Fixed mode-handling in Diff creation, and added assertions to catch this in future

There is still some work todo in terms of how we handle the encoding

Author: Byron

git/diff.py

@@ -217,10 +217,12 @@ def __init__(self, repo, a_path, b_path, a_blob_id, b_blob_id, a_mode,
         if a_blob_id is None:
             self.a_blob = None
         else:
+            assert self.a_mode
             self.a_blob = Blob(repo, hex_to_bin(a_blob_id), mode=self.a_mode, path=a_path)
         if b_blob_id is None:
             self.b_blob = None
         else:
+            assert self.b_mode
             self.b_blob = Blob(repo, hex_to_bin(b_blob_id), mode=self.b_mode, path=b_path)
 
         self.new_file = new_file
@@ -313,8 +315,9 @@ def _index_from_patch_format(cls, repo, stream):
 
             # Make sure the mode is set if the path is set. Otherwise the resulting blob is invalid
             # We just use the one mode we should have parsed
-            index.append(Diff(repo, a_path, b_path, a_blob_id, b_blob_id,
-                              old_mode or deleted_file_mode or b_mode, new_mode or new_file_mode or b_mode,
+            a_mode = old_mode or deleted_file_mode or (a_path and (b_mode or new_mode or new_file_mode))
+            b_mode = b_mode or new_mode or new_file_mode or (b_path and a_mode)
+            index.append(Diff(repo, a_path, b_path, a_blob_id, b_blob_id, a_mode, b_mode,
                               new_file, deleted_file, rename_from, rename_to, None))
 
             previous_header = header

git/test/test_diff.py

@@ -73,7 +73,7 @@ def test_binary_diff(self):
             assert len(list(res.iter_change_type('M'))) == 1
             if res[0].diff:
                 assert res[0].diff == "Binary files a/rps and b/rps differ\n", "in patch mode, we get a diff text"
-                assert isinstance(str(res[0]), str), "This call should just work"
+                assert str(res[0]), "This call should just work"
         # end for each method to test
 
     def test_diff_index(self):
@@ -82,6 +82,7 @@ def test_diff_index(self):
         assert len(res) == 6
         for dr in res:
             assert dr.diff
+            assert str(dr), "Diff to string conversion should be possible"
         # end for each diff
 
         dr = res[3]
@@ -129,6 +130,9 @@ def test_diff_interface(self):
                             assert len(diff_set) == 1
                             assert diff_index[0] == diff_index[0]
                             assert not (diff_index[0] != diff_index[0])
+
+                            for dr in diff_index:
+                                assert str(dr), "Diff to string conversion should be possible"
                         # END diff index checking
                     # END for each patch option
                 # END for each path option