tests/test-rebuildstate.t

revset: optimize missing ancestor expressions

A missing ancestor expression is any expression of the form (::x - ::y) or
equivalent. Such expressions are remarkably common, and so far have involved
multiple walks down the DAG, followed by a set difference operation.

With this patch, such expressions will be transformed into uses of the fast
algorithm at ancestor.missingancestor.

For a repository with over 600,000 revisions, perfrevset for '::tip - ::-10000'
returns:

Before: ! wall 3.999575 comb 4.000000 user 3.910000 sys 0.090000 (best of 3)
After:  ! wall 0.132423 comb 0.130000 user 0.130000 sys 0.000000 (best of 75)

basic test for hg debugrebuildstate

  $ hg init repo
  $ cd repo

  $ touch foo bar
  $ hg ci -Am 'add foo bar'
  adding bar
  adding foo

  $ touch baz
  $ hg add baz
  $ hg rm bar

  $ hg debugrebuildstate

state dump after

  $ hg debugstate --nodates | sort
  n 644         -1 bar
  n 644         -1 foo

status

  $ hg st -A
  ! bar
  ? baz
  C foo

  $ cd ..