revlog: skeleton support for version 2 revlogs
There are a number of improvements we want to make to revlogs
that will require a new version - version 2. It is unclear what the
full set of improvements will be or when we'll be done with them.
What I do know is that the process will likely take longer than a
single release, will require input from various stakeholders to
evaluate changes, and will have many contentious debates and
bikeshedding.
It is unrealistic to develop revlog version 2 up front: there
are just too many uncertainties that we won't know until things
are implemented and experiments are run. Some changes will also
be invasive and prone to bit rot, so sitting on dozens of patches
is not practical.
This commit introduces skeleton support for version 2 revlogs in
a way that is flexible and not bound by backwards compatibility
concerns.
An experimental repo requirement for denoting revlog v2 has been
added. The requirement string has a sub-version component to it.
This will allow us to declare multiple requirements in the course
of developing revlog v2. Whenever we change the in-development
revlog v2 format, we can tweak the string, creating a new
requirement and locking out old clients. This will allow us to
make as many backwards incompatible changes and experiments to
revlog v2 as we want. In other words, we can land code and make
meaningful progress towards revlog v2 while still maintaining
extreme format flexibility up until the point we freeze the
format and remove the experimental labels.
To enable the new repo requirement, you must supply an experimental
and undocumented config option. But not just any boolean flag
will do: you need to explicitly use a value that no sane person
should ever type. This is an additional guard against enabling
revlog v2 on an installation it shouldn't be enabled on. The
specific scenario I'm trying to prevent is say a user with a
4.4 client with a frozen format enabling the option but then
downgrading to 4.3 and accidentally creating repos with an
outdated and unsupported repo format. Requiring a "challenge"
string should prevent this.
Because the format is not yet finalized and I don't want to take
any chances, revlog v2's version is currently 0xDEAD. I figure
squatting on a value we're likely never to use as an actual revlog
version to mean "internal testing only" is acceptable. And
"dead" is easily recognized as something meaningful.
There is a bunch of cleanup that is needed before work on revlog
v2 begins in earnest. I plan on doing that work once this patch
is accepted and we're comfortable with the idea of starting down
this path.
ensure that failing ui.atexit handlers report sensibly
$ cat > $TESTTMP/bailatexit.py <<EOF
> from mercurial import util
> def bail():
> raise RuntimeError('ui.atexit handler exception')
>
> def extsetup(ui):
> ui.atexit(bail)
> EOF
$ hg -q --config extensions.bailatexit=$TESTTMP/bailatexit.py \
> help help
hg help [-ecks] [TOPIC]
show help for a given topic or a help overview
error in exit handlers:
Traceback (most recent call last):
File "*/mercurial/dispatch.py", line *, in _runexithandlers (glob)
func(*args, **kwargs)
File "$TESTTMP/bailatexit.py", line *, in bail (glob)
raise RuntimeError('ui.atexit handler exception')
RuntimeError: ui.atexit handler exception
[255]
$ rm $TESTTMP/bailatexit.py
another bad extension
$ echo 'raise Exception("bit bucket overflow")' > badext.py
$ abspathexc=`pwd`/badext.py
$ cat >baddocext.py <<EOF
> """
> baddocext is bad
> """
> EOF
$ abspathdoc=`pwd`/baddocext.py
$ cat <<EOF >> $HGRCPATH
> [extensions]
> gpg =
> hgext.gpg =
> badext = $abspathexc
> baddocext = $abspathdoc
> badext2 =
> EOF
$ hg -q help help 2>&1 |grep extension
*** failed to import extension badext from $TESTTMP/badext.py: bit bucket overflow
*** failed to import extension badext2: No module named badext2
show traceback
$ hg -q help help --traceback 2>&1 | egrep ' extension|^Exception|Traceback|ImportError'
*** failed to import extension badext from $TESTTMP/badext.py: bit bucket overflow
Traceback (most recent call last):
Exception: bit bucket overflow
*** failed to import extension badext2: No module named badext2
Traceback (most recent call last):
ImportError: No module named badext2
names of extensions failed to load can be accessed via extensions.notloaded()
$ cat <<EOF > showbadexts.py
> from mercurial import commands, extensions, registrar
> cmdtable = {}
> command = registrar.command(cmdtable)
> @command('showbadexts', norepo=True)
> def showbadexts(ui, *pats, **opts):
> ui.write('BADEXTS: %s\n' % ' '.join(sorted(extensions.notloaded())))
> EOF
$ hg --config extensions.badexts=showbadexts.py showbadexts 2>&1 | grep '^BADEXTS'
BADEXTS: badext badext2
show traceback for ImportError of hgext.name if debug is set
(note that --debug option isn't applied yet when loading extensions)
$ (hg -q help help --traceback --config ui.debug=True 2>&1) \
> | grep -v '^ ' \
> | egrep 'extension..[^p]|^Exception|Traceback|ImportError|not import'
*** failed to import extension badext from $TESTTMP/badext.py: bit bucket overflow
Traceback (most recent call last):
Exception: bit bucket overflow
could not import hgext.badext2 (No module named *badext2): trying hgext3rd.badext2 (glob)
Traceback (most recent call last):
ImportError: No module named *badext2 (glob)
could not import hgext3rd.badext2 (No module named *badext2): trying badext2 (glob)
Traceback (most recent call last):
ImportError: No module named *badext2 (glob)
*** failed to import extension badext2: No module named badext2
Traceback (most recent call last):
ImportError: No module named badext2
confirm that there's no crash when an extension's documentation is bad
$ hg help --keyword baddocext
*** failed to import extension badext from $TESTTMP/badext.py: bit bucket overflow
*** failed to import extension badext2: No module named badext2
Topics:
extensions Using Additional Features