Checkout should not use too long filenames

DirCacheCheckout is generating names for temporary files. It was not checking
the length of this filenames. It may happen that a generated filename is
longer than 255 chars which causes problems on certain platforms. Make sure
that filenames for temporary files do not exceed 255 chars.

Bug: 508823
Change-Id: I9475c04351ce3faebdc6ad40ea4faa3c326815f4

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

@@ -1672,6 +1672,20 @@ public class DirCacheCheckoutTest extends RepositoryTestCase {
 		}
 	}
 
+	@Test
+	public void testLongFilename() throws Exception {
+		char[] bytes = new char[253];
+		Arrays.fill(bytes, 'f');
+		String longFileName = new String(bytes);
+		// 1
+		doit(mkmap(longFileName, "a"), mkmap(longFileName, "b"),
+				mkmap(longFileName, "a"));
+		writeTrashFile(longFileName, "a");
+		checkout();
+		assertNoConflicts();
+		assertUpdated(longFileName);
+	}
+
 	public void assertWorkDir(Map<String, String> i)
 			throws CorruptObjectException,
 			IOException {

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

@@ -1299,8 +1299,13 @@ public class DirCacheCheckout {
 			return;
 		}
 
+		String name = f.getName();
+		if (name.length() > 200) {
+			name = name.substring(0, 200);
+		}
 		File tmpFile = File.createTempFile(
-				"._" + f.getName(), null, parentDir); //$NON-NLS-1$
+				"._" + name, null, parentDir); //$NON-NLS-1$
+
 		EolStreamType nonNullEolStreamType;
 		if (checkoutMetadata.eolStreamType != null) {
 			nonNullEolStreamType = checkoutMetadata.eolStreamType;