diff: describe behavior by using --from/--to instead of varying revision count I very recently updated the documentation to prefer `--from`/`--to` over `-r`, but I missed the plain-text description of how the command behaves when given different numbers of revisions (I guess I just scanned the text for "-r"). This patch fixes that. Differential Revision: https://phab.mercurial-scm.org/D9562

histedit: adjust comment describing `edit` action for clarity Differential Revision: https://phab.mercurial-scm.org/D9561

histedit: tweak `edit` message to try and guide users to our workflow histedit predates evolve, so it drops you on an _uncommitted_ version of the commit you're amending/splitting, which is in contrast to git which expects you to use `git commit --amend` (I think - I'm basing this on internal bug reports). My hope is that this output will guide users a little more towards the expected workflow. Differential Revision: https://phab.mercurial-scm.org/D9560

procutil: don't assign stdin to None, use os.devnull instead It will be painful to take care of procutil.stdin being None everywhere. Thanks to Yuya who recommended it.

dispatch: move IOError handling and flushing of streams to `dispatch()` Instead of patching both dispatch code and commandserver code, we directly handle this in `dispatch.dispatch()`. Thanks to Yuya who recommended this.

simplemerge: write output only once it's complete `simplemerge()` can write either to `ui.fout` or to the file context (for in-memory merge). This patch simplifies the code a bit by making it build the output the same way regardless of where it's written, and then writes the whole output at once. I don't think it will be a problem that we don't output anything until the whole file is merged even if the file is large. Differential Revision: https://phab.mercurial-scm.org/D9550

simplemerge: avoid quadratic concatenation when building output text I haven't checked if the difference is measurable, but the new version is no less readable or idiomatic, so I don't think performance numbers are needed. Differential Revision: https://phab.mercurial-scm.org/D9549

simplemerge: work with opts as native strings instead of bytes There was little reason to use `pycompat.byteskwargs()` in `simplemerge()` as far as I could tell. Differential Revision: https://phab.mercurial-scm.org/D9548

hghave: update the check for virtualenv This started as `hghave --test-features` failing on Windows in `test-hghave.t`. IDK how this worked, as neither my Linux nor Windows machines have the old attribute with virtualenv 20.2.2, even on py2. I think this was noticed recently because 357d8415aa27 mentioned an AttributeError, and mitigated by making this py2 only. But as mentioned, this is also a problem on py2 (where the failure was observed). When I got this working by removing the attribute reference, the command in the test failed because the `--no-site-package` argument was removed some time ago. Therefore, this backs out 357d8415aa27 and references a known good attribute (which was done to suppress the warning about an unused import) that also ensures the command does not need the argument. Since there appears to be (minor) broken stuff on py3, manually apply the `no-py3` guard that was backed out of the check itself. Differential Revision: https://phab.mercurial-scm.org/D9547

singlehead: introduce option to restrict to public changes The new experimental.single-head-per-branch:public-changes-only option restricts the single-head-per-branch filter to public changesets. This is useful when serving one repository with different views as publishing and non-publishing repository. Differential Revision: https://phab.mercurial-scm.org/D9525