unidiff: punt on comparing empty files

mercurial/mdiff.py

@@ -1,76 +1,77 b''
 #!/usr/bin/python
 import difflib, struct
 from cStringIO import StringIO
 
 def unidiff(a, b, fn):
+    if not a and not b: return ""
     a = a.splitlines(1)
     b = b.splitlines(1)
-    l = difflib.unified_diff(a, b, fn, fn)
+    l = list(difflib.unified_diff(a, b, fn, fn))
     return "".join(l)
 
 def textdiff(a, b):
     return diff(a.splitlines(1), b.splitlines(1))
 
 def sortdiff(a, b):
     la = lb = 0
 
     while 1:
         if la >= len(a) or lb >= len(b): break
         if b[lb] < a[la]:
             si = lb
             while lb < len(b) and b[lb] < a[la] : lb += 1
             yield "insert", la, la, si, lb
         elif a[la] < b[lb]:
             si = la
             while la < len(a) and a[la] < b[lb]: la += 1
             yield "delete", si, la, lb, lb
         else:
             la += 1
             lb += 1
 
     si = lb
     while lb < len(b):
         lb += 1
         yield "insert", la, la, si, lb
 
     si = la
     while la < len(a):
         la += 1
         yield "delete", si, la, lb, lb
 
 def diff(a, b, sorted=0):
     bin = []
     p = [0]
     for i in a: p.append(p[-1] + len(i))
 
     if sorted:
         d = sortdiff(a, b)
     else:
         d = difflib.SequenceMatcher(None, a, b).get_opcodes()
 
     for o, m, n, s, t in d:
         if o == 'equal': continue
         s = "".join(b[s:t])
         bin.append(struct.pack(">lll", p[m], p[n], len(s)) + s)
 
     return "".join(bin)
 
 def patch(a, bin):
     last = pos = 0
     r = []
 
     while pos < len(bin):
         p1, p2, l = struct.unpack(">lll", bin[pos:pos + 12])
         pos += 12
         r.append(a[last:p1])
         r.append(bin[pos:pos + l])
         pos += l
         last = p2
     r.append(a[last:])
 
     return "".join(r)