manifest: proxy to revlog instance instead of inheriting

Previously, manifestrevlog inherited revlog.revlog and therefore
exposed all its APIs. This inevitably resulted in consumers calling
low-level revlog APIs.

As part of abstracting storage, we want to formalize the interface
for manifest storage. The revlog API is much too large to define as
the interface.

Like we did for filelog, this commit divorces the manifest class
from revlog so that we can standardize on a smaller API surface.

The way I went about this commit was I broke the inheritance, ran
tests, and added proxies until all tests passed. Like filelog, there
are a handful of attributes that don't belong on the interface.
And like filelog, we'll tease these out in the future.

As part of this, we formalize an interface for manifest storage and
add checks that manifestrevlog conforms to the interface.

Adding proxies will introduce some overhead due to extra attribute
lookups and function calls. On the mozilla-unified repository:

$ hg verify
before: real 627.220 secs (user 525.870+0.000 sys 18.800+0.000)
after:  real 628.930 secs (user 532.050+0.000 sys 18.320+0.000)

$ hg serve (for a clone)
before: user 223.580+0.000 sys 14.270+0.000
after:  user 227.720+0.000 sys 13.920+0.000

$ hg clone
before: user 506.390+0.000 sys 29.720+0.000
after:  user 513.080+0.000 sys 28.280+0.000

There appears to be some overhead here. But it appears to be 1-2%.
I think that is an appropriate price to pay for storage abstraction,
which will eventually let us have much nicer things. If the overhead
is noticed in other operations (whose CPU time isn't likely dwarfed by
fulltext resolution) or if we want to cut down on the overhead, we
could dynamically build up a type whose methods are effectively
aliased to a revlog instance's. I'm inclined to punt on that problem
for now. We may have to do it for the changelog. At which point it
could be implemented in a generic way and ported to filelog and
manifestrevlog easily enough I would think.

.. api:: manifest.manifestrevlog no longer inherits from revlog

   The manifestrevlog class now wraps a revlog instance instead of
   inheriting from revlog. Various attributes and methods on instances
   are no longer available.

Differential Revision: https://phab.mercurial-scm.org/D4386

mercurial/manifest.py

@@ -1246,7 +1246,8 b' class manifestfulltextcache(util.lrucach'
             self.write()
         self._read = False
 
-class manifestrevlog(revlog.revlog):
[e-mail](repository.imanifeststorage)
+class manifestrevlog(object):
     '''A revlog that stores manifest texts. This is responsible for caching the
     full-text manifest contents.
     '''
@@ -1291,10 +1292,14 b' class manifestrevlog(revlog.revlog):'
         else:
             self._dirlogcache = {'': self}
 
-        super(manifestrevlog, self).__init__(opener, indexfile,
-                                             # only root indexfile is cached
-                                             checkambig=not bool(tree),
-                                             mmaplargeindex=True)
+        self._revlog = revlog.revlog(opener, indexfile,
+                                     # only root indexfile is cached
+                                     checkambig=not bool(tree),
+                                     mmaplargeindex=True)
+
+        self.index = self._revlog.index
+        self.version = self._revlog.version
+        self._generaldelta = self._revlog._generaldelta
 
     def _setupmanifestcachehooks(self, repo):
         """Persist the manifestfulltextcache on lock release"""
@@ -1323,7 +1328,7 b' class manifestrevlog(revlog.revlog):'
         return self._fulltextcache
 
     def clearcaches(self, clear_persisted_data=False):
-        super(manifestrevlog, self).clearcaches()
+        self._revlog.clearcaches()
         self._fulltextcache.clear(clear_persisted_data=clear_persisted_data)
         self._dirlogcache = {self._tree: self}
 
@@ -1350,9 +1355,10 b' class manifestrevlog(revlog.revlog):'
                                [(x, True) for x in removed])
 
             arraytext, deltatext = m.fastdelta(self.fulltextcache[p1], work)
-            cachedelta = self.rev(p1), deltatext
+            cachedelta = self._revlog.rev(p1), deltatext
             text = util.buffer(arraytext)
-            n = self.addrevision(text, transaction, link, p1, p2, cachedelta)
+            n = self._revlog.addrevision(text, transaction, link, p1, p2,
+                                         cachedelta)
         else:
             # The first parent manifest isn't already loaded, so we'll
             # just encode a fulltext of the manifest and pass that
@@ -1366,7 +1372,7 b' class manifestrevlog(revlog.revlog):'
                 arraytext = None
             else:
                 text = m.text()
-                n = self.addrevision(text, transaction, link, p1, p2)
+                n = self._revlog.addrevision(text, transaction, link, p1, p2)
                 arraytext = bytearray(text)
 
         if arraytext is not None:
@@ -1395,12 +1401,90 b' class manifestrevlog(revlog.revlog):'
                 n = m2.node()
 
         if not n:
-            n = self.addrevision(text, transaction, link, m1.node(), m2.node())
+            n = self._revlog.addrevision(text, transaction, link, m1.node(),
+                                         m2.node())
 
         # Save nodeid so parent manifest can calculate its nodeid
         m.setnode(n)
         return n
 
+    def __len__(self):
+        return len(self._revlog)
+
+    def __iter__(self):
+        return self._revlog.__iter__()
+
+    def rev(self, node):
+        return self._revlog.rev(node)
+
+    def node(self, rev):
+        return self._revlog.node(rev)
+
+    def lookup(self, value):
+        return self._revlog.lookup(value)
+
+    def parentrevs(self, rev):
+        return self._revlog.parentrevs(rev)
+
+    def parents(self, node):
+        return self._revlog.parents(node)
+
+    def linkrev(self, rev):
+        return self._revlog.linkrev(rev)
+
+    def checksize(self):
+        return self._revlog.checksize()
+
+    def revision(self, node, _df=None, raw=False):
+        return self._revlog.revision(node, _df=_df, raw=raw)
+
+    def revdiff(self, rev1, rev2):
+        return self._revlog.revdiff(rev1, rev2)
+
+    def cmp(self, node, text):
+        return self._revlog.cmp(node, text)
+
+    def deltaparent(self, rev):
+        return self._revlog.deltaparent(rev)
+
+    def emitrevisiondeltas(self, requests):
+        return self._revlog.emitrevisiondeltas(requests)
+
+    def addgroup(self, deltas, linkmapper, transaction, addrevisioncb=None):
+        return self._revlog.addgroup(deltas, linkmapper, transaction,
+                                     addrevisioncb=addrevisioncb)
+
+    def getstrippoint(self, minlink):
+        return self._revlog.getstrippoint(minlink)
+
+    def strip(self, minlink, transaction):
+        return self._revlog.strip(minlink, transaction)
+
+    def files(self):
+        return self._revlog.files()
+
+    def clone(self, tr, destrevlog, **kwargs):
+        if not isinstance(destrevlog, manifestrevlog):
+            raise error.ProgrammingError('expected manifestrevlog to clone()')
+
+        return self._revlog.clone(tr, destrevlog._revlog, **kwargs)
+
+    @property
+    def indexfile(self):
+        return self._revlog.indexfile
+
+    @indexfile.setter
+    def indexfile(self, value):
+        self._revlog.indexfile = value
+
+    @property
+    def opener(self):
+        return self._revlog.opener
+
+    @opener.setter
+    def opener(self, value):
+        self._revlog.opener = value
+
 @interfaceutil.implementer(repository.imanifestlog)
 class manifestlog(object):
     """A collection class representing the collection of manifest snapshots

mercurial/repository.py

@@ -988,6 +988,166 b' class imanifestrevisionwritable(imanifes'
         Returns the binary node of the created revision.
         """
 
+class imanifeststorage(interfaceutil.Interface):
+    """Storage interface for manifest data."""
+
+    index = interfaceutil.Attribute(
+        """An ``ifilerevisionssequence`` instance.""")
+
+    indexfile = interfaceutil.Attribute(
+        """Path of revlog index file.
+
+        TODO this is revlog specific and should not be exposed.
+        """)
+
+    opener = interfaceutil.Attribute(
+        """VFS opener to use to access underlying files used for storage.
+
+        TODO this is revlog specific and should not be exposed.
+        """)
+
+    version = interfaceutil.Attribute(
+        """Revlog version number.
+
+        TODO this is revlog specific and should not be exposed.
+        """)
+
+    _generaldelta = interfaceutil.Attribute(
+        """Whether generaldelta storage is being used.
+
+        TODO this is revlog specific and should not be exposed.
+        """)
+
+    fulltextcache = interfaceutil.Attribute(
+        """Dict with cache of fulltexts.
+
+        TODO this doesn't feel appropriate for the storage interface.
+        """)
+
+    def __len__():
+        """Obtain the number of revisions stored for this manifest."""
+
+    def __iter__():
+        """Iterate over revision numbers for this manifest."""
+
+    def rev(node):
+        """Obtain the revision number given a binary node.
+
+        Raises ``error.LookupError`` if the node is not known.
+        """
+
+    def node(rev):
+        """Obtain the node value given a revision number.
+
+        Raises ``error.LookupError`` if the revision is not known.
+        """
+
+    def lookup(value):
+        """Attempt to resolve a value to a node.
+
+        Value can be a binary node, hex node, revision number, or a bytes
+        that can be converted to an integer.
+
+        Raises ``error.LookupError`` if a ndoe could not be resolved.
+
+        TODO this is only used by debug* commands and can probably be deleted
+        easily.
+        """
+
+    def parents(node):
+        """Returns a 2-tuple of parent nodes for a node.
+
+        Values will be ``nullid`` if the parent is empty.
+        """
+
+    def parentrevs(rev):
+        """Like parents() but operates on revision numbers."""
+
+    def linkrev(rev):
+        """Obtain the changeset revision number a revision is linked to."""
+
+    def revision(node, _df=None, raw=False):
+        """Obtain fulltext data for a node."""
+
+    def revdiff(rev1, rev2):
+        """Obtain a delta between two revision numbers.
+
+        The returned data is the result of ``bdiff.bdiff()`` on the raw
+        revision data.
+        """
+
+    def cmp(node, fulltext):
+        """Compare fulltext to another revision.
+
+        Returns True if the fulltext is different from what is stored.
+        """
+
+    def emitrevisiondeltas(requests):
+        """Produce ``irevisiondelta`` from ``irevisiondeltarequest``s.
+
+        See the documentation for ``ifiledata`` for more.
+        """
+
+    def addgroup(deltas, linkmapper, transaction, addrevisioncb=None):
+        """Process a series of deltas for storage.
+
+        See the documentation in ``ifilemutation`` for more.
+        """
+
+    def getstrippoint(minlink):
+        """Find minimum revision that must be stripped to strip a linkrev.
+
+        See the documentation in ``ifilemutation`` for more.
+        """
+
+    def strip(minlink, transaction):
+        """Remove storage of items starting at a linkrev.
+
+        See the documentation in ``ifilemutation`` for more.
+        """
+
+    def checksize():
+        """Obtain the expected sizes of backing files.
+
+        TODO this is used by verify and it should not be part of the interface.
+        """
+
+    def files():
+        """Obtain paths that are backing storage for this manifest.
+
+        TODO this is used by verify and there should probably be a better API
+        for this functionality.
+        """
+
+    def deltaparent(rev):
+        """Obtain the revision that a revision is delta'd against.
+
+        TODO delta encoding is an implementation detail of storage and should
+        not be exposed to the storage interface.
+        """
+
+    def clone(tr, dest, **kwargs):
+        """Clone this instance to another."""
+
+    def clearcaches(clear_persisted_data=False):
+        """Clear any caches associated with this instance."""
+
+    def dirlog(d):
+        """Obtain a manifest storage instance for a tree."""
+
+    def add(m, transaction, link, p1, p2, added, removed, readtree=None):
+        """Add a revision to storage.
+
+        ``m`` is an object conforming to ``imanifestdict``.
+
+        ``link`` is the linkrev revision number.
+
+        ``p1`` and ``p2`` are the parent revision numbers.
+
+        ``added`` and ``removed`` are iterables of added and removed paths,
+        respectively.
+        """
+
 class imanifestlog(interfaceutil.Interface):
     """Interface representing a collection of manifest snapshots.
 

tests/test-check-interfaces.py

@@ -177,6 +177,7 b' def main():'
     ziverify.verifyClass(repository.imanifestrevisionwritable,
                          manifest.memtreemanifestctx)
     ziverify.verifyClass(repository.imanifestlog, manifest.manifestlog)
+    ziverify.verifyClass(repository.imanifeststorage, manifest.manifestrevlog)
 
     vfs = vfsmod.vfs(b'.')
     fl = filelog.filelog(vfs, b'dummy.i')
@@ -198,6 +199,9 b' def main():'
     # Conforms to imanifestdict.
     checkzobject(mctx.read())
 
+    mrl = manifest.manifestrevlog(vfs)
+    checkzobject(mrl)
+
     ziverify.verifyClass(repository.irevisiondelta,
                          revlog.revlogrevisiondelta)
     ziverify.verifyClass(repository.irevisiondeltarequest,