Optimize MergeAlgorithm if ours or theirs is empty

Previously when merging two contents with a non-empty base and one of
the contents was empty (size == 0) and the other was modified there
was a potentially expensive calculation until we finally always come
to the same result -> the complete non-deleted content should collide
with the empty content.

This proposal adds an optimization to detect empty input content and
to produce the appropriate result immediatly.

Change-Id: Ie6a837260c19d808f0e99173f570ff96dd22acd3
Signed-off-by: Christian Halstrick <christian.halstrick@sap.com>

1 files changed, 19 insertions, 1 deletions

diff --git a/org.eclipse.jgit.test/tst/org/eclipse/jgit/merge/MergeAlgorithmTest.java b/org.eclipse.jgit.test/tst/org/eclipse/jgit/merge/MergeAlgorithmTest.java
index aa8f8281e4..8a33425b1d 100644
--- a/org.eclipse.jgit.test/tst/org/eclipse/jgit/merge/MergeAlgorithmTest.java
+++ b/org.eclipse.jgit.test/tst/org/eclipse/jgit/merge/MergeAlgorithmTest.java
@@ -198,6 +198,25 @@ public class MergeAlgorithmTest {
 
 	}
 
+	/**
+	 * Test situations where (at least) one input value is the empty text
+	 *
+	 * @throws IOException
+	 */
+	@Test
+	public void testEmptyTexts() throws IOException {
+		// test modification against deletion
+		assertEquals(t("<AB=>"), merge("A", "AB", ""));
+		assertEquals(t("<=AB>"), merge("A", "", "AB"));
+
+		// test unmodified against deletion
+		assertEquals(t(""), merge("AB", "AB", ""));
+		assertEquals(t(""), merge("AB", "", "AB"));
+
+		// test deletion against deletion
+		assertEquals(t(""), merge("AB", "", ""));
+	}
+
 	private String merge(String commonBase, String ours, String theirs) throws IOException {
 		MergeResult r = new MergeAlgorithm().merge(RawTextComparator.DEFAULT,
 				T(commonBase), T(ours), T(theirs));
@@ -231,5 +250,4 @@ public class MergeAlgorithmTest {
 	public static RawText T(String text) {
 		return new RawText(Constants.encode(t(text)));
 	}
-
 }