--- a/README	Thu Feb 04 10:16:52 2016 +0000
+++ b/README	Thu Feb 04 01:19:14 2016 +0000
@@ -64,6 +64,8 @@
 - evolve: compatibility with Mercurial 3.7
 - evolve: support merge with a single obsolete parent.
 - evolve: prevent added file to be marked as unknown if evolve fails (issue4966)
+- evolve: stop relying on graftstate file for save evolve state
+          (for `hg evolve --continue`)
 
 5.2.2 --
 

--- a/hgext/evolve.py	Thu Feb 04 10:16:52 2016 +0000
+++ b/hgext/evolve.py	Thu Feb 04 01:19:14 2016 +0000
@@ -67,6 +67,7 @@
 import collections
 import socket
 import errno
+import struct
 sha1re = re.compile(r'\b[0-9a-f]{6,40}\b')
 
 import mercurial
@@ -116,6 +117,7 @@
 command = cmdutil.command(cmdtable)
 
 _pack = struct.pack
+_unpack = struct.unpack
 
 if gboptsmap is not None:
     memfilectx = context.memfilectx
@@ -1651,8 +1653,19 @@
             raise error.Abort('cannot specify both "--any" and "--continue"')
         if allopt:
             raise error.Abort('cannot specify both "--all" and "--continue"')
-        graftcmd = commands.table['graft'][0]
-        return graftcmd(ui, repo, old_obsolete=True, **{'continue': True})
+        state = _evolvestateread(repo)
+        if state is None:
+            raise error.Abort('no evolve to continue')
+        orig = repo[state['current']]
+        # XXX This is a terrible terrible hack, please get rid of it.
+        repo.opener.write('graftstate', orig.hex() + '\n')
+        try:
+            graftcmd = commands.table['graft'][0]
+            ret = graftcmd(ui, repo, old_obsolete=True, **{'continue': True})
+            _evolvestatedelete(repo)
+            return ret
+        finally:
+            util.unlinkpath(repo.join('graftstate'), ignoremissing=True)
     cmdutil.bailifchanged(repo)
 
 
@@ -1796,7 +1809,7 @@
         try:
             relocate(repo, orig, target, pctx, keepbranch)
         except MergeFailure:
-            repo.opener.write('graftstate', orig.hex() + '\n')
+            _evolvestatewrite(repo, {'current': orig.node()})
             repo.ui.write_err(_('evolve failed!\n'))
             repo.ui.write_err(
                 _('fix conflict and run "hg evolve --continue"'
@@ -3736,6 +3749,84 @@
     if oldbookmarks or destbookmarks:
         repo._bookmarks.recordchange(tr)
 
+evolvestateversion = 0
+
+@eh.uisetup
+def setupevolveunfinished(ui):
+    data = ('evolvestate', True, False, _('evolve in progress'),
+           _("use 'hg evolve --continue' or 'hg update' to abort"))
+    cmdutil.unfinishedstates.append(data)
+
+@eh.wrapfunction(hg, 'clean')
+def clean(orig, repo, *args, **kwargs):
+    ret = orig(repo, *args, **kwargs)
+    util.unlinkpath(repo.join('evolvestate'), ignoremissing=True)
+    return ret
+
+def _evolvestatewrite(repo, state):
+    # [version]
+    # [type][length][content]
+    #
+    # `version` is a 4 bytes integer (handled at higher level)
+    # `type` is a single character, `length` is a 4 byte integer, and
+    # `content` is an arbitrary byte sequence of length `length`.
+    f = repo.vfs('evolvestate', 'w')
+    try:
+        f.write(_pack('>I', evolvestateversion))
+        current = state['current']
+        key = 'C' # as in 'current'
+        format = '>sI%is' % len(current)
+        f.write(_pack(format, key, len(current), current))
+    finally:
+        f.close()
+
+def _evolvestateread(repo):
+    try:
+        f = repo.vfs('evolvestate')
+    except IOError, err:
+        if err.errno != errno.ENOENT:
+            raise
+        return None
+    try:
+        versionblob = f.read(4)
+        if len(versionblob) < 4:
+            repo.ui.debug('ignoring corrupted evolvestte (file contains %i bits)'
+                          % len(versionblob))
+            return None
+        version = _unpack('>I', versionblob)[0]
+        if version != evolvestateversion:
+            raise error.Abort(_('unknown evolvestate version %i')
+                                % version, hint=_('upgrade your evolve'))
+        records = []
+        data = f.read()
+        off = 0
+        end = len(data)
+        while off < end:
+            rtype = data[off]
+            off += 1
+            length = _unpack('>I', data[off:(off + 4)])[0]
+            off += 4
+            record = data[off:(off + length)]
+            off += length
+            if rtype == 't':
+                rtype, record = record[0], record[1:]
+            records.append((rtype, record))
+        state = {}
+        for rtype, rdata in records:
+            if rtype == 'C':
+                state['current'] = rdata
+            elif rtype.lower():
+                repo.ui.debug('ignore evolve state record type %s' % rtype)
+            else:
+                raise error.Abort(_('unknown evolvestate field type %r')
+                                  % rtype, hint=_('upgrade your evolve'))
+        return state
+    finally:
+        f.close()
+
+def _evolvestatedelete(repo):
+    util.unlinkpath(repo.join('evolvestate'), ignoremissing=True)
+
 def _evolvemerge(repo, orig, dest, pctx, keepbranch):
     """Used by the evolve function to merge dest on top of pctx.
     return the same tuple as merge.graft"""