Fix bugs in TreeWalk#isPathSuffix used by PathSuffixFilter

* It didn't check the first character in the pattern due to a off-by-one
  error. Spotted by James Roper.
* It returned true even when pattern was longer than current path, e.g.
  it returned that ".txt" is suffix of "txt".

Bug: 411999
Change-Id: I9fbcd68a11fb57cc49956b70c387a47271a0424f
Signed-off-by: Robin Stocker <robin@nibor.org>

org.eclipse.jgit.test/tst/org/eclipse/jgit/treewalk/filter/PathSuffixFilterTest.java

@@ -82,6 +82,16 @@ public class PathSuffixFilterTest extends RepositoryTestCase {
 		assertEquals(expected, paths);
 	}
 
+	@Test
+	public void testEdgeCases() throws IOException {
+		ObjectId treeId = createTree("abc", "abcd", "bcd", "c");
+		assertEquals(new ArrayList<String>(), getMatchingPaths("xbcd", treeId));
+		assertEquals(new ArrayList<String>(), getMatchingPaths("abcx", treeId));
+		assertEquals(Arrays.asList("abcd"), getMatchingPaths("abcd", treeId));
+		assertEquals(Arrays.asList("abcd", "bcd"), getMatchingPaths("bcd", treeId));
+		assertEquals(Arrays.asList("abc", "c"), getMatchingPaths("c", treeId));
+	}
+
 	private ObjectId createTree(String... paths) throws IOException {
 		final ObjectInserter odi = db.newObjectInserter();
 		final DirCache dc = db.readDirCache();

org.eclipse.jgit/src/org/eclipse/jgit/treewalk/TreeWalk.java

@@ -835,13 +835,17 @@ public class TreeWalk {
 		final AbstractTreeIterator t = currentHead;
 		final byte[] c = t.path;
 		final int cLen = t.pathLen;
-		int ci;
 
-		for (ci = 1; ci < cLen && ci < pLen; ci++) {
-			if (c[cLen-ci] != p[pLen-ci])
+		for (int i = 1; i <= pLen; i++) {
+			// Pattern longer than current path
+			if (i > cLen)
+				return false;
+			// Current path doesn't match pattern
+			if (c[cLen - i] != p[pLen - i])
 				return false;
 		}
 
+		// Whole pattern tested -> matches
 		return true;
 	}