Fix ResolveMerger when files should be replaced by folders

When during Merge for a certain path OURS & BASE contains a file and
THEIRS contains a folder there was a bug in JGit leading to unnecessary
conflicts. This commit fixes it and adds a test for this situation.
 
Bug: 472693
Change-Id: I71fac5a6a2ef926c01adc266c6f9b3275e870129
Also-by: Clemens Buchacher <drizzd@aon.at>
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

org.eclipse.jgit.test/tst/org/eclipse/jgit/merge/ResolveMergerTest.java

@@ -226,6 +226,80 @@ public class ResolveMergerTest extends RepositoryTestCase {
 				indexState(CONTENT));
 	}
 
+	/**
+	 * A tracked file is replaced by a folder in THEIRS.
+	 *
+	 * @param strategy
+	 * @throws Exception
+	 */
+	@Theory
+	public void checkFileReplacedByFolderInTheirs(MergeStrategy strategy)
+			throws Exception {
+		Git git = Git.wrap(db);
+
+		writeTrashFile("sub", "file");
+		git.add().addFilepattern("sub").call();
+		RevCommit first = git.commit().setMessage("initial").call();
+
+		git.checkout().setCreateBranch(true).setStartPoint(first)
+				.setName("side").call();
+
+		git.rm().addFilepattern("sub").call();
+		writeTrashFile("sub/file", "subfile");
+		git.add().addFilepattern("sub/file").call();
+		RevCommit masterCommit = git.commit().setMessage("file -> folder")
+				.call();
+
+		git.checkout().setName("master").call();
+		writeTrashFile("noop", "other");
+		git.add().addFilepattern("noop").call();
+		git.commit().setAll(true).setMessage("noop").call();
+
+		MergeResult mergeRes = git.merge().setStrategy(strategy)
+				.include(masterCommit).call();
+		assertEquals(MergeStatus.MERGED, mergeRes.getMergeStatus());
+		assertEquals(
+				"[noop, mode:100644, content:other][sub/file, mode:100644, content:subfile]",
+				indexState(CONTENT));
+	}
+
+	/**
+	 * A tracked file is replaced by a folder in OURS.
+	 *
+	 * @param strategy
+	 * @throws Exception
+	 */
+	@Theory
+	public void checkFileReplacedByFolderInOurs(MergeStrategy strategy)
+			throws Exception {
+		Git git = Git.wrap(db);
+
+		writeTrashFile("sub", "file");
+		git.add().addFilepattern("sub").call();
+		RevCommit first = git.commit().setMessage("initial").call();
+
+		git.checkout().setCreateBranch(true).setStartPoint(first)
+				.setName("side").call();
+		writeTrashFile("noop", "other");
+		git.add().addFilepattern("noop").call();
+		RevCommit sideCommit = git.commit().setAll(true).setMessage("noop")
+				.call();
+
+		git.checkout().setName("master").call();
+		git.rm().addFilepattern("sub").call();
+		writeTrashFile("sub/file", "subfile");
+		git.add().addFilepattern("sub/file").call();
+		git.commit().setMessage("file -> folder")
+				.call();
+
+		MergeResult mergeRes = git.merge().setStrategy(strategy)
+				.include(sideCommit).call();
+		assertEquals(MergeStatus.MERGED, mergeRes.getMergeStatus());
+		assertEquals(
+				"[noop, mode:100644, content:other][sub/file, mode:100644, content:subfile]",
+				indexState(CONTENT));
+	}
+
 	/**
 	 * An existing directory without tracked content should not prevent merging
 	 * a file with that name.

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

@@ -525,10 +525,11 @@ public class ResolveMerger extends ThreeWayMerger {
 			}
 		}
 
-		if (nonTree(modeO) && modeB == modeT && tw.idEqual(T_BASE, T_THEIRS)) {
+		if (modeB == modeT && tw.idEqual(T_BASE, T_THEIRS)) {
 			// THEIRS was not changed compared to BASE. All changes must be in
 			// OURS. OURS is chosen. We can keep the existing entry.
-			keep(ourDce);
+			if (ourDce != null)
+				keep(ourDce);
 			// no checkout needed!
 			return true;
 		}
@@ -549,11 +550,12 @@ public class ResolveMerger extends ThreeWayMerger {
 				if (e != null)
 					toBeCheckedOut.put(tw.getPathString(), e);
 				return true;
-			} else if (modeT == 0 && modeB != 0) {
-				// we want THEIRS ... but THEIRS contains the deletion of the
-				// file. Also, do not complain if the file is already deleted
-				// locally. This complements the test in isWorktreeDirty() for
-				// the same case.
+			} else {
+				// we want THEIRS ... but THEIRS contains a folder or the
+				// deletion of the path. Delete what's in the workingtree (the
+				// workingtree is clean) but do not complain if the file is
+				// already deleted locally. This complements the test in
+				// isWorktreeDirty() for the same case.
 				if (tw.getTreeCount() > T_FILE && tw.getRawMode(T_FILE) == 0)
 					return true;
 				toBeDeleted.add(tw.getPathString());