Add getConflictingNames to RefDatabase

This has the same logic as isNameConflicting, but instead of only
returning a boolean, it returns a collection of names that conflict.

It will be used in EGit to provide a better message to the user when
validating a ref name, see Ibea9984121ae88c488858b8a8e73b593195b15e0.

Existing implementations of isNameConflicting could be rewritten like
this:

  return !getConflictingNames(name).isEmpty();

But I'm not sure about that, as isNameConflicting can be implemented in
a faster way than getConflictingNames.

Change-Id: I11e0ba2f300adb8b3612943c304ba68bbe73db8a
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

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

@@ -0,0 +1,148 @@
+/*
+ * Copyright (C) 2013, Robin Stocker <robin@nibor.org>
+ * and other copyright owners as documented in the project's IP log.
+ *
+ * This program and the accompanying materials are made available
+ * under the terms of the Eclipse Distribution License v1.0 which
+ * accompanies this distribution, is reproduced below, and is
+ * available at http://www.eclipse.org/org/documents/edl-v10.php
+ *
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or
+ * without modification, are permitted provided that the following
+ * conditions are met:
+ *
+ * - Redistributions of source code must retain the above copyright
+ *   notice, this list of conditions and the following disclaimer.
+ *
+ * - Redistributions in binary form must reproduce the above
+ *   copyright notice, this list of conditions and the following
+ *   disclaimer in the documentation and/or other materials provided
+ *   with the distribution.
+ *
+ * - Neither the name of the Eclipse Foundation, Inc. nor the
+ *   names of its contributors may be used to endorse or promote
+ *   products derived from this software without specific prior
+ *   written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
+ * CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
+ * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+ * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+ * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+ * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+ * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
+ * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+package org.eclipse.jgit.lib;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertTrue;
+
+import java.io.IOException;
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+
+import org.junit.Test;
+
+public class RefDatabaseConflictingNamesTest {
+
+	private RefDatabase refDatabase = new RefDatabase() {
+		@Override
+		public Map<String, Ref> getRefs(String prefix) throws IOException {
+			if (ALL.equals(prefix)) {
+				Map<String, Ref> existing = new HashMap<String, Ref>();
+				existing.put("refs/heads/a/b", null /* not used */);
+				existing.put("refs/heads/q", null /* not used */);
+				return existing;
+			} else {
+				return Collections.emptyMap();
+			}
+		}
+
+		@Override
+		public Ref peel(Ref ref) throws IOException {
+			return null;
+		}
+
+		@Override
+		public RefUpdate newUpdate(String name, boolean detach)
+				throws IOException {
+			return null;
+		}
+
+		@Override
+		public RefRename newRename(String fromName, String toName)
+				throws IOException {
+			return null;
+		}
+
+		@Override
+		public boolean isNameConflicting(String name) throws IOException {
+			return false;
+		}
+
+		@Override
+		public Ref getRef(String name) throws IOException {
+			return null;
+		}
+
+		@Override
+		public List<Ref> getAdditionalRefs() throws IOException {
+			return null;
+		}
+
+		@Override
+		public void create() throws IOException {
+			// Not needed
+		}
+
+		@Override
+		public void close() {
+			// Not needed
+		}
+	};
+
+	@Test
+	public void testGetConflictingNames() throws IOException {
+		// new references cannot replace an existing container
+		assertConflictingNames("refs", "refs/heads/a/b", "refs/heads/q");
+		assertConflictingNames("refs/heads", "refs/heads/a/b", "refs/heads/q");
+		assertConflictingNames("refs/heads/a", "refs/heads/a/b");
+
+		// existing reference is not conflicting
+		assertNoConflictingNames("refs/heads/a/b");
+
+		// new references are not conflicting
+		assertNoConflictingNames("refs/heads/a/d");
+		assertNoConflictingNames("refs/heads/master");
+
+		// existing reference must not be used as a container
+		assertConflictingNames("refs/heads/a/b/c", "refs/heads/a/b");
+		assertConflictingNames("refs/heads/q/master", "refs/heads/q");
+	}
+
+	private void assertNoConflictingNames(String proposed) throws IOException {
+		assertTrue("expected conflicting names to be empty", refDatabase
+				.getConflictingNames(proposed).isEmpty());
+	}
+
+	private void assertConflictingNames(String proposed, String... conflicts)
+			throws IOException {
+		Set<String> expected = new HashSet<String>(Arrays.asList(conflicts));
+		assertEquals(expected,
+				new HashSet<String>(refDatabase.getConflictingNames(proposed)));
+	}
+}

org.eclipse.jgit/src/org/eclipse/jgit/lib/RefDatabase.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 2010, Google Inc.
+ * Copyright (C) 2010, 2013 Google Inc.
  * and other copyright owners as documented in the project's IP log.
  *
  * This program and the accompanying materials are made available
@@ -44,6 +44,9 @@
 package org.eclipse.jgit.lib;
 
 import java.io.IOException;
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.Collections;
 import java.util.List;
 import java.util.Map;
 
@@ -111,9 +114,45 @@ public abstract class RefDatabase {
 	 *         using this name right now would be safe.
 	 * @throws IOException
 	 *             the database could not be read to check for conflicts.
+	 * @see #getConflictingNames(String)
 	 */
 	public abstract boolean isNameConflicting(String name) throws IOException;
 
+	/**
+	 * Determine if a proposed reference cannot coexist with existing ones. If
+	 * the passed name already exists, it's not considered a conflict.
+	 *
+	 * @param name
+	 *            proposed name to check for conflicts against
+	 * @return a collection of full names of existing refs which would conflict
+	 *         with the passed ref name; empty collection when there are no
+	 *         conflicts
+	 * @throws IOException
+	 * @since 2.3
+	 * @see #isNameConflicting(String)
+	 */
+	public Collection<String> getConflictingNames(String name)
+			throws IOException {
+		Map<String, Ref> allRefs = getRefs(ALL);
+		// Cannot be nested within an existing reference.
+		int lastSlash = name.lastIndexOf('/');
+		while (0 < lastSlash) {
+			String needle = name.substring(0, lastSlash);
+			if (allRefs.containsKey(needle))
+				return Collections.singletonList(needle);
+			lastSlash = name.lastIndexOf('/', lastSlash - 1);
+		}
+
+		List<String> conflicting = new ArrayList<String>();
+		// Cannot be the container of an existing reference.
+		String prefix = name + '/';
+		for (String existing : allRefs.keySet())
+			if (existing.startsWith(prefix))
+				conflicting.add(existing);
+
+		return conflicting;
+	}
+
 	/**
 	 * Create a new update command to create, modify or delete a reference.
 	 *