[meld] Fix chunk-offset logic to deal with None chunks in three-way merges

[Kai Willadsen <kaiw src gnome org>]

commit fc7f372a9e1ef3fcb6fe5221ef96654f754660b0
Author: Kai Willadsen <kai willadsen gmail com>
Date:   Sat Jul 21 07:34:05 2012 +1000

    Fix chunk-offset logic to deal with None chunks in three-way merges
    
    In three-way merges we can have a merged chunk that contains None on
    one side, indicating that e.g., the left and middle chunks are
    identical, while the middle and right chunks differ. This commit fixes
    the recently modified change_sequence logic to handle None chunks.

 meld/diffutil.py |   12 +++++++-----
 1 files changed, 7 insertions(+), 5 deletions(-)
---
diff --git a/meld/diffutil.py b/meld/diffutil.py
index 9f7c3ed..67e8174 100644
--- a/meld/diffutil.py
+++ b/meld/diffutil.py
@@ -188,6 +188,8 @@ class Differ(gobject.GObject):
 
         def offset(c, start, o1, o2):
             """Offset a chunk by o1/o2 if it's after the inserted lines"""
+            if c is None:
+                return None
             start_a = c.start_a + (o1 if c.start_a > start else 0)
             end_a = c.end_a + (o1 if c.end_a > start else 0)
             start_b = c.start_b + (o2 if c.start_b > start else 0)
@@ -200,17 +202,17 @@ class Differ(gobject.GObject):
         self._changed_chunks = tuple()
         chunk_changed = False
         for (c1, c2) in self._merge_cache:
-            print c1, c2
             if sequence == 0:
-                if c1.start_b <= startidx < c1.end_b:
+                if c1 and c1.start_b <= startidx < c1.end_b:
                     chunk_changed = True
                 c1 = offset(c1, startidx, 0, sizechange)
             elif sequence == 2:
-                if c2.start_b <= startidx < c2.end_b:
+                if c2 and c2.start_b <= startidx < c2.end_b:
                     chunk_changed = True
                 c2 = offset(c2, startidx, 0, sizechange)
-            else:  # sequence == 1
-                if c1.start_a <= startidx < c1.end_a:
+            else:
+                # Middle sequence changes alter both chunks
+                if c1 and c1.start_a <= startidx < c1.end_a:
                     chunk_changed = True
                 c1 = offset(c1, startidx, sizechange, 0)
                 if self.num_sequences == 3: