copies: return None instead of ChangingFiles when relevant

If they are not relevant data, they are no need to fetch them.

Differential Revision: https://phab.mercurial-scm.org/D9140

mercurial/changelog.py

@@ -1,618 +1,618
 # changelog.py - changelog class for mercurial
 #
 # 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 .node import (
     bin,
     hex,
     nullid,
 )
 from .thirdparty import attr
 
 from . import (
     encoding,
     error,
     metadata,
     pycompat,
     revlog,
 )
 from .utils import (
     dateutil,
     stringutil,
 )
 from .revlogutils import flagutil
 
 _defaultextra = {b'branch': b'default'}
 
 
 def _string_escape(text):
     """
     >>> from .pycompat import bytechr as chr
     >>> d = {b'nl': chr(10), b'bs': chr(92), b'cr': chr(13), b'nul': chr(0)}
     >>> s = b"ab%(nl)scd%(bs)s%(bs)sn%(nul)s12ab%(cr)scd%(bs)s%(nl)s" % d
     >>> s
     'ab\\ncd\\\\\\\\n\\x0012ab\\rcd\\\\\\n'
     >>> res = _string_escape(s)
     >>> s == _string_unescape(res)
     True
     """
     # subset of the string_escape codec
     text = (
         text.replace(b'\\', b'\\\\')
         .replace(b'\n', b'\\n')
         .replace(b'\r', b'\\r')
     )
     return text.replace(b'\0', b'\\0')
 
 
 def _string_unescape(text):
     if b'\\0' in text:
         # fix up \0 without getting into trouble with \\0
         text = text.replace(b'\\\\', b'\\\\\n')
         text = text.replace(b'\\0', b'\0')
         text = text.replace(b'\n', b'')
     return stringutil.unescapestr(text)
 
 
 def decodeextra(text):
     """
     >>> from .pycompat import bytechr as chr
     >>> sorted(decodeextra(encodeextra({b'foo': b'bar', b'baz': chr(0) + b'2'})
     ...                    ).items())
     [('baz', '\\x002'), ('branch', 'default'), ('foo', 'bar')]
     >>> sorted(decodeextra(encodeextra({b'foo': b'bar',
     ...                                 b'baz': chr(92) + chr(0) + b'2'})
     ...                    ).items())
     [('baz', '\\\\\\x002'), ('branch', 'default'), ('foo', 'bar')]
     """
     extra = _defaultextra.copy()
     for l in text.split(b'\0'):
         if l:
             k, v = _string_unescape(l).split(b':', 1)
             extra[k] = v
     return extra
 
 
 def encodeextra(d):
     # keys must be sorted to produce a deterministic changelog entry
     items = [_string_escape(b'%s:%s' % (k, d[k])) for k in sorted(d)]
     return b"\0".join(items)
 
 
 def stripdesc(desc):
     """strip trailing whitespace and leading and trailing empty lines"""
     return b'\n'.join([l.rstrip() for l in desc.splitlines()]).strip(b'\n')
 
 
 class appender(object):
     '''the changelog index must be updated last on disk, so we use this class
     to delay writes to it'''
 
     def __init__(self, vfs, name, mode, buf):
         self.data = buf
         fp = vfs(name, mode)
         self.fp = fp
         self.offset = fp.tell()
         self.size = vfs.fstat(fp).st_size
         self._end = self.size
 
     def end(self):
         return self._end
 
     def tell(self):
         return self.offset
 
     def flush(self):
         pass
 
     @property
     def closed(self):
         return self.fp.closed
 
     def close(self):
         self.fp.close()
 
     def seek(self, offset, whence=0):
         '''virtual file offset spans real file and data'''
         if whence == 0:
             self.offset = offset
         elif whence == 1:
             self.offset += offset
         elif whence == 2:
             self.offset = self.end() + offset
         if self.offset < self.size:
             self.fp.seek(self.offset)
 
     def read(self, count=-1):
         '''only trick here is reads that span real file and data'''
         ret = b""
         if self.offset < self.size:
             s = self.fp.read(count)
             ret = s
             self.offset += len(s)
             if count > 0:
                 count -= len(s)
         if count != 0:
             doff = self.offset - self.size
             self.data.insert(0, b"".join(self.data))
             del self.data[1:]
             s = self.data[0][doff : doff + count]
             self.offset += len(s)
             ret += s
         return ret
 
     def write(self, s):
         self.data.append(bytes(s))
         self.offset += len(s)
         self._end += len(s)
 
     def __enter__(self):
         self.fp.__enter__()
         return self
 
     def __exit__(self, *args):
         return self.fp.__exit__(*args)
 
 
 class _divertopener(object):
     def __init__(self, opener, target):
         self._opener = opener
         self._target = target
 
     def __call__(self, name, mode=b'r', checkambig=False, **kwargs):
         if name != self._target:
             return self._opener(name, mode, **kwargs)
         return self._opener(name + b".a", mode, **kwargs)
 
     def __getattr__(self, attr):
         return getattr(self._opener, attr)
 
 
 def _delayopener(opener, target, buf):
     """build an opener that stores chunks in 'buf' instead of 'target'"""
 
     def _delay(name, mode=b'r', checkambig=False, **kwargs):
         if name != target:
             return opener(name, mode, **kwargs)
         assert not kwargs
         return appender(opener, name, mode, buf)
 
     return _delay
 
 
 @attr.s
 class _changelogrevision(object):
     # Extensions might modify _defaultextra, so let the constructor below pass
     # it in
     extra = attr.ib()
     manifest = attr.ib(default=nullid)
     user = attr.ib(default=b'')
     date = attr.ib(default=(0, 0))
     files = attr.ib(default=attr.Factory(list))
     filesadded = attr.ib(default=None)
     filesremoved = attr.ib(default=None)
     p1copies = attr.ib(default=None)
     p2copies = attr.ib(default=None)
     description = attr.ib(default=b'')
 
 
 class changelogrevision(object):
     """Holds results of a parsed changelog revision.
 
     Changelog revisions consist of multiple pieces of data, including
     the manifest node, user, and date. This object exposes a view into
     the parsed object.
     """
 
     __slots__ = (
         '_offsets',
         '_text',
         '_sidedata',
         '_cpsd',
         '_changes',
     )
 
     def __new__(cls, text, sidedata, cpsd):
         if not text:
             return _changelogrevision(extra=_defaultextra)
 
         self = super(changelogrevision, cls).__new__(cls)
         # We could return here and implement the following as an __init__.
         # But doing it here is equivalent and saves an extra function call.
 
         # format used:
         # nodeid\n        : manifest node in ascii
         # user\n          : user, no \n or \r allowed
         # time tz extra\n : date (time is int or float, timezone is int)
         #                 : extra is metadata, encoded and separated by '\0'
         #                 : older versions ignore it
         # files\n\n       : files modified by the cset, no \n or \r allowed
         # (.*)            : comment (free text, ideally utf-8)
         #
         # changelog v0 doesn't use extra
 
         nl1 = text.index(b'\n')
         nl2 = text.index(b'\n', nl1 + 1)
         nl3 = text.index(b'\n', nl2 + 1)
 
         # The list of files may be empty. Which means nl3 is the first of the
         # double newline that precedes the description.
         if text[nl3 + 1 : nl3 + 2] == b'\n':
             doublenl = nl3
         else:
             doublenl = text.index(b'\n\n', nl3 + 1)
 
         self._offsets = (nl1, nl2, nl3, doublenl)
         self._text = text
         self._sidedata = sidedata
         self._cpsd = cpsd
         self._changes = None
 
         return self
 
     @property
     def manifest(self):
         return bin(self._text[0 : self._offsets[0]])
 
     @property
     def user(self):
         off = self._offsets
         return encoding.tolocal(self._text[off[0] + 1 : off[1]])
 
     @property
     def _rawdate(self):
         off = self._offsets
         dateextra = self._text[off[1] + 1 : off[2]]
         return dateextra.split(b' ', 2)[0:2]
 
     @property
     def _rawextra(self):
         off = self._offsets
         dateextra = self._text[off[1] + 1 : off[2]]
         fields = dateextra.split(b' ', 2)
         if len(fields) != 3:
             return None
 
         return fields[2]
 
     @property
     def date(self):
         raw = self._rawdate
         time = float(raw[0])
         # Various tools did silly things with the timezone.
         try:
             timezone = int(raw[1])
         except ValueError:
             timezone = 0
 
         return time, timezone
 
     @property
     def extra(self):
         raw = self._rawextra
         if raw is None:
             return _defaultextra
 
         return decodeextra(raw)
 
     @property
     def changes(self):
         if self._changes is not None:
             return self._changes
         if self._cpsd:
             changes = metadata.decode_files_sidedata(self._sidedata)
         else:
             changes = metadata.ChangingFiles(
                 touched=self.files or (),
                 added=self.filesadded or (),
                 removed=self.filesremoved or (),
                 p1_copies=self.p1copies or {},
                 p2_copies=self.p2copies or {},
             )
         self._changes = changes
         return changes
 
     @property
     def files(self):
         if self._cpsd:
             return sorted(self.changes.touched)
         off = self._offsets
         if off[2] == off[3]:
             return []
 
         return self._text[off[2] + 1 : off[3]].split(b'\n')
 
     @property
     def filesadded(self):
         if self._cpsd:
             return self.changes.added
         else:
             rawindices = self.extra.get(b'filesadded')
         if rawindices is None:
             return None
         return metadata.decodefileindices(self.files, rawindices)
 
     @property
     def filesremoved(self):
         if self._cpsd:
             return self.changes.removed
         else:
             rawindices = self.extra.get(b'filesremoved')
         if rawindices is None:
             return None
         return metadata.decodefileindices(self.files, rawindices)
 
     @property
     def p1copies(self):
         if self._cpsd:
             return self.changes.copied_from_p1
         else:
             rawcopies = self.extra.get(b'p1copies')
         if rawcopies is None:
             return None
         return metadata.decodecopies(self.files, rawcopies)
 
     @property
     def p2copies(self):
         if self._cpsd:
             return self.changes.copied_from_p2
         else:
             rawcopies = self.extra.get(b'p2copies')
         if rawcopies is None:
             return None
         return metadata.decodecopies(self.files, rawcopies)
 
     @property
     def description(self):
         return encoding.tolocal(self._text[self._offsets[3] + 2 :])
 
 
 class changelog(revlog.revlog):
     def __init__(self, opener, trypending=False):
         """Load a changelog revlog using an opener.
 
         If ``trypending`` is true, we attempt to load the index from a
         ``00changelog.i.a`` file instead of the default ``00changelog.i``.
         The ``00changelog.i.a`` file contains index (and possibly inline
         revision) data for a transaction that hasn't been finalized yet.
         It exists in a separate file to facilitate readers (such as
         hooks processes) accessing data before a transaction is finalized.
         """
         if trypending and opener.exists(b'00changelog.i.a'):
             indexfile = b'00changelog.i.a'
         else:
             indexfile = b'00changelog.i'
 
         datafile = b'00changelog.d'
         revlog.revlog.__init__(
             self,
             opener,
             indexfile,
             datafile=datafile,
             checkambig=True,
             mmaplargeindex=True,
             persistentnodemap=opener.options.get(b'persistent-nodemap', False),
         )
 
         if self._initempty and (self.version & 0xFFFF == revlog.REVLOGV1):
             # changelogs don't benefit from generaldelta.
 
             self.version &= ~revlog.FLAG_GENERALDELTA
             self._generaldelta = False
 
         # Delta chains for changelogs tend to be very small because entries
         # tend to be small and don't delta well with each. So disable delta
         # chains.
         self._storedeltachains = False
 
         self._realopener = opener
         self._delayed = False
         self._delaybuf = None
         self._divert = False
         self._filteredrevs = frozenset()
         self._filteredrevs_hashcache = {}
         self._copiesstorage = opener.options.get(b'copies-storage')
 
     @property
     def filteredrevs(self):
         return self._filteredrevs
 
     @filteredrevs.setter
     def filteredrevs(self, val):
         # Ensure all updates go through this function
         assert isinstance(val, frozenset)
         self._filteredrevs = val
         self._filteredrevs_hashcache = {}
 
     def delayupdate(self, tr):
         """delay visibility of index updates to other readers"""
 
         if not self._delayed:
             if len(self) == 0:
                 self._divert = True
                 if self._realopener.exists(self.indexfile + b'.a'):
                     self._realopener.unlink(self.indexfile + b'.a')
                 self.opener = _divertopener(self._realopener, self.indexfile)
             else:
                 self._delaybuf = []
                 self.opener = _delayopener(
                     self._realopener, self.indexfile, self._delaybuf
                 )
         self._delayed = True
         tr.addpending(b'cl-%i' % id(self), self._writepending)
         tr.addfinalize(b'cl-%i' % id(self), self._finalize)
 
     def _finalize(self, tr):
         """finalize index updates"""
         self._delayed = False
         self.opener = self._realopener
         # move redirected index data back into place
         if self._divert:
             assert not self._delaybuf
             tmpname = self.indexfile + b".a"
             nfile = self.opener.open(tmpname)
             nfile.close()
             self.opener.rename(tmpname, self.indexfile, checkambig=True)
         elif self._delaybuf:
             fp = self.opener(self.indexfile, b'a', checkambig=True)
             fp.write(b"".join(self._delaybuf))
             fp.close()
             self._delaybuf = None
         self._divert = False
         # split when we're done
         self._enforceinlinesize(tr)
 
     def _writepending(self, tr):
         """create a file containing the unfinalized state for
         pretxnchangegroup"""
         if self._delaybuf:
             # make a temporary copy of the index
             fp1 = self._realopener(self.indexfile)
             pendingfilename = self.indexfile + b".a"
             # register as a temp file to ensure cleanup on failure
             tr.registertmp(pendingfilename)
             # write existing data
             fp2 = self._realopener(pendingfilename, b"w")
             fp2.write(fp1.read())
             # add pending data
             fp2.write(b"".join(self._delaybuf))
             fp2.close()
             # switch modes so finalize can simply rename
             self._delaybuf = None
             self._divert = True
             self.opener = _divertopener(self._realopener, self.indexfile)
 
         if self._divert:
             return True
 
         return False
 
     def _enforceinlinesize(self, tr, fp=None):
         if not self._delayed:
             revlog.revlog._enforceinlinesize(self, tr, fp)
 
     def read(self, node):
         """Obtain data from a parsed changelog revision.
 
         Returns a 6-tuple of:
 
            - manifest node in binary
            - author/user as a localstr
            - date as a 2-tuple of (time, timezone)
            - list of files
            - commit message as a localstr
            - dict of extra metadata
 
         Unless you need to access all fields, consider calling
         ``changelogrevision`` instead, as it is faster for partial object
         access.
         """
         d, s = self._revisiondata(node)
         c = changelogrevision(
             d, s, self._copiesstorage == b'changeset-sidedata'
         )
         return (c.manifest, c.user, c.date, c.files, c.description, c.extra)
 
     def changelogrevision(self, nodeorrev):
         """Obtain a ``changelogrevision`` for a node or revision."""
         text, sidedata = self._revisiondata(nodeorrev)
         return changelogrevision(
             text, sidedata, self._copiesstorage == b'changeset-sidedata'
         )
 
     def readfiles(self, node):
         """
         short version of read that only returns the files modified by the cset
         """
         text = self.revision(node)
         if not text:
             return []
         last = text.index(b"\n\n")
         l = text[:last].split(b'\n')
         return l[3:]
 
     def add(
         self,
         manifest,
         files,
         desc,
         transaction,
         p1,
         p2,
         user,
         date=None,
         extra=None,
     ):
         # Convert to UTF-8 encoded bytestrings as the very first
         # thing: calling any method on a localstr object will turn it
         # into a str object and the cached UTF-8 string is thus lost.
         user, desc = encoding.fromlocal(user), encoding.fromlocal(desc)
 
         user = user.strip()
         # An empty username or a username with a "\n" will make the
         # revision text contain two "\n\n" sequences -> corrupt
         # repository since read cannot unpack the revision.
         if not user:
             raise error.StorageError(_(b"empty username"))
         if b"\n" in user:
             raise error.StorageError(
                 _(b"username %r contains a newline") % pycompat.bytestr(user)
             )
 
         desc = stripdesc(desc)
 
         if date:
             parseddate = b"%d %d" % dateutil.parsedate(date)
         else:
             parseddate = b"%d %d" % dateutil.makedate()
         if extra:
             branch = extra.get(b"branch")
             if branch in (b"default", b""):
                 del extra[b"branch"]
             elif branch in (b".", b"null", b"tip"):
                 raise error.StorageError(
                     _(b'the name \'%s\' is reserved') % branch
                 )
         sortedfiles = sorted(files.touched)
         flags = 0
         sidedata = None
         if self._copiesstorage == b'changeset-sidedata':
             if (
                 files.removed
                 or files.merged
                 or files.salvaged
                 or files.copied_from_p1
                 or files.copied_from_p2
             ):
                 flags |= flagutil.REVIDX_HASCOPIESINFO
             sidedata = metadata.encode_files_sidedata(files)
 
         if extra:
             extra = encodeextra(extra)
             parseddate = b"%s %s" % (parseddate, extra)
         l = [hex(manifest), user, parseddate] + sortedfiles + [b"", desc]
         text = b"\n".join(l)
         return self.addrevision(
-            text, transaction, len(self), p1, p2, sidedata=sidedata
+            text, transaction, len(self), p1, p2, sidedata=sidedata, flags=flags
         )
 
     def branchinfo(self, rev):
         """return the branch name and open/close state of a revision
 
         This function exists because creating a changectx object
         just to access this is costly."""
         extra = self.read(rev)[5]
         return encoding.tolocal(extra.get(b"branch")), b'close' in extra
 
     def _nodeduplicatecallback(self, transaction, node):
         # keep track of revisions that got "re-added", eg: unbunde of know rev.
         #
         # We track them in a list to preserve their order from the source bundle
         duplicates = transaction.changes.setdefault(b'revduplicates', [])
         duplicates.append(self.rev(node))

mercurial/copies.py

@@ -1,1089 +1,1109
 # copies.py - copy detection for Mercurial
 #
 # Copyright 2008 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
 
 import collections
 import os
 
 from .i18n import _
 
 
 from . import (
     match as matchmod,
     node,
     pathutil,
     pycompat,
     util,
 )
 
 
 from .utils import stringutil
 
+from .revlogutils import flagutil
+
 
 def _filter(src, dst, t):
     """filters out invalid copies after chaining"""
 
     # When _chain()'ing copies in 'a' (from 'src' via some other commit 'mid')
     # with copies in 'b' (from 'mid' to 'dst'), we can get the different cases
     # in the following table (not including trivial cases). For example, case 2
     # is where a file existed in 'src' and remained under that name in 'mid' and
     # then was renamed between 'mid' and 'dst'.
     #
     # case src mid dst result
     #   1   x   y   -    -
     #   2   x   y   y   x->y
     #   3   x   y   x    -
     #   4   x   y   z   x->z
     #   5   -   x   y    -
     #   6   x   x   y   x->y
     #
     # _chain() takes care of chaining the copies in 'a' and 'b', but it
     # cannot tell the difference between cases 1 and 2, between 3 and 4, or
     # between 5 and 6, so it includes all cases in its result.
     # Cases 1, 3, and 5 are then removed by _filter().
 
     for k, v in list(t.items()):
         # remove copies from files that didn't exist
         if v not in src:
             del t[k]
         # remove criss-crossed copies
         elif k in src and v in dst:
             del t[k]
         # remove copies to files that were then removed
         elif k not in dst:
             del t[k]
 
 
 def _chain(prefix, suffix):
     """chain two sets of copies 'prefix' and 'suffix'"""
     result = prefix.copy()
     for key, value in pycompat.iteritems(suffix):
         result[key] = prefix.get(value, value)
     return result
 
 
 def _tracefile(fctx, am, basemf):
     """return file context that is the ancestor of fctx present in ancestor
     manifest am
 
     Note: we used to try and stop after a given limit, however checking if that
     limit is reached turned out to be very expensive. we are better off
     disabling that feature."""
 
     for f in fctx.ancestors():
         path = f.path()
         if am.get(path, None) == f.filenode():
             return path
         if basemf and basemf.get(path, None) == f.filenode():
             return path
 
 
 def _dirstatecopies(repo, match=None):
     ds = repo.dirstate
     c = ds.copies().copy()
     for k in list(c):
         if ds[k] not in b'anm' or (match and not match(k)):
             del c[k]
     return c
 
 
 def _computeforwardmissing(a, b, match=None):
     """Computes which files are in b but not a.
     This is its own function so extensions can easily wrap this call to see what
     files _forwardcopies is about to process.
     """
     ma = a.manifest()
     mb = b.manifest()
     return mb.filesnotin(ma, match=match)
 
 
 def usechangesetcentricalgo(repo):
     """Checks if we should use changeset-centric copy algorithms"""
     if repo.filecopiesmode == b'changeset-sidedata':
         return True
     readfrom = repo.ui.config(b'experimental', b'copies.read-from')
     changesetsource = (b'changeset-only', b'compatibility')
     return readfrom in changesetsource
 
 
 def _committedforwardcopies(a, b, base, match):
     """Like _forwardcopies(), but b.rev() cannot be None (working copy)"""
     # files might have to be traced back to the fctx parent of the last
     # one-side-only changeset, but not further back than that
     repo = a._repo
 
     if usechangesetcentricalgo(repo):
         return _changesetforwardcopies(a, b, match)
 
     debug = repo.ui.debugflag and repo.ui.configbool(b'devel', b'debug.copies')
     dbg = repo.ui.debug
     if debug:
         dbg(b'debug.copies:    looking into rename from %s to %s\n' % (a, b))
     am = a.manifest()
     basemf = None if base is None else base.manifest()
 
     # find where new files came from
     # we currently don't try to find where old files went, too expensive
     # this means we can miss a case like 'hg rm b; hg cp a b'
     cm = {}
 
     # Computing the forward missing is quite expensive on large manifests, since
     # it compares the entire manifests. We can optimize it in the common use
     # case of computing what copies are in a commit versus its parent (like
     # during a rebase or histedit). Note, we exclude merge commits from this
     # optimization, since the ctx.files() for a merge commit is not correct for
     # this comparison.
     forwardmissingmatch = match
     if b.p1() == a and b.p2().node() == node.nullid:
         filesmatcher = matchmod.exact(b.files())
         forwardmissingmatch = matchmod.intersectmatchers(match, filesmatcher)
     missing = _computeforwardmissing(a, b, match=forwardmissingmatch)
 
     ancestrycontext = a._repo.changelog.ancestors([b.rev()], inclusive=True)
 
     if debug:
         dbg(b'debug.copies:      missing files to search: %d\n' % len(missing))
 
     for f in sorted(missing):
         if debug:
             dbg(b'debug.copies:        tracing file: %s\n' % f)
         fctx = b[f]
         fctx._ancestrycontext = ancestrycontext
 
         if debug:
             start = util.timer()
         opath = _tracefile(fctx, am, basemf)
         if opath:
             if debug:
                 dbg(b'debug.copies:          rename of: %s\n' % opath)
             cm[f] = opath
         if debug:
             dbg(
                 b'debug.copies:          time: %f seconds\n'
                 % (util.timer() - start)
             )
     return cm
 
 
 def _revinfo_getter(repo):
     """returns a function that returns the following data given a <rev>"
 
     * p1: revision number of first parent
     * p2: revision number of first parent
     * changes: a ChangingFiles object
     """
     cl = repo.changelog
     parents = cl.parentrevs
+    flags = cl.flags
+
+    HASCOPIESINFO = flagutil.REVIDX_HASCOPIESINFO
 
     changelogrevision = cl.changelogrevision
 
     # A small cache to avoid doing the work twice for merges
     #
     # In the vast majority of cases, if we ask information for a revision
     # about 1 parent, we'll later ask it for the other. So it make sense to
     # keep the information around when reaching the first parent of a merge
     # and dropping it after it was provided for the second parents.
     #
     # It exists cases were only one parent of the merge will be walked. It
     # happens when the "destination" the copy tracing is descendant from a
     # new root, not common with the "source". In that case, we will only walk
     # through merge parents that are descendant of changesets common
     # between "source" and "destination".
     #
     # With the current case implementation if such changesets have a copy
     # information, we'll keep them in memory until the end of
     # _changesetforwardcopies. We don't expect the case to be frequent
     # enough to matters.
     #
     # In addition, it would be possible to reach pathological case, were
     # many first parent are met before any second parent is reached. In
     # that case the cache could grow. If this even become an issue one can
     # safely introduce a maximum cache size. This would trade extra CPU/IO
     # time to save memory.
     merge_caches = {}
 
     def revinfo(rev):
         p1, p2 = parents(rev)
         value = None
         e = merge_caches.pop(rev, None)
         if e is not None:
             return e
-        value = (p1, p2, changelogrevision(rev).changes)
+        changes = None
+        if flags(rev) & HASCOPIESINFO:
+            changes = changelogrevision(rev).changes
+        value = (p1, p2, changes)
         if p1 != node.nullrev and p2 != node.nullrev:
             # XXX some case we over cache, IGNORE
             merge_caches[rev] = value
         return value
 
     return revinfo
 
 
 def _changesetforwardcopies(a, b, match):
     if a.rev() in (node.nullrev, b.rev()):
         return {}
 
     repo = a.repo().unfiltered()
     children = {}
 
     cl = repo.changelog
     isancestor = cl.isancestorrev  # XXX we should had chaching to this.
     missingrevs = cl.findmissingrevs(common=[a.rev()], heads=[b.rev()])
     mrset = set(missingrevs)
     roots = set()
     for r in missingrevs:
         for p in cl.parentrevs(r):
             if p == node.nullrev:
                 continue
             if p not in children:
                 children[p] = [r]
             else:
                 children[p].append(r)
             if p not in mrset:
                 roots.add(p)
     if not roots:
         # no common revision to track copies from
         return {}
     min_root = min(roots)
 
     from_head = set(
         cl.reachableroots(min_root, [b.rev()], list(roots), includepath=True)
     )
 
     iterrevs = set(from_head)
     iterrevs &= mrset
     iterrevs.update(roots)
     iterrevs.remove(b.rev())
     revs = sorted(iterrevs)
 
     if repo.filecopiesmode == b'changeset-sidedata':
         revinfo = _revinfo_getter(repo)
         return _combine_changeset_copies(
             revs, children, b.rev(), revinfo, match, isancestor
         )
     else:
         revinfo = _revinfo_getter_extra(repo)
         return _combine_changeset_copies_extra(
             revs, children, b.rev(), revinfo, match, isancestor
         )
 
 
 def _combine_changeset_copies(
     revs, children, targetrev, revinfo, match, isancestor
 ):
     """combine the copies information for each item of iterrevs
 
     revs: sorted iterable of revision to visit
     children: a {parent: [children]} mapping.
     targetrev: the final copies destination revision (not in iterrevs)
     revinfo(rev): a function that return (p1, p2, p1copies, p2copies, removed)
     match: a matcher
 
     It returns the aggregated copies information for `targetrev`.
     """
     all_copies = {}
     alwaysmatch = match.always()
     for r in revs:
         copies = all_copies.pop(r, None)
         if copies is None:
             # this is a root
             copies = {}
         for i, c in enumerate(children[r]):
             p1, p2, changes = revinfo(c)
+            childcopies = {}
             if r == p1:
                 parent = 1
+                if changes is not None:
                 childcopies = changes.copied_from_p1
             else:
                 assert r == p2
                 parent = 2
+                if changes is not None:
                 childcopies = changes.copied_from_p2
             if not alwaysmatch:
                 childcopies = {
                     dst: src for dst, src in childcopies.items() if match(dst)
                 }
             newcopies = copies
             if childcopies:
                 newcopies = copies.copy()
                 for dest, source in pycompat.iteritems(childcopies):
                     prev = copies.get(source)
                     if prev is not None and prev[1] is not None:
                         source = prev[1]
                     newcopies[dest] = (c, source)
                 assert newcopies is not copies
+            if changes is not None:
             for f in changes.removed:
                 if f in newcopies:
                     if newcopies is copies:
                         # copy on write to avoid affecting potential other
                         # branches.  when there are no other branches, this
                         # could be avoided.
                         newcopies = copies.copy()
                     newcopies[f] = (c, None)
             othercopies = all_copies.get(c)
             if othercopies is None:
                 all_copies[c] = newcopies
             else:
                 # we are the second parent to work on c, we need to merge our
                 # work with the other.
                 #
                 # In case of conflict, parent 1 take precedence over parent 2.
                 # This is an arbitrary choice made anew when implementing
                 # changeset based copies. It was made without regards with
                 # potential filelog related behavior.
                 if parent == 1:
                     _merge_copies_dict(
                         othercopies, newcopies, isancestor, changes
                     )
                 else:
                     _merge_copies_dict(
                         newcopies, othercopies, isancestor, changes
                     )
                     all_copies[c] = newcopies
 
     final_copies = {}
     for dest, (tt, source) in all_copies[targetrev].items():
         if source is not None:
             final_copies[dest] = source
     return final_copies
 
 
 def _merge_copies_dict(minor, major, isancestor, changes):
     """merge two copies-mapping together, minor and major
 
     In case of conflict, value from "major" will be picked.
 
     - `isancestors(low_rev, high_rev)`: callable return True if `low_rev` is an
                                         ancestors of `high_rev`,
 
     - `ismerged(path)`: callable return True if `path` have been merged in the
                         current revision,
     """
     for dest, value in major.items():
         other = minor.get(dest)
         if other is None:
             minor[dest] = value
         else:
             new_tt = value[0]
             other_tt = other[0]
             if value[1] == other[1]:
                 continue
             # content from "major" wins, unless it is older
             # than the branch point or there is a merge
             if new_tt == other_tt:
                 minor[dest] = value
-            elif value[1] is None and dest in changes.salvaged:
+            elif (
+                changes is not None
+                and value[1] is None
+                and dest in changes.salvaged
+            ):
                 pass
-            elif other[1] is None and dest in changes.salvaged:
+            elif (
+                changes is not None
+                and other[1] is None
+                and dest in changes.salvaged
+            ):
                 minor[dest] = value
             elif not isancestor(new_tt, other_tt):
                 minor[dest] = value
-            elif dest in changes.merged:
+            elif changes is not None and dest in changes.merged:
                 minor[dest] = value
 
 
 def _revinfo_getter_extra(repo):
     """return a function that return multiple data given a <rev>"i
 
     * p1: revision number of first parent
     * p2: revision number of first parent
     * p1copies: mapping of copies from p1
     * p2copies: mapping of copies from p2
     * removed: a list of removed files
     * ismerged: a callback to know if file was merged in that revision
     """
     cl = repo.changelog
     parents = cl.parentrevs
 
     def get_ismerged(rev):
         ctx = repo[rev]
 
         def ismerged(path):
             if path not in ctx.files():
                 return False
             fctx = ctx[path]
             parents = fctx._filelog.parents(fctx._filenode)
             nb_parents = 0
             for n in parents:
                 if n != node.nullid:
                     nb_parents += 1
             return nb_parents >= 2
 
         return ismerged
 
     def revinfo(rev):
         p1, p2 = parents(rev)
         ctx = repo[rev]
         p1copies, p2copies = ctx._copies
         removed = ctx.filesremoved()
         return p1, p2, p1copies, p2copies, removed, get_ismerged(rev)
 
     return revinfo
 
 
 def _combine_changeset_copies_extra(
     revs, children, targetrev, revinfo, match, isancestor
 ):
     """version of `_combine_changeset_copies` that works with the Google
     specific "extra" based storage for copy information"""
     all_copies = {}
     alwaysmatch = match.always()
     for r in revs:
         copies = all_copies.pop(r, None)
         if copies is None:
             # this is a root
             copies = {}
         for i, c in enumerate(children[r]):
             p1, p2, p1copies, p2copies, removed, ismerged = revinfo(c)
             if r == p1:
                 parent = 1
                 childcopies = p1copies
             else:
                 assert r == p2
                 parent = 2
                 childcopies = p2copies
             if not alwaysmatch:
                 childcopies = {
                     dst: src for dst, src in childcopies.items() if match(dst)
                 }
             newcopies = copies
             if childcopies:
                 newcopies = copies.copy()
                 for dest, source in pycompat.iteritems(childcopies):
                     prev = copies.get(source)
                     if prev is not None and prev[1] is not None:
                         source = prev[1]
                     newcopies[dest] = (c, source)
                 assert newcopies is not copies
             for f in removed:
                 if f in newcopies:
                     if newcopies is copies:
                         # copy on write to avoid affecting potential other
                         # branches.  when there are no other branches, this
                         # could be avoided.
                         newcopies = copies.copy()
                     newcopies[f] = (c, None)
             othercopies = all_copies.get(c)
             if othercopies is None:
                 all_copies[c] = newcopies
             else:
                 # we are the second parent to work on c, we need to merge our
                 # work with the other.
                 #
                 # In case of conflict, parent 1 take precedence over parent 2.
                 # This is an arbitrary choice made anew when implementing
                 # changeset based copies. It was made without regards with
                 # potential filelog related behavior.
                 if parent == 1:
                     _merge_copies_dict_extra(
                         othercopies, newcopies, isancestor, ismerged
                     )
                 else:
                     _merge_copies_dict_extra(
                         newcopies, othercopies, isancestor, ismerged
                     )
                     all_copies[c] = newcopies
 
     final_copies = {}
     for dest, (tt, source) in all_copies[targetrev].items():
         if source is not None:
             final_copies[dest] = source
     return final_copies
 
 
 def _merge_copies_dict_extra(minor, major, isancestor, ismerged):
     """version of `_merge_copies_dict` that works with the Google
     specific "extra" based storage for copy information"""
     for dest, value in major.items():
         other = minor.get(dest)
         if other is None:
             minor[dest] = value
         else:
             new_tt = value[0]
             other_tt = other[0]
             if value[1] == other[1]:
                 continue
             # content from "major" wins, unless it is older
             # than the branch point or there is a merge
             if (
                 new_tt == other_tt
                 or not isancestor(new_tt, other_tt)
                 or ismerged(dest)
             ):
                 minor[dest] = value
 
 
 def _forwardcopies(a, b, base=None, match=None):
     """find {dst@b: src@a} copy mapping where a is an ancestor of b"""
 
     if base is None:
         base = a
     match = a.repo().narrowmatch(match)
     # check for working copy
     if b.rev() is None:
         cm = _committedforwardcopies(a, b.p1(), base, match)
         # combine copies from dirstate if necessary
         copies = _chain(cm, _dirstatecopies(b._repo, match))
     else:
         copies = _committedforwardcopies(a, b, base, match)
     return copies
 
 
 def _backwardrenames(a, b, match):
     if a._repo.ui.config(b'experimental', b'copytrace') == b'off':
         return {}
 
     # Even though we're not taking copies into account, 1:n rename situations
     # can still exist (e.g. hg cp a b; hg mv a c). In those cases we
     # arbitrarily pick one of the renames.
     # We don't want to pass in "match" here, since that would filter
     # the destination by it. Since we're reversing the copies, we want
     # to filter the source instead.
     f = _forwardcopies(b, a)
     r = {}
     for k, v in sorted(pycompat.iteritems(f)):
         if match and not match(v):
             continue
         # remove copies
         if v in a:
             continue
         r[v] = k
     return r
 
 
 def pathcopies(x, y, match=None):
     """find {dst@y: src@x} copy mapping for directed compare"""
     repo = x._repo
     debug = repo.ui.debugflag and repo.ui.configbool(b'devel', b'debug.copies')
     if debug:
         repo.ui.debug(
             b'debug.copies: searching copies from %s to %s\n' % (x, y)
         )
     if x == y or not x or not y:
         return {}
     if y.rev() is None and x == y.p1():
         if debug:
             repo.ui.debug(b'debug.copies: search mode: dirstate\n')
         # short-circuit to avoid issues with merge states
         return _dirstatecopies(repo, match)
     a = y.ancestor(x)
     if a == x:
         if debug:
             repo.ui.debug(b'debug.copies: search mode: forward\n')
         copies = _forwardcopies(x, y, match=match)
     elif a == y:
         if debug:
             repo.ui.debug(b'debug.copies: search mode: backward\n')
         copies = _backwardrenames(x, y, match=match)
     else:
         if debug:
             repo.ui.debug(b'debug.copies: search mode: combined\n')
         base = None
         if a.rev() != node.nullrev:
             base = x
         copies = _chain(
             _backwardrenames(x, a, match=match),
             _forwardcopies(a, y, base, match=match),
         )
     _filter(x, y, copies)
     return copies
 
 
 def mergecopies(repo, c1, c2, base):
     """
     Finds moves and copies between context c1 and c2 that are relevant for
     merging. 'base' will be used as the merge base.
 
     Copytracing is used in commands like rebase, merge, unshelve, etc to merge
     files that were moved/ copied in one merge parent and modified in another.
     For example:
 
     o          ---> 4 another commit
     |
     |   o      ---> 3 commit that modifies a.txt
     |  /
     o /        ---> 2 commit that moves a.txt to b.txt
     |/
     o          ---> 1 merge base
 
     If we try to rebase revision 3 on revision 4, since there is no a.txt in
     revision 4, and if user have copytrace disabled, we prints the following
     message:
 
     ```other changed <file> which local deleted```
 
     Returns a tuple where:
 
     "branch_copies" an instance of branch_copies.
 
     "diverge" is a mapping of source name -> list of destination names
     for divergent renames.
 
     This function calls different copytracing algorithms based on config.
     """
     # avoid silly behavior for update from empty dir
     if not c1 or not c2 or c1 == c2:
         return branch_copies(), branch_copies(), {}
 
     narrowmatch = c1.repo().narrowmatch()
 
     # avoid silly behavior for parent -> working dir
     if c2.node() is None and c1.node() == repo.dirstate.p1():
         return (
             branch_copies(_dirstatecopies(repo, narrowmatch)),
             branch_copies(),
             {},
         )
 
     copytracing = repo.ui.config(b'experimental', b'copytrace')
     if stringutil.parsebool(copytracing) is False:
         # stringutil.parsebool() returns None when it is unable to parse the
         # value, so we should rely on making sure copytracing is on such cases
         return branch_copies(), branch_copies(), {}
 
     if usechangesetcentricalgo(repo):
         # The heuristics don't make sense when we need changeset-centric algos
         return _fullcopytracing(repo, c1, c2, base)
 
     # Copy trace disabling is explicitly below the node == p1 logic above
     # because the logic above is required for a simple copy to be kept across a
     # rebase.
     if copytracing == b'heuristics':
         # Do full copytracing if only non-public revisions are involved as
         # that will be fast enough and will also cover the copies which could
         # be missed by heuristics
         if _isfullcopytraceable(repo, c1, base):
             return _fullcopytracing(repo, c1, c2, base)
         return _heuristicscopytracing(repo, c1, c2, base)
     else:
         return _fullcopytracing(repo, c1, c2, base)
 
 
 def _isfullcopytraceable(repo, c1, base):
     """ Checks that if base, source and destination are all no-public branches,
     if yes let's use the full copytrace algorithm for increased capabilities
     since it will be fast enough.
 
     `experimental.copytrace.sourcecommitlimit` can be used to set a limit for
     number of changesets from c1 to base such that if number of changesets are
     more than the limit, full copytracing algorithm won't be used.
     """
     if c1.rev() is None:
         c1 = c1.p1()
     if c1.mutable() and base.mutable():
         sourcecommitlimit = repo.ui.configint(
             b'experimental', b'copytrace.sourcecommitlimit'
         )
         commits = len(repo.revs(b'%d::%d', base.rev(), c1.rev()))
         return commits < sourcecommitlimit
     return False
 
 
 def _checksinglesidecopies(
     src, dsts1, m1, m2, mb, c2, base, copy, renamedelete
 ):
     if src not in m2:
         # deleted on side 2
         if src not in m1:
             # renamed on side 1, deleted on side 2
             renamedelete[src] = dsts1
     elif src not in mb:
         # Work around the "short-circuit to avoid issues with merge states"
         # thing in pathcopies(): pathcopies(x, y) can return a copy where the
         # destination doesn't exist in y.
         pass
     elif mb[src] != m2[src] and not _related(c2[src], base[src]):
         return
     elif mb[src] != m2[src] or mb.flags(src) != m2.flags(src):
         # modified on side 2
         for dst in dsts1:
             copy[dst] = src
 
 
 class branch_copies(object):
     """Information about copies made on one side of a merge/graft.
 
     "copy" is a mapping from destination name -> source name,
     where source is in c1 and destination is in c2 or vice-versa.
 
     "movewithdir" is a mapping from source name -> destination name,
     where the file at source present in one context but not the other
     needs to be moved to destination by the merge process, because the
     other context moved the directory it is in.
 
     "renamedelete" is a mapping of source name -> list of destination
     names for files deleted in c1 that were renamed in c2 or vice-versa.
 
     "dirmove" is a mapping of detected source dir -> destination dir renames.
     This is needed for handling changes to new files previously grafted into
     renamed directories.
     """
 
     def __init__(
         self, copy=None, renamedelete=None, dirmove=None, movewithdir=None
     ):
         self.copy = {} if copy is None else copy
         self.renamedelete = {} if renamedelete is None else renamedelete
         self.dirmove = {} if dirmove is None else dirmove
         self.movewithdir = {} if movewithdir is None else movewithdir
 
     def __repr__(self):
         return (
             '<branch_copies\n  copy=%r\n  renamedelete=%r\n  dirmove=%r\n  movewithdir=%r\n>'
             % (self.copy, self.renamedelete, self.dirmove, self.movewithdir,)
         )
 
 
 def _fullcopytracing(repo, c1, c2, base):
     """ The full copytracing algorithm which finds all the new files that were
     added from merge base up to the top commit and for each file it checks if
     this file was copied from another file.
 
     This is pretty slow when a lot of changesets are involved but will track all
     the copies.
     """
     m1 = c1.manifest()
     m2 = c2.manifest()
     mb = base.manifest()
 
     copies1 = pathcopies(base, c1)
     copies2 = pathcopies(base, c2)
 
     if not (copies1 or copies2):
         return branch_copies(), branch_copies(), {}
 
     inversecopies1 = {}
     inversecopies2 = {}
     for dst, src in copies1.items():
         inversecopies1.setdefault(src, []).append(dst)
     for dst, src in copies2.items():
         inversecopies2.setdefault(src, []).append(dst)
 
     copy1 = {}
     copy2 = {}
     diverge = {}
     renamedelete1 = {}
     renamedelete2 = {}
     allsources = set(inversecopies1) | set(inversecopies2)
     for src in allsources:
         dsts1 = inversecopies1.get(src)
         dsts2 = inversecopies2.get(src)
         if dsts1 and dsts2:
             # copied/renamed on both sides
             if src not in m1 and src not in m2:
                 # renamed on both sides
                 dsts1 = set(dsts1)
                 dsts2 = set(dsts2)
                 # If there's some overlap in the rename destinations, we
                 # consider it not divergent. For example, if side 1 copies 'a'
                 # to 'b' and 'c' and deletes 'a', and side 2 copies 'a' to 'c'
                 # and 'd' and deletes 'a'.
                 if dsts1 & dsts2:
                     for dst in dsts1 & dsts2:
                         copy1[dst] = src
                         copy2[dst] = src
                 else:
                     diverge[src] = sorted(dsts1 | dsts2)
             elif src in m1 and src in m2:
                 # copied on both sides
                 dsts1 = set(dsts1)
                 dsts2 = set(dsts2)
                 for dst in dsts1 & dsts2:
                     copy1[dst] = src
                     copy2[dst] = src
             # TODO: Handle cases where it was renamed on one side and copied
             # on the other side
         elif dsts1:
             # copied/renamed only on side 1
             _checksinglesidecopies(
                 src, dsts1, m1, m2, mb, c2, base, copy1, renamedelete1
             )
         elif dsts2:
             # copied/renamed only on side 2
             _checksinglesidecopies(
                 src, dsts2, m2, m1, mb, c1, base, copy2, renamedelete2
             )
 
     # find interesting file sets from manifests
     addedinm1 = m1.filesnotin(mb, repo.narrowmatch())
     addedinm2 = m2.filesnotin(mb, repo.narrowmatch())
     u1 = sorted(addedinm1 - addedinm2)
     u2 = sorted(addedinm2 - addedinm1)
 
     header = b"  unmatched files in %s"
     if u1:
         repo.ui.debug(b"%s:\n   %s\n" % (header % b'local', b"\n   ".join(u1)))
     if u2:
         repo.ui.debug(b"%s:\n   %s\n" % (header % b'other', b"\n   ".join(u2)))
 
     if repo.ui.debugflag:
         renamedeleteset = set()
         divergeset = set()
         for dsts in diverge.values():
             divergeset.update(dsts)
         for dsts in renamedelete1.values():
             renamedeleteset.update(dsts)
         for dsts in renamedelete2.values():
             renamedeleteset.update(dsts)
 
         repo.ui.debug(
             b"  all copies found (* = to merge, ! = divergent, "
             b"% = renamed and deleted):\n"
         )
         for side, copies in ((b"local", copies1), (b"remote", copies2)):
             if not copies:
                 continue
             repo.ui.debug(b"   on %s side:\n" % side)
             for f in sorted(copies):
                 note = b""
                 if f in copy1 or f in copy2:
                     note += b"*"
                 if f in divergeset:
                     note += b"!"
                 if f in renamedeleteset:
                     note += b"%"
                 repo.ui.debug(
                     b"    src: '%s' -> dst: '%s' %s\n" % (copies[f], f, note)
                 )
         del renamedeleteset
         del divergeset
 
     repo.ui.debug(b"  checking for directory renames\n")
 
     dirmove1, movewithdir2 = _dir_renames(repo, c1, copy1, copies1, u2)
     dirmove2, movewithdir1 = _dir_renames(repo, c2, copy2, copies2, u1)
 
     branch_copies1 = branch_copies(copy1, renamedelete1, dirmove1, movewithdir1)
     branch_copies2 = branch_copies(copy2, renamedelete2, dirmove2, movewithdir2)
 
     return branch_copies1, branch_copies2, diverge
 
 
 def _dir_renames(repo, ctx, copy, fullcopy, addedfiles):
     """Finds moved directories and files that should move with them.
 
     ctx: the context for one of the sides
     copy: files copied on the same side (as ctx)
     fullcopy: files copied on the same side (as ctx), including those that
               merge.manifestmerge() won't care about
     addedfiles: added files on the other side (compared to ctx)
     """
     # generate a directory move map
     d = ctx.dirs()
     invalid = set()
     dirmove = {}
 
     # examine each file copy for a potential directory move, which is
     # when all the files in a directory are moved to a new directory
     for dst, src in pycompat.iteritems(fullcopy):
         dsrc, ddst = pathutil.dirname(src), pathutil.dirname(dst)
         if dsrc in invalid:
             # already seen to be uninteresting
             continue
         elif dsrc in d and ddst in d:
             # directory wasn't entirely moved locally
             invalid.add(dsrc)
         elif dsrc in dirmove and dirmove[dsrc] != ddst:
             # files from the same directory moved to two different places
             invalid.add(dsrc)
         else:
             # looks good so far
             dirmove[dsrc] = ddst
 
     for i in invalid:
         if i in dirmove:
             del dirmove[i]
     del d, invalid
 
     if not dirmove:
         return {}, {}
 
     dirmove = {k + b"/": v + b"/" for k, v in pycompat.iteritems(dirmove)}
 
     for d in dirmove:
         repo.ui.debug(
             b"   discovered dir src: '%s' -> dst: '%s'\n" % (d, dirmove[d])
         )
 
     movewithdir = {}
     # check unaccounted nonoverlapping files against directory moves
     for f in addedfiles:
         if f not in fullcopy:
             for d in dirmove:
                 if f.startswith(d):
                     # new file added in a directory that was moved, move it
                     df = dirmove[d] + f[len(d) :]
                     if df not in copy:
                         movewithdir[f] = df
                         repo.ui.debug(
                             b"   pending file src: '%s' -> dst: '%s'\n"
                             % (f, df)
                         )
                     break
 
     return dirmove, movewithdir
 
 
 def _heuristicscopytracing(repo, c1, c2, base):
     """ Fast copytracing using filename heuristics
 
     Assumes that moves or renames are of following two types:
 
     1) Inside a directory only (same directory name but different filenames)
     2) Move from one directory to another
                     (same filenames but different directory names)
 
     Works only when there are no merge commits in the "source branch".
     Source branch is commits from base up to c2 not including base.
 
     If merge is involved it fallbacks to _fullcopytracing().
 
     Can be used by setting the following config:
 
         [experimental]
         copytrace = heuristics
 
     In some cases the copy/move candidates found by heuristics can be very large
     in number and that will make the algorithm slow. The number of possible
     candidates to check can be limited by using the config
     `experimental.copytrace.movecandidateslimit` which defaults to 100.
     """
 
     if c1.rev() is None:
         c1 = c1.p1()
     if c2.rev() is None:
         c2 = c2.p1()
 
     changedfiles = set()
     m1 = c1.manifest()
     if not repo.revs(b'%d::%d', base.rev(), c2.rev()):
         # If base is not in c2 branch, we switch to fullcopytracing
         repo.ui.debug(
             b"switching to full copytracing as base is not "
             b"an ancestor of c2\n"
         )
         return _fullcopytracing(repo, c1, c2, base)
 
     ctx = c2
     while ctx != base:
         if len(ctx.parents()) == 2:
             # To keep things simple let's not handle merges
             repo.ui.debug(b"switching to full copytracing because of merges\n")
             return _fullcopytracing(repo, c1, c2, base)
         changedfiles.update(ctx.files())
         ctx = ctx.p1()
 
     copies2 = {}
     cp = _forwardcopies(base, c2)
     for dst, src in pycompat.iteritems(cp):
         if src in m1:
             copies2[dst] = src
 
     # file is missing if it isn't present in the destination, but is present in
     # the base and present in the source.
     # Presence in the base is important to exclude added files, presence in the
     # source is important to exclude removed files.
     filt = lambda f: f not in m1 and f in base and f in c2
     missingfiles = [f for f in changedfiles if filt(f)]
 
     copies1 = {}
     if missingfiles:
         basenametofilename = collections.defaultdict(list)
         dirnametofilename = collections.defaultdict(list)
 
         for f in m1.filesnotin(base.manifest()):
             basename = os.path.basename(f)
             dirname = os.path.dirname(f)
             basenametofilename[basename].append(f)
             dirnametofilename[dirname].append(f)
 
         for f in missingfiles:
             basename = os.path.basename(f)
             dirname = os.path.dirname(f)
             samebasename = basenametofilename[basename]
             samedirname = dirnametofilename[dirname]
             movecandidates = samebasename + samedirname
             # f is guaranteed to be present in c2, that's why
             # c2.filectx(f) won't fail
             f2 = c2.filectx(f)
             # we can have a lot of candidates which can slow down the heuristics
             # config value to limit the number of candidates moves to check
             maxcandidates = repo.ui.configint(
                 b'experimental', b'copytrace.movecandidateslimit'
             )
 
             if len(movecandidates) > maxcandidates:
                 repo.ui.status(
                     _(
                         b"skipping copytracing for '%s', more "
                         b"candidates than the limit: %d\n"
                     )
                     % (f, len(movecandidates))
                 )
                 continue
 
             for candidate in movecandidates:
                 f1 = c1.filectx(candidate)
                 if _related(f1, f2):
                     # if there are a few related copies then we'll merge
                     # changes into all of them. This matches the behaviour
                     # of upstream copytracing
                     copies1[candidate] = f
 
     return branch_copies(copies1), branch_copies(copies2), {}
 
 
 def _related(f1, f2):
     """return True if f1 and f2 filectx have a common ancestor
 
     Walk back to common ancestor to see if the two files originate
     from the same file. Since workingfilectx's rev() is None it messes
     up the integer comparison logic, hence the pre-step check for
     None (f1 and f2 can only be workingfilectx's initially).
     """
 
     if f1 == f2:
         return True  # a match
 
     g1, g2 = f1.ancestors(), f2.ancestors()
     try:
         f1r, f2r = f1.linkrev(), f2.linkrev()
 
         if f1r is None:
             f1 = next(g1)
         if f2r is None:
             f2 = next(g2)
 
         while True:
             f1r, f2r = f1.linkrev(), f2.linkrev()
             if f1r > f2r:
                 f1 = next(g1)
             elif f2r > f1r:
                 f2 = next(g2)
             else:  # f1 and f2 point to files in the same linkrev
                 return f1 == f2  # true if they point to the same file
     except StopIteration:
         return False
 
 
 def graftcopies(wctx, ctx, base):
     """reproduce copies between base and ctx in the wctx
 
     Unlike mergecopies(), this function will only consider copies between base
     and ctx; it will ignore copies between base and wctx. Also unlike
     mergecopies(), this function will apply copies to the working copy (instead
     of just returning information about the copies). That makes it cheaper
     (especially in the common case of base==ctx.p1()) and useful also when
     experimental.copytrace=off.
 
     merge.update() will have already marked most copies, but it will only
     mark copies if it thinks the source files are related (see
     merge._related()). It will also not mark copies if the file wasn't modified
     on the local side. This function adds the copies that were "missed"
     by merge.update().
     """
     new_copies = pathcopies(base, ctx)
     _filter(wctx.p1(), wctx, new_copies)
     for dst, src in pycompat.iteritems(new_copies):
         wctx[dst].markcopied(src)