tests/test-push-checkheads-pruned-B8.t

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outdated and unsupported repo format.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.

====================================
Testing head checking code: Case B-2
====================================

Mercurial checks for the introduction of new heads on push. Evolution comes
into play to detect if existing branches on the server are being replaced by
some of the new one we push.

This case is part of a series of tests checking this behavior.

Category B: simple case involving pruned changesets
TestCase 2: multi-changeset branch, head is pruned, rest is superceeded, through other

.. old-state:
..
.. * 2 changeset branch
..
.. new-state:
..
.. * old head is rewritten then pruned
.. * 1 new branch succeeding to the other changeset in the old branch (through another obsolete branch)
..
.. expected-result:
..
.. * push allowed
..
.. graph-summary:
..
..   B ø⇠⊗ B'
..     | | A'
..   A ø⇠ø⇠◔ A''
..     |/ /
..     | /
..     |/
..     ●

  $ . $TESTDIR/testlib/push-checkheads-util.sh

Test setup
----------

  $ mkdir B8
  $ cd B8
  $ setuprepos
  creating basic server and client repo
  updating to branch default
  2 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ cd server
  $ mkcommit B0
  $ cd ../client
  $ hg pull
  pulling from $TESTTMP/B8/server (glob)
  searching for changes
  adding changesets
  adding manifests
  adding file changes
  added 1 changesets with 1 changes to 1 files
  (run 'hg update' to get a working copy)
  $ hg up 0
  0 files updated, 0 files merged, 1 files removed, 0 files unresolved
  $ mkcommit A1
  created new head
  $ mkcommit B1
  $ hg up 0
  0 files updated, 0 files merged, 2 files removed, 0 files unresolved
  $ mkcommit A2
  created new head
  $ hg debugobsolete `getid "desc(A0)" ` `getid "desc(A1)"`
  $ hg debugobsolete `getid "desc(B0)" ` `getid "desc(B1)"`
  $ hg debugobsolete --record-parents `getid "desc(B1)"`
  $ hg debugobsolete `getid "desc(A1)" ` `getid "desc(A2)"`
  $ hg log -G --hidden
  @  c1f8d089020f (draft): A2
  |
  | x  262c8c798096 (draft): B1
  | |
  | x  f6082bc4ffef (draft): A1
  |/
  | x  d73caddc5533 (draft): B0
  | |
  | x  8aaa48160adc (draft): A0
  |/
  o  1e4be0697311 (public): root
  

Actual testing
--------------

  $ hg push
  pushing to $TESTTMP/B8/server (glob)
  searching for changes
  adding changesets
  adding manifests
  adding file changes
  added 1 changesets with 1 changes to 1 files (+1 heads)
  4 new obsolescence markers

  $ cd ../..