Added tag 5.2.1 for changeset a50fecefa691

py3: make a pycompat.osdevnull, use it in extdiff Differential Revision: https://phab.mercurial-scm.org/D7545

subrepo: use pycompat.open directly instead of importing open from pycompat Differential Revision: https://phab.mercurial-scm.org/D7544

rust-dirs: address failing tests for `dirs` impl with a temporary fix https://phab.mercurial-scm.org/D7252 (5d40317d42b7083b49467502549e25f144888cb3) introduced a regression in Rust tests. This is a temporary fix that replicates the behavior of the C and Python impl, pending the resolution of the discussion (in the phabricator link) about how we actually want to solve this problem. Differential Revision: https://phab.mercurial-scm.org/D7503

cleanup: fix docstring formatting This is just removing the b'' prefix (except demandimportpy2), and making sure it is triple quoted. I skipped the mapping.py module in zope because that's 3rd party code. Differential Revision: https://phab.mercurial-scm.org/D7539

copies: split the combination of the copies mapping in its own function In some case, this part take up to 95% of the copy tracing that take about a hundred second. This poor performance comes from the fact we keep duplciating and merging dictionary that are mostly similar. I want to experiment with smarter native code to do this, so I need to isolate the function first.

copies: do not initialize the dictionary with root in changeset copies We don't strictly need the dict to be prefiled with `{}`. Not doing so will make the next changeset simpler. This part of a preparation to use native code for this part of copy tracing.