repository: establish API for emitting revision deltas

With our revision delta and revision delta request interfaces
defined, it is now time to define a method on storage interfaces
for using them.

So far, the only storage interface that is well-defined and used
is file storage. So that is the only interface we need to add a
method on.

We define an ``emitrevisiondeltas()`` method that takes an
iterable of ``irevisiondeltarequest``s and turns them into
``irevisiondelta`` instances.

changegroup._handlerevisiondeltarequest() and the looping logic
from changegroup.deltagroup() has effectively been moved to
revlog.emitrevisiondeltas().

Our filelog wrapper class proxies its emitrevisiondeltas() to
the internal revlog instance.

The simple store test extension used to verify sanity of storage
abstractions has also implemented emitrevisiondeltas() for
file storage and the test harness when run with this extension doesn't
seem to exhibit any regressions.

Rather than create a shared type to represent revision deltas,
each storage backend has its own type and the class name identifies
where the revision delta was derived from.

Differential Revision: https://phab.mercurial-scm.org/D4226

mercurial/changegroup.py

@@ -31,7 +31,6 b' from . import ('
     phases,
     pycompat,
     repository,
-    revlog,
     util,
 )
 
@@ -512,19 +511,6 b' class revisiondeltarequest(object):'
     basenode = attr.ib()
     ellipsis = attr.ib(default=False)
 
[e-mail](repository.irevisiondelta)
-@attr.s(slots=True, frozen=True)
-class revisiondelta(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()
-
 def _revisiondeltatochunks(delta, headerfn):
     """Serialize a revisiondelta to changegroup chunks."""
 
@@ -583,77 +569,6 b' def _sortnodesellipsis(store, nodes, cl,'
     key = lambda n: cl.rev(lookup(n))
     return [store.rev(n) for n in sorted(nodes, key=key)]
 
-def _handlerevisiondeltarequest(store, request, prevnode):
-    """Obtain a revisiondelta from a revisiondeltarequest"""
-
-    node = request.node
-    rev = store.rev(node)
-
-    # Requesting a full revision.
-    if request.basenode == nullid:
-        baserev = nullrev
-    # Requesting an explicit revision.
-    elif request.basenode is not None:
-        baserev = store.rev(request.basenode)
-    # Allowing us to choose.
-    else:
-        p1, p2 = store.parentrevs(rev)
-        dp = store.deltaparent(rev)
-
-        if dp == nullrev and store.storedeltachains:
-            # Avoid sending full revisions when delta parent is null. Pick prev
-            # in that case. It's tempting to pick p1 in this case, as p1 will
-            # be smaller in the common case. However, computing a delta against
-            # p1 may require resolving the raw text of p1, which could be
-            # expensive. The revlog caches should have prev cached, meaning
-            # less CPU for changegroup generation. There is likely room to add
-            # a flag and/or config option to control this behavior.
-            baserev = store.rev(prevnode)
-        elif dp == nullrev:
-            # revlog is configured to use full snapshot for a reason,
-            # stick to full snapshot.
-            baserev = nullrev
-        elif dp not in (p1, p2, store.rev(prevnode)):
-            # Pick prev when we can't be sure remote has the base revision.
-            baserev = store.rev(prevnode)
-        else:
-            baserev = dp
-
-        if baserev != nullrev and not store.candelta(baserev, rev):
-            baserev = nullrev
-
-    revision = None
-    delta = None
-    baserevisionsize = None
-
-    if store.iscensored(baserev) or store.iscensored(rev):
-        try:
-            revision = store.revision(node, raw=True)
-        except error.CensoredNodeError as e:
-            revision = e.tombstone
-
-        if baserev != nullrev:
-            baserevisionsize = store.rawsize(baserev)
-
-    elif baserev == nullrev:
-        revision = store.revision(node, raw=True)
-    else:
-        delta = store.revdiff(baserev, rev)
-
-    extraflags = revlog.REVIDX_ELLIPSIS if request.ellipsis else 0
-
-    return revisiondelta(
-        node=node,
-        p1node=request.p1node,
-        p2node=request.p2node,
-        linknode=request.linknode,
-        basenode=store.node(baserev),
-        flags=store.flags(rev) | extraflags,
-        baserevisionsize=baserevisionsize,
-        revision=revision,
-        delta=delta,
-    )
-
 def _makenarrowdeltarequest(cl, store, ischangelog, rev, node, linkrev,
                             linknode, clrevtolocalrev, fullclnodes,
                             precomputedellipsis):
@@ -832,17 +747,12 b' def deltagroup(repo, store, nodes, ischa'
         progress = repo.ui.makeprogress(_('bundling'), unit=units,
                                         total=len(requests))
 
-    prevnode = store.node(revs[0])
-    for i, request in enumerate(requests):
+    for i, delta in enumerate(store.emitrevisiondeltas(requests)):
         if progress:
             progress.update(i + 1)
 
-        delta = _handlerevisiondeltarequest(store, request, prevnode)
-
         yield delta
 
-        prevnode = request.node
-
     if progress:
         progress.complete()
 

mercurial/filelog.py

@@ -95,6 +95,9 b' class filelog(object):'
     def revdiff(self, rev1, rev2):
         return self._revlog.revdiff(rev1, rev2)
 
+    def emitrevisiondeltas(self, requests):
+        return self._revlog.emitrevisiondeltas(requests)
+
     def addrevision(self, revisiondata, transaction, linkrev, p1, p2,
                     node=None, flags=revlog.REVIDX_DEFAULT_FLAGS,
                     cachedelta=None):

mercurial/repository.py

@@ -621,6 +621,30 b' class ifiledata(interfaceutil.Interface)'
         revision data.
         """
 
+    def emitrevisiondeltas(requests):
+        """Produce ``irevisiondelta`` from ``irevisiondeltarequest``s.
+
+        Given an iterable of objects conforming to the ``irevisiondeltarequest``
+        interface, emits objects conforming to the ``irevisiondelta``
+        interface.
+
+        This method is a generator.
+
+        ``irevisiondelta`` should be emitted in the same order of
+        ``irevisiondeltarequest`` that was passed in.
+
+        The emitted objects MUST conform by the results of
+        ``irevisiondeltarequest``. Namely, they must respect any requests
+        for building a delta from a specific ``basenode`` if defined.
+
+        When sending deltas, implementations must take into account whether
+        the client has the base delta before encoding a delta against that
+        revision. A revision encountered previously in ``requests`` is
+        always a suitable base revision. An example of a bad delta is a delta
+        against a non-ancestor revision. Another example of a bad delta is a
+        delta against a censored revision.
+        """
+
 class ifilemutation(interfaceutil.Interface):
     """Storage interface for mutation events of a tracked file."""
 

mercurial/revlog.py

@@ -45,10 +45,12 b' from . import ('
     mdiff,
     policy,
     pycompat,
+    repository,
     templatefilters,
     util,
 )
 from .utils import (
+    interfaceutil,
     stringutil,
 )
 
@@ -821,6 +823,19 b' class _revisioninfo(object):'
     cachedelta = attr.ib()
     flags = attr.ib()
 
[e-mail](repository.irevisiondelta)
+@attr.s(slots=True, frozen=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()
+
 # index v0:
 #  4 bytes: offset
 #  4 bytes: compressed length
@@ -2950,6 +2965,87 b' class revlog(object):'
             res.append(self.datafile)
         return res
 
+    def emitrevisiondeltas(self, requests):
+        frev = self.rev
+
+        prevrev = None
+        for request in requests:
+            node = request.node
+            rev = frev(node)
+
+            if prevrev is None:
+                prevrev = self.index[rev][5]
+
+            # Requesting a full revision.
+            if request.basenode == nullid:
+                baserev = nullrev
+            # Requesting an explicit revision.
+            elif request.basenode is not None:
+                baserev = frev(request.basenode)
+            # Allowing us to choose.
+            else:
+                p1rev, p2rev = self.parentrevs(rev)
+                deltaparentrev = self.deltaparent(rev)
+
+                # Avoid sending full revisions when delta parent is null. Pick
+                # prev in that case. It's tempting to pick p1 in this case, as
+                # p1 will be smaller in the common case. However, computing a
+                # delta against p1 may require resolving the raw text of p1,
+                # which could be expensive. The revlog caches should have prev
+                # cached, meaning less CPU for delta generation. There is
+                # likely room to add a flag and/or config option to control this
+                # behavior.
+                if deltaparentrev == nullrev and self.storedeltachains:
+                    baserev = prevrev
+
+                # Revlog is configured to use full snapshot for a reason.
+                # Stick to full snapshot.
+                elif deltaparentrev == nullrev:
+                    baserev = nullrev
+
+                # Pick previous when we can't be sure the base is available
+                # on consumer.
+                elif deltaparentrev not in (p1rev, p2rev, prevrev):
+                    baserev = prevrev
+                else:
+                    baserev = deltaparentrev
+
+                if baserev != nullrev and not self.candelta(baserev, rev):
+                    baserev = nullrev
+
+            revision = None
+            delta = None
+            baserevisionsize = None
+
+            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:
+                revision = self.revision(node, raw=True)
+            else:
+                delta = self.revdiff(baserev, rev)
+
+            extraflags = REVIDX_ELLIPSIS if request.ellipsis else 0
+
+            yield revlogrevisiondelta(
+                node=node,
+                p1node=request.p1node,
+                p2node=request.p2node,
+                linknode=request.linknode,
+                basenode=self.node(baserev),
+                flags=self.flags(rev) | extraflags,
+                baserevisionsize=baserevisionsize,
+                revision=revision,
+                delta=delta)
+
+            prevrev = rev
+
     DELTAREUSEALWAYS = 'always'
     DELTAREUSESAMEREVS = 'samerevs'
     DELTAREUSENEVER = 'never'

tests/simplestorerepo.py

@@ -22,6 +22,7 b' from mercurial.node import ('
     nullrev,
 )
 from mercurial.thirdparty import (
+    attr,
     cbor,
 )
 from mercurial import (
@@ -60,6 +61,19 b' def validaterev(rev):'
     if not isinstance(rev, int):
         raise ValueError('expected int')
 
[e-mail](repository.irevisiondelta)
+@attr.s(slots=True, frozen=True)
+class simplestorerevisiondelta(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()
+
 @interfaceutil.implementer(repository.ifilestorage)
 class filestorage(object):
     """Implements storage for a tracked path.
@@ -500,6 +514,54 b' class filestorage(object):'
         return mdiff.textdiff(self.revision(node1, raw=True),
                               self.revision(node2, raw=True))
 
+    def emitrevisiondeltas(self, requests):
+        for request in requests:
+            node = request.node
+            rev = self.rev(node)
+
+            if request.basenode == nullid:
+                baserev = nullrev
+            elif request.basenode is not None:
+                baserev = self.rev(request.basenode)
+            else:
+                # This is a test extension and we can do simple things
+                # for choosing a delta parent.
+                baserev = self.deltaparent(rev)
+
+                if baserev != nullrev and not self.candelta(baserev, rev):
+                    baserev = nullrev
+
+            revision = None
+            delta = None
+            baserevisionsize = None
+
+            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:
+                revision = self.revision(node, raw=True)
+            else:
+                delta = self.revdiff(baserev, rev)
+
+            extraflags = revlog.REVIDX_ELLIPSIS if request.ellipsis else 0
+
+            yield simplestorerevisiondelta(
+                node=node,
+                p1node=request.p1node,
+                p2node=request.p2node,
+                linknode=request.linknode,
+                basenode=self.node(baserev),
+                flags=self.flags(rev) | extraflags,
+                baserevisionsize=baserevisionsize,
+                revision=revision,
+                delta=delta)
+
     def headrevs(self):
         # Assume all revisions are heads by default.
         revishead = {rev: True for rev in self._indexbyrev}

tests/test-check-interfaces.py

@@ -29,6 +29,7 b' from mercurial import ('
     manifest,
     pycompat,
     repository,
+    revlog,
     sshpeer,
     statichttprepo,
     ui as uimod,
@@ -198,11 +199,11 b' def main():'
     checkzobject(mctx.read())
 
     ziverify.verifyClass(repository.irevisiondelta,
-                         changegroup.revisiondelta)
+                         revlog.revlogrevisiondelta)
     ziverify.verifyClass(repository.irevisiondeltarequest,
                          changegroup.revisiondeltarequest)
 
-    rd = changegroup.revisiondelta(
+    rd = revlog.revlogrevisiondelta(
         node=b'',
         p1node=b'',
         p2node=b'',