diff: move index header generation to patch

In an upcoming patch, we will add index information to all git diffs, not
only binary diffs, so this code needs to be moved to a more appropriate
place.

Also, since this information is used for patch headers, it makes more
sense to be in the patch module, along with other patch-related metadata.

mercurial/mdiff.py

@@ -8,7 +8,6 b''
 from i18n import _
 import bdiff, mpatch, util
 import re, struct, base85, zlib
-from node import hex, nullid
 
 def splitnewlines(text):
     '''like str.splitlines, but only split on newlines.'''
@@ -301,14 +300,6 b' def _unidiff(t1, t2, l1, l2, opts=defaul'
 
 def b85diff(to, tn):
     '''print base85-encoded binary diff'''
-    def gitindex(text):
-        if not text:
-            return hex(nullid)
-        l = len(text)
-        s = util.sha1('blob %d\0' % l)
-        s.update(text)
-        return s.hexdigest()
-
     def fmtline(line):
         l = len(line)
         if l <= 26:
@@ -324,17 +315,22 b' def b85diff(to, tn):'
             yield text[i:i + csize]
             i += csize
 
-    tohash = gitindex(to)
-    tnhash = gitindex(tn)
-    if tohash == tnhash:
-        return ""
+    if to is None:
+        to = ''
+    if tn is None:
+        tn = ''
+
+    if to == tn:
+        return ''
 
     # TODO: deltas
-    ret = ['index %s..%s\nGIT binary patch\nliteral %s\n' %
-           (tohash, tnhash, len(tn))]
+    ret = []
+    ret.append('GIT binary patch\n')
+    ret.append('literal %s\n' % len(tn))
     for l in chunk(zlib.compress(tn)):
         ret.append(fmtline(l))
     ret.append('\n')
+
     return ''.join(ret)
 
 def patchtext(bin):

mercurial/patch.py

@@ -10,7 +10,7 b' import cStringIO, email.Parser, os, errn'
 import tempfile, zlib, shutil
 
 from i18n import _
-from node import hex, short
+from node import hex, nullid, short
 import base85, mdiff, scmutil, util, diffhelpers, copies, encoding, error
 import context
 
@@ -1662,6 +1662,22 b' def trydiff(repo, revs, ctx1, ctx2, modi'
             header.append('old mode %s\n' % omode)
             header.append('new mode %s\n' % nmode)
 
+    def addindexmeta(meta, revs):
+        if opts.git:
+            i = len(revs)
+            if i==2:
+                meta.append('index %s..%s\n' % tuple(revs))
+            elif i==3:
+                meta.append('index %s,%s..%s\n' % tuple(revs))
+
+    def gitindex(text):
+        if not text:
+            return hex(nullid)
+        l = len(text)
+        s = util.sha1('blob %d\0' % l)
+        s.update(text)
+        return s.hexdigest()
+
     def diffline(a, b, revs):
         if opts.git:
             line = 'diff --git a/%s b/%s\n' % (a, b)
@@ -1763,6 +1779,8 b' def trydiff(repo, revs, ctx1, ctx2, modi'
                 header.insert(0, diffline(join(a), join(b), revs))
             if dodiff == 'binary':
                 text = mdiff.b85diff(to, tn)
+                if text:
+                    addindexmeta(header, [gitindex(to), gitindex(tn)])
             else:
                 text = mdiff.unidiff(to, date1,
                                     # ctx2 date may be dynamic