Fixed Merge Algorithm regarding concurrent file creations

When in OURS and THEIRS a new file is created we want a conflict
when the two contents differ. If on two branches the same file
with the same content is created this should not be a conflict.
But: the current merge algorithm is throwing NPEs in this case.
Fix this by choosing an empty RawText as common base if the
base is empty.

Change-Id: I21cb23f852965b82fb82ccd66ec961c7edb3ac3d
Signed-off-by: Christian Halstrick <christian.halstrick@sap.com>

org.eclipse.jgit.test/tst/org/eclipse/jgit/api/MergeCommandTest.java

@@ -247,6 +247,57 @@ public class MergeCommandTest extends RepositoryTestCase {
 		assertEquals(RepositoryState.MERGING, db.getRepositoryState());
 	}
 
+	public void testMultipleCreations() throws Exception {
+		Git git = new Git(db);
+
+		writeTrashFile("a", "1\na\n3\n");
+		git.add().addFilepattern("a").call();
+		RevCommit initialCommit = git.commit().setMessage("initial").call();
+
+		createBranch(initialCommit, "refs/heads/side");
+		checkoutBranch("refs/heads/side");
+
+		writeTrashFile("b", "1\nb(side)\n3\n");
+		git.add().addFilepattern("b").call();
+		RevCommit secondCommit = git.commit().setMessage("side").call();
+
+		checkoutBranch("refs/heads/master");
+
+		writeTrashFile("b", "1\nb(main)\n3\n");
+		git.add().addFilepattern("b").call();
+		git.commit().setMessage("main").call();
+
+		MergeResult result = git.merge().include(secondCommit.getId())
+				.setStrategy(MergeStrategy.RESOLVE).call();
+		assertEquals(MergeStatus.CONFLICTING, result.getMergeStatus());
+	}
+
+	public void testMultipleCreationsSameContent() throws Exception {
+		Git git = new Git(db);
+
+		writeTrashFile("a", "1\na\n3\n");
+		git.add().addFilepattern("a").call();
+		RevCommit initialCommit = git.commit().setMessage("initial").call();
+
+		createBranch(initialCommit, "refs/heads/side");
+		checkoutBranch("refs/heads/side");
+
+		writeTrashFile("b", "1\nb(1)\n3\n");
+		git.add().addFilepattern("b").call();
+		RevCommit secondCommit = git.commit().setMessage("side").call();
+
+		checkoutBranch("refs/heads/master");
+
+		writeTrashFile("b", "1\nb(1)\n3\n");
+		git.add().addFilepattern("b").call();
+		git.commit().setMessage("main").call();
+
+		MergeResult result = git.merge().include(secondCommit.getId())
+				.setStrategy(MergeStrategy.RESOLVE).call();
+		assertEquals(MergeStatus.MERGED, result.getMergeStatus());
+		assertEquals("1\nb(1)\n3\n", read(new File(db.getWorkTree(), "b")));
+	}
+
 	public void testSuccessfulContentMerge() throws Exception {
 		Git git = new Git(db);
 
@@ -415,6 +466,34 @@ public class MergeCommandTest extends RepositoryTestCase {
 				read(new File(db.getWorkTree(), "c/c/c")));
 	}
 
+	public void testMultipleDeletions() throws Exception {
+		Git git = new Git(db);
+
+		writeTrashFile("a", "1\na\n3\n");
+		git.add().addFilepattern("a").call();
+		RevCommit initialCommit = git.commit().setMessage("initial").call();
+
+		createBranch(initialCommit, "refs/heads/side");
+		checkoutBranch("refs/heads/side");
+
+		assertTrue(new File(db.getWorkTree(), "a").delete());
+		git.add().addFilepattern("a").setUpdate(true).call();
+		RevCommit secondCommit = git.commit().setMessage("side").call();
+
+		assertFalse(new File(db.getWorkTree(), "a").exists());
+		checkoutBranch("refs/heads/master");
+		assertTrue(new File(db.getWorkTree(), "a").exists());
+
+		assertTrue(new File(db.getWorkTree(), "a").delete());
+		git.add().addFilepattern("a").setUpdate(true).call();
+		git.commit().setMessage("main").call();
+
+		// We are merging a deletion into our branch
+		MergeResult result = git.merge().include(secondCommit.getId())
+				.setStrategy(MergeStrategy.RESOLVE).call();
+		assertEquals(MergeStatus.MERGED, result.getMergeStatus());
+	}
+
 	public void testDeletionAndConflict() throws Exception {
 		Git git = new Git(db);
 

org.eclipse.jgit/src/org/eclipse/jgit/diff/RawText.java

@@ -66,6 +66,9 @@ import org.eclipse.jgit.util.RawParseUtils;
  * they are converting from "line number" to "element index".
  */
 public class RawText extends Sequence {
+	/** A Rawtext of length 0 */
+	public static final RawText EMPTY_TEXT = new RawText(new byte[0]);
+
 	/** Number of bytes to check for heuristics in {@link #isBinary(byte[])} */
 	private static final int FIRST_FEW_BYTES = 8000;
 

org.eclipse.jgit/src/org/eclipse/jgit/merge/ResolveMerger.java

@@ -467,10 +467,12 @@ public class ResolveMerger extends ThreeWayMerger {
 			throws FileNotFoundException, IllegalStateException, IOException {
 		MergeFormatter fmt = new MergeFormatter();
 
+		RawText baseText = base == null ? RawText.EMPTY_TEXT : getRawText(
+				base.getEntryObjectId(), db);
+
 		// do the merge
-		MergeResult<RawText> result = mergeAlgorithm.merge(
-				RawTextComparator.DEFAULT,
-				getRawText(base.getEntryObjectId(), db),
+		MergeResult<RawText> result = MergeAlgorithm.merge(
+				RawTextComparator.DEFAULT, baseText,
 				getRawText(ours.getEntryObjectId(), db),
 				getRawText(theirs.getEntryObjectId(), db));