Describe: add support for core.abbrev config option

If core.abbrev is unset or "auto" estimate abbreviation length like C
git does:
- Estimate repository's object count by only considering packed objects,
  round up to next power of 2
- With the order of 2^len objects, we expect a collision at 2^(len/2).
  But we also care about hex chars, not bits, and there are 4 bits per
  hex. So all together we need to divide by 2; but we also want to round
  odd numbers up, hence adding one before dividing.
- For small repos use at least 7 hexdigits
- If object database fails to determine object count use 7 hexdigits as
  fallback

If it is set to "no" do not abbreviate object-ids.

Otherwise set it to the configured value capped to the range between 4
and length of an unabbreviated object-id.

Change-Id: I425f9724b69813dbb57872466bf2d2e1d6dc72c6

1 files changed, 128 insertions, 0 deletions

diff --git a/org.eclipse.jgit.test/tst/org/eclipse/jgit/lib/AbbrevConfigTest.java b/org.eclipse.jgit.test/tst/org/eclipse/jgit/lib/AbbrevConfigTest.java
new file mode 100644
index 0000000000..96ace08dd1
--- /dev/null
+++ b/org.eclipse.jgit.test/tst/org/eclipse/jgit/lib/AbbrevConfigTest.java
@@ -0,0 +1,128 @@
+/*
+ * Copyright (C) 2022, Matthias Sohn <matthias.sohn@sap.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.lib;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertThrows;
+
+import java.io.IOException;
+
+import org.eclipse.jgit.api.errors.InvalidConfigurationException;
+import org.eclipse.jgit.junit.RepositoryTestCase;
+import org.eclipse.jgit.storage.file.FileBasedConfig;
+import org.junit.Test;
+
+public class AbbrevConfigTest extends RepositoryTestCase {
+
+	@Test
+	public void testDefault() throws Exception {
+		assertEquals(7, testCoreAbbrev(null));
+	}
+
+	@Test
+	public void testAuto() throws Exception {
+		assertEquals(7, testCoreAbbrev("auto"));
+	}
+
+	@Test
+	public void testNo() throws Exception {
+		assertEquals(40, testCoreAbbrev("no"));
+	}
+
+	@Test
+	public void testValidMin() throws Exception {
+		assertEquals(4, testCoreAbbrev("4"));
+	}
+
+	@Test
+	public void testValid() throws Exception {
+		assertEquals(22, testCoreAbbrev("22"));
+	}
+
+	@Test
+	public void testValidMax() throws Exception {
+		assertEquals(40, testCoreAbbrev("40"));
+	}
+
+	@Test
+	public void testInvalid() {
+		assertThrows(InvalidConfigurationException.class,
+				() -> testCoreAbbrev("foo"));
+	}
+
+	@Test
+	public void testInvalid2() {
+		assertThrows(InvalidConfigurationException.class,
+				() -> testCoreAbbrev("2k"));
+	}
+
+	@Test
+	public void testInvalidNegative() {
+		assertThrows(InvalidConfigurationException.class,
+				() -> testCoreAbbrev("-1000"));
+	}
+
+	@Test
+	public void testInvalidBelowRange() {
+		assertThrows(InvalidConfigurationException.class,
+				() -> testCoreAbbrev("3"));
+	}
+
+	@Test
+	public void testInvalidBelowRange2() {
+		assertThrows(InvalidConfigurationException.class,
+				() -> testCoreAbbrev("-1"));
+	}
+
+	@Test
+	public void testInvalidAboveRange() {
+		assertThrows(InvalidConfigurationException.class,
+				() -> testCoreAbbrev("41"));
+	}
+
+	@Test
+	public void testInvalidAboveRange2() {
+		assertThrows(InvalidConfigurationException.class,
+				() -> testCoreAbbrev("100000"));
+	}
+
+	@Test
+	public void testToStringNo()
+			throws InvalidConfigurationException, IOException {
+		assertEquals("40", setCoreAbbrev("no").toString());
+	}
+
+	@Test
+	public void testToString()
+			throws InvalidConfigurationException, IOException {
+		assertEquals("7", setCoreAbbrev("auto").toString());
+	}
+
+	@Test
+	public void testToString12()
+			throws InvalidConfigurationException, IOException {
+		assertEquals("12", setCoreAbbrev("12").toString());
+	}
+
+	private int testCoreAbbrev(String value)
+			throws InvalidConfigurationException, IOException {
+		return setCoreAbbrev(value).get();
+	}
+
+	private AbbrevConfig setCoreAbbrev(String value)
+			throws IOException, InvalidConfigurationException {
+		FileBasedConfig config = db.getConfig();
+		config.setString(ConfigConstants.CONFIG_CORE_SECTION, null,
+				ConfigConstants.CONFIG_KEY_ABBREV, value);
+		config.save();
+		return AbbrevConfig.parseFromConfig(db);
+	}
+
+}