[meld/Python3] filediff: Fix DiffChunk sorting tuple-of-maybe-tuples (bgo#767744)

[Kai Willadsen <kaiw src gnome org>]

commit bc1878d13c93ffa7e405202679063238ecf44b7e
Author: Kai Willadsen <kai willadsen gmail com>
Date:   Fri Jun 17 07:19:54 2016 +1000

    filediff: Fix DiffChunk sorting tuple-of-maybe-tuples (bgo#767744)
    
    We were sorting a tuple of DiffChunk-or-None elements, which no longer
    compare in Python 3. In addition, the sort (which I believe exists only
    so that we rehighlight in a predictable order) was doing a native
    sort, which resulted in sorting first based on chunk type.
    
    With this change, we handle None in merged chunks correctly (by
    ignoring it) and sort based on a chunk's start location in the middle
    column.

 meld/diffutil.py |    7 +++++++
 meld/filediff.py |    8 ++++++--
 2 files changed, 13 insertions(+), 2 deletions(-)
---
diff --git a/meld/diffutil.py b/meld/diffutil.py
index 2475cf2..da8097b 100644
--- a/meld/diffutil.py
+++ b/meld/diffutil.py
@@ -29,6 +29,13 @@ opcode_reverse = {
 }
 
 
+def merged_chunk_order(merged_chunk):
+    if not merged_chunk:
+        return 0
+    chunk = merged_chunk[0] or merged_chunk[1]
+    return chunk.start_a
+
+
 def reverse_chunk(chunk):
     tag = opcode_reverse[chunk[0]]
     return DiffChunk._make((tag, chunk[3], chunk[4], chunk[1], chunk[2]))
diff --git a/meld/filediff.py b/meld/filediff.py
index 0fefee9..83f0aa2 100644
--- a/meld/filediff.py
+++ b/meld/filediff.py
@@ -1209,8 +1209,12 @@ class FileDiff(melddoc.MeldDoc, gnomeglade.Component):
 
         # We need to clear removed and modified chunks, and need to
         # re-highlight added and modified chunks.
-        need_clearing = sorted(list(removed_chunks))
-        need_highlighting = sorted(list(added_chunks) + [modified_chunks])
+        need_clearing = sorted(
+            list(removed_chunks),
+            key=diffutil.merged_chunk_order)
+        need_highlighting = sorted(
+            list(added_chunks) + [modified_chunks],
+            key=diffutil.merged_chunk_order)
 
         alltags = [b.get_tag_table().lookup("inline") for b in self.textbuffer]