view mercurial/similar.py @ 33800:f257943e47ab

repository: formalize peer interface with abstract base class

There are various interfaces for interacting with repositories
and peers. They form a contract for how one should interact with
a repo or peer object.

The contracts today aren't very well-defined or enforced. There
have been several bugs over the years where peers or repo types
have forgotten to implement certain methods. In addition, the
inheritance of some classes is wonky. For example, localrepository
doesn't inherit from an interface and the god-object nature of
that class means the repository interface isn't well-defined. Other
repository types inherit from localrepository then stub out
methods that don't make sense (e.g. statichttprepository
re-defining locking methods to fail fast).

Not having well-defined interfaces makes implementing alternate
storage backends, wire protocol transports, and repository types
difficult because it isn't clear what exactly needs to be
implemented.

This patch starts the process of attempting to establish more
order to the type system around repositories and peers.

Our first patch starts with a problem space that already has a
partial solution: peers. The peer.peerrepository class already
somewhat defines a peer interface. But it is missing a few things
and the total interface isn't well-defined because it is combined
with wireproto.wirepeer.

Our newly-established basepeer class uses the abc module to
declare an abstract base class with the properties and methods that
a generic peer must implement.

We create a new class that inherits from it. This class will hold
our other future abstract base classes / interfaces so we can expose
a unified base class/interface.

We don't yet use the new interface because subsequent additions
will break existing code without some refactoring first.

A new module (repository.py) was created to hold the interfaces.
I could have put things in peer.py. However, I have plans to
eventually add interfaces to define repository and storage types.
These almost certainly require a new module. And I figured having
all the interfaces live in one module makes sense. So I created
repository.py to be that future home.

Differential Revision: https://phab.mercurial-scm.org/D332

# similar.py - mechanisms for finding similar files
#
# Copyright 2005-2007 Matt Mackall <[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 .i18n import _
from . import (
    mdiff,
)

def _findexactmatches(repo, added, removed):
    '''find renamed files that have no changes

    Takes a list of new filectxs and a list of removed filectxs, and yields
    (before, after) tuples of exact matches.
    '''
    numfiles = len(added) + len(removed)

    # Build table of removed files: {hash(fctx.data()): [fctx, ...]}.
    # We use hash() to discard fctx.data() from memory.
    hashes = {}
    for i, fctx in enumerate(removed):
        repo.ui.progress(_('searching for exact renames'), i, total=numfiles,
                         unit=_('files'))
        h = hash(fctx.data())
        if h not in hashes:
            hashes[h] = [fctx]
        else:
            hashes[h].append(fctx)

    # For each added file, see if it corresponds to a removed file.
    for i, fctx in enumerate(added):
        repo.ui.progress(_('searching for exact renames'), i + len(removed),
                total=numfiles, unit=_('files'))
        adata = fctx.data()
        h = hash(adata)
        for rfctx in hashes.get(h, []):
            # compare between actual file contents for exact identity
            if adata == rfctx.data():
                yield (rfctx, fctx)
                break

    # Done
    repo.ui.progress(_('searching for exact renames'), None)

def _ctxdata(fctx):
    # lazily load text
    orig = fctx.data()
    return orig, mdiff.splitnewlines(orig)

def _score(fctx, otherdata):
    orig, lines = otherdata
    text = fctx.data()
    # mdiff.blocks() returns blocks of matching lines
    # count the number of bytes in each
    equal = 0
    matches = mdiff.blocks(text, orig)
    for x1, x2, y1, y2 in matches:
        for line in lines[y1:y2]:
            equal += len(line)

    lengths = len(text) + len(orig)
    return equal * 2.0 / lengths

def score(fctx1, fctx2):
    return _score(fctx1, _ctxdata(fctx2))

def _findsimilarmatches(repo, added, removed, threshold):
    '''find potentially renamed files based on similar file content

    Takes a list of new filectxs and a list of removed filectxs, and yields
    (before, after, score) tuples of partial matches.
    '''
    copies = {}
    for i, r in enumerate(removed):
        repo.ui.progress(_('searching for similar files'), i,
                         total=len(removed), unit=_('files'))

        data = None
        for a in added:
            bestscore = copies.get(a, (None, threshold))[1]
            if data is None:
                data = _ctxdata(r)
            myscore = _score(a, data)
            if myscore > bestscore:
                copies[a] = (r, myscore)
    repo.ui.progress(_('searching'), None)

    for dest, v in copies.iteritems():
        source, bscore = v
        yield source, dest, bscore

def _dropempty(fctxs):
    return [x for x in fctxs if x.size() > 0]

def findrenames(repo, added, removed, threshold):
    '''find renamed files -- yields (before, after, score) tuples'''
    wctx = repo[None]
    pctx = wctx.p1()

    # Zero length files will be frequently unrelated to each other, and
    # tracking the deletion/addition of such a file will probably cause more
    # harm than good. We strip them out here to avoid matching them later on.
    addedfiles = _dropempty(wctx[fp] for fp in sorted(added))
    removedfiles = _dropempty(pctx[fp] for fp in sorted(removed) if fp in pctx)

    # Find exact matches.
    matchedfiles = set()
    for (a, b) in _findexactmatches(repo, addedfiles, removedfiles):
        matchedfiles.add(b)
        yield (a.path(), b.path(), 1.0)

    # If the user requested similar files to be matched, search for them also.
    if threshold < 1.0:
        addedfiles = [x for x in addedfiles if x not in matchedfiles]
        for (a, b, score) in _findsimilarmatches(repo, addedfiles,
                                                 removedfiles, threshold):
            yield (a.path(), b.path(), score)