Fix DirCacheCheckout to return CheckoutConflictException

Problem occurs when the checkout wants to create a file 'd/f' but
the workingtree contains a dirty file 'd'. In order to create d/f the
file 'd' would have to be deleted and since the file is dirty that
content would be lost. This should lead to a CheckoutConflictException
for d/f when failOnConflict was set to true.

This fix also changes jgit checkout semantics to be more like native
gits checkout semantics. If during a checkout jgit wants to delete a
folder but finds that the working tree contains a dirty file at this
path then JGit will now throw an exception instead of silently keeping
the dirty file. Like in this example:

	git init
	touch b
	git add b
	git commit -m addB
	mkdir a
	touch a/c
	git add a/c
	git commit -m addAC
	rm -fr a
	touch a
	git checkout HEAD~

Change-Id: I9089123179e09dd565285d50b0caa308d290cccd
Signed-off-by: Rüdiger Herrmann <ruediger.herrmann@gmx.de>
Also-by: Rüdiger Herrmann <ruediger.herrmann@gmx.de>

org.eclipse.jgit.pgm.test/tst/org/eclipse/jgit/pgm/CheckoutTest.java

@@ -47,6 +47,7 @@ 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.nio.file.Files;
@@ -236,8 +237,8 @@ public class CheckoutTest extends CLIRepositoryTestCase {
 	 * <li>Checkout branch '1'
 	 * </ol>
 	 * <p>
-	 * The working tree should contain 'a' with FileMode.REGULAR_FILE after the
-	 * checkout.
+	 * The checkout has to delete folder but the workingtree contains a dirty
+	 * file at this path. The checkout should fail like in native git.
 	 *
 	 * @throws Exception
 	 */
@@ -266,11 +267,15 @@ public class CheckoutTest extends CLIRepositoryTestCase {
 					db.getFS());
 			assertEquals(FileMode.REGULAR_FILE, entry.getMode());
 
-			git.checkout().setName(branch_1.getName()).call();
-
-			entry = new FileTreeIterator.FileEntry(new File(db.getWorkTree(), "a"),
-					db.getFS());
-			assertEquals(FileMode.REGULAR_FILE, entry.getMode());
+			try {
+				git.checkout().setName(branch_1.getName()).call();
+				fail("Don't get the expected conflict");
+			} catch (CheckoutConflictException e) {
+				assertEquals("[a]", e.getConflictingPaths().toString());
+				entry = new FileTreeIterator.FileEntry(
+						new File(db.getWorkTree(), "a"), db.getFS());
+				assertEquals(FileMode.REGULAR_FILE, entry.getMode());
+			}
 		}
 	}
 

org.eclipse.jgit.test/tst/org/eclipse/jgit/lib/DirCacheCheckoutTest.java

@@ -1614,6 +1614,64 @@ public class DirCacheCheckoutTest extends RepositoryTestCase {
 		assertNotNull(git.checkout().setName(Constants.MASTER).call());
 	}
 
+	@Test(expected = CheckoutConflictException.class)
+	public void testFolderFileConflict() throws Exception {
+		RevCommit headCommit = commitFile("f/a", "initial content", "master");
+		RevCommit checkoutCommit = commitFile("f/a", "side content", "side");
+		FileUtils.delete(new File(db.getWorkTree(), "f"), FileUtils.RECURSIVE);
+		writeTrashFile("f", "file instead of folder");
+		new DirCacheCheckout(db, headCommit.getTree(), db.lockDirCache(),
+				checkoutCommit.getTree()).checkout();
+	}
+
+	@Test
+	public void testMultipleContentConflicts() throws Exception {
+		commitFile("a", "initial content", "master");
+		RevCommit headCommit = commitFile("b", "initial content", "master");
+		commitFile("a", "side content", "side");
+		RevCommit checkoutCommit = commitFile("b", "side content", "side");
+		writeTrashFile("a", "changed content");
+		writeTrashFile("b", "changed content");
+
+		try {
+			new DirCacheCheckout(db, headCommit.getTree(), db.lockDirCache(),
+					checkoutCommit.getTree()).checkout();
+			fail();
+		} catch (CheckoutConflictException expected) {
+			assertEquals(2, expected.getConflictingFiles().length);
+			assertTrue(Arrays.asList(expected.getConflictingFiles())
+					.contains("a"));
+			assertTrue(Arrays.asList(expected.getConflictingFiles())
+					.contains("b"));
+			assertEquals("changed content", read("a"));
+			assertEquals("changed content", read("b"));
+		}
+	}
+
+	@Test
+	public void testFolderFileAndContentConflicts() throws Exception {
+		RevCommit headCommit = commitFile("f/a", "initial content", "master");
+		commitFile("b", "side content", "side");
+		RevCommit checkoutCommit = commitFile("f/a", "side content", "side");
+		FileUtils.delete(new File(db.getWorkTree(), "f"), FileUtils.RECURSIVE);
+		writeTrashFile("f", "file instead of a folder");
+		writeTrashFile("b", "changed content");
+
+		try {
+			new DirCacheCheckout(db, headCommit.getTree(), db.lockDirCache(),
+					checkoutCommit.getTree()).checkout();
+			fail();
+		} catch (CheckoutConflictException expected) {
+			assertEquals(2, expected.getConflictingFiles().length);
+			assertTrue(Arrays.asList(expected.getConflictingFiles())
+					.contains("b"));
+			assertTrue(Arrays.asList(expected.getConflictingFiles())
+					.contains("f"));
+			assertEquals("file instead of a folder", read("f"));
+			assertEquals("changed content", read("b"));
+		}
+	}
+
 	public void assertWorkDir(Map<String, String> i)
 			throws CorruptObjectException,
 			IOException {

org.eclipse.jgit/src/org/eclipse/jgit/dircache/DirCacheCheckout.java

@@ -718,10 +718,23 @@ public class DirCacheCheckout {
 			return;
 		}
 
-		// if we have no file at all then there is nothing to do
-		if ((ffMask & 0x222) == 0
-				&& (f == null || FileMode.TREE.equals(f.getEntryFileMode())))
-			return;
+		if ((ffMask & 0x222) == 0) {
+			// HEAD, MERGE and index don't contain a file (e.g. all contain a
+			// folder)
+			if (f == null || FileMode.TREE.equals(f.getEntryFileMode())) {
+				// the workingtree entry doesn't exist or also contains a folder
+				// -> no problem
+				return;
+			} else {
+				// the workingtree entry exists and is not a folder
+				if (!idEqual(h, m)) {
+					// Because HEAD and MERGE differ we will try to update the
+					// workingtree with a folder -> return a conflict
+					conflict(name, null, null, null);
+				}
+				return;
+			}
+		}
 
 		if ((ffMask == 0x00F) && f != null && FileMode.TREE.equals(f.getEntryFileMode())) {
 			// File/Directory conflict case #20
@@ -1004,6 +1017,17 @@ public class DirCacheCheckout {
 		}
 	}
 
+	private static boolean idEqual(AbstractTreeIterator a,
+			AbstractTreeIterator b) {
+		if (a == b) {
+			return true;
+		}
+		if (a == null || b == null) {
+			return false;
+		}
+		return a.getEntryObjectId().equals(b.getEntryObjectId());
+	}
+
 	/**
 	 * A conflict is detected - add the three different stages to the index
 	 * @param path the path of the conflicting entry