view tests/test-issue1175.t @ 32697:19b9fc40cc51

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outdated and unsupported repo format.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.

https://bz.mercurial-scm.org/1175

  $ hg init
  $ touch a
  $ hg ci -Am0
  adding a

  $ hg mv a a1
  $ hg ci -m1

  $ hg co 0
  1 files updated, 0 files merged, 1 files removed, 0 files unresolved

  $ hg mv a a2
  $ hg up
  note: possible conflict - a was renamed multiple times to:
   a2
   a1
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved

  $ hg ci -m2

  $ touch a
  $ hg ci -Am3
  adding a

  $ hg mv a b
  $ hg ci -Am4 a

  $ hg ci --debug --traceback -Am5 b
  committing files:
  b
  warning: can't find ancestor for 'b' copied from 'a'!
  committing manifest
  committing changelog
  updating the branch cache
  committed changeset 5:83a687e8a97c80992ba385bbfd766be181bfb1d1

  $ hg verify
  checking changesets
  checking manifests
  crosschecking files in changesets and manifests
  checking files
  4 files, 6 changesets, 4 total revisions

  $ hg export --git tip
  # HG changeset patch
  # User test
  # Date 0 0
  #      Thu Jan 01 00:00:00 1970 +0000
  # Node ID 83a687e8a97c80992ba385bbfd766be181bfb1d1
  # Parent  1d1625283f71954f21d14c3d44d0ad3c019c597f
  5
  
  diff --git a/b b/b
  new file mode 100644

https://bz.mercurial-scm.org/show_bug.cgi?id=4476

  $ hg init foo
  $ cd foo
  $ touch a && hg ci -Aqm a
  $ hg mv a b
  $ echo b1 >> b
  $ hg ci -Aqm b1
  $ hg up 0
  1 files updated, 0 files merged, 1 files removed, 0 files unresolved
  $ hg mv a b
  $ echo b2 >> b
  $ hg ci -Aqm b2
  $ hg graft 1
  grafting 1:5974126fad84 "b1"
  merging b
  warning: conflicts while merging b! (edit, then use 'hg resolve --mark')
  abort: unresolved conflicts, can't continue
  (use 'hg resolve' and 'hg graft --continue')
  [255]
  $ echo a > b
  $ echo b3 >> b
  $ hg resolve --mark b
  (no more unresolved files)
  continue: hg graft --continue
  $ hg graft --continue
  grafting 1:5974126fad84 "b1"
  warning: can't find ancestor for 'b' copied from 'a'!
  $ hg log -f b -T 'changeset:   {rev}:{node|short}\nsummary:     {desc}\n\n'
  changeset:   3:376d30ccffc0
  summary:     b1
  
  changeset:   2:416baaa2e5e4
  summary:     b2
  
  changeset:   0:3903775176ed
  summary:     a