Support parsing git describe style output

We now match on the -gABBREV style output created by git describe
when its describing a non-tagged commit, and resolve that back to
the full ObjectId using the abbreviation resolution feature that
we already support.

Change-Id: Ib3033f9483d9e1c66c8bb721ff48d4485bcdaef1
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

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

@@ -48,6 +48,8 @@ package org.eclipse.jgit.lib;
 
 import java.io.IOException;
 
+import org.eclipse.jgit.errors.IncorrectObjectTypeException;
+
 public class RepositoryResolveTest extends SampleDataRepositoryTestCase {
 
 	public void testObjectId_existing() throws IOException {
@@ -140,4 +142,22 @@ public class RepositoryResolveTest extends SampleDataRepositoryTestCase {
 		assertEquals("856ec208ae6cadac25a6d74f19b12bb27a24fe24",db.resolve("refs/tags/B10th^{tree}").name());
 	}
 
+	public void testParseGitDescribeOutput() throws IOException {
+		ObjectId exp = db.resolve("b");
+		assertEquals(exp, db.resolve("B-g7f82283")); // old style
+		assertEquals(exp, db.resolve("B-6-g7f82283")); // new style
+
+		assertEquals(exp, db.resolve("B-6-g7f82283^0"));
+		assertEquals(exp, db.resolve("B-6-g7f82283^{commit}"));
+
+		try {
+			db.resolve("B-6-g7f82283^{blob}");
+			fail("expected IncorrectObjectTypeException");
+		} catch (IncorrectObjectTypeException badType) {
+			// Expected
+		}
+
+		assertEquals(db.resolve("b^1"), db.resolve("B-6-g7f82283^1"));
+		assertEquals(db.resolve("b~2"), db.resolve("B-6-g7f82283~2"));
+	}
 }

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

@@ -375,8 +375,6 @@ public abstract class Repository {
 	 * Currently supported is combinations of these.
 	 * <ul>
 	 * <li>SHA-1 - a SHA-1</li>
-	 * <li>SHA-1 abbreviation - a leading prefix of a SHA-1. At least the first
-	 * two bytes must be supplied.</li>
 	 * <li>refs/... - a ref name</li>
 	 * <li>ref^n - nth parent reference</li>
 	 * <li>ref~n - distance via parent reference</li>
@@ -387,7 +385,6 @@ public abstract class Repository {
 	 *
 	 * Not supported is:
 	 * <ul>
-	 * <li>tag-NNN-gcommit - a non tagged revision from git describe</li>
 	 * <li>timestamps in reflogs, ref@{full or relative timestamp}</li>
 	 * </ul>
 	 *
@@ -562,6 +559,25 @@ public abstract class Repository {
 							revstr);
 				i = m - 1;
 				break;
+			case '-':
+				if (i + 4 < rev.length && rev[i + 1] == 'g'
+						&& isHex(rev[i + 2]) && isHex(rev[i + 3])) {
+					// Possibly output from git describe?
+					// Resolve longest valid abbreviation.
+					int cnt = 2;
+					while (i + 2 + cnt < rev.length && isHex(rev[i + 2 + cnt]))
+						cnt++;
+					String s = new String(rev, i + 2, cnt);
+					if (AbbreviatedObjectId.isId(s)) {
+						ObjectId id = resolveAbbreviation(s);
+						if (id != null) {
+							ref = rw.parseAny(id);
+							i += 1 + s.length();
+						}
+					}
+				}
+				break;
+
 			default:
 				if (ref != null)
 					throw new RevisionSyntaxException(revstr);
@@ -570,6 +586,12 @@ public abstract class Repository {
 		return ref != null ? ref.copy() : resolveSimple(revstr);
 	}
 
+	private static boolean isHex(char c) {
+		return ('0' <= c && c <= '9') //
+				|| ('a' <= c && c <= 'f') //
+				|| ('A' <= c && c <= 'F');
+	}
+
 	private RevObject parseSimple(RevWalk rw, String revstr) throws IOException {
 		ObjectId id = resolveSimple(revstr);
 		return id != null ? rw.parseAny(id) : null;
@@ -583,23 +605,29 @@ public abstract class Repository {
 		if (r != null)
 			return r.getObjectId();
 
-		if (AbbreviatedObjectId.isId(revstr)) {
+		if (AbbreviatedObjectId.isId(revstr))
+			return resolveAbbreviation(revstr);
+
+		return null;
+	}
+
+	private ObjectId resolveAbbreviation(final String revstr) throws IOException,
+			AmbiguousObjectException {
 		AbbreviatedObjectId id = AbbreviatedObjectId.fromString(revstr);
 		ObjectReader reader = newObjectReader();
 		try {
 			Collection<ObjectId> matches = reader.resolve(id);
-				if (matches.size() == 1)
+			if (matches.size() == 0)
+				return null;
+			else if (matches.size() == 1)
 				return matches.iterator().next();
-				if (1 < matches.size())
+			else
 				throw new AmbiguousObjectException(id, matches);
 		} finally {
 			reader.release();
 		}
 	}
 
-		return null;
-	}
-
 	/** Increment the use counter by one, requiring a matched {@link #close()}. */
 	public void incrementOpen() {
 		useCnt.incrementAndGet();