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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 ======= ============== =====================
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@ -35,9 +35,13 @@ def _findexactmatches(repo, added, removed):
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for i, fctx in enumerate(added):
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repo.ui.progress(_('searching for exact renames'), i + len(removed),
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total=numfiles, unit=_('files'))
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h = hashlib.sha1(fctx.data()).digest()
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adata = fctx.data()
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h = hashlib.sha1(adata).digest()
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if h in hashes:
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yield (hashes[h], fctx)
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rfctx = hashes[h]
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# compare between actual file contents for exact identity
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if adata == rfctx.data():
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yield (rfctx, fctx)
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# Done
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repo.ui.progress(_('searching for exact renames'), None)
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