tests: add test extension implementing custom filelog storage

In order to better support partial clones, we'll need alternate
repository storage mechanisms that aren't based on revlogs.

Today, the interface for repository storage isn't very well defined.
And there are various layering violations and assumptions made
throughout the code that storage is backed by revlogs.

In order to support alternate storage mechanisms, we'll need to
formally declare and adhere to interfaces for storage. This will
be a long, arduous process.

This commit creates an extension that implements non-revlog storage
for files. It defines a custom type that quacks like the existing
revlog/filelog API but isn't backed by a revlog. The backing storage
is - for simplicity reasons - a CBOR index and per-node files
representing fulltext data.

The localrepository class is modified so file(f) returns instances of
this class instead of filelog instances.

The purpose of this extension is to tease out what the actual filelog
interface is - based on running the test harness - so we can formalize
that interface and then implement a *real* alternate storage backend.

Using `run-tests.py --extra-config-opt` to run the test harness
with this extension enabled yields 83 failures out of 634 ran
tests.

The most common test failures are due to:

* Issues with `hg verify`
* LFS and largefiles (probably flags processing related)
* Narrow.
* Any test touching or inspecting individual filelog paths.
* help and error output that is confused by the presence of an
  extension.
* `hg debug*` commands doing low-level, revlog-y things.

An 88% pass rate is pretty good for an initial implementation if you
ask me!

There is a bit of duplicate code in the new extension. That's by
design: a point of this code is to tease out dependencies on revlog.
That being said, there is opportunity to consolidate code by moving
things out of the revlog API. For example, DAG traversal operations
don't necessarily need to be implemented at the storage level. (Although
for performance reasons they probably do.) Once we have a more
well-defined interface, we could probably define the default
implementations in terms of the base interface, pull those in via
class inheritance, and have implementations override with faster
versions if they so choose. (Or something like that.) But for now,
the duplicate code should be acceptable.

Differential Revision: https://phab.mercurial-scm.org/D3029

tests/simplestorerepo.py

@@ -0,0 +1,589 b''
+# simplestorerepo.py - Extension that swaps in alternate repository storage.
+#
+# Copyright 2018 Gregory Szorc <[e-mail]>
+#
+# This software may be used and distributed according to the terms of the
+# GNU General Public License version 2 or any later version.
+
+from __future__ import absolute_import
+
+from mercurial.i18n import _
+from mercurial.node import (
+    bin,
+    hex,
+    nullid,
+    nullrev,
+)
+from mercurial.thirdparty import (
+    cbor,
+)
+from mercurial import (
+    ancestor,
+    error,
+    filelog,
+    mdiff,
+    pycompat,
+    revlog,
+)
+
+# Note for extension authors: ONLY specify testedwith = 'ships-with-hg-core' for
+# extensions which SHIP WITH MERCURIAL. Non-mainline extensions should
+# be specifying the version(s) of Mercurial they are tested with, or
+# leave the attribute unspecified.
+testedwith = 'ships-with-hg-core'
+
+def validatenode(node):
+    if isinstance(node, int):
+        raise ValueError('expected node; got int')
+
+    if len(node) != 20:
+        raise ValueError('expected 20 byte node')
+
+def validaterev(rev):
+    if not isinstance(rev, int):
+        raise ValueError('expected int')
+
+class filestorage(object):
+    """Implements storage for a tracked path.
+
+    Data is stored in the VFS in a directory corresponding to the tracked
+    path.
+
+    Index data is stored in an ``index`` file using CBOR.
+
+    Fulltext data is stored in files having names of the node.
+    """
+
+    def __init__(self, svfs, path):
+        self._svfs = svfs
+        self._path = path
+
+        self._storepath = b'/'.join([b'data', path])
+        self._indexpath = b'/'.join([self._storepath, b'index'])
+
+        indexdata = self._svfs.tryread(self._indexpath)
+        if indexdata:
+            indexdata = cbor.loads(indexdata)
+
+        self._indexdata = indexdata or []
+        self._indexbynode = {}
+        self._indexbyrev = {}
+        self.index = []
+        self._refreshindex()
+
+        # This is used by changegroup code :/
+        self._generaldelta = True
+        self.storedeltachains = False
+
+        self.version = 1
+
+    def _refreshindex(self):
+        self._indexbynode.clear()
+        self._indexbyrev.clear()
+        self.index = []
+
+        for i, entry in enumerate(self._indexdata):
+            self._indexbynode[entry[b'node']] = entry
+            self._indexbyrev[i] = entry
+
+        self._indexbynode[nullid] = {
+            b'node': nullid,
+            b'p1': nullid,
+            b'p2': nullid,
+            b'linkrev': nullrev,
+            b'flags': 0,
+        }
+
+        self._indexbyrev[nullrev] = {
+            b'node': nullid,
+            b'p1': nullid,
+            b'p2': nullid,
+            b'linkrev': nullrev,
+            b'flags': 0,
+        }
+
+        for i, entry in enumerate(self._indexdata):
+            p1rev, p2rev = self.parentrevs(self.rev(entry[b'node']))
+
+            # start, length, rawsize, chainbase, linkrev, p1, p2, node
+            self.index.append((0, 0, 0, -1, entry[b'linkrev'], p1rev, p2rev,
+                               entry[b'node']))
+
+        self.index.append((0, 0, 0, -1, -1, -1, -1, nullid))
+
+    def __len__(self):
+        return len(self._indexdata)
+
+    def __iter__(self):
+        return iter(range(len(self)))
+
+    def revs(self, start=0, stop=None):
+        step = 1
+        if stop is not None:
+            if start > stop:
+                step = -1
+
+            stop += step
+        else:
+            stop = len(self)
+
+        return range(start, stop, step)
+
+    def parents(self, node):
+        validatenode(node)
+
+        if node not in self._indexbynode:
+            raise KeyError('unknown node')
+
+        entry = self._indexbynode[node]
+
+        return entry[b'p1'], entry[b'p2']
+
+    def parentrevs(self, rev):
+        p1, p2 = self.parents(self._indexbyrev[rev][b'node'])
+        return self.rev(p1), self.rev(p2)
+
+    def rev(self, node):
+        validatenode(node)
+
+        # Will raise KeyError.
+        self._indexbynode[node]
+
+        for rev, entry in self._indexbyrev.items():
+            if entry[b'node'] == node:
+                return rev
+
+        raise error.ProgrammingError('this should not occur')
+
+    def node(self, rev):
+        validaterev(rev)
+
+        return self._indexbyrev[rev][b'node']
+
+    def lookup(self, node):
+        if isinstance(node, int):
+            return self.node(node)
+
+        if len(node) == 20:
+            try:
+                self.rev(node)
+                return node
+            except LookupError:
+                pass
+
+        try:
+            rev = int(node)
+            if '%d' % rev != node:
+                raise ValueError
+
+            if rev < 0:
+                rev = len(self) + rev
+            if rev < 0 or rev >= len(self):
+                raise ValueError
+
+            return self.node(rev)
+        except (ValueError, OverflowError):
+            pass
+
+        if len(node) == 40:
+            try:
+                rawnode = bin(node)
+                self.rev(rawnode)
+                return rawnode
+            except (TypeError, LookupError):
+                pass
+
+        raise LookupError(node, self._path, _('invalid lookup input'))
+
+    def linkrev(self, rev):
+        validaterev(rev)
+
+        return self._indexbyrev[rev][b'linkrev']
+
+    def flags(self, rev):
+        validaterev(rev)
+
+        return self._indexbyrev[rev][b'flags']
+
+    def deltaparent(self, rev):
+        validaterev(rev)
+
+        p1node = self.parents(self.node(rev))[0]
+        return self.rev(p1node)
+
+    def candelta(self, baserev, rev):
+        validaterev(baserev)
+        validaterev(rev)
+
+        if ((self.flags(baserev) & revlog.REVIDX_RAWTEXT_CHANGING_FLAGS)
+            or (self.flags(rev) & revlog.REVIDX_RAWTEXT_CHANGING_FLAGS)):
+            return False
+
+        return True
+
+    def rawsize(self, rev):
+        validaterev(rev)
+        node = self.node(rev)
+        return len(self.revision(node, raw=True))
+
+    def _processflags(self, text, flags, operation, raw=False):
+        if flags == 0:
+            return text, True
+
+        validatehash = True
+        # Depending on the operation (read or write), the order might be
+        # reversed due to non-commutative transforms.
+        orderedflags = revlog.REVIDX_FLAGS_ORDER
+        if operation == 'write':
+            orderedflags = reversed(orderedflags)
+
+        for flag in orderedflags:
+            # If a flagprocessor has been registered for a known flag, apply the
+            # related operation transform and update result tuple.
+            if flag & flags:
+                vhash = True
+
+                if flag not in revlog._flagprocessors:
+                    message = _("missing processor for flag '%#x'") % (flag)
+                    raise revlog.RevlogError(message)
+
+                processor = revlog._flagprocessors[flag]
+                if processor is not None:
+                    readtransform, writetransform, rawtransform = processor
+
+                    if raw:
+                        vhash = rawtransform(self, text)
+                    elif operation == 'read':
+                        text, vhash = readtransform(self, text)
+                    else:  # write operation
+                        text, vhash = writetransform(self, text)
+                validatehash = validatehash and vhash
+
+        return text, validatehash
+
+    def checkhash(self, text, node, p1=None, p2=None, rev=None):
+        if p1 is None and p2 is None:
+            p1, p2 = self.parents(node)
+        if node != revlog.hash(text, p1, p2):
+            raise error.RevlogError(_("integrity check failed on %s") %
+                self._path)
+
+    def revision(self, node, raw=False):
+        validatenode(node)
+
+        if node == nullid:
+            return b''
+
+        self._indexbynode[node]
+
+        rev = self.rev(node)
+        flags = self.flags(rev)
+
+        path = b'/'.join([self._storepath, hex(node)])
+        rawtext = self._svfs.read(path)
+
+        text, validatehash = self._processflags(rawtext, flags, 'read', raw=raw)
+        if validatehash:
+            self.checkhash(text, node, rev=rev)
+
+        return text
+
+    def read(self, node):
+        validatenode(node)
+
+        revision = self.revision(node)
+
+        if not revision.startswith(b'\1\n'):
+            return revision
+
+        start = revision.index(b'\1\n', 2)
+        return revision[start + 2:]
+
+    def renamed(self, node):
+        validatenode(node)
+
+        if self.parents(node)[0] != nullid:
+            return False
+
+        fulltext = self.revision(node)
+        m = filelog.parsemeta(fulltext)[0]
+
+        if m and 'copy' in m:
+            return m['copy'], bin(m['copyrev'])
+
+        return False
+
+    def cmp(self, node, text):
+        validatenode(node)
+
+        t = text
+
+        if text.startswith(b'\1\n'):
+            t = b'\1\n\1\n' + text
+
+        p1, p2 = self.parents(node)
+
+        if revlog.hash(t, p1, p2) == node:
+            return False
+
+        if self.iscensored(self.rev(node)):
+            return text != b''
+
+        if self.renamed(node):
+            t2 = self.read(node)
+            return t2 != text
+
+        return True
+
+    def size(self, rev):
+        validaterev(rev)
+
+        node = self._indexbyrev[rev][b'node']
+
+        if self.renamed(node):
+            return len(self.read(node))
+
+        if self.iscensored(rev):
+            return 0
+
+        return len(self.revision(node))
+
+    def iscensored(self, rev):
+        validaterev(rev)
+
+        return self.flags(rev) & revlog.REVIDX_ISCENSORED
+
+    def commonancestorsheads(self, a, b):
+        validatenode(a)
+        validatenode(b)
+
+        a = self.rev(a)
+        b = self.rev(b)
+
+        ancestors = ancestor.commonancestorsheads(self.parentrevs, a, b)
+        return pycompat.maplist(self.node, ancestors)
+
+    def descendants(self, revs):
+        # This is a copy of revlog.descendants()
+        first = min(revs)
+        if first == nullrev:
+            for i in self:
+                yield i
+            return
+
+        seen = set(revs)
+        for i in self.revs(start=first + 1):
+            for x in self.parentrevs(i):
+                if x != nullrev and x in seen:
+                    seen.add(i)
+                    yield i
+                    break
+
+    # Required by verify.
+    def files(self):
+        entries = self._svfs.listdir(self._storepath)
+
+        # Strip out undo.backup.* files created as part of transaction
+        # recording.
+        entries = [f for f in entries if not f.startswith('undo.backup.')]
+
+        return [b'/'.join((self._storepath, f)) for f in entries]
+
+    # Required by verify.
+    def checksize(self):
+        return 0, 0
+
+    def add(self, text, meta, transaction, linkrev, p1, p2):
+        if meta or text.startswith(b'\1\n'):
+            text = filelog.packmeta(meta, text)
+
+        return self.addrevision(text, transaction, linkrev, p1, p2)
+
+    def addrevision(self, text, transaction, linkrev, p1, p2, node=None,
+                    flags=0):
+        validatenode(p1)
+        validatenode(p2)
+
+        if flags:
+            node = node or revlog.hash(text, p1, p2)
+
+        rawtext, validatehash = self._processflags(text, flags, 'write')
+
+        node = node or revlog.hash(text, p1, p2)
+
+        if node in self._indexbynode:
+            return node
+
+        if validatehash:
+            self.checkhash(rawtext, node, p1=p1, p2=p2)
+
+        path = b'/'.join([self._storepath, hex(node)])
+
+        self._svfs.write(path, text)
+
+        self._indexdata.append({
+            b'node': node,
+            b'p1': p1,
+            b'p2': p2,
+            b'linkrev': linkrev,
+            b'flags': flags,
+        })
+
+        self._reflectindexupdate()
+
+        return node
+
+    def _reflectindexupdate(self):
+        self._refreshindex()
+        self._svfs.write(self._indexpath, cbor.dumps(self._indexdata))
+
+    def addgroup(self, deltas, linkmapper, transaction, addrevisioncb=None):
+        nodes = []
+
+        transaction.addbackup(self._indexpath)
+
+        for node, p1, p2, linknode, deltabase, delta, flags in deltas:
+            linkrev = linkmapper(linknode)
+
+            nodes.append(node)
+
+            if node in self._indexbynode:
+                continue
+
+            # Need to resolve the fulltext from the delta base.
+            if deltabase == nullid:
+                text = mdiff.patch(b'', delta)
+            else:
+                text = mdiff.patch(self.revision(deltabase), delta)
+
+            self.addrevision(text, transaction, linkrev, p1, p2, flags)
+
+            if addrevisioncb:
+                addrevisioncb(self, node)
+
+        return nodes
+
+    def revdiff(self, rev1, rev2):
+        validaterev(rev1)
+        validaterev(rev2)
+
+        node1 = self.node(rev1)
+        node2 = self.node(rev2)
+
+        return mdiff.textdiff(self.revision(node1, raw=True),
+                              self.revision(node2, raw=True))
+
+    def headrevs(self):
+        # Assume all revisions are heads by default.
+        ishead = {rev: True for rev in self._indexbyrev}
+
+        for rev, entry in self._indexbyrev.items():
+            # Unset head flag for all seen parents.
+            ishead[self.rev(entry[b'p1'])] = False
+            ishead[self.rev(entry[b'p2'])] = False
+
+        return [rev for rev, ishead in sorted(ishead.items())
+                if ishead]
+
+    def heads(self, start=None, stop=None):
+        # This is copied from revlog.py.
+        if start is None and stop is None:
+            if not len(self):
+                return [nullid]
+            return [self.node(r) for r in self.headrevs()]
+
+        if start is None:
+            start = nullid
+        if stop is None:
+            stop = []
+        stoprevs = set([self.rev(n) for n in stop])
+        startrev = self.rev(start)
+        reachable = {startrev}
+        heads = {startrev}
+
+        parentrevs = self.parentrevs
+        for r in self.revs(start=startrev + 1):
+            for p in parentrevs(r):
+                if p in reachable:
+                    if r not in stoprevs:
+                        reachable.add(r)
+                    heads.add(r)
+                if p in heads and p not in stoprevs:
+                    heads.remove(p)
+
+        return [self.node(r) for r in heads]
+
+    def children(self, node):
+        validatenode(node)
+
+        # This is a copy of revlog.children().
+        c = []
+        p = self.rev(node)
+        for r in self.revs(start=p + 1):
+            prevs = [pr for pr in self.parentrevs(r) if pr != nullrev]
+            if prevs:
+                for pr in prevs:
+                    if pr == p:
+                        c.append(self.node(r))
+            elif p == nullrev:
+                c.append(self.node(r))
+        return c
+
+    def getstrippoint(self, minlink):
+
+        # This is largely a copy of revlog.getstrippoint().
+        brokenrevs = set()
+        strippoint = len(self)
+
+        heads = {}
+        futurelargelinkrevs = set()
+        for head in self.headrevs():
+            headlinkrev = self.linkrev(head)
+            heads[head] = headlinkrev
+            if headlinkrev >= minlink:
+                futurelargelinkrevs.add(headlinkrev)
+
+        # This algorithm involves walking down the rev graph, starting at the
+        # heads. Since the revs are topologically sorted according to linkrev,
+        # once all head linkrevs are below the minlink, we know there are
+        # no more revs that could have a linkrev greater than minlink.
+        # So we can stop walking.
+        while futurelargelinkrevs:
+            strippoint -= 1
+            linkrev = heads.pop(strippoint)
+
+            if linkrev < minlink:
+                brokenrevs.add(strippoint)
+            else:
+                futurelargelinkrevs.remove(linkrev)
+
+            for p in self.parentrevs(strippoint):
+                if p != nullrev:
+                    plinkrev = self.linkrev(p)
+                    heads[p] = plinkrev
+                    if plinkrev >= minlink:
+                        futurelargelinkrevs.add(plinkrev)
+
+        return strippoint, brokenrevs
+
+    def strip(self, minlink, transaction):
+        if not len(self):
+            return
+
+        rev, _ignored = self.getstrippoint(minlink)
+        if rev == len(self):
+            return
+
+        # Purge index data starting at the requested revision.
+        self._indexdata[rev:] = []
+        self._reflectindexupdate()
+
+def reposetup(ui, repo):
+    if not repo.local():
+        return
+
+    class simplestorerepo(repo.__class__):
+        def file(self, f):
+            return filestorage(self.svfs, f)
+
+    repo.__class__ = simplestorerepo