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
======= ============== =====================
#!/usr/bin/env python
# Filter output by pyflakes to control which warnings we check
from __future__ import absolute_import, print_function
import re
import sys
lines = []
for line in sys.stdin:
# We blacklist tests that are too noisy for us
pats = [
r"undefined name '(WindowsError|memoryview)'",
r"redefinition of unused '[^']+' from line",
]
keep = True
for pat in pats:
if re.search(pat, line):
keep = False
break # pattern matches
if keep:
fn = line.split(':', 1)[0]
f = open(fn)
data = f.read()
f.close()
if 'no-' 'check-code' in data:
continue
lines.append(line)
for line in lines:
sys.stdout.write(line)
print()
# self test of "undefined name" detection for other than 'memoryview'
if False:
print(memoryview)
print(undefinedname)