Don't keep empty ignore rules in the ignore node list

Change-Id: Icd893dfaba06561bbe5cc60ebf866ec5d8301c22
Signed-off-by: Andrey Loskutov <loskutov@gmx.de>

org.eclipse.jgit.test/tst/org/eclipse/jgit/ignore/IgnoreNodeTest.java

@@ -44,12 +44,15 @@ package org.eclipse.jgit.ignore;
 
 import static org.eclipse.jgit.junit.Assert.assertEquals;
 import static org.junit.Assert.assertEquals;
-import static org.junit.Assert.assertTrue;
 import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertNotNull;
+import static org.junit.Assert.assertTrue;
 
+import java.io.ByteArrayInputStream;
 import java.io.File;
 import java.io.IOException;
+import java.io.InputStream;
+import java.util.ArrayList;
 import java.util.Arrays;
 
 import org.eclipse.jgit.errors.CorruptObjectException;
@@ -323,6 +326,15 @@ public class IgnoreNodeTest extends RepositoryTestCase {
 				node.isIgnored("", false, true));
 	}
 
+	@Test
+	public void testEmptyIgnoreRules() throws IOException {
+		IgnoreNode node = new IgnoreNode();
+		node.parse(writeToString("", "#", "!", "[[=a=]]"));
+		assertEquals(new ArrayList<>(), node.getRules());
+		node.parse(writeToString(" ", " / "));
+		assertEquals(2, node.getRules().size());
+	}
+
 	@Test
 	public void testSlashOnlyMatchesDirectory() throws IOException {
 		writeIgnoreFile(".gitignore", "out/");
@@ -472,4 +484,12 @@ public class IgnoreNodeTest extends RepositoryTestCase {
 			data.append(line + "\n");
 		writeTrashFile(name, data.toString());
 	}
+
+	private InputStream writeToString(String... rules) throws IOException {
+		StringBuilder data = new StringBuilder();
+		for (String line : rules) {
+			data.append(line + "\n");
+		}
+		return new ByteArrayInputStream(data.toString().getBytes("UTF-8"));
+	}
 }

org.eclipse.jgit/src/org/eclipse/jgit/ignore/FastIgnoreRule.java

@@ -188,6 +188,14 @@ public class FastIgnoreRule {
 		return !inverse;
 	}
 
+	/**
+	 * @return true if the rule never matches (comment line or broken pattern)
+	 * @since 4.1
+	 */
+	public boolean isEmpty() {
+		return matcher == NO_MATCH;
+	}
+
 	@Override
 	public String toString() {
 		StringBuilder sb = new StringBuilder();

org.eclipse.jgit/src/org/eclipse/jgit/ignore/IgnoreNode.java

@@ -110,7 +110,10 @@ public class IgnoreNode {
 		String txt;
 		while ((txt = br.readLine()) != null) {
 			if (txt.length() > 0 && !txt.startsWith("#") && !txt.equals("/")) { //$NON-NLS-1$ //$NON-NLS-2$
-				rules.add(new FastIgnoreRule(txt));
+				FastIgnoreRule rule = new FastIgnoreRule(txt);
+				if (!rule.isEmpty()) {
+					rules.add(rule);
+				}
 			}
 		}
 	}