Fully implement SHA-1 abbreviations

ObjectReader implementations are now responsible for creating the
unique abbreviation of an ObjectId, or for resolving an abbreviation
back to its full form.  In this latter case the reader can offer up
multiple candidates to the caller, who may be able to disambiguate
them based on context.

Repository.resolve() doesn't take multiple candidates into account
right now, but it could in the future by looking for a remaining
^0 or ^{commit} suffix and take an expansion if there is only one
commit that matches the input abbreviation.  It could also use
the distance from an annotated tag to resolve "tag-NNN-gcommit"
style strings that are often output by `git describe`.

Change-Id: Icd3250adc8177ae05278b858933afdca0cbbdb56
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

3 files changed, 230 insertions, 5 deletions

diff --git a/org.eclipse.jgit.test/tst/org/eclipse/jgit/diff/DiffFormatterTest.java b/org.eclipse.jgit.test/tst/org/eclipse/jgit/diff/DiffFormatterTest.java
index 996ee35a1e..92d4fa114f 100644
--- a/org.eclipse.jgit.test/tst/org/eclipse/jgit/diff/DiffFormatterTest.java
+++ b/org.eclipse.jgit.test/tst/org/eclipse/jgit/diff/DiffFormatterTest.java
@@ -74,6 +74,7 @@ public class DiffFormatterTest extends RepositoryTestCase {
 		testDb = new TestRepository(db);
 		df = new DiffFormatter(DisabledOutputStream.INSTANCE);
 		df.setRepository(db);
+		df.setAbbreviationLength(8);
 	}
 
 	public void testCreateFileHeader_Modify() throws Exception {
@@ -159,8 +160,8 @@ public class DiffFormatterTest extends RepositoryTestCase {
 
 	private String makeDiffHeader(String pathA, String pathB, ObjectId aId,
 			ObjectId bId) {
-		String a = aId.abbreviate(db).name();
-		String b = bId.abbreviate(db).name();
+		String a = aId.abbreviate(8).name();
+		String b = bId.abbreviate(8).name();
 		return DIFF + "a/" + pathA + " " + "b/" + pathB + "\n" + //
 				"index " + a + ".." + b + " " + REGULAR_FILE + "\n" + //
 				"--- a/" + pathA + "\n" + //
@@ -169,8 +170,8 @@ public class DiffFormatterTest extends RepositoryTestCase {
 
 	private String makeDiffHeaderModeChange(String pathA, String pathB,
 			ObjectId aId, ObjectId bId, String modeA, String modeB) {
-		String a = aId.abbreviate(db).name();
-		String b = bId.abbreviate(db).name();
+		String a = aId.abbreviate(8).name();
+		String b = bId.abbreviate(8).name();
 		return DIFF + "a/" + pathA + " " + "b/" + pathB + "\n" + //
 				"old mode " + modeA + "\n" + //
 				"new mode " + modeB + "\n" + //
@@ -182,5 +183,4 @@ public class DiffFormatterTest extends RepositoryTestCase {
 	private ObjectId blob(String content) throws Exception {
 		return testDb.blob(content).copy();
 	}
-
 }
diff --git a/org.eclipse.jgit.test/tst/org/eclipse/jgit/lib/AbbreviatedObjectIdTest.java b/org.eclipse.jgit.test/tst/org/eclipse/jgit/lib/AbbreviatedObjectIdTest.java
index 45f8907da7..9430a20e73 100644
--- a/org.eclipse.jgit.test/tst/org/eclipse/jgit/lib/AbbreviatedObjectIdTest.java
+++ b/org.eclipse.jgit.test/tst/org/eclipse/jgit/lib/AbbreviatedObjectIdTest.java
@@ -348,4 +348,30 @@ public class AbbreviatedObjectIdTest extends TestCase {
 		assertTrue(a.prefixCompare(i3) > 0);
 		assertFalse(i3.startsWith(a));
 	}
+
+	public void testIsId() {
+		// These are all too short.
+		assertFalse(AbbreviatedObjectId.isId(""));
+		assertFalse(AbbreviatedObjectId.isId("a"));
+
+		// These are too long.
+		assertFalse(AbbreviatedObjectId.isId(ObjectId.fromString(
+				"7b6e8067ec86acef9a4184b43210d583b6d2f99a").name()
+				+ "0"));
+		assertFalse(AbbreviatedObjectId.isId(ObjectId.fromString(
+				"7b6e8067ec86acef9a4184b43210d583b6d2f99a").name()
+				+ "c0ffee"));
+
+		// These contain non-hex characters.
+		assertFalse(AbbreviatedObjectId.isId("01notahexstring"));
+
+		// These should all work.
+		assertTrue(AbbreviatedObjectId.isId("ab"));
+		assertTrue(AbbreviatedObjectId.isId("abc"));
+		assertTrue(AbbreviatedObjectId.isId("abcd"));
+		assertTrue(AbbreviatedObjectId.isId("abcd0"));
+		assertTrue(AbbreviatedObjectId.isId("abcd09"));
+		assertTrue(AbbreviatedObjectId.isId(ObjectId.fromString(
+				"7b6e8067ec86acef9a4184b43210d583b6d2f99a").name()));
+	}
 }
diff --git a/org.eclipse.jgit.test/tst/org/eclipse/jgit/storage/file/AbbreviationTest.java b/org.eclipse.jgit.test/tst/org/eclipse/jgit/storage/file/AbbreviationTest.java
new file mode 100644
index 0000000000..5e8f72b5ba
--- /dev/null
+++ b/org.eclipse.jgit.test/tst/org/eclipse/jgit/storage/file/AbbreviationTest.java
@@ -0,0 +1,199 @@
+/*
+ * Copyright (C) 2010, Google Inc.
+ * 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.storage.file;
+
+import static org.eclipse.jgit.lib.Constants.OBJECT_ID_LENGTH;
+import static org.eclipse.jgit.lib.Constants.OBJECT_ID_STRING_LENGTH;
+
+import java.io.BufferedOutputStream;
+import java.io.ByteArrayOutputStream;
+import java.io.File;
+import java.io.FileOutputStream;
+import java.io.IOException;
+import java.io.OutputStream;
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.List;
+
+import org.eclipse.jgit.junit.LocalDiskRepositoryTestCase;
+import org.eclipse.jgit.junit.TestRepository;
+import org.eclipse.jgit.lib.AbbreviatedObjectId;
+import org.eclipse.jgit.lib.ObjectId;
+import org.eclipse.jgit.lib.ObjectReader;
+import org.eclipse.jgit.revwalk.RevBlob;
+import org.eclipse.jgit.transport.PackedObjectInfo;
+
+public class AbbreviationTest extends LocalDiskRepositoryTestCase {
+	private FileRepository db;
+
+	private ObjectReader reader;
+
+	private TestRepository<FileRepository> test;
+
+	public void setUp() throws Exception {
+		super.setUp();
+		db = createBareRepository();
+		reader = db.newObjectReader();
+		test = new TestRepository<FileRepository>(db);
+	}
+
+	public void tearDown() throws Exception {
+		if (reader != null)
+			reader.release();
+	}
+
+	public void testAbbreviateOnEmptyRepository() throws IOException {
+		ObjectId id = id("9d5b926ed164e8ee88d3b8b1e525d699adda01ba");
+
+		assertEquals(id.abbreviate(2), reader.abbreviate(id, 2));
+		assertEquals(id.abbreviate(7), reader.abbreviate(id, 7));
+		assertEquals(id.abbreviate(8), reader.abbreviate(id, 8));
+		assertEquals(id.abbreviate(10), reader.abbreviate(id, 10));
+		assertEquals(id.abbreviate(16), reader.abbreviate(id, 16));
+
+		assertEquals(AbbreviatedObjectId.fromObjectId(id), //
+				reader.abbreviate(id, OBJECT_ID_STRING_LENGTH));
+
+		Collection<ObjectId> matches;
+
+		matches = reader.resolve(reader.abbreviate(id, 8));
+		assertNotNull(matches);
+		assertEquals(0, matches.size());
+
+		matches = reader.resolve(AbbreviatedObjectId.fromObjectId(id));
+		assertNotNull(matches);
+		assertEquals(1, matches.size());
+		assertEquals(id, matches.iterator().next());
+	}
+
+	public void testAbbreviateLooseBlob() throws Exception {
+		ObjectId id = test.blob("test");
+
+		assertEquals(id.abbreviate(2), reader.abbreviate(id, 2));
+		assertEquals(id.abbreviate(7), reader.abbreviate(id, 7));
+		assertEquals(id.abbreviate(8), reader.abbreviate(id, 8));
+		assertEquals(id.abbreviate(10), reader.abbreviate(id, 10));
+		assertEquals(id.abbreviate(16), reader.abbreviate(id, 16));
+
+		Collection<ObjectId> matches = reader.resolve(reader.abbreviate(id, 8));
+		assertNotNull(matches);
+		assertEquals(1, matches.size());
+		assertEquals(id, matches.iterator().next());
+
+		assertEquals(id, db.resolve(reader.abbreviate(id, 8).name()));
+	}
+
+	public void testAbbreviatePackedBlob() throws Exception {
+		RevBlob id = test.blob("test");
+		test.branch("master").commit().add("test", id).child();
+		test.packAndPrune();
+		assertTrue(reader.has(id));
+
+		assertEquals(id.abbreviate(7), reader.abbreviate(id, 7));
+		assertEquals(id.abbreviate(8), reader.abbreviate(id, 8));
+		assertEquals(id.abbreviate(10), reader.abbreviate(id, 10));
+		assertEquals(id.abbreviate(16), reader.abbreviate(id, 16));
+
+		Collection<ObjectId> matches = reader.resolve(reader.abbreviate(id, 8));
+		assertNotNull(matches);
+		assertEquals(1, matches.size());
+		assertEquals(id, matches.iterator().next());
+
+		assertEquals(id, db.resolve(reader.abbreviate(id, 8).name()));
+	}
+
+	@SuppressWarnings("unchecked")
+	public void testAbbreviateIsActuallyUnique() throws Exception {
+		// This test is far more difficult. We have to manually craft
+		// an input that contains collisions at a particular prefix,
+		// but this is computationally difficult. Instead we force an
+		// index file to have what we want.
+		//
+
+		ObjectId id = id("9d5b926ed164e8ee88d3b8b1e525d699adda01ba");
+		byte[] idBuf = toByteArray(id);
+		List<PackedObjectInfo> objects = new ArrayList<PackedObjectInfo>();
+		for (int i = 0; i < 256; i++) {
+			idBuf[9] = (byte) i;
+			objects.add(new PackedObjectInfo(ObjectId.fromRaw(idBuf)));
+		}
+
+		String packName = "pack-" + id.name();
+		File packDir = new File(db.getObjectDatabase().getDirectory(), "pack");
+		File idxFile = new File(packDir, packName + ".idx");
+		File packFile = new File(packDir, packName + ".pack");
+		packDir.mkdir();
+		OutputStream dst = new BufferedOutputStream(new FileOutputStream(
+				idxFile));
+		try {
+			PackIndexWriter writer = new PackIndexWriterV2(dst);
+			writer.write(objects, new byte[OBJECT_ID_LENGTH]);
+		} finally {
+			dst.close();
+		}
+		new FileOutputStream(packFile).close();
+		db.openPack(packFile, idxFile);
+
+		assertEquals(id.abbreviate(20), reader.abbreviate(id, 2));
+
+		Collection<ObjectId> matches = reader.resolve(id.abbreviate(8));
+		assertNotNull(matches);
+		assertEquals(objects.size(), matches.size());
+		for (PackedObjectInfo info : objects)
+			assertTrue("contains " + info.name(), matches.contains(info));
+
+		assertNull("cannot resolve", db.resolve(id.abbreviate(8).name()));
+		assertEquals(id, db.resolve(id.abbreviate(20).name()));
+	}
+
+	private static ObjectId id(String name) {
+		return ObjectId.fromString(name);
+	}
+
+	private static byte[] toByteArray(ObjectId id) throws IOException {
+		ByteArrayOutputStream buf = new ByteArrayOutputStream(OBJECT_ID_LENGTH);
+		id.copyRawTo(buf);
+		return buf.toByteArray();
+	}
+}