Delay locating .gitattributes until requested

Instead of checking every entry for .gitattributes only look for the
entry on request by TreeWalk.  This avoids impacting uses like RevWalk
filtering history.

When the attrs is requested skip to the start of the tree and look for
.gitattributes until either it is found, or it is impossible to be
present.  Due to the sorting rules of tree entries .gitattributes
should be among the first or second entries in the tree so very few
entries will need to be considered.

Waiting to find the .gitattributes file by native ordering may miss
attrs for files like .config, which sorts before .gitattributes.
Starting from the front of the tree on demand ensures the attributes
are parsed as early as necessary to process any entry in the tree.

Due to TreeWalk recursively processing up the tree of iterators we
cannot just reset the current CanonicalTreeParser to the start as
parent parsers share the same path buffer as their children.
Resetting a parent to look for .gitattributes may overwrite path
buffer data used by a child iterator.  Work around this by building a
new temporary CanonicalTreeParser instance.

Change-Id: Ife950253b687be325340d27e9915c9a40df2641c

1 files changed, 41 insertions, 0 deletions

diff --git a/org.eclipse.jgit.test/tst/org/eclipse/jgit/treewalk/CanonicalTreeParserTest.java b/org.eclipse.jgit.test/tst/org/eclipse/jgit/treewalk/CanonicalTreeParserTest.java
index 52da69ef52..f5e97c2dc2 100644
--- a/org.eclipse.jgit.test/tst/org/eclipse/jgit/treewalk/CanonicalTreeParserTest.java
+++ b/org.eclipse.jgit.test/tst/org/eclipse/jgit/treewalk/CanonicalTreeParserTest.java
@@ -43,6 +43,8 @@
 
 package org.eclipse.jgit.treewalk;
 
+import static org.eclipse.jgit.lib.FileMode.REGULAR_FILE;
+import static org.eclipse.jgit.lib.FileMode.SYMLINK;
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertSame;
@@ -50,9 +52,11 @@ import static org.junit.Assert.assertTrue;
 
 import java.io.ByteArrayOutputStream;
 
+import org.eclipse.jgit.errors.CorruptObjectException;
 import org.eclipse.jgit.lib.Constants;
 import org.eclipse.jgit.lib.FileMode;
 import org.eclipse.jgit.lib.ObjectId;
+import org.eclipse.jgit.lib.TreeFormatter;
 import org.eclipse.jgit.util.RawParseUtils;
 import org.junit.Before;
 import org.junit.Test;
@@ -369,4 +373,41 @@ public class CanonicalTreeParserTest {
 		assertEquals(name, RawParseUtils.decode(Constants.CHARSET, ctp.path,
 				ctp.pathOffset, ctp.pathLen));
 	}
+
+	@Test
+	public void testFindAttributesWhenFirst() throws CorruptObjectException {
+		TreeFormatter tree = new TreeFormatter();
+		tree.append(".gitattributes", REGULAR_FILE, hash_a);
+		ctp.reset(tree.toByteArray());
+
+		assertTrue(ctp.findFile(".gitattributes"));
+		assertEquals(REGULAR_FILE.getBits(), ctp.getEntryRawMode());
+		assertEquals(".gitattributes", ctp.getEntryPathString());
+		assertEquals(hash_a, ctp.getEntryObjectId());
+	}
+
+	@Test
+	public void testFindAttributesWhenSecond() throws CorruptObjectException {
+		TreeFormatter tree = new TreeFormatter();
+		tree.append(".config", SYMLINK, hash_a);
+		tree.append(".gitattributes", REGULAR_FILE, hash_foo);
+		ctp.reset(tree.toByteArray());
+
+		assertTrue(ctp.findFile(".gitattributes"));
+		assertEquals(REGULAR_FILE.getBits(), ctp.getEntryRawMode());
+		assertEquals(".gitattributes", ctp.getEntryPathString());
+		assertEquals(hash_foo, ctp.getEntryObjectId());
+	}
+
+	@Test
+	public void testFindAttributesWhenMissing() throws CorruptObjectException {
+		TreeFormatter tree = new TreeFormatter();
+		tree.append("src", REGULAR_FILE, hash_a);
+		tree.append("zoo", REGULAR_FILE, hash_foo);
+		ctp.reset(tree.toByteArray());
+
+		assertFalse(ctp.findFile(".gitattributes"));
+		assertEquals(11, ctp.idOffset()); // Did not walk the entire tree.
+		assertEquals("src", ctp.getEntryPathString());
+	}
 }