hg-core: Add a limited read only `revlog` implementation Only covers the needs of the upcoming `rhg debugdata` command. Differential Revision: https://phab.mercurial-scm.org/D8958

mergestate: define NO_OP_ACTION in module scope instead of inside mergeresult This makes sure it isn't intended to be overridden by subclasses. Thanks to Yuya for the nice suggestion. Differential Revision: https://phab.mercurial-scm.org/D9025

mergestate: introduce a new ACTION_KEEP_NEW `ACTION_KEEP` is overloaded and it's hard to figure out how we end up with this KEEP, what was the state of things. In a previous patch, we introduced `ACTION_KEEP_ABSENT` which represents files which are kept absent in the working directory. There is another special case where we keep the file when it's not present on both ancestor and remote side. We introduce a dedicated action for that. The goal is to use these information to make bid merge smarter. Differential Revision: https://phab.mercurial-scm.org/D9002

repoview: don't crash if mergestate points to non-existent node Differential Revision: https://phab.mercurial-scm.org/D9078

tests: demonstrate crash caused by pinning of non-existent mergestate node If the mergestate somehow contains a reference to a non-existent node, it causes most commands to crash since aaeccdb6e654 (repoview: pin revisions for `local` and `other` when a merge is active, 2020-09-04). This patch adds a test showing that. Differential Revision: https://phab.mercurial-scm.org/D9077

git: also convert timezone to int (issue6359) Credit to moshez for testing this in the wild. Differential Revision: https://phab.mercurial-scm.org/D9062

chg: fallback to original hg if stdio fds are missing If stdio fds are missing (ex. fd 0 is not present), chg might open fds that take the numbers 0, and attachio would send the wrong fds to the client, which might cause unwanted behaviors. Avoid that by detecting the missing fds and falling back to the original hg. Differential Revision: https://phab.mercurial-scm.org/D9058

locking: remove support for inheriting locks in subprocess This seems to have been added for merge driver, and since merge driver is now gone... Differential Revision: https://phab.mercurial-scm.org/D9053

mergedriver: delete it The merge driver code was added in late 2015. I think '406a654b::6f045b56 & user("sid0")' is a reasonable revset for finding the relevant commits, including preparation for it. The code is very poorly tested, which makes it very hard to maintain. It seems it's only used by FB and they don't use this code base anymore, so let's remove the code to make it easier for us to maintain our product. Differential Revision: https://phab.mercurial-scm.org/D9041

rust-cpython: switch logging facade from `simple_logger` to `env_logger` `simple_logger` is just too simple. `env_logger` supports logging to `stderr`, and logging filtering, for example, which are becoming necessary now. The project is nicely active. Differential Revision: https://phab.mercurial-scm.org/D8990