automation: install Rust in Linux environment This will install Rust 1.31.1, 1.34.2, and whatever stable is at the time the install runs. We install 1.31.1 as our minimum supported Rust version (I think that's what we're currently targeting) and 1.34 because that's what Debian 10 is shipping. Differential Revision: https://phab.mercurial-scm.org/D6715

automation: update packages in requirements files We like keeping up to date. The content of the autogenerated files changed slightly because I used a newer version of `pip-compile` than what was used previously. Differential Revision: https://phab.mercurial-scm.org/D6714

automation: install latest Python versions This required bumping the pyenv commit so the new versions are available. Differential Revision: https://phab.mercurial-scm.org/D6713

upgrade: introduce the internal code for revlog cloning selection For now we still clone every single revlogs but all the selection mechanism is now in place in the lower layer. The next changesets will introduce the user interface part of the selection.

relnotes: copy "next" to "5.1" and clear "next" To avoid merge conflicts, we want to avoid modifying the file on multiple branches in parallel. This patch is therefore meant to be applied to the stable branch and then quickly be merged to default (at least before edits are made to relnotes/next there). Another option would have been to copy the file on the stable branch and to clear it on the default branch. However, that still results in conflicts if the copy is edited on the stable branch (Mercurial would try to apply the changes from the default branch to it). We could also delete the file in one commit and recreate it in another commit. However, Mercurial is quite inconsistent in what it considers a break in history (see test-copies-unrelated.t), so I'd like to avoid that. Differential Revision: https://phab.mercurial-scm.org/D6705

upgrade: introduce a _copyrevlog method This function copies a revlog from the old store to the new one, without re-adding all deltas manually. This will eventually save a lot of time when some revlog does not needs any conversions. Code actually using this will be introduced in later changesets.

upgrade: rename `_copyrevlogs` to `_clonerevlogs` The underlying revlog method is named `clone`, keeping the naming consistent seems clearer. This is motivated to clarify the difference with an (upcoming) function that simply copy revlog files as is.

upgrade: walk the source store file only once I don't expect this to have a significant performance impact, but it seems simpler and saner to do the operation only once and to keep the result around.

upgrade: always use full text if "full-add" mode is enable We should not be using a delta since the goal is to perform a full addition from scratch in all cases. Without this patch, `hg debugupgraderepo --optimize re-delta-fulladd --run` can crash.

byteify-strings: fix misalignment with multi-line parenthesis This improves the current fix to also take into account cases where the last line ended on the opening `(`, `[` or `{` and adds a regression test.