Add options for setting context lines and prefixes to DiffCommand

Change-Id: I539f3531e94c11c0f0a3e7096c0eb1b1c309898a

org.eclipse.jgit.test/tst/org/eclipse/jgit/api/DiffCommandTest.java

@@ -178,6 +178,50 @@ public class DiffCommandTest extends RepositoryTestCase {
 		assertEquals(expected.toString(), actual);
 	}
 
+	@Test
+	public void testDiffWithPrefixes() throws Exception {
+		write(new File(db.getWorkTree(), "test.txt"), "test");
+		Git git = new Git(db);
+		git.add().addFilepattern(".").call();
+		git.commit().setMessage("Initial commit").call();
+		write(new File(db.getWorkTree(), "test.txt"), "test change");
+
+		OutputStream out = new ByteArrayOutputStream();
+		git.diff().setOutputStream(out).setSourcePrefix("old/")
+				.setDestinationPrefix("new/")
+				.call();
+
+		String actual = out.toString();
+		String expected = "diff --git old/test.txt new/test.txt\n"
+				+ "index 30d74d2..4dba797 100644\n" + "--- old/test.txt\n"
+				+ "+++ new/test.txt\n" + "@@ -1 +1 @@\n" + "-test\n"
+				+ "\\ No newline at end of file\n" + "+test change\n"
+				+ "\\ No newline at end of file\n";
+		assertEquals(expected.toString(), actual);
+	}
+
+	@Test
+	public void testDiffWithNegativeLineCount() throws Exception {
+		write(new File(db.getWorkTree(), "test.txt"),
+				"0\n1\n2\n3\n4\n5\n6\n7\n8\n9");
+		Git git = new Git(db);
+		git.add().addFilepattern(".").call();
+		git.commit().setMessage("Initial commit").call();
+		write(new File(db.getWorkTree(), "test.txt"),
+				"0\n1\n2\n3\n4a\n5\n6\n7\n8\n9");
+
+		OutputStream out = new ByteArrayOutputStream();
+		git.diff().setOutputStream(out).setContextLines(1)
+				.call();
+
+		String actual = out.toString();
+		String expected = "diff --git a/test.txt b/test.txt\n"
+				+ "index f55b5c9..c5ec8fd 100644\n" + "--- a/test.txt\n"
+				+ "+++ b/test.txt\n" + "@@ -4,3 +4,3 @@\n" + " 3\n" + "-4\n"
+				+ "+4a\n" + " 5\n";
+		assertEquals(expected.toString(), actual);
+	}
+
 	private AbstractTreeIterator getTreeIterator(String name)
 			throws IOException {
 		final ObjectId id = db.resolve(name);

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

@@ -82,6 +82,12 @@ public class DiffCommand extends GitCommand<List<DiffEntry>> {
 
 	private OutputStream out;
 
+	private int contextLines = -1;
+
+	private String sourcePrefix;
+
+	private String destinationPrefix;
+
 	/**
 	 * @param repo
 	 */
@@ -125,6 +131,12 @@ public class DiffCommand extends GitCommand<List<DiffEntry>> {
 			}
 
 			diffFmt.setPathFilter(pathFilter);
+			if (contextLines >= 0)
+				diffFmt.setContext(contextLines);
+			if (destinationPrefix != null)
+				diffFmt.setNewPrefix(destinationPrefix);
+			if (sourcePrefix != null)
+				diffFmt.setOldPrefix(sourcePrefix);
 
 			List<DiffEntry> result = diffFmt.scan(oldTree, newTree);
 			if (showNameAndStatusOnly) {
@@ -199,4 +211,40 @@ public class DiffCommand extends GitCommand<List<DiffEntry>> {
 		this.out = out;
 		return this;
 	}
+
+	/**
+	 * Set number of context lines instead of the usual three.
+	 *
+	 * @param contextLines
+	 *            the number of context lines
+	 * @return this instance
+	 */
+	public DiffCommand setContextLines(int contextLines) {
+		this.contextLines = contextLines;
+		return this;
+	}
+
+	/**
+	 * Set the given source prefix instead of "a/".
+	 *
+	 * @param sourcePrefix
+	 *            the prefix
+	 * @return this instance
+	 */
+	public DiffCommand setSourcePrefix(String sourcePrefix) {
+		this.sourcePrefix = sourcePrefix;
+		return this;
+	}
+
+	/**
+	 * Set the given destination prefix instead of "b/".
+	 *
+	 * @param destinationPrefix
+	 *            the prefix
+	 * @return this instance
+	 */
+	public DiffCommand setDestinationPrefix(String destinationPrefix) {
+		this.destinationPrefix = destinationPrefix;
+		return this;
+	}
 }