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localrepo: iteratively derive local repository type...
localrepo: iteratively derive local repository type This commit implements the dynamic local repository type derivation that was explained in the recent commit bfeab472e3c0 "localrepo: create new function for instantiating a local repo object." Instead of a static localrepository class/type which must be customized after construction, we now dynamically construct a type by building up base classes/types to represent specific repository interfaces. Conceptually, the end state is similar to what was happening when various extensions would monkeypatch the __class__ of newly-constructed repo instances. However, the approach is inverted. Instead of making the instance then customizing it, we do the customization up front by influencing the behavior of the type then we instantiate that custom type. This approach gives us much more flexibility. For example, we can use completely separate classes for implementing different aspects of the repository. For example, we could have one class representing revlog-based file storage and another representing non-revlog based file storage. When then choose which implementation to use based on the presence of repo requirements. A concern with this approach is that it creates a lot more types and complexity and that complexity adds overhead. Yes, it is true that this approach will result in more types being created. Yes, this is more complicated than traditional "instantiate a static type." However, I believe the alternatives to supporting alternate storage backends are just as complicated. (Before I arrived at this solution, I had patches storing factory functions on local repo instances for e.g. constructing a file storage instance. We ended up having a handful of these. And this was logically identical to assigning custom methods. Since we were logically changing the type of the instance, I figured it would be better to just use specialized types instead of introducing levels of abstraction at run-time.) On the performance front, I don't believe that having N base classes has any significant performance overhead compared to just a single base class. Intuition says that Python will need to iterate the base classes to find an attribute. However, CPython caches method lookups: as long as the __class__ or MRO isn't changing, method attribute lookup should be constant time after first access. And non-method attributes are stored in __dict__, of which there is only 1 per object, so the number of base classes for __dict__ is irrelevant. Anyway, this commit splits up the monolithic completelocalrepository interface into sub-interfaces: 1 for file storage and 1 representing everything else. We've taught ``makelocalrepository()`` to call a series of factory functions which will produce types implementing specific interfaces. It then calls type() to create a new type from the built-up list of base types. This commit should be considered a start and not the end state. I suspect we'll hit a number of problems as we start to implement alternate storage backends: * Passing custom arguments to __init__ and setting custom attributes on __dict__. * Customizing the set of interfaces that are needed. e.g. the "readonly" intent could translate to not requesting an interface providing methods related to writing. * More ergonomic way for extensions to insert themselves so their callbacks aren't unconditionally called. * Wanting to modify vfs instances, other arguments passed to __init__. That being said, this code is usable in its current state and I'm convinced future commits will demonstrate the value in this approach. Differential Revision: https://phab.mercurial-scm.org/D4642

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filelog.py
227 lines | 6.6 KiB | text/x-python | PythonLexer
# filelog.py - file history class for mercurial
#
# Copyright 2005-2007 Matt Mackall <mpm@selenic.com>
#
# 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 . import (
error,
repository,
revlog,
)
from .utils import (
interfaceutil,
)
@interfaceutil.implementer(repository.ifilestorage)
class filelog(object):
def __init__(self, opener, path):
self._revlog = revlog.revlog(opener,
'/'.join(('data', path + '.i')),
censorable=True)
# full name of the user visible file, relative to the repository root
self.filename = path
self.index = self._revlog.index
self.version = self._revlog.version
self._generaldelta = self._revlog._generaldelta
def __len__(self):
return len(self._revlog)
def __iter__(self):
return self._revlog.__iter__()
def revs(self, start=0, stop=None):
return self._revlog.revs(start=start, stop=stop)
def parents(self, node):
return self._revlog.parents(node)
def parentrevs(self, rev):
return self._revlog.parentrevs(rev)
def rev(self, node):
return self._revlog.rev(node)
def node(self, rev):
return self._revlog.node(rev)
def lookup(self, node):
return self._revlog.lookup(node)
def linkrev(self, rev):
return self._revlog.linkrev(rev)
def flags(self, rev):
return self._revlog.flags(rev)
def commonancestorsheads(self, node1, node2):
return self._revlog.commonancestorsheads(node1, node2)
def descendants(self, revs):
return self._revlog.descendants(revs)
def headrevs(self):
return self._revlog.headrevs()
def heads(self, start=None, stop=None):
return self._revlog.heads(start, stop)
def children(self, node):
return self._revlog.children(node)
def deltaparent(self, rev):
return self._revlog.deltaparent(rev)
def iscensored(self, rev):
return self._revlog.iscensored(rev)
def rawsize(self, rev):
return self._revlog.rawsize(rev)
def checkhash(self, text, node, p1=None, p2=None, rev=None):
return self._revlog.checkhash(text, node, p1=p1, p2=p2, rev=rev)
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 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):
return self._revlog.addrevision(revisiondata, transaction, linkrev,
p1, p2, node=node, flags=flags,
cachedelta=cachedelta)
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 checksize(self):
return self._revlog.checksize()
def read(self, node):
t = self.revision(node)
if not t.startswith('\1\n'):
return t
s = t.index('\1\n', 2)
return t[s + 2:]
def add(self, text, meta, transaction, link, p1=None, p2=None):
if meta or text.startswith('\1\n'):
text = revlog.packmeta(meta, text)
return self.addrevision(text, transaction, link, p1, p2)
def renamed(self, node):
if self.parents(node)[0] != revlog.nullid:
return False
t = self.revision(node)
m = revlog.parsemeta(t)[0]
# copy and copyrev occur in pairs. In rare cases due to bugs,
# one can occur without the other.
if m and "copy" in m and "copyrev" in m:
return (m["copy"], revlog.bin(m["copyrev"]))
return False
def size(self, rev):
"""return the size of a given revision"""
# for revisions with renames, we have to go the slow way
node = self.node(rev)
if self.renamed(node):
return len(self.read(node))
if self.iscensored(rev):
return 0
# XXX if self.read(node).startswith("\1\n"), this returns (size+4)
return self._revlog.size(rev)
def cmp(self, node, text):
"""compare text with a given file revision
returns True if text is different than what is stored.
"""
t = text
if text.startswith('\1\n'):
t = '\1\n\1\n' + text
samehashes = not self._revlog.cmp(node, t)
if samehashes:
return False
# censored files compare against the empty file
if self.iscensored(self.rev(node)):
return text != ''
# renaming a file produces a different hash, even if the data
# remains unchanged. Check if it's the case (slow):
if self.renamed(node):
t2 = self.read(node)
return t2 != text
return True
@property
def filename(self):
return self._revlog.filename
@filename.setter
def filename(self, value):
self._revlog.filename = value
# TODO these aren't part of the interface and aren't internal methods.
# Callers should be fixed to not use them.
@property
def indexfile(self):
return self._revlog.indexfile
@indexfile.setter
def indexfile(self, value):
self._revlog.indexfile = value
@property
def datafile(self):
return self._revlog.datafile
@property
def opener(self):
return self._revlog.opener
def clone(self, tr, destrevlog, **kwargs):
if not isinstance(destrevlog, filelog):
raise error.ProgrammingError('expected filelog to clone()')
return self._revlog.clone(tr, destrevlog._revlog, **kwargs)
def start(self, rev):
return self._revlog.start(rev)
def end(self, rev):
return self._revlog.end(rev)
def length(self, rev):
return self._revlog.length(rev)
def compress(self, data):
return self._revlog.compress(data)
def _addrevision(self, *args, **kwargs):
return self._revlog._addrevision(*args, **kwargs)