Merge branch 'stable-5.6'

* stable-5.6:
  Introduce RefDatabase#hasFastTipsWithSha1
  Update Orbit to R20191126223242 for 2019-12
  Prepare 5.6.0-SNAPSHOT builds
  JGit v5.6.0.201912041214-rc1
  Prepare 5.6.0-SNAPSHOT builds
  JGit v5.6.0.201911271000-m3

Change-Id: Id33b054131bbcd27a0ae7200f564775049698d2c

org.eclipse.jgit.http.server/META-INF/MANIFEST.MF

@@ -18,7 +18,7 @@ Bundle-ActivationPolicy: lazy
 Bundle-RequiredExecutionEnvironment: JavaSE-1.8
 Import-Package: javax.servlet;version="[2.5.0,3.2.0)",
  javax.servlet.http;version="[2.5.0,3.2.0)",
- org.eclipse.jgit.annotations;version="[5.5.0,5.7.0)",
+ org.eclipse.jgit.annotations;version="[5.6.0,5.7.0)",
  org.eclipse.jgit.errors;version="[5.6.0,5.7.0)",
  org.eclipse.jgit.internal.storage.dfs;version="[5.6.0,5.7.0)",
  org.eclipse.jgit.internal.storage.file;version="[5.6.0,5.7.0)",

org.eclipse.jgit.packaging/org.eclipse.jgit.target/jgit-4.10.target

@@ -1,7 +1,7 @@
 <?xml version="1.0" encoding="UTF-8" standalone="no"?>
 <?pde?>
 <!-- generated with https://github.com/eclipse-cbi/targetplatform-dsl -->
-<target name="jgit-4.10" sequenceNumber="1574722378">
+<target name="jgit-4.10" sequenceNumber="1575495623">
   <locations>
     <location includeMode="slicer" includeAllPlatforms="false" includeSource="true" includeConfigurePhase="true" type="InstallableUnit">
       <unit id="org.eclipse.jetty.client" version="9.4.22.v20191022"/>
@@ -82,7 +82,7 @@
       <unit id="org.slf4j.impl.log4j12.source" version="1.7.2.v20131105-2200"/>
       <unit id="org.tukaani.xz" version="1.8.0.v20180207-1613"/>
       <unit id="org.tukaani.xz.source" version="1.8.0.v20180207-1613"/>
-      <repository location="https://download.eclipse.org/tools/orbit/downloads/drops/S20191118194249/repository"/>
+      <repository location="https://download.eclipse.org/tools/orbit/downloads/drops/R20191126223242/repository"/>
     </location>
     <location includeMode="slicer" includeAllPlatforms="false" includeSource="true" includeConfigurePhase="true" type="InstallableUnit">
       <unit id="org.eclipse.osgi" version="0.0.0"/>

org.eclipse.jgit.packaging/org.eclipse.jgit.target/jgit-4.10.tpd

@@ -1,7 +1,7 @@
 target "jgit-4.10" with source configurePhase
 
 include "projects/jetty-9.4.22.tpd"
-include "orbit/S20191118194249.tpd"
+include "orbit/R20191126223242-2019-12.tpd"
 
 location "http://download.eclipse.org/releases/2018-12/" {
 	org.eclipse.osgi lazy

org.eclipse.jgit.packaging/org.eclipse.jgit.target/jgit-4.11.target

@@ -1,7 +1,7 @@
 <?xml version="1.0" encoding="UTF-8" standalone="no"?>
 <?pde?>
 <!-- generated with https://github.com/eclipse-cbi/targetplatform-dsl -->
-<target name="jgit-4.11" sequenceNumber="1574722378">
+<target name="jgit-4.11" sequenceNumber="1575495623">
   <locations>
     <location includeMode="slicer" includeAllPlatforms="false" includeSource="true" includeConfigurePhase="true" type="InstallableUnit">
       <unit id="org.eclipse.jetty.client" version="9.4.22.v20191022"/>
@@ -82,7 +82,7 @@
       <unit id="org.slf4j.impl.log4j12.source" version="1.7.2.v20131105-2200"/>
       <unit id="org.tukaani.xz" version="1.8.0.v20180207-1613"/>
       <unit id="org.tukaani.xz.source" version="1.8.0.v20180207-1613"/>
-      <repository location="https://download.eclipse.org/tools/orbit/downloads/drops/S20191118194249/repository"/>
+      <repository location="https://download.eclipse.org/tools/orbit/downloads/drops/R20191126223242/repository"/>
     </location>
     <location includeMode="slicer" includeAllPlatforms="false" includeSource="true" includeConfigurePhase="true" type="InstallableUnit">
       <unit id="org.eclipse.osgi" version="0.0.0"/>

org.eclipse.jgit.packaging/org.eclipse.jgit.target/jgit-4.11.tpd

@@ -1,7 +1,7 @@
 target "jgit-4.11" with source configurePhase
 
 include "projects/jetty-9.4.22.tpd"
-include "orbit/S20191118194249.tpd"
+include "orbit/R20191126223242-2019-12.tpd"
 
 location "http://download.eclipse.org/releases/2019-03/" {
 	org.eclipse.osgi lazy

org.eclipse.jgit.packaging/org.eclipse.jgit.target/jgit-4.12.target

@@ -1,7 +1,7 @@
 <?xml version="1.0" encoding="UTF-8" standalone="no"?>
 <?pde?>
 <!-- generated with https://github.com/eclipse-cbi/targetplatform-dsl -->
-<target name="jgit-4.12" sequenceNumber="1574722378">
+<target name="jgit-4.12" sequenceNumber="1575495623">
   <locations>
     <location includeMode="slicer" includeAllPlatforms="false" includeSource="true" includeConfigurePhase="true" type="InstallableUnit">
       <unit id="org.eclipse.jetty.client" version="9.4.22.v20191022"/>
@@ -82,7 +82,7 @@
       <unit id="org.slf4j.impl.log4j12.source" version="1.7.2.v20131105-2200"/>
       <unit id="org.tukaani.xz" version="1.8.0.v20180207-1613"/>
       <unit id="org.tukaani.xz.source" version="1.8.0.v20180207-1613"/>
-      <repository location="https://download.eclipse.org/tools/orbit/downloads/drops/S20191118194249/repository"/>
+      <repository location="https://download.eclipse.org/tools/orbit/downloads/drops/R20191126223242/repository"/>
     </location>
     <location includeMode="slicer" includeAllPlatforms="false" includeSource="true" includeConfigurePhase="true" type="InstallableUnit">
       <unit id="org.eclipse.osgi" version="0.0.0"/>

org.eclipse.jgit.packaging/org.eclipse.jgit.target/jgit-4.12.tpd

@@ -1,7 +1,7 @@
 target "jgit-4.12" with source configurePhase
 
 include "projects/jetty-9.4.22.tpd"
-include "orbit/S20191118194249.tpd"
+include "orbit/R20191126223242-2019-12.tpd"
 
 location "http://download.eclipse.org/releases/2019-06/" {
 	org.eclipse.osgi lazy

org.eclipse.jgit.packaging/org.eclipse.jgit.target/jgit-4.13.target

@@ -1,7 +1,7 @@
 <?xml version="1.0" encoding="UTF-8" standalone="no"?>
 <?pde?>
 <!-- generated with https://github.com/eclipse-cbi/targetplatform-dsl -->
-<target name="jgit-4.13" sequenceNumber="1574722378">
+<target name="jgit-4.13" sequenceNumber="1575495624">
   <locations>
     <location includeMode="slicer" includeAllPlatforms="false" includeSource="true" includeConfigurePhase="true" type="InstallableUnit">
       <unit id="org.eclipse.jetty.client" version="9.4.22.v20191022"/>
@@ -82,7 +82,7 @@
       <unit id="org.slf4j.impl.log4j12.source" version="1.7.2.v20131105-2200"/>
       <unit id="org.tukaani.xz" version="1.8.0.v20180207-1613"/>
       <unit id="org.tukaani.xz.source" version="1.8.0.v20180207-1613"/>
-      <repository location="https://download.eclipse.org/tools/orbit/downloads/drops/S20191118194249/repository"/>
+      <repository location="https://download.eclipse.org/tools/orbit/downloads/drops/R20191126223242/repository"/>
     </location>
     <location includeMode="slicer" includeAllPlatforms="false" includeSource="true" includeConfigurePhase="true" type="InstallableUnit">
       <unit id="org.eclipse.osgi" version="0.0.0"/>

org.eclipse.jgit.packaging/org.eclipse.jgit.target/jgit-4.13.tpd

@@ -1,7 +1,7 @@
 target "jgit-4.13" with source configurePhase
 
 include "projects/jetty-9.4.22.tpd"
-include "orbit/S20191118194249.tpd"
+include "orbit/R20191126223242-2019-12.tpd"
 
 location "http://download.eclipse.org/releases/2019-09/" {
 	org.eclipse.osgi lazy

org.eclipse.jgit.packaging/org.eclipse.jgit.target/jgit-4.14-staging.target

@@ -1,7 +1,7 @@
 <?xml version="1.0" encoding="UTF-8" standalone="no"?>
 <?pde?>
 <!-- generated with https://github.com/eclipse-cbi/targetplatform-dsl -->
-<target name="jgit-4.14-staging" sequenceNumber="1574722378">
+<target name="jgit-4.14-staging" sequenceNumber="1575495626">
   <locations>
     <location includeMode="slicer" includeAllPlatforms="false" includeSource="true" includeConfigurePhase="true" type="InstallableUnit">
       <unit id="org.eclipse.jetty.client" version="9.4.22.v20191022"/>
@@ -82,7 +82,7 @@
       <unit id="org.slf4j.impl.log4j12.source" version="1.7.2.v20131105-2200"/>
       <unit id="org.tukaani.xz" version="1.8.0.v20180207-1613"/>
       <unit id="org.tukaani.xz.source" version="1.8.0.v20180207-1613"/>
-      <repository location="https://download.eclipse.org/tools/orbit/downloads/drops/S20191118194249/repository"/>
+      <repository location="https://download.eclipse.org/tools/orbit/downloads/drops/R20191126223242/repository"/>
     </location>
     <location includeMode="slicer" includeAllPlatforms="false" includeSource="true" includeConfigurePhase="true" type="InstallableUnit">
       <unit id="org.eclipse.osgi" version="0.0.0"/>

org.eclipse.jgit.packaging/org.eclipse.jgit.target/jgit-4.14-staging.tpd

@@ -1,7 +1,7 @@
 target "jgit-4.14-staging" with source configurePhase
 
 include "projects/jetty-9.4.22.tpd"
-include "orbit/S20191118194249.tpd"
+include "orbit/R20191126223242-2019-12.tpd"
 
 location "http://download.eclipse.org/staging/2019-12/" {
 	org.eclipse.osgi lazy

org.eclipse.jgit.packaging/org.eclipse.jgit.target/jgit-4.6.target

@@ -1,7 +1,7 @@
 <?xml version="1.0" encoding="UTF-8" standalone="no"?>
 <?pde?>
 <!-- generated with https://github.com/eclipse-cbi/targetplatform-dsl -->
-<target name="jgit-4.6" sequenceNumber="1574722378">
+<target name="jgit-4.6" sequenceNumber="1575495636">
   <locations>
     <location includeMode="slicer" includeAllPlatforms="false" includeSource="true" includeConfigurePhase="true" type="InstallableUnit">
       <unit id="org.eclipse.jetty.client" version="9.4.22.v20191022"/>
@@ -82,7 +82,7 @@
       <unit id="org.slf4j.impl.log4j12.source" version="1.7.2.v20131105-2200"/>
       <unit id="org.tukaani.xz" version="1.8.0.v20180207-1613"/>
       <unit id="org.tukaani.xz.source" version="1.8.0.v20180207-1613"/>
-      <repository location="https://download.eclipse.org/tools/orbit/downloads/drops/S20191118194249/repository"/>
+      <repository location="https://download.eclipse.org/tools/orbit/downloads/drops/R20191126223242/repository"/>
     </location>
     <location includeMode="slicer" includeAllPlatforms="false" includeSource="true" includeConfigurePhase="true" type="InstallableUnit">
       <unit id="org.eclipse.osgi" version="0.0.0"/>

org.eclipse.jgit.packaging/org.eclipse.jgit.target/jgit-4.6.tpd

@@ -1,7 +1,7 @@
 target "jgit-4.6" with source configurePhase
 
 include "projects/jetty-9.4.22.tpd"
-include "orbit/S20191118194249.tpd"
+include "orbit/R20191126223242-2019-12.tpd"
 
 location "http://download.eclipse.org/releases/neon/" {
 	org.eclipse.osgi lazy

org.eclipse.jgit.packaging/org.eclipse.jgit.target/jgit-4.7.target

@@ -1,7 +1,7 @@
 <?xml version="1.0" encoding="UTF-8" standalone="no"?>
 <?pde?>
 <!-- generated with https://github.com/eclipse-cbi/targetplatform-dsl -->
-<target name="jgit-4.7" sequenceNumber="1574722378">
+<target name="jgit-4.7" sequenceNumber="1575495628">
   <locations>
     <location includeMode="slicer" includeAllPlatforms="false" includeSource="true" includeConfigurePhase="true" type="InstallableUnit">
       <unit id="org.eclipse.jetty.client" version="9.4.22.v20191022"/>
@@ -82,7 +82,7 @@
       <unit id="org.slf4j.impl.log4j12.source" version="1.7.2.v20131105-2200"/>
       <unit id="org.tukaani.xz" version="1.8.0.v20180207-1613"/>
       <unit id="org.tukaani.xz.source" version="1.8.0.v20180207-1613"/>
-      <repository location="https://download.eclipse.org/tools/orbit/downloads/drops/S20191118194249/repository"/>
+      <repository location="https://download.eclipse.org/tools/orbit/downloads/drops/R20191126223242/repository"/>
     </location>
     <location includeMode="slicer" includeAllPlatforms="false" includeSource="true" includeConfigurePhase="true" type="InstallableUnit">
       <unit id="org.eclipse.osgi" version="0.0.0"/>

org.eclipse.jgit.packaging/org.eclipse.jgit.target/jgit-4.7.tpd

@@ -1,7 +1,7 @@
 target "jgit-4.7" with source configurePhase
 
 include "projects/jetty-9.4.22.tpd"
-include "orbit/S20191118194249.tpd"
+include "orbit/R20191126223242-2019-12.tpd"
 
 location "http://download.eclipse.org/releases/oxygen/" {
 	org.eclipse.osgi lazy

org.eclipse.jgit.packaging/org.eclipse.jgit.target/jgit-4.8.target

@@ -1,7 +1,7 @@
 <?xml version="1.0" encoding="UTF-8" standalone="no"?>
 <?pde?>
 <!-- generated with https://github.com/eclipse-cbi/targetplatform-dsl -->
-<target name="jgit-4.8" sequenceNumber="1574722378">
+<target name="jgit-4.8" sequenceNumber="1575495623">
   <locations>
     <location includeMode="slicer" includeAllPlatforms="false" includeSource="true" includeConfigurePhase="true" type="InstallableUnit">
       <unit id="org.eclipse.jetty.client" version="9.4.22.v20191022"/>
@@ -82,7 +82,7 @@
       <unit id="org.slf4j.impl.log4j12.source" version="1.7.2.v20131105-2200"/>
       <unit id="org.tukaani.xz" version="1.8.0.v20180207-1613"/>
       <unit id="org.tukaani.xz.source" version="1.8.0.v20180207-1613"/>
-      <repository location="https://download.eclipse.org/tools/orbit/downloads/drops/S20191118194249/repository"/>
+      <repository location="https://download.eclipse.org/tools/orbit/downloads/drops/R20191126223242/repository"/>
     </location>
     <location includeMode="slicer" includeAllPlatforms="false" includeSource="true" includeConfigurePhase="true" type="InstallableUnit">
       <unit id="org.eclipse.osgi" version="0.0.0"/>

org.eclipse.jgit.packaging/org.eclipse.jgit.target/jgit-4.8.tpd

@@ -1,7 +1,7 @@
 target "jgit-4.8" with source configurePhase
 
 include "projects/jetty-9.4.22.tpd"
-include "orbit/S20191118194249.tpd"
+include "orbit/R20191126223242-2019-12.tpd"
 
 location "http://download.eclipse.org/releases/photon/" {
 	org.eclipse.osgi lazy

org.eclipse.jgit.packaging/org.eclipse.jgit.target/jgit-4.9.target

@@ -1,7 +1,7 @@
 <?xml version="1.0" encoding="UTF-8" standalone="no"?>
 <?pde?>
 <!-- generated with https://github.com/eclipse-cbi/targetplatform-dsl -->
-<target name="jgit-4.9" sequenceNumber="1574722364">
+<target name="jgit-4.9" sequenceNumber="1575495623">
   <locations>
     <location includeMode="slicer" includeAllPlatforms="false" includeSource="true" includeConfigurePhase="true" type="InstallableUnit">
       <unit id="org.eclipse.jetty.client" version="9.4.22.v20191022"/>
@@ -82,7 +82,7 @@
       <unit id="org.slf4j.impl.log4j12.source" version="1.7.2.v20131105-2200"/>
       <unit id="org.tukaani.xz" version="1.8.0.v20180207-1613"/>
       <unit id="org.tukaani.xz.source" version="1.8.0.v20180207-1613"/>
-      <repository location="https://download.eclipse.org/tools/orbit/downloads/drops/S20191118194249/repository"/>
+      <repository location="https://download.eclipse.org/tools/orbit/downloads/drops/R20191126223242/repository"/>
     </location>
     <location includeMode="slicer" includeAllPlatforms="false" includeSource="true" includeConfigurePhase="true" type="InstallableUnit">
       <unit id="org.eclipse.osgi" version="0.0.0"/>

org.eclipse.jgit.packaging/org.eclipse.jgit.target/jgit-4.9.tpd

@@ -1,7 +1,7 @@
 target "jgit-4.9" with source configurePhase
 
 include "projects/jetty-9.4.22.tpd"
-include "orbit/S20191118194249.tpd"
+include "orbit/R20191126223242-2019-12.tpd"
 
 location "http://download.eclipse.org/releases/2018-09/" {
 	org.eclipse.osgi lazy

org.eclipse.jgit.packaging/org.eclipse.jgit.target/orbit/R20191126223242-2019-12.tpd

@@ -1,7 +1,7 @@
-target "S20191118194249" with source configurePhase
+target "R20191126223242-2019-12" with source configurePhase
 // see http://download.eclipse.org/tools/orbit/downloads/
 
-location "https://download.eclipse.org/tools/orbit/downloads/drops/S20191118194249/repository" {
+location "https://download.eclipse.org/tools/orbit/downloads/drops/R20191126223242/repository" {
 	com.google.gson [2.8.2.v20180104-1110,2.8.2.v20180104-1110]
 	com.google.gson.source [2.8.2.v20180104-1110,2.8.2.v20180104-1110]
 	com.jcraft.jsch [0.1.55.v20190404-1902,0.1.55.v20190404-1902]

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

@@ -155,6 +155,8 @@ public class FileReftableTest extends SampleDataRepositoryTestCase {
 		assertFalse(b.isSymbolic());
 		assertTrue(b.isPeeled());
 		assertEquals(bCommit, b.getObjectId().name());
+
+		assertTrue(db.getRefDatabase().hasFastTipsWithSha1());
 	}
 
 	@Test
@@ -169,6 +171,8 @@ public class FileReftableTest extends SampleDataRepositoryTestCase {
 		assertFalse(b.isSymbolic());
 		assertTrue(b.isPeeled());
 		assertEquals(bCommit, b.getObjectId().name());
+
+		assertFalse(db.getRefDatabase().hasFastTipsWithSha1());
 	}
 
 	@Test

org.eclipse.jgit.test/tst/org/eclipse/jgit/internal/storage/reftable/ReftableTest.java

@@ -176,6 +176,67 @@ public class ReftableTest {
 		assertEquals(expBytes, table.length);
 	}
 
+	@Test
+	public void hasObjMapRefs() throws IOException {
+		ArrayList<Ref> refs = new ArrayList<>();
+		refs.add(ref(MASTER, 1));
+		byte[] table = write(refs);
+		ReftableReader t = read(table);
+		assertTrue(t.hasObjectMap());
+	}
+
+	@Test
+	public void hasObjMapRefsSmallTable() throws IOException {
+		ArrayList<Ref> refs = new ArrayList<>();
+		ReftableConfig cfg = new ReftableConfig();
+		cfg.setIndexObjects(false);
+		refs.add(ref(MASTER, 1));
+		byte[] table = write(refs);
+		ReftableReader t = read(table);
+		assertTrue(t.hasObjectMap());
+	}
+
+	@Test
+	public void hasObjLogs() throws IOException {
+		PersonIdent who = new PersonIdent("Log", "Ger", 1500079709, -8 * 60);
+		String msg = "test";
+		ReftableConfig cfg = new ReftableConfig();
+		cfg.setIndexObjects(false);
+
+		ByteArrayOutputStream buffer = new ByteArrayOutputStream();
+		ReftableWriter writer = new ReftableWriter(buffer)
+			.setMinUpdateIndex(1)
+			.setConfig(cfg)
+			.setMaxUpdateIndex(1)
+			.begin();
+
+		writer.writeLog("master", 1, who, ObjectId.zeroId(), id(1), msg);
+		writer.finish();
+		byte[] table = buffer.toByteArray();
+
+		ReftableReader t = read(table);
+		assertTrue(t.hasObjectMap());
+	}
+
+	@Test
+	public void hasObjMapRefsNoIndexObjects() throws IOException {
+		ArrayList<Ref> refs = new ArrayList<>();
+		ReftableConfig cfg = new ReftableConfig();
+		cfg.setIndexObjects(false);
+		cfg.setRefBlockSize(256);
+		cfg.setAlignBlocks(true);
+
+		// Fill up 5 blocks.
+		int N = 256 * 5 / 25;
+		for (int i= 0; i < N; i++) {
+			refs.add(ref(String.format("%02d/xxxxxxxxxx", i), i));
+		}
+		byte[] table = write(refs, cfg);
+
+		ReftableReader t = read(table);
+		assertFalse(t.hasObjectMap());
+	}
+
 	@Test
 	public void oneIdRef() throws IOException {
 		Ref exp = ref(MASTER, 1);
@@ -936,8 +997,13 @@ public class ReftableTest {
 	}
 
 	private byte[] write(Collection<Ref> refs) throws IOException {
+		return write(refs, new ReftableConfig());
+	}
+
+	private byte[] write(Collection<Ref> refs, ReftableConfig cfg) throws IOException {
 		ByteArrayOutputStream buffer = new ByteArrayOutputStream();
 		stats = new ReftableWriter(buffer)
+				.setConfig(cfg)
 				.begin()
 				.sortAndWriteRefs(refs)
 				.finish()

org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/dfs/DfsReftableDatabase.java

@@ -216,6 +216,12 @@ public class DfsReftableDatabase extends DfsRefDatabase {
 		return reftableDatabase.getTipsWithSha1(id);
 	}
 
+	/** {@inheritDoc} */
+	@Override
+	public boolean hasFastTipsWithSha1() throws IOException {
+		return reftableDatabase.hasFastTipsWithSha1();
+	}
+
 	/** {@inheritDoc} */
 	@Override
 	public Ref peel(Ref ref) throws IOException {

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

@@ -125,6 +125,12 @@ public class FileReftableDatabase extends RefDatabase {
 				&& new File(repoDir, Constants.REFTABLE).isDirectory();
 	}
 
+	/** {@inheritDoc} */
+	@Override
+	public boolean hasFastTipsWithSha1() throws IOException {
+		return reftableDatabase.hasFastTipsWithSha1();
+	}
+
 	/**
 	 * Runs a full compaction for GC purposes.
 	 * @throws IOException on I/O errors

org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/reftable/MergedReftable.java

@@ -98,6 +98,16 @@ public class MergedReftable extends Reftable {
 				: 0;
 	}
 
+	/** {@inheritDoc} */
+	@Override
+	public boolean hasObjectMap() throws IOException {
+		boolean has = true;
+		for (int i = 0; has && i < tables.length; i++) {
+			has = has && tables[i].hasObjectMap();
+		};
+		return has;
+	}
+
 	/** {@inheritDoc} */
 	@Override
 	public RefCursor allRefs() throws IOException {

org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/reftable/Reftable.java

@@ -161,6 +161,12 @@ public abstract class Reftable {
 	 */
 	public abstract RefCursor byObjectId(AnyObjectId id) throws IOException;
 
+	/**
+	 * @return whether this reftable can do a fast SHA1 => ref lookup.
+	 * @throws IOException on I/O problems.
+	 */
+	public abstract boolean hasObjectMap() throws IOException;
+
 	/**
 	 * Seek reader to read log records.
 	 *

org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/reftable/ReftableDatabase.java

@@ -298,6 +298,19 @@ public abstract class ReftableDatabase {
 		return Collections.unmodifiableList(all);
 	}
 
+	/**
+	 * @return whether there is a fast SHA1 to ref map.
+	 * @throws IOException in case of I/O problems.
+	 */
+	public boolean hasFastTipsWithSha1() throws IOException {
+		lock.lock();
+		try {
+			return reader().hasObjectMap();
+		} finally {
+			lock.unlock();
+		}
+	}
+
 	/**
 	 * Returns all refs that resolve directly to the given {@link ObjectId}.
 	 * Includes peeled {@linkObjectId}s.

org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/reftable/ReftableReader.java

@@ -128,6 +128,16 @@ public class ReftableReader extends Reftable implements AutoCloseable {
 		return blockSize;
 	}
 
+	@Override
+	public boolean hasObjectMap() throws IOException {
+		if (objIndexPosition == -1) {
+			readFileFooter();
+		}
+
+		// We have the map, we have no refs, or the table is small.
+		return (objPosition > 0 || refEnd == 24 || refIndexPosition == 0);
+	}
+
 	/**
 	 * Get the minimum update index for log entries that appear in this
 	 * reftable.

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

@@ -496,6 +496,20 @@ public abstract class RefDatabase {
 				|| id.equals(r.getPeeledObjectId())).collect(toSet());
 	}
 
+	/**
+	 * If the ref database does not support fast inverse queries, it may
+	 * be advantageous to build a complete SHA1 to ref map in advance for
+	 * multiple uses. To let applications decide on this decision,
+	 * this function indicates whether the inverse map is available.
+	 *
+	 * @return whether this RefDatabase supports fast inverse ref queries.
+	 * @throws IOException on I/O problems.
+	 * @since 5.6
+	 */
+	public boolean hasFastTipsWithSha1() throws IOException {
+		return false;
+	}
+
 	/**
 	 * Check if any refs exist in the ref database.
 	 * <p>