Cap describe abbrev option

- minimum is 4 [1]
- maximum is length of a full ObjectId

[1] https://git-scm.com/docs/git-config#Documentation/git-config.txt-coreabbrev

Change-Id: I145bde1a218f71b87b8d8260761dd0853770bb76

2 files changed, 19 insertions, 11 deletions

diff --git a/org.eclipse.jgit.test/tst/org/eclipse/jgit/api/DescribeCommandTest.java b/org.eclipse.jgit.test/tst/org/eclipse/jgit/api/DescribeCommandTest.java
index 48980ad6e4..ab87fa9662 100644
--- a/org.eclipse.jgit.test/tst/org/eclipse/jgit/api/DescribeCommandTest.java
+++ b/org.eclipse.jgit.test/tst/org/eclipse/jgit/api/DescribeCommandTest.java
@@ -14,7 +14,6 @@ import static org.eclipse.jgit.lib.Constants.OBJECT_ID_ABBREV_STRING_LENGTH;
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertNotNull;
 import static org.junit.Assert.assertNull;
-import static org.junit.Assert.assertThrows;
 import static org.junit.Assert.assertTrue;
 
 import java.io.BufferedWriter;
@@ -104,6 +103,10 @@ public class DescribeCommandTest extends RepositoryTestCase {
 			assertEquals("bob-t2-1-g3e563c5", describe(c4, "a*", "b*", "c*"));
 
 			assertEquals("bob-t2", describe(c4, false, true, 0));
+			assertEquals("bob-t2-1-g3e56", describe(c4, false, true, 1));
+			assertEquals("bob-t2-1-g3e56", describe(c4, false, true, -10));
+			assertEquals("bob-t2-1-g3e563c55927905f21e3bc7c00a3d83a31bf4ed3a",
+					describe(c4, false, true, 50));
 		} else {
 			assertEquals(null, describe(c2));
 			assertEquals(null, describe(c3));
@@ -117,16 +120,13 @@ public class DescribeCommandTest extends RepositoryTestCase {
 			assertEquals("44579ebe7f", describe(c3, false, true, 10));
 			assertEquals("3e563c5592", describe(c4, false, true, 10));
 
-			assertEquals("3e", describe(c4, false, true, 2));
+			assertEquals("3e56", describe(c4, false, true, -10));
+			assertEquals("3e56", describe(c4, false, true, 0));
+			assertEquals("3e56", describe(c4, false, true, 2));
 			assertEquals("3e563c55927905f21e3bc7c00a3d83a31bf4ed3a",
 					describe(c4, false, true, 40));
-
-			assertThrows(StringIndexOutOfBoundsException.class,
-					() -> describe(c4, false, true, -10));
-			assertThrows(StringIndexOutOfBoundsException.class,
-					() -> describe(c4, false, true, 1));
-			assertThrows(StringIndexOutOfBoundsException.class,
-					() -> describe(c4, false, true, 41));
+			assertEquals("3e563c55927905f21e3bc7c00a3d83a31bf4ed3a",
+					describe(c4, false, true, 42));
 		}
 
 		// test default target
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/api/DescribeCommand.java b/org.eclipse.jgit/src/org/eclipse/jgit/api/DescribeCommand.java
index 955d147691..2480e2ebd7 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/api/DescribeCommand.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/api/DescribeCommand.java
@@ -232,7 +232,13 @@ public class DescribeCommand extends GitCommand<String> {
 		}
 		return String.format("%s-%d-g%s", formatRefName(tag.getName()), //$NON-NLS-1$
 				Integer.valueOf(depth),
-				w.getObjectReader().abbreviate(tip, abbrev).name());
+				w.getObjectReader().abbreviate(tip, getCappedAbbrev()).name());
+	}
+
+	private int getCappedAbbrev() {
+		int len = Math.max(abbrev, 4);
+		len = Math.min(len, Constants.OBJECT_ID_STRING_LENGTH);
+		return len;
 	}
 
 	/**
@@ -436,7 +442,9 @@ public class DescribeCommand extends GitCommand<String> {
 			// if all the nodes are dominated by all the tags, the walk stops
 			if (candidates.isEmpty()) {
 				return always
-						? w.getObjectReader().abbreviate(target, abbrev).name()
+						? w.getObjectReader()
+								.abbreviate(target, getCappedAbbrev())
+								.name()
 						: null;
 			}