similar: compare between actual file contents for exact identity
Before this patch, similarity detection logic (for addremove and
automv) depends entirely on SHA-1 digesting. But this causes incorrect
rename detection, if:
- removing file A and adding file B occur at same committing, and
- SHA-1 hash values of file A and B are same
This may prevent security experts from managing sample files for
SHAttered issue in Mercurial repository, for example.
https://security.googleblog.com/2017/02/announcing-first-sha1-collision.html
https://shattered.it/
Hash collision itself isn't so serious for core repository
functionality of Mercurial, described by mpm as below, though.
https://www.mercurial-scm.org/wiki/mpm/SHA1
This patch compares between actual file contents after hash comparison
for exact identity.
Even after this patch, SHA-1 is still used, because it is reasonable
enough to quickly detect existence of "(almost) same" file.
- replacing SHA-1 causes decreasing performance, and
- replacement of it has ambiguity, yet
Getting content of removed file (= rfctx.data()) at each exact
comparison should be cheap enough, even though getting content of
added one costs much.
======= ============== =====================
file fctx data() reads from
======= ============== =====================
removed filectx in-memory revlog data
added workingfilectx storage
======= ============== =====================
# Extension to write out fake unsupported records into the merge state
#
#
from __future__ import absolute_import
from mercurial import (
cmdutil,
merge,
)
cmdtable = {}
command = cmdutil.command(cmdtable)
@command('fakemergerecord',
[('X', 'mandatory', None, 'add a fake mandatory record'),
('x', 'advisory', None, 'add a fake advisory record')], '')
def fakemergerecord(ui, repo, *pats, **opts):
with repo.wlock():
ms = merge.mergestate.read(repo)
records = ms._makerecords()
if opts.get('mandatory'):
records.append(('X', 'mandatory record'))
if opts.get('advisory'):
records.append(('x', 'advisory record'))
ms._writerecords(records)