rust: fix possible out-of-bounds read through index_get_parents() index_get_parents() is an internal function, which doesn't check if the specified rev is valid. If rustlazyancestors() were instantiated with an invalid stoprev, it would access to invalid memory region. This is NOT a security fix as there's no Python code triggering the bug, but included in this series to not give a notion about the memory issue fixed by the previous patch.

revlog: fix out-of-bounds access by negative parents read from revlog (SEC) 82d6a35cf432 wasn't enough. Several callers don't check negative revisions but for -1 (nullrev), which would directly lead to out-of-bounds read, and buffer overflow could follow. RCE might be doable with carefully crafted revlog structure, though I don't think this would be useful attack surface.

rust: peek_mut optim for lazy ancestors This is one of the two optimizations that are also present in the Python code: replacing pairs of pop/push on the BinaryHeap by single updates, hence having it under the hood maintain its consistency (sift) only once. On Mozilla central, the measured gain (see details below) is around 7%. Creating the PeekMut object by calling peek_mut() right away instead of peek() first is less efficient (gain is only 4%, stats not included). Our interpretation is that its creation has a cost which is vasted in the cases where it ends by droping the value (Peekmut::pop() just does self.heap.pop() anyway). On the other hand, the immutable peek() is very fast: it's just taking a reference in the underlying vector. The Python version still has another optimization: if parent(current) == current-1, then the heap doesn't need to maintain its consistency, since we already know that it's bigger than all the others in the heap. Rust's BinaryHeap doesn't allow us to mutate its biggest element with no housekeeping, but we tried it anyway, with a copy of the BinaryHeap implementation with a dedicaded added method: it's not worth the technical debt in our opinion (we measured only a further 1.6% improvement). One possible explanation would be that the sift is really fast anyway in that case, whereas it's not in the case of Python, because it's at least partly done in slow Python code. Still it's possible that replacing BinaryHeap by something more dedicated to discrete ordered types could be faster. Measurements on mozilla-central: Three runs of 'hg perfancestors' on the parent changeset: Moyenne des médianes: 0.100587 ! wall 0.100062 comb 0.100000 user 0.100000 sys 0.000000 (best of 98) ! wall 0.135804 comb 0.130000 user 0.130000 sys 0.000000 (max of 98) ! wall 0.102864 comb 0.102755 user 0.099286 sys 0.003469 (avg of 98) ! wall 0.101486 comb 0.110000 user 0.110000 sys 0.000000 (median of 98) ! wall 0.096804 comb 0.090000 user 0.090000 sys 0.000000 (best of 100) ! wall 0.132235 comb 0.130000 user 0.120000 sys 0.010000 (max of 100) ! wall 0.100258 comb 0.100300 user 0.096000 sys 0.004300 (avg of 100) ! wall 0.098384 comb 0.100000 user 0.100000 sys 0.000000 (median of 100) ! wall 0.099925 comb 0.100000 user 0.100000 sys 0.000000 (best of 98) ! wall 0.133518 comb 0.140000 user 0.130000 sys 0.010000 (max of 98) ! wall 0.102381 comb 0.102449 user 0.098265 sys 0.004184 (avg of 98) ! wall 0.101891 comb 0.090000 user 0.090000 sys 0.000000 (median of 98) Mean of the medians: 0.100587 On the present changeset: ! wall 0.091344 comb 0.090000 user 0.090000 sys 0.000000 (best of 100) ! wall 0.122728 comb 0.120000 user 0.110000 sys 0.010000 (max of 100) ! wall 0.093268 comb 0.093300 user 0.089300 sys 0.004000 (avg of 100) ! wall 0.092567 comb 0.100000 user 0.090000 sys 0.010000 (median of 100) ! wall 0.093294 comb 0.080000 user 0.080000 sys 0.000000 (best of 100) ! wall 0.144887 comb 0.150000 user 0.140000 sys 0.010000 (max of 100) ! wall 0.097708 comb 0.097700 user 0.093400 sys 0.004300 (avg of 100) ! wall 0.094980 comb 0.100000 user 0.090000 sys 0.010000 (median of 100) ! wall 0.091262 comb 0.090000 user 0.080000 sys 0.010000 (best of 100) ! wall 0.123772 comb 0.130000 user 0.120000 sys 0.010000 (max of 100) ! wall 0.093188 comb 0.093200 user 0.089300 sys 0.003900 (avg of 100) ! wall 0.092364 comb 0.100000 user 0.090000 sys 0.010000 (median of 100) Mean of the medians is 0.0933 Differential Revision: https://phab.mercurial-scm.org/D5358

fuzz: grep away HAVE_GETC_UNLOCKED in pyconfig.h to avoid msan badness Per discussion with Greg Smith and the patches on https://bugs.python.org/issue35214. This, combined with the previous patch, fixes msan builds on oss-fuzz. Differential Revision: https://phab.mercurial-scm.org/D5363

fuzz: more correctly specify CFLAGS and LDFLAGS when building Python Gets us closer to a working msan build alongside our asan build. Differential Revision: https://phab.mercurial-scm.org/D5362

tests: stabilize test-blackbox.t on Windows I didn't look into why the error is more detailed, but that seems like it's a good thing (other than for recording tests).

tests: stabilize for recent wcache changes This goes with 47e3f554df35::d5622dfe4ba3. I'm not sure if it was really expected that there would be no wcache directory if neither execbit nor symlink is supported.

extdiff: avoid double backslashes in the displayed tool path on Windows This shows the tool path in the help, and changed in 67b180c0e263. uirepr() already does the same thing, but that undoes the mangling in its call to repr().

contrib: add a helper script that help to build interesting repositories The script is dedicated to building a couple of repositories that should be interesting to run discovery from one another. It seems a common enough need to contribute it upstream.

py3: listify filter() to call len() on it Differential Revision: https://phab.mercurial-scm.org/D5354