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

Author: Byron

CHANGES

@@ -6,7 +6,8 @@ CHANGES
  * ConcurrentWriteOperation was removed, and replaced by LockedFD
  * IndexFile.get_entries_key was renamed to entry_key
  * IndexEntry instances contained in IndexFile.entries now use binary sha's. Use
-   the .hexsha property to obtain the hexadecimal version
+   the .hexsha property to obtain the hexadecimal version. The .sha property
+   was removed to make the use of the respective sha more explicit.
  * IndexFile.write_tree: removed missing_ok keyword, its always True now
    Instead of raising GitCommandError it raises UnmergedEntriesError
  * diff.Diff.null_hex_sha renamed to NULL_HEX_SHA, to be conforming with 

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")

lib/git/ext/gitdb

@@ -530,9 +530,7 @@ def write_tree(self):
 		: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 @@ def move(self, items, skip_errors=False, **kwargs):
 
 		return out
 
-	@default_index
 	def commit(self, message, parent_commits=None, head=True):
 		"""
 		Commit the current default index file, creating a commit object.

lib/git/index/base.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
 

lib/git/index/fun.py

@@ -114,6 +114,36 @@ def assert_entries(entries, num_entries, has_conflict=False):
 		trees = [tb, th, tm]
 		assert_entries(aggressive_tree_merge(odb, trees), 2)
 
+		# same file added in both, differently
+		fa = mkfile('1', shab)
+		th = mktree(odb, [fa])
+		fb = mkfile('1', shac)
+		tm = mktree(odb, [fb])
+		
+		# expect conflict
+		trees = [tb, th, tm]
+		assert_entries(aggressive_tree_merge(odb, trees), 2, True)
+		
+		# same file added, different mode
+		fa = mkfile('1', shab)
+		th = mktree(odb, [fa])
+		fb = mkcommit('1', shab)
+		tm = mktree(odb, [fb])
+		
+		# expect conflict
+		trees = [tb, th, tm]
+		assert_entries(aggressive_tree_merge(odb, trees), 2, True)
+		
+		# same file added in both
+		fa = mkfile('1', shab)
+		th = mktree(odb, [fa])
+		fb = mkfile('1', shab)
+		tm = mktree(odb, [fb])
+		
+		# expect conflict
+		trees = [tb, th, tm]
+		assert_entries(aggressive_tree_merge(odb, trees), 1)
+		
 		# modify same base file, differently
 		fa = mkfile(bfn, shab)
 		th = mktree(odb, [fa])