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 ======= ============== =====================