Cherry-Pick: Support --mainline to pick merges

By specifying a mainline parent, a merge is cherry picked as if this
parent was its only parent. If no mainline parent is given, cherry
picking merges is not allowed, as before.

Change-Id: I391cb73bf8f49e2df61428c17b40fae8c86a8b76
Signed-off-by: Konrad Kügler <swamblumat-eclipsebugs@yahoo.de>

4 files changed, 101 insertions, 9 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 2668c116a0..df73435803 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
@@ -46,6 +46,7 @@ import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertNotNull;
 import static org.junit.Assert.assertTrue;
+import static org.junit.Assert.fail;
 
 import java.io.File;
 import java.io.IOException;
@@ -55,11 +56,13 @@ import org.eclipse.jgit.api.CherryPickResult.CherryPickStatus;
 import org.eclipse.jgit.api.ResetCommand.ResetType;
 import org.eclipse.jgit.api.errors.GitAPIException;
 import org.eclipse.jgit.api.errors.JGitInternalException;
+import org.eclipse.jgit.api.errors.MultipleParentsNotAllowedException;
 import org.eclipse.jgit.dircache.DirCache;
 import org.eclipse.jgit.junit.RepositoryTestCase;
 import org.eclipse.jgit.lib.ConfigConstants;
 import org.eclipse.jgit.lib.Constants;
 import org.eclipse.jgit.lib.FileMode;
+import org.eclipse.jgit.lib.ObjectId;
 import org.eclipse.jgit.lib.ReflogReader;
 import org.eclipse.jgit.lib.RepositoryState;
 import org.eclipse.jgit.merge.ResolveMerger.MergeFailureReason;
@@ -336,4 +339,59 @@ public class CherryPickCommandTest extends RepositoryTestCase {
 					.startsWith("cherry-pick: "));
 		}
 	}
+
+	/**
+	 * Cherry-picking merge commit M onto T
+	 * <pre>
+	 *    M
+	 *    |\
+	 *    C D
+	 *    |/
+	 * T  B
+	 * | /
+	 * A
+	 * </pre>
+	 * @throws Exception
+	 */
+	@Test
+	public void testCherryPickMerge() throws Exception {
+		Git git = new Git(db);
+
+		commitFile("file", "1\n2\n3\n", "master");
+		commitFile("file", "1\n2\n3\n", "side");
+		checkoutBranch("refs/heads/side");
+		RevCommit commitD = commitFile("file", "1\n2\n3\n4\n5\n", "side2");
+		commitFile("file", "a\n2\n3\n", "side");
+		MergeResult mergeResult = git.merge().include(commitD).call();
+		ObjectId commitM = mergeResult.getNewHead();
+		checkoutBranch("refs/heads/master");
+		RevCommit commitT = commitFile("another", "t", "master");
+
+		try {
+			git.cherryPick().include(commitM).call();
+			fail("merges should not be cherry-picked by default");
+		} catch (MultipleParentsNotAllowedException e) {
+			// expected
+		}
+		try {
+			git.cherryPick().include(commitM).setMainlineParentNumber(3).call();
+			fail("specifying a non-existent parent should fail");
+		} catch (JGitInternalException e) {
+			// expected
+			assertTrue(e.getMessage().endsWith(
+					"does not have a parent number 3."));
+		}
+
+		CherryPickResult result = git.cherryPick().include(commitM)
+				.setMainlineParentNumber(1).call();
+		assertEquals(CherryPickStatus.OK, result.getStatus());
+		checkFile(new File(db.getWorkTree(), "file"), "1\n2\n3\n4\n5\n");
+
+		git.reset().setMode(ResetType.HARD).setRef(commitT.getName()).call();
+
+		CherryPickResult result2 = git.cherryPick().include(commitM)
+				.setMainlineParentNumber(2).call();
+		assertEquals(CherryPickStatus.OK, result2.getStatus());
+		checkFile(new File(db.getWorkTree(), "file"), "a\n2\n3\n");
+	}
 }
diff --git a/org.eclipse.jgit/resources/org/eclipse/jgit/internal/JGitText.properties b/org.eclipse.jgit/resources/org/eclipse/jgit/internal/JGitText.properties
index b3049b07f4..7b073217a5 100644
--- a/org.eclipse.jgit/resources/org/eclipse/jgit/internal/JGitText.properties
+++ b/org.eclipse.jgit/resources/org/eclipse/jgit/internal/JGitText.properties
@@ -85,6 +85,7 @@ cannotUnloadAModifiedTree=Cannot unload a modified tree.
 cannotWorkWithOtherStagesThanZeroRightNow=Cannot work with other stages than zero right now. Won't write corrupt index.
 canOnlyCherryPickCommitsWithOneParent=Cannot cherry-pick commit ''{0}'' because it has {1} parents, only commits with exactly one parent are supported.
 canOnlyRevertCommitsWithOneParent=Cannot revert commit ''{0}'' because it has {1} parents, only commits with exactly one parent are supported
+commitDoesNotHaveGivenParent=The commit ''{0}'' does not have a parent number {1}.
 cantFindObjectInReversePackIndexForTheSpecifiedOffset=Can't find object in (reverse) pack index for the specified offset {0}
 cantPassMeATree=Can't pass me a tree!
 channelMustBeInRange0_255=channel {0} must be in range [0, 255]
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 b3415b3505..cf50160da5 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/api/CherryPickCommand.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/api/CherryPickCommand.java
@@ -56,6 +56,7 @@ import org.eclipse.jgit.api.errors.NoMessageException;
 import org.eclipse.jgit.api.errors.UnmergedPathsException;
 import org.eclipse.jgit.api.errors.WrongRepositoryStateException;
 import org.eclipse.jgit.dircache.DirCacheCheckout;
+import org.eclipse.jgit.errors.MissingObjectException;
 import org.eclipse.jgit.internal.JGitText;
 import org.eclipse.jgit.lib.AnyObjectId;
 import org.eclipse.jgit.lib.Constants;
@@ -90,6 +91,8 @@ public class CherryPickCommand extends GitCommand<CherryPickResult> {
 
 	private MergeStrategy strategy = MergeStrategy.RECURSIVE;
 
+	private Integer mainlineParentNumber;
+
 	/**
 	 * @param repo
 	 */
@@ -139,15 +142,7 @@ public class CherryPickCommand extends GitCommand<CherryPickResult> {
 				RevCommit srcCommit = revWalk.parseCommit(srcObjectId);
 
 				// get the parent of the commit to cherry-pick
-				if (srcCommit.getParentCount() != 1)
-					throw new MultipleParentsNotAllowedException(
-							MessageFormat.format(
-									JGitText.get().canOnlyCherryPickCommitsWithOneParent,
-									srcCommit.name(),
-									Integer.valueOf(srcCommit.getParentCount())));
-
-				RevCommit srcParent = srcCommit.getParent(0);
-				revWalk.parseHeaders(srcParent);
+				final RevCommit srcParent = getParentCommit(srcCommit, revWalk);
 
 				String ourName = calculateOurName(headRef);
 				String cherryPickName = srcCommit.getId().abbreviate(7).name()
@@ -200,6 +195,31 @@ public class CherryPickCommand extends GitCommand<CherryPickResult> {
 		return new CherryPickResult(newHead, cherryPickedRefs);
 	}
 
+	private RevCommit getParentCommit(RevCommit srcCommit, RevWalk revWalk)
+			throws MultipleParentsNotAllowedException, MissingObjectException,
+			IOException {
+		final RevCommit srcParent;
+		if (mainlineParentNumber == null) {
+			if (srcCommit.getParentCount() != 1)
+				throw new MultipleParentsNotAllowedException(
+						MessageFormat.format(
+								JGitText.get().canOnlyCherryPickCommitsWithOneParent,
+								srcCommit.name(),
+								Integer.valueOf(srcCommit.getParentCount())));
+			srcParent = srcCommit.getParent(0);
+		} else {
+			if (mainlineParentNumber.intValue() > srcCommit.getParentCount())
+				throw new JGitInternalException(MessageFormat.format(
+						JGitText.get().commitDoesNotHaveGivenParent, srcCommit,
+						mainlineParentNumber));
+			srcParent = srcCommit
+					.getParent(mainlineParentNumber.intValue() - 1);
+		}
+
+		revWalk.parseHeaders(srcParent);
+		return srcParent;
+	}
+
 	/**
 	 * @param commit
 	 *            a reference to a commit which is cherry-picked to the current
@@ -271,6 +291,18 @@ public class CherryPickCommand extends GitCommand<CherryPickResult> {
 		return this;
 	}
 
+	/**
+	 * @param mainlineParentNumber
+	 *            the (1-based) parent number to diff against. This allows
+	 *            cherry-picking of merges.
+	 * @return {@code this}
+	 * @since 3.4
+	 */
+	public CherryPickCommand setMainlineParentNumber(int mainlineParentNumber) {
+		this.mainlineParentNumber = Integer.valueOf(mainlineParentNumber);
+		return this;
+	}
+
 	private String calculateOurName(Ref headRef) {
 		if (ourCommitName != null)
 			return ourCommitName;
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/JGitText.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/JGitText.java
index 576ba0f493..39f203ca8b 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/internal/JGitText.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/internal/JGitText.java
@@ -147,6 +147,7 @@ public class JGitText extends TranslationBundle {
 	/***/ public String cannotWorkWithOtherStagesThanZeroRightNow;
 	/***/ public String canOnlyCherryPickCommitsWithOneParent;
 	/***/ public String canOnlyRevertCommitsWithOneParent;
+	/***/ public String commitDoesNotHaveGivenParent;
 	/***/ public String cantFindObjectInReversePackIndexForTheSpecifiedOffset;
 	/***/ public String cantPassMeATree;
 	/***/ public String channelMustBeInRange0_255;