Teach BranchTrackingStatus to handle tracking of local branches

EGit wasn't able to decorate local branches tracking another local
branch with number of commits the checked out local branch differs from
the other local branch it's tracking.

Bug: 376970 
Change-Id: I74e932d5eacd74dbf6b0dffcfc65ba3222a8250e
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

org.eclipse.jgit.test/tst/org/eclipse/jgit/lib/BranchConfigTest.java

 /*
  * Copyright (C) 2011, Robin Stocker <robin@nibor.org>
+ * Copyright (C) 2012, Matthias Sohn <matthias.sohn@sap.com>
  * and other copyright owners as documented in the project's IP log.
  *
  * This program and the accompanying materials are made available
 		assertNull(branchConfig.getRemoteTrackingBranch());
 	}
 
+	@Test
+	public void getTrackingBranchShouldReturnMergeBranchForLocalBranch() {
+		Config c = parse("" //
+				+ "[remote \"origin\"]\n"
+				+ "  fetch = +refs/heads/*:refs/remotes/origin/*\n"
+				+ "[branch \"master\"]\n"
+				+ "  remote = .\n"
+				+ "  merge = refs/heads/master\n");
+
+		BranchConfig branchConfig = new BranchConfig(c, "master");
+		assertEquals("refs/heads/master",
+				branchConfig.getTrackingBranch());
+	}
+
+	@Test
+	public void getTrackingBranchShouldReturnNullWithoutMergeBranchForLocalBranch() {
+		Config c = parse("" //
+				+ "[remote \"origin\"]\n"
+				+ "  fetch = +refs/heads/onlyone:refs/remotes/origin/onlyone\n"
+				+ "[branch \"master\"]\n" //
+				+ "  remote = .\n");
+		BranchConfig branchConfig = new BranchConfig(c, "master");
+		assertNull(branchConfig.getTrackingBranch());
+	}
+
+	@Test
+	public void getTrackingBranchShouldHandleNormalCaseForRemoteTrackingBranch() {
+		Config c = parse("" //
+				+ "[remote \"origin\"]\n"
+				+ "  fetch = +refs/heads/*:refs/remotes/origin/*\n"
+				+ "[branch \"master\"]\n"
+				+ "  remote = origin\n"
+				+ "  merge = refs/heads/master\n");
+
+		BranchConfig branchConfig = new BranchConfig(c, "master");
+		assertEquals("refs/remotes/origin/master",
+				branchConfig.getTrackingBranch());
+	}
+
 	private Config parse(final String content) {
 		final Config c = new Config(null);
 		try {

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

 /*
  * Copyright (C) 2011, Robin Stocker <robin@nibor.org>
+ * Copyright (C) 2012, Matthias Sohn <matthias.sohn@sap.com>
  * and other copyright owners as documented in the project's IP log.
  *
  * This program and the accompanying materials are made available
 	}
 
 	/**
-	 * @return the full remote-tracking branch name or <code>null</code> if it
-	 *         could not be determined
+	 * @return the full tracking branch name or <code>null</code> if it could
+	 *         not be determined
+	 */
+	public String getTrackingBranch() {
+		String remote = getRemote();
+		String mergeRef = getMergeBranch();
+		if (remote == null || mergeRef == null)
+			return null;
+
+		if (remote.equals("."))
+			return mergeRef;
+
+		return findRemoteTrackingBranch(remote, mergeRef);
+	}
+
+	/**
+	 * @return the full remote-tracking branch name or {@code null} if it could
+	 *         not be determined. If you also want local tracked branches use
+	 *         {@link #getTrackingBranch()} instead.
 	 */
 	public String getRemoteTrackingBranch() {
 		String remote = getRemote();
 		if (remote == null || mergeRef == null)
 			return null;
 
+		return findRemoteTrackingBranch(remote, mergeRef);
+	}
+
+	/**
+	 * Finds the tracked remote tracking branch
+	 *
+	 * @param remote
+	 *            Remote name
+	 * @param mergeRef
+	 *            merge Ref of the local branch tracking the remote tracking
+	 *            branch
+	 * @return full remote tracking branch name or null
+	 */
+	private String findRemoteTrackingBranch(String remote, String mergeRef) {
 		RemoteConfig remoteConfig;
 		try {
 			remoteConfig = new RemoteConfig(config, remote);

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

 /*
  * Copyright (C) 2011, Robin Stocker <robin@nibor.org>
+ * Copyright (C) 2012, Matthias Sohn <matthias.sohn@sap.com>
  * and other copyright owners as documented in the project's IP log.
  *
  * This program and the accompanying materials are made available
 		BranchConfig branchConfig = new BranchConfig(repository.getConfig(),
 				branchName);
 
-		String remoteTrackingBranch = branchConfig.getRemoteTrackingBranch();
-		if (remoteTrackingBranch == null)
+		String trackingBranch = branchConfig.getTrackingBranch();
+		if (trackingBranch == null)
 			return null;
 
-		Ref tracking = repository.getRef(remoteTrackingBranch);
+		Ref tracking = repository.getRef(trackingBranch);
 		if (tracking == null)
 			return null;
 
 		int aheadCount = RevWalkUtils.count(walk, localCommit, mergeBase);
 		int behindCount = RevWalkUtils.count(walk, trackingCommit, mergeBase);
 
-		return new BranchTrackingStatus(remoteTrackingBranch, aheadCount, behindCount);
+		return new BranchTrackingStatus(trackingBranch, aheadCount, behindCount);
 	}
 
 	private final String remoteTrackingBranch;