--- a/mercurial/revlog.py	Mon Sep 24 09:41:42 2018 -0700
+++ b/mercurial/revlog.py	Fri Sep 21 14:28:21 2018 -0700
@@ -59,6 +59,7 @@
 )
 from . import (
     ancestor,
+    dagop,
     error,
     mdiff,
     policy,
@@ -242,17 +243,17 @@
     flags = attr.ib()
 
 @interfaceutil.implementer(repository.irevisiondelta)
-@attr.s(slots=True, frozen=True)
+@attr.s(slots=True)
 class revlogrevisiondelta(object):
     node = attr.ib()
     p1node = attr.ib()
     p2node = attr.ib()
     basenode = attr.ib()
-    linknode = attr.ib()
     flags = attr.ib()
     baserevisionsize = attr.ib()
     revision = attr.ib()
     delta = attr.ib()
+    linknode = attr.ib(default=None)
 
 @interfaceutil.implementer(repository.iverifyproblem)
 @attr.s(frozen=True)
@@ -2374,6 +2375,122 @@
 
             prevrev = rev
 
+    def emitrevisions(self, nodes, nodesorder=None, revisiondata=False,
+                      assumehaveparentrevisions=False, deltaprevious=False):
+        if nodesorder not in ('nodes', 'storage', None):
+            raise error.ProgrammingError('unhandled value for nodesorder: %s' %
+                                         nodesorder)
+
+        if nodesorder is None and not self._generaldelta:
+            nodesorder = 'storage'
+
+        frev = self.rev
+        fnode = self.node
+
+        if nodesorder == 'nodes':
+            revs = [frev(n) for n in nodes]
+        elif nodesorder == 'storage':
+            revs = sorted(frev(n) for n in nodes)
+        else:
+            assert self._generaldelta
+            revs = set(frev(n) for n in nodes)
+            revs = dagop.linearize(revs, self.parentrevs)
+
+        prevrev = None
+
+        if deltaprevious or assumehaveparentrevisions:
+            prevrev = self.parentrevs(revs[0])[0]
+
+        # Set of revs available to delta against.
+        available = set()
+
+        for rev in revs:
+            if rev == nullrev:
+                continue
+
+            node = fnode(rev)
+            deltaparentrev = self.deltaparent(rev)
+            p1rev, p2rev = self.parentrevs(rev)
+
+            # Forced delta against previous mode.
+            if deltaprevious:
+                baserev = prevrev
+
+            # Revlog is configured to use full snapshots. Stick to that.
+            elif not self._storedeltachains:
+                baserev = nullrev
+
+            # There is a delta in storage. We try to use that because it
+            # amounts to effectively copying data from storage and is
+            # therefore the fastest.
+            elif deltaparentrev != nullrev:
+                # Base revision was already emitted in this group. We can
+                # always safely use the delta.
+                if deltaparentrev in available:
+                    baserev = deltaparentrev
+
+                # Base revision is a parent that hasn't been emitted already.
+                # Use it if we can assume the receiver has the parent revision.
+                elif (assumehaveparentrevisions
+                      and deltaparentrev in (p1rev, p2rev)):
+                    baserev = deltaparentrev
+
+                # No guarantee the receiver has the delta parent. Send delta
+                # against last revision (if possible), which in the common case
+                # should be similar enough to this revision that the delta is
+                # reasonable.
+                elif prevrev is not None:
+                    baserev = prevrev
+                else:
+                    baserev = nullrev
+
+            # Storage has a fulltext revision.
+
+            # Let's use the previous revision, which is as good a guess as any.
+            # There is definitely room to improve this logic.
+            elif prevrev is not None:
+                baserev = prevrev
+            else:
+                baserev = nullrev
+
+            # But we can't actually use our chosen delta base for whatever
+            # reason. Reset to fulltext.
+            if baserev != nullrev and not self.candelta(baserev, rev):
+                baserev = nullrev
+
+            revision = None
+            delta = None
+            baserevisionsize = None
+
+            if revisiondata:
+                if self.iscensored(baserev) or self.iscensored(rev):
+                    try:
+                        revision = self.revision(node, raw=True)
+                    except error.CensoredNodeError as e:
+                        revision = e.tombstone
+
+                    if baserev != nullrev:
+                        baserevisionsize = self.rawsize(baserev)
+
+                elif baserev == nullrev and not deltaprevious:
+                    revision = self.revision(node, raw=True)
+                    available.add(rev)
+                else:
+                    delta = self.revdiff(baserev, rev)
+                    available.add(rev)
+
+            yield revlogrevisiondelta(
+                node=node,
+                p1node=fnode(p1rev),
+                p2node=fnode(p2rev),
+                basenode=fnode(baserev),
+                flags=self.flags(rev),
+                baserevisionsize=baserevisionsize,
+                revision=revision,
+                delta=delta)
+
+            prevrev = rev
+
     DELTAREUSEALWAYS = 'always'
     DELTAREUSESAMEREVS = 'samerevs'
     DELTAREUSENEVER = 'never'