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
======= ============== =====================
# See http://EditorConfig.org for the specification
root = true
[*.py]
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indent_style = space
trim_trailing_whitespace = true
[*.{c,h}]
indent_size = 8
indent_style = tab
trim_trailing_whitespace = true