Add `numberOfPackFilesAfterBitmap` to RepoStatistics

Introduce a `numberOfPackFilesAfterBitmap` that contains the number of
packfiles created since the latest bitmap generation.

Notes:
* the `repo.getObjectDatabase().getPacks()` that obtains the list of
  packs (in the existing `getStatistics` function) uses
  `PackDirectory.scanPacks` that boils down to call to
  `PackDirectory.scanPacksImpl` which is sorting packs prior returning
  them therefore the `numberOfPackFilesAfterBitmap` is just all packs
  before the one that has bitmap attached
* the improved version of `packAndPrune` function (one that skips
  non-existent packfiles) was introduced for testing

Change-Id: I608011462f104fc002ac527aa405f492a8a4b0c2

1 files changed, 180 insertions, 0 deletions

diff --git a/org.eclipse.jgit.test/tst/org/eclipse/jgit/internal/storage/file/GcNumberOfPackFilesAfterBitmapStatisticsTest.java b/org.eclipse.jgit.test/tst/org/eclipse/jgit/internal/storage/file/GcNumberOfPackFilesAfterBitmapStatisticsTest.java
new file mode 100644
index 0000000000..820f0c768d
--- /dev/null
+++ b/org.eclipse.jgit.test/tst/org/eclipse/jgit/internal/storage/file/GcNumberOfPackFilesAfterBitmapStatisticsTest.java
@@ -0,0 +1,180 @@
+/*
+ * Copyright (c) 2024 Jacek Centkowski <geminica.programs@gmail.com> and others.
+ *
+ * This program and the accompanying materials are made available under the
+ * terms of the Eclipse Distribution License v. 1.0 which is available at
+ * https://www.eclipse.org/org/documents/edl-v10.php.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+package org.eclipse.jgit.internal.storage.file;
+
+import static org.junit.Assert.assertEquals;
+
+import java.io.BufferedOutputStream;
+import java.io.FileOutputStream;
+import java.io.IOException;
+import java.io.OutputStream;
+import java.nio.file.Files;
+import java.util.HashSet;
+import java.util.Set;
+import java.util.stream.StreamSupport;
+
+import org.eclipse.jgit.internal.storage.file.PackIndex.MutableEntry;
+import org.eclipse.jgit.internal.storage.pack.PackExt;
+import org.eclipse.jgit.internal.storage.pack.PackWriter;
+import org.eclipse.jgit.junit.TestRepository;
+import org.eclipse.jgit.lib.NullProgressMonitor;
+import org.eclipse.jgit.lib.ObjectId;
+import org.eclipse.jgit.lib.PersonIdent;
+import org.eclipse.jgit.lib.Ref;
+import org.eclipse.jgit.revwalk.RevCommit;
+import org.eclipse.jgit.util.FileUtils;
+import org.junit.Test;
+
+public class GcNumberOfPackFilesAfterBitmapStatisticsTest extends GcTestCase {
+	@Test
+	public void testShouldReportZeroObjectsForInitializedRepo()
+			throws IOException {
+		assertEquals(0L, gc.getStatistics().numberOfPackFilesAfterBitmap);
+	}
+
+	@Test
+	public void testShouldReportAllPackFilesWhenNoGcWasPerformed()
+			throws Exception {
+		packAndPrune();
+		long result = gc.getStatistics().numberOfPackFilesAfterBitmap;
+
+		assertEquals(repo.getObjectDatabase().getPacks().size(), result);
+	}
+
+	@Test
+	public void testShouldReportNoObjectsDirectlyAfterGc() throws Exception {
+		// given
+		addCommit(null);
+		gc.gc().get();
+		assertEquals(1L, repositoryBitmapFiles());
+		assertEquals(0L, gc.getStatistics().numberOfPackFilesAfterBitmap);
+	}
+
+	@Test
+	public void testShouldReportNewObjectsAfterGcWhenRepositoryProgresses()
+			throws Exception {
+		// commit & gc
+		RevCommit parent = addCommit(null);
+		gc.gc().get();
+		assertEquals(1L, repositoryBitmapFiles());
+
+		// progress & pack
+		addCommit(parent);
+		packAndPrune();
+
+		assertEquals(1L, gc.getStatistics().numberOfPackFilesAfterBitmap);
+	}
+
+	@Test
+	public void testShouldReportNewObjectsFromTheLatestBitmapWhenRepositoryProgresses()
+			throws Exception {
+		// commit & gc
+		RevCommit parent = addCommit(null);
+		gc.gc().get();
+		assertEquals(1L, repositoryBitmapFiles());
+
+		// progress & gc
+		parent = addCommit(parent);
+		gc.gc().get();
+		assertEquals(2L, repositoryBitmapFiles());
+
+		// progress & pack
+		addCommit(parent);
+		packAndPrune();
+
+		assertEquals(1L, gc.getStatistics().numberOfPackFilesAfterBitmap);
+	}
+
+	private void packAndPrune() throws Exception {
+		try (SkipNonExistingFilesTestRepository testRepo = new SkipNonExistingFilesTestRepository(
+				repo)) {
+			testRepo.packAndPrune();
+		}
+	}
+
+	private RevCommit addCommit(RevCommit parent) throws Exception {
+		PersonIdent ident = new PersonIdent("repo-metrics", "repo@metrics.com");
+		TestRepository<FileRepository>.CommitBuilder builder = tr.commit()
+				.author(ident);
+		if (parent != null) {
+			builder.parent(parent);
+		}
+		RevCommit commit = builder.create();
+		tr.update("master", commit);
+		parent = commit;
+		return parent;
+	}
+
+	private long repositoryBitmapFiles() throws IOException {
+		return StreamSupport
+				.stream(Files
+						.newDirectoryStream(repo.getObjectDatabase()
+								.getPackDirectory().toPath(), "pack-*.bitmap")
+						.spliterator(), false)
+				.count();
+	}
+
+	/**
+	 * The TestRepository has a {@link TestRepository#packAndPrune()} function
+	 * but it fails in the last step after GC was performed as it doesn't
+	 * SKIP_MISSING files. In order to circumvent it was copied and improved
+	 * here.
+	 */
+	private static class SkipNonExistingFilesTestRepository
+			extends TestRepository<FileRepository> {
+		private final FileRepository repo;
+
+		private SkipNonExistingFilesTestRepository(FileRepository db) throws IOException {
+			super(db);
+			repo = db;
+		}
+
+		@Override
+		public void packAndPrune() throws Exception {
+			ObjectDirectory odb = repo.getObjectDatabase();
+			NullProgressMonitor m = NullProgressMonitor.INSTANCE;
+
+			final PackFile pack, idx;
+			try (PackWriter pw = new PackWriter(repo)) {
+				Set<ObjectId> all = new HashSet<>();
+				for (Ref r : repo.getRefDatabase().getRefs())
+					all.add(r.getObjectId());
+				pw.preparePack(m, all, PackWriter.NONE);
+
+				pack = new PackFile(odb.getPackDirectory(), pw.computeName(),
+						PackExt.PACK);
+				try (OutputStream out = new BufferedOutputStream(
+						new FileOutputStream(pack))) {
+					pw.writePack(m, m, out);
+				}
+				pack.setReadOnly();
+
+				idx = pack.create(PackExt.INDEX);
+				try (OutputStream out = new BufferedOutputStream(
+						new FileOutputStream(idx))) {
+					pw.writeIndex(out);
+				}
+				idx.setReadOnly();
+			}
+
+			odb.openPack(pack);
+			updateServerInfo();
+
+			// alternative packAndPrune implementation that skips missing files
+			// after GC.
+			for (Pack p : odb.getPacks()) {
+				for (MutableEntry e : p)
+					FileUtils.delete(odb.fileFor(e.toObjectId()),
+							FileUtils.SKIP_MISSING);
+			}
+		}
+	}
+}