028c1a6d8c6b97b2a3c)</code>
+	 * </pre>
+	 *
+	 * This is similar to <code>-x</code> flag in git-scm (see <a href=
+	 * "https://git-scm.com/docs/git-cherry-pick#_options">https://git-scm.com/docs/git-cherry-pick#_options</a>)
+	 */
+	static final CherryPickCommitMessageProvider ORIGINAL_WITH_REFERENCE = srcCommit -> {
+		String fullMessage = srcCommit.getFullMessage();
+
+		// Don't add extra new line after footer (aka trailer)
+		// https://stackoverflow.com/questions/70007405/git-log-exclude-cherry-pick-messages-for-trailers
+		// https://lore.kernel.org/git/7vmx136cdc.fsf@alter.siamese.dyndns.org
+		String separator = messageEndsWithFooter(srcCommit) ? "\n" : "\n\n"; //$NON-NLS-1$//$NON-NLS-2$
+		String revisionString = srcCommit.getName();
+		return String.format("%s%s(cherry picked from commit %s)", //$NON-NLS-1$
+				fullMessage, separator, revisionString);
+	};
+
+	/**
+	 * @param srcCommit
+	 *            original cherry-picked commit
+	 * @return target cherry-picked commit message
+	 */
+	String getCherryPickedCommitMessage(RevCommit srcCommit);
+
+	private static boolean messageEndsWithFooter(RevCommit srcCommit) {
+		byte[] rawBuffer = srcCommit.getRawBuffer();
+		List<FooterLine> footers = srcCommit.getFooterLines();
+		int maxFooterEnd = footers.stream().mapToInt(FooterLine::getEndOffset)
+				.max().orElse(-1);
+		return rawBuffer.length == maxFooterEnd;
+	}
+}
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/revwalk/FooterLine.java b/org.eclipse.jgit/src/org/eclipse/jgit/revwalk/FooterLine.java
index 227ea0fd65..fa7fb316c9 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/revwalk/FooterLine.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/revwalk/FooterLine.java
@@ -251,6 +251,28 @@ public final class FooterLine {
 		return RawParseUtils.decode(enc, buffer, lt, gt - 1);
 	}
 
+	/**
+	 * @return start offset of the footer relative to the original raw message
+	 *         byte buffer
+	 *
+	 * @see #fromMessage(byte[])
+	 * @since 6.9
+	 */
+	public int getStartOffset() {
+		return keyStart;
+	}
+
+	/**
+	 * @return end offset of the footer relative to the original raw message
+	 *         byte buffer
+	 *
+	 * @see #fromMessage(byte[])
+	 * @since 6.9
+	 */
+	public int getEndOffset() {
+		return valEnd;
+	}
+
 	@Override
 	public String toString() {
 		return getKey() + ": " + getValue(); //$NON-NLS-1$