TestRepository: Add a cherryPick method

CherryPickCommand only works on a non-bare repository, as it must
modify the working tree and index in case of a merge conflict. In
tests, being able to recover from a merge conflict is less important,
as the caller should be able to control the full contents of files in
advance of the cherry-pick.

Change-Id: Ic332e44df1308b9336e884666b08c1f6db64513d

org.eclipse.jgit.junit/META-INF/MANIFEST.MF

@@ -14,6 +14,7 @@ Import-Package: org.eclipse.jgit.api;version="[4.0.0,4.1.0)",
  org.eclipse.jgit.internal.storage.file;version="[4.0.0,4.1.0)",
  org.eclipse.jgit.internal.storage.pack;version="[4.0.0,4.1.0)",
  org.eclipse.jgit.lib;version="[4.0.0,4.1.0)",
+ org.eclipse.jgit.merge;version="[4.0.0,4.1.0)",
  org.eclipse.jgit.revwalk;version="[4.0.0,4.1.0)",
  org.eclipse.jgit.storage.file;version="[4.0.0,4.1.0)",
  org.eclipse.jgit.treewalk;version="[4.0.0,4.1.0)",

org.eclipse.jgit.junit/src/org/eclipse/jgit/junit/TestRepository.java

@@ -52,11 +52,13 @@ import java.io.IOException;
 import java.io.OutputStream;
 import java.security.MessageDigest;
 import java.util.ArrayList;
+import java.util.Arrays;
 import java.util.Collections;
 import java.util.Date;
 import java.util.HashSet;
 import java.util.List;
 import java.util.Set;
+import java.util.TimeZone;
 
 import org.eclipse.jgit.api.Git;
 import org.eclipse.jgit.dircache.DirCache;
@@ -88,6 +90,8 @@ import org.eclipse.jgit.lib.RefUpdate;
 import org.eclipse.jgit.lib.RefWriter;
 import org.eclipse.jgit.lib.Repository;
 import org.eclipse.jgit.lib.TagBuilder;
+import org.eclipse.jgit.merge.MergeStrategy;
+import org.eclipse.jgit.merge.ThreeWayMerger;
 import org.eclipse.jgit.revwalk.ObjectWalk;
 import org.eclipse.jgit.revwalk.RevBlob;
 import org.eclipse.jgit.revwalk.RevCommit;
@@ -187,6 +191,11 @@ public class TestRepository<R extends Repository> {
 		return new Date(now);
 	}
 
+	/** @return timezone used for default identities. */
+	public TimeZone getTimeZone() {
+		return defaultCommitter.getTimeZone();
+	}
+
 	/**
 	 * Adjust the current time that will used by the next commit.
 	 *
@@ -615,6 +624,59 @@ public class TestRepository<R extends Repository> {
 		}
 	}
 
+	/**
+	 * Cherry-pick a commit onto HEAD.
+	 * <p>
+	 * This differs from {@code git cherry-pick} in that it works in a bare
+	 * repository. As a result, any merge failure results in an exception, as
+	 * there is no way to recover.
+	 *
+	 * @param id
+	 *            commit-ish to cherry-pick.
+	 * @return newly created commit, or null if no work was done due to the
+	 *         resulting tree being identical.
+	 * @throws Exception
+	 */
+	public RevCommit cherryPick(AnyObjectId id) throws Exception {
+		RevCommit commit = pool.parseCommit(id);
+		pool.parseBody(commit);
+		if (commit.getParentCount() != 1)
+			throw new IOException(String.format(
+					"Expected 1 parent for %s, found: %s",
+					id.name(), Arrays.asList(commit.getParents())));
+		RevCommit parent = commit.getParent(0);
+		pool.parseHeaders(parent);
+
+		Ref headRef = db.getRef(Constants.HEAD);
+		if (headRef == null)
+			throw new IOException("Missing HEAD");
+		RevCommit head = pool.parseCommit(headRef.getObjectId());
+
+		ThreeWayMerger merger = MergeStrategy.RECURSIVE.newMerger(db, true);
+		merger.setBase(parent.getTree());
+		if (merger.merge(head, commit)) {
+			if (AnyObjectId.equals(head.getTree(), merger.getResultTreeId()))
+				return null;
+			tick(1);
+			org.eclipse.jgit.lib.CommitBuilder b =
+					new org.eclipse.jgit.lib.CommitBuilder();
+			b.setParentId(head);
+			b.setTreeId(merger.getResultTreeId());
+			b.setAuthor(commit.getAuthorIdent());
+			b.setCommitter(new PersonIdent(defaultCommitter, new Date(now)));
+			b.setMessage(commit.getFullMessage());
+			ObjectId result;
+			try (ObjectInserter ins = inserter) {
+				result = ins.insert(b);
+				ins.flush();
+			}
+			update(Constants.HEAD, result);
+			return pool.parseCommit(result);
+		} else {
+			throw new IOException("Merge conflict");
+		}
+	}
+
 	/**
 	 * Update the dumb client server info files.
 	 *

org.eclipse.jgit.test/tst/org/eclipse/jgit/junit/TestRepositoryTest.java

@@ -46,6 +46,7 @@ package org.eclipse.jgit.junit;
 import static java.nio.charset.StandardCharsets.UTF_8;
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertNotEquals;
 import static org.junit.Assert.assertNull;
 import static org.junit.Assert.assertSame;
 import static org.junit.Assert.assertTrue;
@@ -55,9 +56,9 @@ import java.util.regex.Pattern;
 
 import org.eclipse.jgit.internal.storage.dfs.DfsRepositoryDescription;
 import org.eclipse.jgit.internal.storage.dfs.InMemoryRepository;
-import org.eclipse.jgit.lib.ObjectId;
 import org.eclipse.jgit.lib.AnyObjectId;
 import org.eclipse.jgit.lib.Constants;
+import org.eclipse.jgit.lib.ObjectId;
 import org.eclipse.jgit.lib.ObjectLoader;
 import org.eclipse.jgit.lib.PersonIdent;
 import org.eclipse.jgit.lib.Ref;
@@ -296,6 +297,83 @@ public class TestRepositoryTest {
 		assertEquals("refs/heads/master", ref.getTarget().getName());
 	}
 
+	@Test
+	public void cherryPick() throws Exception {
+		repo.updateRef("HEAD").link("refs/heads/master");
+		RevCommit head = tr.branch("master").commit()
+				.add("foo", "foo contents\n")
+				.create();
+		rw.parseBody(head);
+		RevCommit toPick = tr.commit()
+				.parent(tr.commit().create()) // Can't cherry-pick root.
+				.author(new PersonIdent("Cherrypick Author", "cpa@example.com",
+						tr.getClock(), tr.getTimeZone()))
+				.author(new PersonIdent("Cherrypick Committer", "cpc@example.com",
+						tr.getClock(), tr.getTimeZone()))
+				.message("message to cherry-pick")
+				.add("bar", "bar contents\n")
+				.create();
+		RevCommit result = tr.cherryPick(toPick);
+		rw.parseBody(result);
+
+		Ref headRef = tr.getRepository().getRef("HEAD");
+		assertEquals(result, headRef.getObjectId());
+		assertTrue(headRef.isSymbolic());
+		assertEquals("refs/heads/master", headRef.getLeaf().getName());
+
+		assertEquals(1, result.getParentCount());
+		assertEquals(head, result.getParent(0));
+		assertEquals(toPick.getAuthorIdent(), result.getAuthorIdent());
+
+		// Committer name/email matches default, and time was incremented.
+		assertEquals(new PersonIdent(head.getCommitterIdent(), new Date(0)),
+				new PersonIdent(result.getCommitterIdent(), new Date(0)));
+		assertTrue(toPick.getCommitTime() < result.getCommitTime());
+
+		assertEquals("message to cherry-pick", result.getFullMessage());
+		assertEquals("foo contents\n", blobAsString(result, "foo"));
+		assertEquals("bar contents\n", blobAsString(result, "bar"));
+	}
+
+	@Test
+	public void cherryPickWithContentMerge() throws Exception {
+		RevCommit base = tr.branch("HEAD").commit()
+				.add("foo", "foo contents\n\n")
+				.create();
+		tr.branch("HEAD").commit()
+				.add("foo", "foo contents\n\nlast line\n")
+				.create();
+		RevCommit toPick = tr.commit()
+				.message("message to cherry-pick")
+				.parent(base)
+				.add("foo", "changed foo contents\n\n")
+				.create();
+		RevCommit result = tr.cherryPick(toPick);
+		rw.parseBody(result);
+
+		assertEquals("message to cherry-pick", result.getFullMessage());
+		assertEquals("changed foo contents\n\nlast line\n",
+				blobAsString(result, "foo"));
+	}
+
+	@Test
+	public void cherryPickWithIdenticalContents() throws Exception {
+		RevCommit base = tr.branch("HEAD").commit().add("foo", "foo contents\n")
+				.create();
+		RevCommit head = tr.branch("HEAD").commit()
+				.parent(base)
+				.add("bar", "bar contents\n")
+				.create();
+		RevCommit toPick = tr.commit()
+				.parent(base)
+				.message("message to cherry-pick")
+				.add("bar", "bar contents\n")
+				.create();
+		assertNotEquals(head, toPick);
+		assertNull(tr.cherryPick(toPick));
+		assertEquals(head, repo.getRef("HEAD").getObjectId());
+	}
+
 	private String blobAsString(AnyObjectId treeish, String path)
 			throws Exception {
 		RevObject obj = tr.get(rw.parseTree(treeish), path);