rhg: add support for narrow clones and sparse checkouts This adds a minimal support that can be implemented without parsing the narrowspec. We can parse the narrowspec and add support for more operations later. The reason we need so few code changes is as follows: Most operations need no special treatment of sparse because some of them only read dirstate (`rhg files` without `-r`), which bakes in the filtering, some of them only read store (`rhg files -r`, `rhg cat`), and some of them read no data at all (`rhg root`, `rhg debugrequirements`). `status` is the command that might care about sparse, so we just disable rhg on it. For narrow clones, `rhg files` clearly needs the narrowspec to work correctly, so we fall back. `rhg cat` seems to work consistently with `hg cat` if the file exists. If the file is hidden by narrow spec, the error message is different and confusing, so that's something that we should improve in follow-up patches. Differential Revision: https://phab.mercurial-scm.org/D11764

update: reformat the `commands.update.check` help This make the various option clearer. Differential Revision: https://phab.mercurial-scm.org/D11852

update: properly overwrite `check` config with `--no-` variants Before this change `--merge` override `commands.update.check=abort/noconflict`, and `--check` "override" `commands.update.check=none/linear`. However the `--no-merge` and `--no-check` version where not doing anything. The `--no-` two flags now behave properly. Differential Revision: https://phab.mercurial-scm.org/D11851

update: add a test for `--merge` overriding the "abort" config I don't see this behavior tested anywhere. Differential Revision: https://phab.mercurial-scm.org/D11850

update: use long version of the flag in the test This helps readability and searchability. Differential Revision: https://phab.mercurial-scm.org/D11848

backout: backed out changeset 5d83a40cd3f8 This is the re-send of the backout in D11757 that I accidentally queued. I'll rewrite the original commit message: ...sigh We do not have Python 3 packaging for thg on Windows where the vast majority of of users use the thg installer for Mercurial. Until this is done (hopefully this cycle), we're keeping Python. (end of the old commit message) On top of this, we have a solid lead to have competent people take care of this packaging issue for us in time for the 6.1 release, which is really the main reason for us to wait. We're trying our best to make this work, so please bear with us. Differential Revision: https://phab.mercurial-scm.org/D11770

status: keep second-ambiguous mtimes during fixup Now that we support the feature, we can keep "second ambiguous" mtime during the fixup phase. These are the mtime that would be ambiguous if we did not had sub-second précions. See the v2 format documentation for details. Differential Revision: https://phab.mercurial-scm.org/D11847

dirstate-item: make sure we load `mtime-second-ambiguous` from disk Now that we support the associated logic, we can safely load it from it. It is no longer necessary to ignore the stored mtime when the flag is encountered. Differential Revision: https://phab.mercurial-scm.org/D11846

dirstate-item: make sure we set the mtime-second-ambiguous on v2 write We want to preserve the second-ambiguity alongside the ambiguous mtime. So we use the decimated flag for that. note: the C code was already doing so. No change was needed to it. Differential Revision: https://phab.mercurial-scm.org/D11845

dirstate-item: ignore mtime to write v1 when `mtime-second-ambiguous` is set We cannot preserve that information in the v1 format so that mtime is ambiguous. Differential Revision: https://phab.mercurial-scm.org/D11844