Add support for config "pull.ff

When the configuration entry 'pull.ff' exists the merge of the pull will
use the value as fast forward option.

Bug: 474174
Change-Id: Ic8db2f00095ed81528667b064ff523911e6c122e
Signed-off-by: Mattias Neuling <neuling@dakosy.de>
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

org.eclipse.jgit/src/org/eclipse/jgit/api/PullCommand.java

@@ -48,6 +48,8 @@ import java.io.IOException;
 import java.text.MessageFormat;
 
 import org.eclipse.jgit.annotations.Nullable;
+import org.eclipse.jgit.api.MergeCommand.FastForwardMode;
+import org.eclipse.jgit.api.MergeCommand.FastForwardMode.Merge;
 import org.eclipse.jgit.api.RebaseCommand.Operation;
 import org.eclipse.jgit.api.errors.CanceledException;
 import org.eclipse.jgit.api.errors.DetachedHeadException;
@@ -351,6 +353,7 @@ public class PullCommand extends TransportCommand<PullCommand, PullResult> {
 			merge.include(upstreamName, commitToMerge);
 			merge.setStrategy(strategy);
 			merge.setProgressMonitor(monitor);
+			merge.setFastForward(getFastForwardMode());
 			MergeResult mergeRes = merge.call();
 			monitor.update(1);
 			result = new PullResult(fetchRes, remote, mergeRes);
@@ -472,4 +475,12 @@ public class PullCommand extends TransportCommand<PullCommand, PullResult> {
 		}
 		return mode;
 	}
+
+	private FastForwardMode getFastForwardMode() {
+		Config config = repo.getConfig();
+		Merge ffMode = config.getEnum(Merge.values(),
+				ConfigConstants.CONFIG_PULL_SECTION, null,
+				ConfigConstants.CONFIG_KEY_FF, null);
+		return ffMode != null ? FastForwardMode.valueOf(ffMode) : null;
+	}
 }

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

@@ -107,6 +107,12 @@ public class ConfigConstants {
 	 */
 	public static final String CONFIG_PULL_SECTION = "pull";
 
+	/**
+	 * The "merge" section
+	 * @since 4.9
+	 */
+	public static final String CONFIG_MERGE_SECTION = "merge";
+
 	/**
 	 * The "filter" section
 	 * @since 4.6