aggressive_tree_merge: fixed incorrect handling of one branch, it was just not implemented causing incorrect merge results. Added test to cover this issue

Diff: added NULL_BIN_SHA constant for completeness

4 files changed, 12 insertions, 5 deletions

diff --git a/lib/git/diff.py b/lib/git/diff.py
index f9a0a66f..36b216e3 100644
--- a/lib/git/diff.py
+++ b/lib/git/diff.py
@@ -197,6 +197,7 @@ class Diff(object):
                             """, re.VERBOSE | re.MULTILINE)
     # can be used for comparisons
     NULL_HEX_SHA = "0"*40
+    NULL_BIN_SHA = "\0"*20
     
     __slots__ = ("a_blob", "b_blob", "a_mode", "b_mode", "new_file", "deleted_file", 
                  "rename_from", "rename_to", "diff")
diff --git a/lib/git/ext/gitdb b/lib/git/ext/gitdb
-Subproject 9b53ab02cb44571e6167a125a5296b7c3395563
+Subproject d3a0037dd5a11459985e7dc4b6819f6292f20c1
diff --git a/lib/git/index/base.py b/lib/git/index/base.py
index 771f1710..7568b476 100644
--- a/lib/git/index/base.py
+++ b/lib/git/index/base.py
@@ -530,9 +530,7 @@ class IndexFile(LazyMixin, diff.Diffable, Serializable):
 		:raise ValueError: if there are no entries in the cache
 		:raise UnmergedEntriesError: """
 		# we obtain no lock as we just flush our contents to disk as tree
-		if not self.entries:
-			raise ValueError("Cannot write empty index")
-		
+		# If we are a new index, the entries access will load our data accordingly
 		mdb = MemoryDB()
 		entries = self._entries_sorted()
 		binsha, tree_items = write_tree_from_cache(entries, mdb, slice(0, len(entries)))
@@ -892,7 +890,6 @@ class IndexFile(LazyMixin, diff.Diffable, Serializable):
 
 		return out
 
-	@default_index
 	def commit(self, message, parent_commits=None, head=True):
 		"""
 		Commit the current default index file, creating a commit object.
diff --git a/lib/git/index/fun.py b/lib/git/index/fun.py
index 23a6d8f9..14a47fdc 100644
--- a/lib/git/index/fun.py
+++ b/lib/git/index/fun.py
@@ -283,7 +283,16 @@ def aggressive_tree_merge(odb, tree_shas):
 			elif theirs is None:
 				# added in our branch
 				out_append(_tree_entry_to_baseindexentry(ours, 0))
-			# END hanle heads
+			else:
+				# both have it, except for the base, see whether it changed
+				if ours[0] != theirs[0] or ours[1] != theirs[1]:
+					out_append(_tree_entry_to_baseindexentry(ours, 2))
+					out_append(_tree_entry_to_baseindexentry(theirs, 3))
+				else:
+					# it was added the same in both
+					out_append(_tree_entry_to_baseindexentry(ours, 0))
+				# END handle two items
+			# END handle heads
 		# END handle base exists
 	# END for each entries tuple