manifest: repurpose flagsdiff() into (node-and-flag)diff()

The manifestdict class already has a method for diff flags between two
manifests (presumably because there is no full access to the private
_flags field). The only caller is merge.manifestmerge(), which also
wants a diff of files between the same manifests. Let's combine the
code for diffing files and flags into a single method on
manifestdict. This puts all the manifest diffing in one place and will
allow for further simplification. It might also be useful for it to be
encapsulated in manifestdict if we later decide to to shard
manifests. The docstring is intentionally unclear about missing
entries for now.

mercurial/manifest.py

@@ -38,8 +38,15 b' class manifestdict(dict):'
                 if flags:
                     ret._flags[fn] = flags
         return ret
-    def flagsdiff(self, d2):
-        return dicthelpers.diff(self._flags, d2._flags, "")
+
+    def diff(self, m2):
+        '''Finds changes between the current manifest and m2. The result is
+        returned as a dict with filename as key and values of the form
+        ((n1,n2),(fl1,fl2)), where n1/n2 is the nodeid in the current/other
+        manifest and fl1/fl2 is the flag in the current/other manifest.'''
+        flagsdiff = dicthelpers.diff(self._flags, m2._flags, "")
+        fdiff = dicthelpers.diff(self, m2)
+        return dicthelpers.join(fdiff, flagsdiff)
 
     def text(self):
         """Get the full data of this manifest as a bytestring."""

mercurial/merge.py

@@ -10,7 +10,7 b' import struct'
 from node import nullid, nullrev, hex, bin
 from i18n import _
 from mercurial import obsolete
-import error as errormod, util, filemerge, copies, subrepo, worker, dicthelpers
+import error as errormod, util, filemerge, copies, subrepo, worker
 import errno, os, shutil
 
 _pack = struct.pack
@@ -422,11 +422,9 b' def manifestmerge(repo, wctx, p2, pa, br'
 
     aborts = []
     # Compare manifests
-    fdiff = dicthelpers.diff(m1, m2)
-    flagsdiff = m1.flagsdiff(m2)
-    diff12 = dicthelpers.join(fdiff, flagsdiff)
+    diff = m1.diff(m2)
 
-    for f, (n12, fl12) in diff12.iteritems():
+    for f, (n12, fl12) in diff.iteritems():
         if n12:
             n1, n2 = n12
         else: # file contents didn't change, but flags did