Make 'inCoreLimit' of LocalFile used in ResolveMerger configurable

This change makes it possible to configure the 'inCoreLimit' of LocalFile
used in ResolveMerger#insertMergeResult. Since LocalFile itself has some
risks, e.g. it may be left behind as garbage in case of failure. It should
be good to be able to control the size limit for using LocalFile.

Change-Id: I3dc545ade370b2bbdb7c610ed45d5dd4d39b9e8e
Signed-off-by: Changcheng Xiao <xchangcheng@google.com>

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

@@ -370,6 +370,13 @@ public class ConfigConstants {
 	 */
 	public static final String CONFIG_KEY_RENAMES = "renames";
 
+	/**
+	 * The "inCoreLimit" key in the "merge section". It's a size limit (bytes) used to
+	 * control a file to be stored in {@code Heap} or {@code LocalFile} during the merge.
+	 * @since 4.9
+	 */
+	public static final String CONFIG_KEY_IN_CORE_LIMIT = "inCoreLimit";
+
 	/**
 	 * The "prune" key
 	 * @since 3.3

org.eclipse.jgit/src/org/eclipse/jgit/merge/ResolveMerger.java

@@ -85,6 +85,7 @@ import org.eclipse.jgit.errors.IndexWriteException;
 import org.eclipse.jgit.errors.MissingObjectException;
 import org.eclipse.jgit.errors.NoWorkTreeException;
 import org.eclipse.jgit.lib.Config;
+import org.eclipse.jgit.lib.ConfigConstants;
 import org.eclipse.jgit.lib.FileMode;
 import org.eclipse.jgit.lib.ObjectId;
 import org.eclipse.jgit.lib.ObjectInserter;
@@ -272,6 +273,12 @@ public class ResolveMerger extends ThreeWayMerger {
 	 */
 	protected MergeAlgorithm mergeAlgorithm;
 
+	/**
+	 * The size limit (bytes) which controls a file to be stored in {@code Heap} or
+	 * {@code LocalFile} during the merge.
+	 */
+	private int inCoreLimit;
+
 	private static MergeAlgorithm getMergeAlgorithm(Config config) {
 		SupportedAlgorithm diffAlg = config.getEnum(
 				CONFIG_DIFF_SECTION, null, CONFIG_KEY_ALGORITHM,
@@ -279,6 +286,11 @@ public class ResolveMerger extends ThreeWayMerger {
 		return new MergeAlgorithm(DiffAlgorithm.getAlgorithm(diffAlg));
 	}
 
+	private static int getInCoreLimit(Config config) {
+		return config.getInt(
+				ConfigConstants.CONFIG_MERGE_SECTION, ConfigConstants.CONFIG_KEY_IN_CORE_LIMIT, 10 << 20);
+	}
+
 	private static String[] defaultCommitNames() {
 		return new String[] { "BASE", "OURS", "THEIRS" }; //$NON-NLS-1$ //$NON-NLS-2$ //$NON-NLS-3$
 	}
@@ -289,7 +301,9 @@ public class ResolveMerger extends ThreeWayMerger {
 	 */
 	protected ResolveMerger(Repository local, boolean inCore) {
 		super(local);
-		mergeAlgorithm = getMergeAlgorithm(local.getConfig());
+		Config config = local.getConfig();
+		mergeAlgorithm = getMergeAlgorithm(config);
+		inCoreLimit = getInCoreLimit(config);
 		commitNames = defaultCommitNames();
 		this.inCore = inCore;
 
@@ -835,7 +849,7 @@ public class ResolveMerger extends ThreeWayMerger {
 	private ObjectId insertMergeResult(MergeResult<RawText> result)
 			throws IOException {
 		TemporaryBuffer.LocalFile buf = new TemporaryBuffer.LocalFile(
-				db != null ? nonNullRepo().getDirectory() : null, 10 << 20);
+				db != null ? nonNullRepo().getDirectory() : null, inCoreLimit);
 		try {
 			new MergeFormatter().formatMerge(buf, result,
 					Arrays.asList(commitNames), CHARACTER_ENCODING);