Fix NPE in DirCacheCheckout

If a file exists in head, merge, and the working tree, but not in
the index, and we're doing a force checkout, the checkout must be
an "update", not a "keep".

This is a follow-up on If3a9b9e60064459d187c7db04eb4471a72c6cece.

Bug: 569962
Change-Id: I59a7ac41898ddc1dd90e86b09b621a41fdf45667
Signed-off-by: Thomas Wolf <thomas.wolf@paranor.ch>

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

@@ -146,6 +146,55 @@ public class CheckoutCommandTest extends RepositoryTestCase {
 		assertTrue(testFile.exists());
 	}
 
+	@Test
+	public void testCheckoutForcedNoChangeNotInIndex() throws Exception {
+		git.checkout().setCreateBranch(true).setName("test2").call();
+		File f = writeTrashFile("NewFile.txt", "New file");
+		git.add().addFilepattern("NewFile.txt").call();
+		git.commit().setMessage("New file created").call();
+		git.checkout().setName("test").call();
+		assertFalse("NewFile.txt should not exist", f.exists());
+		writeTrashFile("NewFile.txt", "New file");
+		git.add().addFilepattern("NewFile.txt").call();
+		git.commit().setMessage("New file created again with same content")
+				.call();
+		// Now remove the file from the index only. So it exists in both
+		// commits, and in the working tree, but not in the index.
+		git.rm().addFilepattern("NewFile.txt").setCached(true).call();
+		assertTrue("NewFile.txt should exist", f.isFile());
+		git.checkout().setForced(true).setName("test2").call();
+		assertTrue("NewFile.txt should exist", f.isFile());
+		assertEquals(Constants.R_HEADS + "test2", git.getRepository()
+				.exactRef(Constants.HEAD).getTarget().getName());
+		assertTrue("Force checkout should have undone git rm --cached",
+				git.status().call().isClean());
+	}
+
+	@Test
+	public void testCheckoutNoChangeNotInIndex() throws Exception {
+		git.checkout().setCreateBranch(true).setName("test2").call();
+		File f = writeTrashFile("NewFile.txt", "New file");
+		git.add().addFilepattern("NewFile.txt").call();
+		git.commit().setMessage("New file created").call();
+		git.checkout().setName("test").call();
+		assertFalse("NewFile.txt should not exist", f.exists());
+		writeTrashFile("NewFile.txt", "New file");
+		git.add().addFilepattern("NewFile.txt").call();
+		git.commit().setMessage("New file created again with same content")
+				.call();
+		// Now remove the file from the index only. So it exists in both
+		// commits, and in the working tree, but not in the index.
+		git.rm().addFilepattern("NewFile.txt").setCached(true).call();
+		assertTrue("NewFile.txt should exist", f.isFile());
+		git.checkout().setName("test2").call();
+		assertTrue("NewFile.txt should exist", f.isFile());
+		assertEquals(Constants.R_HEADS + "test2", git.getRepository()
+				.exactRef(Constants.HEAD).getTarget().getName());
+		org.eclipse.jgit.api.Status status = git.status().call();
+		assertEquals("[NewFile.txt]", status.getRemoved().toString());
+		assertEquals("[NewFile.txt]", status.getUntracked().toString());
+	}
+
 	@Test
 	public void testCreateBranchOnCheckout() throws Exception {
 		git.checkout().setCreateBranch(true).setName("test2").call();

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

@@ -13,7 +13,6 @@
 package org.eclipse.jgit.lib;
 
 import static java.nio.charset.StandardCharsets.UTF_8;
-import static org.eclipse.jgit.dircache.DirCacheCheckout.checkoutEntry;
 import static org.junit.Assert.assertArrayEquals;
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertFalse;
@@ -48,7 +47,6 @@ import org.eclipse.jgit.errors.CorruptObjectException;
 import org.eclipse.jgit.errors.NoWorkTreeException;
 import org.eclipse.jgit.events.ChangeRecorder;
 import org.eclipse.jgit.events.ListenerHandle;
-import org.eclipse.jgit.internal.storage.dfs.InMemoryRepository;
 import org.eclipse.jgit.junit.RepositoryTestCase;
 import org.eclipse.jgit.junit.TestRepository;
 import org.eclipse.jgit.junit.TestRepository.BranchBuilder;
@@ -2148,11 +2146,4 @@ public class DirCacheCheckoutTest extends RepositoryTestCase {
 			assertEquals("WorkDir has not the right size.", i.size(), nrFiles);
 		}
 	}
-
-	@Test
-	public void shouldReturnAndNotThrowNPEWhenCheckoutEntryIsCalledWithNullEntry() throws Exception{
-		checkoutEntry(new InMemoryRepository(null), null, null, true, new CheckoutMetadata(null, null));
-	}
-
-
 }

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

@@ -946,12 +946,14 @@ public class DirCacheCheckout {
 				// called before). Ignore the cached deletion and use what we
 				// find in Merge. Potentially updates the file.
 				if (equalIdAndMode(hId, hMode, mId, mMode)) {
-					if (initialCheckout)
+					if (initialCheckout || force) {
 						update(name, mId, mMode);
-					else
+					} else {
 						keep(name, dce, f);
-				} else
+					}
+				} else {
 					conflict(name, dce, h, m);
+				}
 			}
 		} else {
 			// Something in Index
@@ -1214,10 +1216,13 @@ public class DirCacheCheckout {
 
 	private void keep(String path, DirCacheEntry e, WorkingTreeIterator f)
 			throws IOException {
-		if (e != null && !FileMode.TREE.equals(e.getFileMode())) {
+		if (e == null) {
+			return;
+		}
+		if (!FileMode.TREE.equals(e.getFileMode())) {
 			builder.add(e);
 		}
-		if (e != null && force) {
+		if (force) {
 			if (f == null || f.isModified(e, true, walk.getObjectReader())) {
 				kept.add(path);
 				checkoutEntry(repo, e, walk.getObjectReader(), false,
@@ -1448,9 +1453,6 @@ public class DirCacheCheckout {
 	public static void checkoutEntry(Repository repo, DirCacheEntry entry,
 			ObjectReader or, boolean deleteRecursive,
 			CheckoutMetadata checkoutMetadata) throws IOException {
-		if (entry == null) {
-			return;
-		}
 		if (checkoutMetadata == null)
 			checkoutMetadata = CheckoutMetadata.EMPTY;
 		ObjectLoader ol = or.open(entry.getObjectId());