Make diff patch parsing more reliable

The a_path and b_path cannot reliably be read from the first diff line
as it's ambiguous.  From the git-diff manpage:

  > The a/ and b/ filenames are the same unless rename/copy is involved.
  > Especially, **even for a creation or a deletion**, /dev/null is not
  > used in place of the a/ or b/ filenames.

This patch changes the a_path and b_path detection to read it from the
more reliable locations further down the diff headers.  Two use cases
are fixed by this:

  - As the man page snippet above states, for new/deleted files the a
    or b path will now be properly None.
  - File names with spaces in it are now properly parsed.

Working on this patch, I realized the --- and +++ lines really belong to
the diff header, not the diff contents.  This means that when parsing
the patch format, the --- and +++ will now be swallowed, and not end up
anymore as part of the diff contents.  The diff contents now always
start with an @@ line.

This may be a breaking change for some users that rely on this
behaviour.  However, those users could now access that information more
reliably via the normal Diff properties a_path and b_path now.

1 files changed, 9 insertions, 2 deletions

diff --git a/git/test/test_diff.py b/git/test/test_diff.py
index 56e395fd..05f8f3ae 100644
--- a/git/test/test_diff.py
+++ b/git/test/test_diff.py
@@ -76,7 +76,7 @@ class TestDiff(TestBase):
         self._assert_diff_format(diffs)
 
         assert_equal(1, len(diffs))
-        assert_equal(10, len(diffs[0].diff.splitlines()))
+        assert_equal(8, len(diffs[0].diff.splitlines()))
 
     def test_diff_with_rename(self):
         output = StringProcessAdapter(fixture('diff_rename'))
@@ -140,7 +140,8 @@ class TestDiff(TestBase):
 
         # ...and with creating a patch
         diff_index = initial_commit.diff(NULL_TREE, create_patch=True)
-        assert diff_index[0].b_path == 'CHANGES'
+        assert diff_index[0].a_path is None, repr(diff_index[0].a_path)
+        assert diff_index[0].b_path == 'CHANGES', repr(diff_index[0].b_path)
         assert diff_index[0].new_file
         assert diff_index[0].diff == fixture('diff_initial')
 
@@ -156,6 +157,12 @@ class TestDiff(TestBase):
             Diff._index_from_patch_format(self.rorepo, diff_proc.stdout)
         # END for each fixture
 
+    def test_diff_with_spaces(self):
+        data = StringProcessAdapter(fixture('diff_file_with_spaces'))
+        diff_index = Diff._index_from_patch_format(self.rorepo, data.stdout)
+        assert diff_index[0].a_path is None, repr(diff_index[0].a_path)
+        assert diff_index[0].b_path == u'file with spaces', repr(diff_index[0].b_path)
+
     def test_diff_interface(self):
         # test a few variations of the main diff routine
         assertion_map = dict()