revlog: code for `revlogv0` in its own module This code is mostly unused compatiblity code. Yet it take a prohiminent place in the `revlog.py` module. That module is already quite big, so we move all that code in a dedicated module. Differential Revision: https://phab.mercurial-scm.org/D10511

revlog: have an explicit "pack_header" method Having to pass the version header when retrieving the binary version of every single entry is a bit silly. So we extract that special logic in its own method. This also prepare the move to newer revlog format, not storing the header within an actual entry… Differential Revision: https://phab.mercurial-scm.org/D10510

revlog: remove the revlogio class The class only contains a single `parseindex` method. Lets just make it a function and remove the `revlogio` class. It served us well but became thinner and thinner overtime. Differential Revision: https://phab.mercurial-scm.org/D10509

revlog: fix some comment style They displease check-code. Differential Revision: https://phab.mercurial-scm.org/D10542

revlog: add a `entry_binary` method on index The revlog index is already responsible for unpacking the binary entry, it would be simpler to make it responsible for packing them. In practice the C version of the index is already doing this internally. We introduce a "entry_binary" method that return the binary version of an existing revision. The method currently need to also take the revlog header to deal with the "first revision" special case. We will introduce further refactor in a later changeset to split that logic out. Differential Revision: https://phab.mercurial-scm.org/D10508

template: make an explicit closure for formatting entry in peerurls This is about to be become significantly more complicated as `ui.path[x]` will become a list. Differential Revision: https://phab.mercurial-scm.org/D10443

template: use `list_paths` in `peerurls` Using common code will make it simpler to update the logic behind the path definition and storage. Differential Revision: https://phab.mercurial-scm.org/D10442

paths: use `list_paths` in `hg paths` Using common code will make it simpler to update the logic behind the path definition and storage. Differential Revision: https://phab.mercurial-scm.org/D10441

urlutil: introduce a new `list_paths` function This function will be useful for command and template that wants to display path related information. Differential Revision: https://phab.mercurial-scm.org/D10440

urlutil: deprecate `getpath` There as no remaining user of that function. Differential Revision: https://phab.mercurial-scm.org/D10439

urlutil: inline the relevant part of `getpath` in `get_push_paths` The part that `get_push_paths` needs is quite simple, inclining will help us to deprecated `getpath`. Differential Revision: https://phab.mercurial-scm.org/D10438

url_util: introduce a `try_path` function That function… try a build a path, returning None on failure. This helps us to simplify various part of the existing code. Differential Revision: https://phab.mercurial-scm.org/D10437

narrow: add more status messages when narrowing Each of the steps I added status messages for in this patch frequently take minutes or tens of minutes for our internal users. It would be nice to also have a progress bar but that will have to come later. Differential Revision: https://phab.mercurial-scm.org/D10503

narrow: add progress-reporting when looking for local changes in `hg tracked` Looking for local changes (changes not on the given remote) can take a long time, so we should have progress-reporting for it. Differential Revision: https://phab.mercurial-scm.org/D10501

chg: pass --no-profile to disable profiling when starting hg serve If profiling is enabled via global/user config (as far as I can tell, this doesn't affect use of the --profile flag, but it probably does affect --config profiling.enabled=1), then the profiling data can be *cumulative* for the lifetime of the chg process. This leads to some "interesting" results where hg claims the walltime is something like 200s on a command that took only a second or two to run. Worse, however, is that with at least some profilers (such as the default "stat" profiler), this can cause a large slowdown while generating the profiler output. Differential Revision: https://phab.mercurial-scm.org/D10470

profiling: add --no-profile to disable profiling enabled via config Differential Revision: https://phab.mercurial-scm.org/D10469

tests: fix test-chg to ignore a warning about being unable to set locale This is apparently coming from bash when bash is providing the sh that we're using to execute the .sh file generated by run-tests for this test. Bash on my machine: ``` $ sh --version GNU bash, version 5.1.4(1)-release (x86_64-pc-linux-gnu) Copyright (C) 2020 Free Software Foundation, Inc. License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html> This is free software; you are free to change and redistribute it. There is NO WARRANTY, to the extent permitted by law. $ sh sh-5.1$ LC_CTYPE=unsupported_value echo hi sh: warning: setlocale: LC_CTYPE: cannot change locale (unsupported_value): No such file or directory hi ``` Differential Revision: https://phab.mercurial-scm.org/D10468

branch: delete obsolete message about changing branch of obsolete commit We now rely on `rewriteutil.precheck()` to check for divergence, so we don't need the extra check in `cmdutil.changebranch()`. The former check is a little less strict in that it allows you to rewrite a commit without non-obsolete successors. Differential Revision: https://phab.mercurial-scm.org/D10519

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.

repoview: fix memory leak of filtered repo classes The leak occurs in long-running server processes with extensions, and is measured at 110kB per request. Before this change, the contents of the `_filteredrepotypes` cache are not properly garbage collected, despite it begin a `WeakKeyDictionary`. Extensions have a tendency to generate a new repository class for each `localrepo` instantiation. Server processes based on `hgwebdir_mod` will instantiate a new `localrepo` for each HTTP request that involves a repository. As a result, with a testing process that repeatedly opens a repository with several extensions activated (`topic` notably among them), we see a steady increase in resident memory of 110kB per repository instantiation before this change. This is also true, if we call `gc.collect()` at each instantiation, like `hgwebdir_mod` does, or not. The cause of the leak is that the *values* aren't weak references. This change uses `weakref.ref` for the values, and this makes in our measurements the resident size increase drop to 5kB per repository instantiation, with no explicit call of `gc.collect()` at all. There is currently no reason to believe that this remaining leak of 5kB is related to or even due to Mercurial core. We've also seen evidence that `ui.ui` instances weren't properly garbage collected before the change (with the change, they are). This could explain why the figures are relatively high. In theory, the collection of weak references could lead to much more misses in the cache, so we measured the impact on the original case that was motivation for introducing that cache in 7e89bd0cfb86 (see also issue5043): `hg convert` of the mozilla-central repository. The bad news here is that there is a major memory leak there, both with and without the present changeset. There were no more cache misses, and we could see no more memory leak with this change: the resident size after importing roughly 100000 changesets was at 12.4GB before, and 12.5GB after. The small increase is mentioned for completeness only, and we believe that it should be ignored, at least as long as the main leak isn't fixed. At less than 1% of the main leak, even finding out whether it is merely noise would be wasteful. Original context where this was spotted and first mitigated: https://foss.heptapod.net/heptapod/heptapod/-/issues/466 The leak reduction was also obtained in Heptapod inner HTTP server, which amounts to the same as `hgwebdir_mod` for these questions. The measurements done with Python 3.9, similar figures seen with 3.8. More work on our side would be needed to give measurements with 2.7, because of testing server process does not support it.

repoview: style change in newtype() cache handling This way of writing it does not change the logic at all, but is more fit for the change we want to make in the next changeset. If anything, that's one dict lookup less in the hot path, but that should be non measurable.