patch: Fix nullid for binary git diffs (issue4054)

The index for an empty file in git is not 0, but sha-1("blobl 0\0").

mercurial/patch.py

@@ -10,7 +10,7 import cStringIO, email.Parser, os, errn
 import tempfile, zlib, shutil
 
 from i18n import _
-from node import hex, nullid, short
+from node import hex, short
 import base85, mdiff, scmutil, util, diffhelpers, copies, encoding, error
 import context
 
@@ -1658,7 +1658,7 def trydiff(repo, revs, ctx1, ctx2, modi
 
     def gitindex(text):
         if not text:
-            return hex(nullid)
+            text = ""
         l = len(text)
         s = util.sha1('blob %d\0' % l)
         s.update(text)

tests/test-diff-upgrade.t

@@ -183,7 +183,7 git=auto: regular diff for regular files
   % git=auto: git diff for newbinary
   diff --git a/newbinary b/newbinary
   new file mode 100644
-  index 0000000000000000000000000000000000000000..f76dd238ade08917e6712764a16a22005a50573d
+  index e69de29bb2d1d6434b8b29ae775ad8c2e48c5391..f76dd238ade08917e6712764a16a22005a50573d
   GIT binary patch
   literal 1
   Ic${MZ000310RR91
@@ -200,7 +200,7 git=auto: regular diff for regular files
   % git=auto: git diff for rmbinary
   diff --git a/rmbinary b/rmbinary
   deleted file mode 100644
-  index f76dd238ade08917e6712764a16a22005a50573d..0000000000000000000000000000000000000000
+  index f76dd238ade08917e6712764a16a22005a50573d..e69de29bb2d1d6434b8b29ae775ad8c2e48c5391
   GIT binary patch
   literal 0
   Hc$@<O00001

tests/test-git-export.t

@@ -113,7 +113,7 Binary diff:
   $ cat b.diff
   diff --git a/binfile.bin b/binfile.bin
   new file mode 100644
-  index 0000000000000000000000000000000000000000..37ba3d1c6f17137d9c5f5776fa040caf5fe73ff9
+  index e69de29bb2d1d6434b8b29ae775ad8c2e48c5391..37ba3d1c6f17137d9c5f5776fa040caf5fe73ff9
   GIT binary patch
   literal 593
   zc$@)I0<QguP)<h;3K|Lk000e1NJLTq000mG000mO0ssI2kdbIM00009a7bBm000XU