tests/test-empty-dir.t

narrow: intersect provided matcher with narrowmatcher in `hg diff`

This provides significant speedups when running diff, and no change in behavior
that I'm aware of (or that the tests found). I tested with a repo that I started
using narrow in after it was created and attempted to run `hg diff -c .` and
similar commands in it on a commit that had files not in the narrowspec.

Timing numbers below, using a similar setup as my previous commits.
before=9db85644, m-u is mozilla-unified at eb39298e432d (flatmanifest) and
0553b7f29eaf (treemanifest). l-d-r is a repo simulating a situation I've
encountered where there's one directory with 30k+ subdirectories. N means
narrow, T means treemanifest. The narrowspec is pretty small when in use, and
importantly the narrowspec is applied *after* doing the initial checkout
(without narrowing), so all of these files exist in the filesystem, which is not
normally the case if someone has been using narrow for the entire life of the
clone.

Anything less than a 5% difference in performance is most likely noise.

    diff --git:
    repo  | N | T | before (mean +- stdev) | after (mean +- stdev) | % of before
    ------+---+---+------------------------+-----------------------+------------
    m-u   |   |   | 1.292 s +-  0.009 s    | 1.295 s +-  0.010 s   | 100.2%
    m-u   |   | x | 1.296 s +-  0.042 s    | 1.299 s +-  0.026 s   | 100.2%
    m-u   | x |   | 1.292 s +-  0.010 s    | 1.297 s +-  0.021 s   | 100.4%
    m-u   | x | x | 84.2 ms +-   1.2 ms    | 83.6 ms +-   0.2 ms   |  99.3%
    l-d-r |   |   | 188.7 ms +-   2.7 ms   | 188.8 ms +-   2.0 ms  | 100.1%
    l-d-r |   | x | 189.9 ms +-   1.5 ms   | 189.4 ms +-   1.2 ms  |  99.7%
    l-d-r | x |   | 97.1 ms +-   1.0 ms    | 87.1 ms +-   1.0 ms   |  89.7% <--
    l-d-r | x | x | 96.9 ms +-   0.8 ms    | 87.2 ms +-   0.7 ms   |  90.0% <--

    diff -c . --git:
    repo  | N | T | before (mean +- stdev) | after (mean +- stdev) | % of before
    ------+---+---+------------------------+-----------------------+------------
    m-u   |   |   | 231.6 ms +-   3.1 ms   | 228.9 ms +-   1.6 ms  |  98.8%
    m-u   |   | x | 150.5 ms +-   1.7 ms   | 150.7 ms +-   1.4 ms  | 100.1%
    m-u   | x |   | 233.7 ms +-   2.4 ms   | 232.2 ms +-   1.9 ms  |  99.4%
    m-u   | x | x | 126.1 ms +-   1.2 ms   | 126.8 ms +-   1.2 ms  | 100.6%
    l-d-r |   |   | 82.1 ms +-   2.0 ms    | 81.8 ms +-   1.4 ms   |  99.6%
    l-d-r |   | x | 3.732 s +-  0.020 s    | 3.746 s +-  0.027 s   | 100.4%
    l-d-r | x |   | 83.1 ms +-   0.8 ms    | 107.6 ms +-   2.4 ms  | 129.5% <--
    l-d-r | x | x | 758.2 ms +-  38.8 ms   | 188.5 ms +-   1.8 ms  |  24.9% <--

    rebase -r . --keep -d .^^:
    repo  | N | T | before (mean +- stdev) | after (mean +- stdev) | % of before
    ------+---+---+------------------------+-----------------------+------------
    m-u   |   |   | 5.532 s +-  0.087 s    | 5.496 s +-  0.016 s   |  99.3%
    m-u   |   | x | 5.554 s +-  0.061 s    | 5.532 s +-  0.013 s   |  99.6%
    m-u   | x |   | 5.602 s +-  0.134 s    | 5.508 s +-  0.035 s   |  98.3%
    m-u   | x | x | 582.2 ms +-  15.2 ms   | 572.9 ms +-  12.0 ms  |  98.4%
    l-d-r |   |   | 629.5 ms +-  12.3 ms   | 622.5 ms +-   7.3 ms  |  98.9%
    l-d-r |   | x | 6.173 s +-  0.062 s    | 6.185 s +-  0.076 s   | 100.2%
    l-d-r | x |   | 274.5 ms +-  10.0 ms   | 272.1 ms +-   6.2 ms  |  99.1%
    l-d-r | x | x | 4.835 s +-  0.056 s    | 4.826 s +-  0.034 s   |  99.8%

    status --change . --copies:
    repo  | N | T | before (mean +- stdev) | after (mean +- stdev) | % of before
    ------+---+---+------------------------+-----------------------+------------
    m-u   |   |   | 214.4 ms +-   1.4 ms   | 212.2 ms +-   1.7 ms  |  99.0%
    m-u   |   | x | 130.9 ms +-   1.2 ms   | 131.7 ms +-   1.1 ms  | 100.6%
    m-u   | x |   | 215.0 ms +-   2.1 ms   | 214.9 ms +-   2.7 ms  | 100.0%
    m-u   | x | x | 109.5 ms +-   2.3 ms   | 107.8 ms +-   0.9 ms  |  98.4%
    l-d-r |   |   | 79.6 ms +-   0.9 ms    | 79.8 ms +-   1.6 ms   | 100.3%
    l-d-r |   | x | 3.799 s +-  0.037 s    | 3.928 s +-  0.021 s   | 103.4% <--?
    l-d-r | x |   | 82.7 ms +-   0.7 ms    | 83.2 ms +-   1.0 ms   | 100.6%
    l-d-r | x | x | 746.8 ms +-   6.1 ms   | 739.0 ms +-   4.2 ms  |  99.0%

    status --copies:
    repo  | N | T | before (mean +- stdev) | after (mean +- stdev) | % of before
    ------+---+---+------------------------+-----------------------+------------
    m-u   |   |   | 1.884 s +-  0.012 s    | 1.885 s +-  0.013 s   | 100.1%
    m-u   |   | x | 1.897 s +-  0.027 s    | 1.909 s +-  0.077 s   | 100.6%
    m-u   | x |   | 1.886 s +-  0.021 s    | 1.891 s +-  0.030 s   | 100.3%
    m-u   | x | x | 92.0 ms +-   0.7 ms    | 92.4 ms +-   0.4 ms   | 100.4%
    l-d-r |   |   | 570.3 ms +-  18.7 ms   | 552.2 ms +-   4.5 ms  |  96.8%
    l-d-r |   | x | 568.9 ms +-  16.1 ms   | 567.2 ms +-  11.9 ms  |  99.7%
    l-d-r | x |   | 171.1 ms +-   2.5 ms   | 170.4 ms +-   1.2 ms  |  99.6%
    l-d-r | x | x | 171.6 ms +-   3.4 ms   | 171.5 ms +-   1.7 ms  |  99.9%

    update $rev^; ~/src/hg/hg{hg}/hg update $rev:
    repo  | N | T | before (mean +- stdev) | after (mean +- stdev) | % of before
    ------+---+---+------------------------+-----------------------+------------
    m-u   |   |   | 3.107 s +-  0.017 s    | 3.116 s +-  0.012 s   | 100.3%
    m-u   |   | x | 2.943 s +-  0.010 s    | 2.945 s +-  0.019 s   | 100.1%
    m-u   | x |   | 3.116 s +-  0.033 s    | 3.118 s +-  0.027 s   | 100.1%
    m-u   | x | x | 318.5 ms +-   2.7 ms   | 320.8 ms +-   4.8 ms  | 100.7%
    l-d-r |   |   | 428.9 ms +-   4.4 ms   | 429.5 ms +-   4.0 ms  | 100.1%
    l-d-r |   | x | 9.593 s +-  0.081 s    | 9.869 s +-  0.043 s   | 102.9%
    l-d-r | x |   | 253.2 ms +-   3.6 ms   | 254.0 ms +-   2.8 ms  | 100.3%
    l-d-r | x | x | 1.613 s +-  0.009 s    | 1.630 s +-  0.017 s   | 101.1%

Differential Revision: https://phab.mercurial-scm.org/D4587

  $ hg init

  $ echo 123 > a
  $ hg add a
  $ hg commit -m "first" a

  $ mkdir sub
  $ echo 321 > sub/b
  $ hg add sub/b
  $ hg commit -m "second" sub/b

  $ cat sub/b
  321

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

  $ cat sub/b 2>/dev/null || echo "sub/b not present"
  sub/b not present

  $ test -d sub || echo "sub not present"
  sub not present