revlog: add a way to control sidedata changes during revlog.clone

We introduce a new argument to pass a callable dealing with the side data logic.
Since the side data are usually associated to higher level logic, the revlog
code itself is unlikely to know that to do itself. As a result the higher level
upgrade code will be responsible to decide what needs to changes. The lower
level revlog.clone just get simple instructions to apply.

Differential Revision: https://phab.mercurial-scm.org/D6941

mercurial/revlog.py

@@ -2542,6 +2542,7 b' class revlog(object):'
         addrevisioncb=None,
         deltareuse=DELTAREUSESAMEREVS,
         forcedeltabothparents=None,
+        sidedatacompanion=None,
     ):
         """Copy this revlog to another, possibly with format changes.
 
@@ -2583,6 +2584,20 b' class revlog(object):'
         In addition to the delta policy, the ``forcedeltabothparents``
         argument controls whether to force compute deltas against both parents
         for merges. By default, the current default is used.
+
+        If not None, the `sidedatacompanion` is callable that accept two
+        arguments:
+
+            (srcrevlog, rev)
+
+        and return a triplet that control changes to sidedata content from the
+        old revision to the new clone result:
+
+            (dropall, filterout, update)
+
+        * if `dropall` is True, all sidedata should be dropped
+        * `filterout` is a set of sidedata keys that should be dropped
+        * `update` is a mapping of additionnal/new key -> value
         """
         if deltareuse not in self.DELTAREUSEALL:
             raise ValueError(
@@ -2617,7 +2632,12 b' class revlog(object):'
             destrevlog._deltabothparents = forcedeltabothparents or oldamd
 
             self._clone(
-                tr, destrevlog, addrevisioncb, deltareuse, forcedeltabothparents
+                tr,
+                destrevlog,
+                addrevisioncb,
+                deltareuse,
+                forcedeltabothparents,
+                sidedatacompanion,
             )
 
         finally:
@@ -2626,7 +2646,13 b' class revlog(object):'
             destrevlog._deltabothparents = oldamd
 
     def _clone(
-        self, tr, destrevlog, addrevisioncb, deltareuse, forcedeltabothparents
+        self,
+        tr,
+        destrevlog,
+        addrevisioncb,
+        deltareuse,
+        forcedeltabothparents,
+        sidedatacompanion,
     ):
         """perform the core duty of `revlog.clone` after parameter processing"""
         deltacomputer = deltautil.deltacomputer(destrevlog)
@@ -2642,12 +2668,24 b' class revlog(object):'
             p2 = index[entry[6]][7]
             node = entry[7]
 
+            sidedataactions = (False, [], {})
+            if sidedatacompanion is not None:
+                sidedataactions = sidedatacompanion(self, rev)
+
             # (Possibly) reuse the delta from the revlog if allowed and
             # the revlog chunk is a delta.
             cachedelta = None
             rawtext = None
-            if deltareuse == self.DELTAREUSEFULLADD:
-                text = self.revision(rev)
+            if any(sidedataactions) or deltareuse == self.DELTAREUSEFULLADD:
+                dropall, filterout, update = sidedataactions
+                text, sidedata = self._revisiondata(rev)
+                if dropall:
+                    sidedata = {}
+                for key in filterout:
+                    sidedata.pop(key, None)
+                sidedata.update(update)
+                if not sidedata:
+                    sidedata = None
                 destrevlog.addrevision(
                     text,
                     tr,
@@ -2658,6 +2696,7 b' class revlog(object):'
                     node=node,
                     flags=flags,
                     deltacomputer=deltacomputer,
+                    sidedata=sidedata,
                 )
             else:
                 if destrevlog._lazydelta: