tests/test-issue2137.t

revset: make parents() O(number of parents)

Strip executes a revset like this:

max(parents(_intlist('1234\x001235')) - _intlist('1234\x001235'))

Previously the parents() revset would do 'subset & parents' which iterates over
each item in the subset and checks if it's in parents.  subset is usually the
entire repo (a spanset) so this takes a while.

Reversing the parameters to be 'parents & subset' means the operation becomes
O(number of parents) instead of O(size of repo). It also means the result gets
evaluated immediately (since parents isn't a lazy set), but I think this is a
win in most scenarios.

This shaves 0.3 seconds off strip (amend/histedit/rebase/etc) for large repositories.

revset #0: parents(20000)
0) obsolete feature not enabled but 54243 markers found!
! wall 0.006256 comb 0.010000 user 0.010000 sys 0.000000 (best of 289)
1) obsolete feature not enabled but 54243 markers found!
! wall 0.000391 comb 0.000000 user 0.000000 sys 0.000000 (best of 4323)

http://mercurial.selenic.com/bts/issue2137

Setup:

create a little extension that has 3 side-effects:
1) ensure changelog data is not inlined
2) make revlog to use lazyparser
3) test that repo.lookup() works
1 and 2 are preconditions for the bug; 3 is the bug.

  $ cat > commitwrapper.py <<EOF
  > from mercurial import extensions, node, revlog
  > 
  > def reposetup(ui, repo):
  >     class wraprepo(repo.__class__):
  >         def commit(self, *args, **kwargs):
  >             result = super(wraprepo, self).commit(*args, **kwargs)
  >             tip1 = node.short(repo.changelog.tip())
  >             tip2 = node.short(repo.lookup(tip1))
  >             assert tip1 == tip2
  >             ui.write('new tip: %s\n' % tip1)
  >             return result
  >     repo.__class__ = wraprepo
  > 
  > def extsetup(ui):
  >     revlog._maxinline = 8             # split out 00changelog.d early
  >     revlog._prereadsize = 8           # use revlog.lazyparser
  > EOF

  $ cat >> $HGRCPATH <<EOF
  > [extensions]
  > commitwrapper = `pwd`/commitwrapper.py
  > EOF

  $ hg init repo1
  $ cd repo1
  $ echo a > a
  $ hg commit -A -m'add a with a long commit message to make the changelog a bit bigger'
  adding a
  new tip: 553596fad57b

Test that new changesets are visible to repo.lookup():

  $ echo a >> a
  $ hg commit -m'one more commit to demonstrate the bug'
  new tip: 799ae3599e0e

  $ hg tip
  changeset:   1:799ae3599e0e
  tag:         tip
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     one more commit to demonstrate the bug
  

  $ cd ..