CommitGraph: teach ObjectReader to get commit-graph

FileRepository's ObjectReader#getCommitGraph will return commit-graph
when it exists and core.commitGraph is true.

DfsRepository is not supported currently.

Change-Id: I992d43d104cf542797e6949470e95e56de025107
Signed-off-by: kylezhao <kylezhao@tencent.com>

org.eclipse.jgit.test/tst/org/eclipse/jgit/internal/storage/file/ObjectDirectoryTest.java

@@ -236,6 +236,26 @@ public void testOpenLooseObjectPropagatesIOExceptions() throws Exception {
 		assertThrows(IOException.class, () -> mock.open(curs, id));
 	}
 
+	@Test
+	public void testWindowCursorGetCommitGraph() throws Exception {
+		db.getConfig().setBoolean(ConfigConstants.CONFIG_CORE_SECTION, null,
+				ConfigConstants.CONFIG_COMMIT_GRAPH, true);
+		db.getConfig().setBoolean(ConfigConstants.CONFIG_GC_SECTION, null,
+				ConfigConstants.CONFIG_KEY_WRITE_COMMIT_GRAPH, true);
+
+		WindowCursor curs = new WindowCursor(db.getObjectDatabase());
+		assertTrue(curs.getCommitGraph().isEmpty());
+		commitFile("file.txt", "content", "master");
+		GC gc = new GC(db);
+		gc.gc();
+		assertTrue(curs.getCommitGraph().isPresent());
+
+		db.getConfig().setBoolean(ConfigConstants.CONFIG_CORE_SECTION, null,
+				ConfigConstants.CONFIG_COMMIT_GRAPH, false);
+
+		assertTrue(curs.getCommitGraph().isEmpty());
+	}
+
 	@Test
 	public void testShallowFileCorrupt() throws Exception {
 		FileRepository repository = createBareRepository();

org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/ObjectDirectory.java

@@ -41,6 +41,7 @@
 import org.eclipse.jgit.internal.storage.commitgraph.CommitGraph;
 import org.eclipse.jgit.lib.Config;
 import org.eclipse.jgit.lib.Constants;
+import org.eclipse.jgit.lib.CoreConfig;
 import org.eclipse.jgit.lib.ObjectDatabase;
 import org.eclipse.jgit.lib.ObjectId;
 import org.eclipse.jgit.lib.ObjectLoader;
@@ -235,7 +236,10 @@ public long getApproximateObjectCount() {
 	/** {@inheritDoc} */
 	@Override
 	public Optional<CommitGraph> getCommitGraph() {
-		return Optional.ofNullable(fileCommitGraph.get());
+		if (config.get(CoreConfig.KEY).enableCommitGraph()) {
+			return Optional.ofNullable(fileCommitGraph.get());
+		}
+		return Optional.empty();
 	}
 
 	/**

org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/WindowCursor.java

@@ -16,6 +16,7 @@
 import java.util.Collections;
 import java.util.HashSet;
 import java.util.List;
+import java.util.Optional;
 import java.util.Set;
 import java.util.zip.DataFormatException;
 import java.util.zip.Inflater;
@@ -34,6 +35,7 @@
 import org.eclipse.jgit.lib.AnyObjectId;
 import org.eclipse.jgit.lib.BitmapIndex;
 import org.eclipse.jgit.lib.BitmapIndex.BitmapBuilder;
+import org.eclipse.jgit.internal.storage.commitgraph.CommitGraph;
 import org.eclipse.jgit.lib.Constants;
 import org.eclipse.jgit.lib.InflaterCache;
 import org.eclipse.jgit.lib.ObjectId;
@@ -94,6 +96,12 @@ public BitmapIndex getBitmapIndex() throws IOException {
 		return null;
 	}
 
+	/** {@inheritDoc} */
+	@Override
+	public Optional<CommitGraph> getCommitGraph() {
+		return db.getCommitGraph();
+	}
+
 	/** {@inheritDoc} */
 	@Override
 	public Collection<CachedPack> getCachedPacksAndUpdate(

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

@@ -17,6 +17,7 @@
 import java.util.Collection;
 import java.util.Iterator;
 import java.util.List;
+import java.util.Optional;
 import java.util.Set;
 
 import org.eclipse.jgit.annotations.NonNull;
@@ -27,6 +28,7 @@
 import org.eclipse.jgit.internal.revwalk.BitmappedReachabilityChecker;
 import org.eclipse.jgit.internal.revwalk.PedestrianObjectReachabilityChecker;
 import org.eclipse.jgit.internal.revwalk.PedestrianReachabilityChecker;
+import org.eclipse.jgit.internal.storage.commitgraph.CommitGraph;
 import org.eclipse.jgit.revwalk.ObjectReachabilityChecker;
 import org.eclipse.jgit.revwalk.ObjectWalk;
 import org.eclipse.jgit.revwalk.ReachabilityChecker;
@@ -499,6 +501,23 @@ public ObjectReachabilityChecker createObjectReachabilityChecker(
 		return new PedestrianObjectReachabilityChecker(ow);
 	}
 
+	/**
+	 * Get the commit-graph for this repository if available.
+	 * <p>
+	 * The commit graph can be created/modified/deleted while the repository is
+	 * open and specific implementations decide when to refresh it.
+	 *
+	 * @return the commit-graph or empty if the commit-graph does not exist or
+	 *         is invalid; always returns empty when core.commitGraph is false
+	 *         (default is
+	 *         {@value org.eclipse.jgit.lib.CoreConfig#DEFAULT_COMMIT_GRAPH_ENABLE}).
+	 *
+	 * @since 6.5
+	 */
+	public Optional<CommitGraph> getCommitGraph() {
+		return Optional.empty();
+	}
+
 	/**
 	 * Get the {@link org.eclipse.jgit.lib.ObjectInserter} from which this
 	 * reader was created using {@code inserter.newReader()}
@@ -641,6 +660,11 @@ public BitmapIndex getBitmapIndex() throws IOException {
 			return delegate().getBitmapIndex();
 		}
 
+		@Override
+		public Optional<CommitGraph> getCommitGraph() {
+			return delegate().getCommitGraph();
+		}
+
 		@Override
 		@Nullable
 		public ObjectInserter getCreatedFromInserter() {