fuzz: new target to fuzz jsonescapeu8fast This code just feels complicated enough we should go ahead and give it a dedicated fuzzer: we've found bugs in similar things before. Differential Revision: https://phab.mercurial-scm.org/D7034

fuzz: new fuzzer for fncache-related functions Not all of these are strictly fncache-related, but they all have th same signature and similar-enough behavior that we may as well fuzz them together. No obvious bugs for once, but these felt like they were just complicated enough to cover. Differential Revision: https://phab.mercurial-scm.org/D7033

fuzz: exercise a little more revlog code Differential Revision: https://phab.mercurial-scm.org/D7032

fuzz: new fuzzer for dirs.c This found a six-year-old bug immediately, and then I put it through a few CPU-days of time before sending it. Differential Revision: https://phab.mercurial-scm.org/D7031

dirs: fix trivial over-read of input data This code, introduced in 8c0a7eeda06d, was intentionally over-reading an input string to avoid getting a shared string object for a one-byte input. Unfortunately with an empty input (like in the case of a fuzzer getting started) this was a trivial over-read and triggered an AddressSanitizer failure. I went out of my way to make sure the code still does the copy-avoidance tricks. I don't think this change will cost us much performance since the one-character strings should be cached aggressively anyway. Differential Revision: https://phab.mercurial-scm.org/D7030

sidedatacopies: deal with upgrading and downgrading to that format This is quite useful to test this on real life data. Differential Revision: https://phab.mercurial-scm.org/D6955

sidedatacopies: move various copies related function to the copies modules We will need to access these logic form the copies module. So we move them from their higher level module to the lower level `copies` module. We cannot use them from their top level module as it would create cycles. Differential Revision: https://phab.mercurial-scm.org/D6954

sidedatacopies: read rename information from sidedata Repository using the new format now use changeset centric algorithm and read the copies information from the changelog sidedata. Differential Revision: https://phab.mercurial-scm.org/D6953

changelog: make copies related function return None or a valid value With the previous code, existing but empty value were not "decoded", leading to the method returning one of `None`, some valid value (`list` or `dict`) or `b''`. On a general basis, not explicitly checking for None is a source of bugs. Having a clean return types will help the side-data copies code in future changesets. Differential Revision: https://phab.mercurial-scm.org/D7037

test: fix zstd related output in pure tests Differential Revision: https://phab.mercurial-scm.org/D7036