remote-hg: use notes to keep track of Hg revisions

Keep track of Mercurial revisions as Git notes under the 'refs/notes/hg'
ref.  This way, the user can easily see which Mercurial revision
corresponds to certain Git commit.

Unfortunately, there's no way to efficiently update the notes after
doing an export (push), so they'll have to be updated when importing
(fetching).

Signed-off-by: Felipe Contreras <felipe.contreras@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

contrib/remote-helpers/git-remote-hg

@@ -23,7 +23,11 @@ import subprocess
 import urllib
 import atexit
 import urlparse, hashlib
+import time as ptime
 
+#
+# If you want to see Mercurial revisions as Git commit notes:
+# git config core.notesRef refs/notes/hg
 #
 # If you are not in hg-git-compat mode and want to disable the tracking of
 # named branches:
@@ -126,6 +130,7 @@ class Marks:
         self.rev_marks = {}
         self.last_mark = 0
         self.version = 0
+        self.last_note = 0
 
     def load(self):
         if not os.path.exists(self.path):
@@ -137,6 +142,7 @@ class Marks:
         self.marks = tmp['marks']
         self.last_mark = tmp['last-mark']
         self.version = tmp.get('version', 1)
+        self.last_note = tmp.get('last-note', 0)
 
         for rev, mark in self.marks.iteritems():
             self.rev_marks[mark] = rev
@@ -150,7 +156,7 @@ class Marks:
         self.version = 2
 
     def dict(self):
-        return { 'tips': self.tips, 'marks': self.marks, 'last-mark' : self.last_mark, 'version' : self.version }
+        return { 'tips': self.tips, 'marks': self.marks, 'last-mark' : self.last_mark, 'version' : self.version, 'last-note' : self.last_note }
 
     def store(self):
         json.dump(self.dict(), open(self.path, 'w'))
@@ -512,6 +518,31 @@ def export_ref(repo, name, kind, head):
     print "from :%u" % rev_to_mark(head)
     print
 
+    pending_revs = set(revs) - notes
+    if pending_revs:
+        note_mark = marks.next_mark()
+        ref = "refs/notes/hg"
+
+        print "commit %s" % ref
+        print "mark :%d" % (note_mark)
+        print "committer remote-hg <> %s" % (ptime.strftime('%s %z'))
+        desc = "Notes for %s\n" % (name)
+        print "data %d" % (len(desc))
+        print desc
+        if marks.last_note:
+            print "from :%u" % marks.last_note
+
+        for rev in pending_revs:
+            notes.add(rev)
+            c = repo[rev]
+            print "N inline :%u" % rev_to_mark(c)
+            msg = c.hex()
+            print "data %d" % (len(msg))
+            print msg
+        print
+
+        marks.last_note = note_mark
+
     marks.set_tip(ename, head.hex())
 
 def export_tag(repo, tag):
@@ -1113,6 +1144,7 @@ def main(args):
     global filenodes
     global fake_bmark, hg_version
     global dry_run
+    global notes, alias
 
     alias = args[1]
     url = args[2]
@@ -1152,6 +1184,7 @@ def main(args):
     except:
         hg_version = None
     dry_run = False
+    notes = set()
 
     repo = get_repo(url, alias)
     prefix = 'refs/hg/%s' % alias