Set config "extensions" option when converting ref storage format

When converting to reftable format the option extensions.refStorage must
be set to "reftable" [1]. When converting back to refdir format this
config option needs to be removed.

Introduce constants for refStorage config options, also for the
"reftree" format.

[1] https://git.eclipse.org/r/plugins/gitiles/jgit/jgit/+/master/Documentation/technical/reftable.md#Version-1

Change-Id: I190222fa5edc1ad7309daa9be17ca934ff7971e3
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

org.eclipse.jgit.pgm/src/org/eclipse/jgit/pgm/debug/RebuildRefTree.java

@@ -52,6 +52,7 @@ import java.util.List;
 import org.eclipse.jgit.internal.storage.reftree.RefTree;
 import org.eclipse.jgit.internal.storage.reftree.RefTreeDatabase;
 import org.eclipse.jgit.lib.CommitBuilder;
+import org.eclipse.jgit.lib.ConfigConstants;
 import org.eclipse.jgit.lib.ObjectId;
 import org.eclipse.jgit.lib.ObjectInserter;
 import org.eclipse.jgit.lib.ObjectReader;
@@ -133,8 +134,11 @@ class RebuildRefTree extends TextBuiltin {
 
 			if (enable && !(db.getRefDatabase() instanceof RefTreeDatabase)) {
 				StoredConfig cfg = db.getConfig();
-				cfg.setInt("core", null, "repositoryformatversion", 1); //$NON-NLS-1$ //$NON-NLS-2$
-				cfg.setString("extensions", null, "refStorage", "reftree"); //$NON-NLS-1$ //$NON-NLS-2$ //$NON-NLS-3$
+				cfg.setInt(ConfigConstants.CONFIG_CORE_SECTION, null,
+						ConfigConstants.CONFIG_KEY_REPO_FORMAT_VERSION, 1);
+				cfg.setString(ConfigConstants.CONFIG_EXTENSIONS_SECTION, null,
+						ConfigConstants.CONFIG_KEY_REFSTORAGE,
+						ConfigConstants.CONFIG_REFSTORAGE_REFTREE);
 				cfg.save();
 				errw.println("Enabled reftree."); //$NON-NLS-1$
 				errw.flush();

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

@@ -205,12 +205,15 @@ public class FileRepository extends Repository {
 				ConfigConstants.CONFIG_KEY_REPO_FORMAT_VERSION, 0);
 
 		String reftype = repoConfig.getString(
-				"extensions", null, "refStorage"); //$NON-NLS-1$ //$NON-NLS-2$
+				ConfigConstants.CONFIG_EXTENSIONS_SECTION, null,
+				ConfigConstants.CONFIG_KEY_REFSTORAGE);
 		if (repositoryFormatVersion >= 1 && reftype != null) {
-			if (StringUtils.equalsIgnoreCase(reftype, "reftable")) { //$NON-NLS-1$
+			if (StringUtils.equalsIgnoreCase(reftype,
+					ConfigConstants.CONFIG_REFSTORAGE_REFTABLE)) {
 				refs = new FileReftableDatabase(this,
 						new File(getDirectory(), "refs")); //$NON-NLS-1$
-			} else if (StringUtils.equalsIgnoreCase(reftype, "reftree")) { //$NON-NLS-1$
+			} else if (StringUtils.equalsIgnoreCase(reftype,
+					ConfigConstants.CONFIG_REFSTORAGE_REFTREE)) {
 				refs = new RefTreeDatabase(this, new RefDirectory(this));
 			} else {
 				throw new IOException(JGitText.get().unknownRepositoryFormat);
@@ -721,6 +724,10 @@ public class FileRepository extends Repository {
 			FileUtils.delete(reftableDir,
 					FileUtils.RECURSIVE | FileUtils.IGNORE_ERRORS);
 		}
+
+		repoConfig.unset(ConfigConstants.CONFIG_EXTENSIONS_SECTION, null,
+				ConfigConstants.CONFIG_KEY_REFSTORAGE);
+		repoConfig.save();
 	}
 
 	@SuppressWarnings("nls")
@@ -774,6 +781,11 @@ public class FileRepository extends Repository {
 
 		refs.close();
 		refs = new FileReftableDatabase(this, refsFile);
+
+		repoConfig.setString(ConfigConstants.CONFIG_EXTENSIONS_SECTION, null,
+				ConfigConstants.CONFIG_KEY_REFSTORAGE,
+				ConfigConstants.CONFIG_REFSTORAGE_REFTABLE);
+		repoConfig.save();
 	}
 
 	/**

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

@@ -503,8 +503,31 @@ public final class ConfigConstants {
 
 	/**
 	 * The "minRacyThreshold" key
-	 *
 	 * @since 5.1.9
 	 */
 	public static final String CONFIG_KEY_MIN_RACY_THRESHOLD = "minRacyThreshold";
+
+	/**
+	 * The "extensions" section
+	 * @since 5.7
+	 */
+	public static final String CONFIG_EXTENSIONS_SECTION = "extensions";
+
+	/**
+	 * The extensions.refStorage key
+	 * @since 5.7
+	 */
+	public static final String CONFIG_KEY_REFSTORAGE = "refStorage";
+
+	/**
+	 * The "reftable" refStorage format
+	 * @since 5.7
+	 */
+	public static final String CONFIG_REFSTORAGE_REFTABLE = "reftable";
+
+	/**
+	 * The "reftree" refStorage format
+	 * @since 5.7
+	 */
+	public static final String CONFIG_REFSTORAGE_REFTREE = "reftree";
 }