rewriteutil: check for divergence This code is adapted from the code in the evolve extension. It seems to be equivalent as far as the evolve extension's test suite can tell (the only impact when making their `precheck()` delegate to our version is that error messages are less detailed). I had to change the error message to work with "change branch of" being inserted as the action. Differential Revision: https://phab.mercurial-scm.org/D10518

rewriteutil: adapt "cannot %s while merging" to work with "change branch of" `rewriteutil.precheck()` creates error messages by inserting a given verb into a sentence. The `hg branch -r` command passes in "change branch of" as the verb. That doesn't work well with "cannot %s while merging" (making it "cannot change branch of while merging"). Let's insert a "changeset" there to make it work better. Building sentences like this seems obviously bad for i18n, but fixing that is out of scope for this series, IMO. Differential Revision: https://phab.mercurial-scm.org/D10530

rewriteutil: point to help about instability when rewriting creates orphan This replicates the message from the evolve extension. Differential Revision: https://phab.mercurial-scm.org/D10517

help: add topic about evolution, based on text from evolve extension I've taken the text produced by `hg help evolution` when the evolve extension is enabled and made that available by the same command with just hg core. Changes I've made: * Added "(EXPERIMENTAL)" to the title. (That doesn't hide the topic from `hg help`, though.) * Replaced old-style `experimental.evolution=<names>` config by new-style `experimental.evolution.<name>=true`. * Replaces a "obsolete markers" by "obsolescence markers". * Removed most content from "Current feature status". When the evolve extension is enabled, its help text takes precedence. Differential Revision: https://phab.mercurial-scm.org/D10516

rewriteutil: add devel warning if precheck is called with contexts I'm trying to upstream parts from the evolve extension. This check exists there. Differential Revision: https://phab.mercurial-scm.org/D10515

rewriteutil: replace "null changeset" by "the null revision" in error message The evolve extension uses "the null revision" and we seem to use that term much more frequently in core too. Differential Revision: https://phab.mercurial-scm.org/D10514

relnotes: copy contents of "next" to "5.8" and clear "next" The same procedure as every year^Wcycle. Unlike previous cycles, I haven't actually recorded the copy because we don't want to propagate further changes in "next" (from the stable branch) to "5.8". Differential Revision: https://phab.mercurial-scm.org/D10500

dirstateguard: use mktemp-like functionality to generate the backup filenames Previously these were generated with names like: `dirstate.backup.commit.<memory address of dirstateguard>` This could cause problems if two hg commands ran at the same time that used the same memory address, (which is apparently not uncommon if chg is involved), as memory addresses are not unique across processes. This issue was reported in the post-review comments on http://phab.mercurial-scm.org/D9952. Differential Revision: https://phab.mercurial-scm.org/D10504

node: replace nullid and friends with nodeconstants class The introduction of 256bit hashes require changes to nullid and other constant magic values. Start pushing them down from repository and revlog where sensible. Differential Revision: https://phab.mercurial-scm.org/D9465

repoview: separate concerns in _filteredrepotypes comment The cited issue in Python bugtracker is closed, but hasn't been fixed. We've been able to use the attached example and reproduce it with Python 3.9. The point where it turns from needless stress on the GC to the an actual leak is when one factors in the fact that the GC was before Python 3.4 unable to collect some types (see PEP 442). Note that even with Python 2.7, the simple example of cycles due to __mro__ are collectable. This was seen again with the example attached on the CPython issue.