tests/test-issue1877.t

revset: optimize "draft() & ::x" pattern

The `draft() & ::x` type query could be common for selecting one or more
draft feature branches being worked on.

Before this patch, `::x` may travel through the changelog DAG for a long
distance until it gets a smaller revision number than `min(draft())`. It
could be very slow on long changelog with distant (in terms of revision
numbers) drafts.

This patch adds a fast path for this situation, and will stop traveling the
changelog DAG once `::x` hits a non-draft revision.

The fast path also works for `secret()` and `not public()`.

To measure the performance difference, I used drawdag to create a repo that
emulates distant drafts:

          DRAFT4
           |
          DRAFT3 # draft
          /
  PUBLIC9999 # public
      |
  PUBLIC9998
      |
      .   DRAFT2
      .    |
      .   DRAFT1 # draft
      |   /
  PUBLIC0001 # public

And measured the performance using the repo:

  (BEFORE)
  $ hg perfrevset 'draft() & ::(DRAFT2+DRAFT4)'
  ! wall 0.017132 comb 0.010000 user 0.010000 sys 0.000000 (best of 156)
  $ hg perfrevset 'draft() & ::(all())'
  ! wall 0.024221 comb 0.030000 user 0.030000 sys 0.000000 (best of 113)
  (AFTER)
  $ hg perfrevset 'draft() & ::(DRAFT2+DRAFT4)'
  ! wall 0.000243 comb 0.000000 user 0.000000 sys 0.000000 (best of 9303)
  $ hg perfrevset 'draft() & ::(all())'
  ! wall 0.004319 comb 0.000000 user 0.000000 sys 0.000000 (best of 655)

Differential Revision: https://phab.mercurial-scm.org/D441

https://bz.mercurial-scm.org/1877

  $ hg init a
  $ cd a
  $ echo a > a
  $ hg add a
  $ hg ci -m 'a'
  $ echo b > a
  $ hg ci -m'b'
  $ hg up 0
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg book main
  $ hg book
   * main                      0:cb9a9f314b8b
  $ echo c > c
  $ hg add c
  $ hg ci -m'c'
  created new head
  $ hg book
   * main                      2:d36c0562f908
  $ hg heads
  changeset:   2:d36c0562f908
  bookmark:    main
  tag:         tip
  parent:      0:cb9a9f314b8b
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     c
  
  changeset:   1:1e6c11564562
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     b
  
  $ hg up 1e6c11564562
  1 files updated, 0 files merged, 1 files removed, 0 files unresolved
  (leaving bookmark main)
  $ hg merge main
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  (branch merge, don't forget to commit)
  $ hg book
     main                      2:d36c0562f908
  $ hg ci -m'merge'
  $ hg book
     main                      2:d36c0562f908

  $ cd ..