tests/test-narrow-shallow.t

dirstate-tree: Avoid BTreeMap double-lookup when inserting a dirstate entry

The child nodes of a given node in the tree-shaped dirstate are kept in a
`BTreeMap` where keys are file names as strings. Finding or inserting a value
in the map takes `O(log(n))` string comparisons, which adds up when constructing
the tree.

The `entry` API allows finding a "spot" in the map that may or may not be
occupied and then access that value or insert a new one without doing map
lookup again. However the current API is limited in that calling `entry`
requires an owned key (and so a memory allocation), even if it ends up not
being used in the case where the map already has a value with an equal key.

This is still a win, with 4% better end-to-end time for `hg status` measured
here with hyperfine:

```
Benchmark #1: ../hg2/hg status -R $REPO --config=experimental.dirstate-tree.in-memory=1
  Time (mean ± σ):      1.337 s ±  0.018 s    [User: 892.9 ms, System: 437.5 ms]
  Range (min … max):    1.316 s …  1.373 s    10 runs

Benchmark #2: ./hg status -R $REPO --config=experimental.dirstate-tree.in-memory=1
  Time (mean ± σ):      1.291 s ±  0.008 s    [User: 853.4 ms, System: 431.1 ms]
  Range (min … max):    1.283 s …  1.309 s    10 runs

Summary
  './hg status -R $REPO --config=experimental.dirstate-tree.in-memory=1' ran
    1.04 ± 0.02 times faster than '../hg2/hg status -R $REPO --config=experimental.dirstate-tree.in-memory=1'
```

* ./hg is this revision
* ../hg2/hg is its parent
* $REPO is an old snapshot of mozilla-central

Differential Revision: https://phab.mercurial-scm.org/D10550

#require no-reposimplestore

  $ . "$TESTDIR/narrow-library.sh"

  $ hg init master
  $ cd master
  $ cat >> .hg/hgrc <<EOF
  > [narrow]
  > serveellipses=True
  > EOF
  $ for x in `$TESTDIR/seq.py 10`
  > do
  >   echo $x > "f$x"
  >   hg add "f$x"
  > done
  $ hg commit -m "Add root files"
  $ mkdir d1 d2
  $ for x in `$TESTDIR/seq.py 10`
  > do
  >   echo d1/$x > "d1/f$x"
  >   hg add "d1/f$x"
  >   echo d2/$x > "d2/f$x"
  >   hg add "d2/f$x"
  > done
  $ hg commit -m "Add d1 and d2"
  $ for x in `$TESTDIR/seq.py 10`
  > do
  >   echo f$x rev2 > "f$x"
  >   echo d1/f$x rev2 > "d1/f$x"
  >   echo d2/f$x rev2 > "d2/f$x"
  >   hg commit -m "Commit rev2 of f$x, d1/f$x, d2/f$x"
  > done
  $ cd ..

narrow and shallow clone the d2 directory

  $ hg clone --narrow ssh://user@dummy/master shallow --include "d2" --depth 2
  requesting all changes
  adding changesets
  adding manifests
  adding file changes
  added 4 changesets with 13 changes to 10 files
  new changesets *:* (glob)
  updating to branch default
  10 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ cd shallow
  $ hg log -T '{rev}{if(ellipsis,"...")}: {desc}\n'
  3: Commit rev2 of f10, d1/f10, d2/f10
  2: Commit rev2 of f9, d1/f9, d2/f9
  1: Commit rev2 of f8, d1/f8, d2/f8
  0...: Commit rev2 of f7, d1/f7, d2/f7
  $ hg update 0
  3 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ cat d2/f7 d2/f8
  d2/f7 rev2
  d2/8

  $ cd ..

change every upstream file once

  $ cd master
  $ for x in `$TESTDIR/seq.py 10`
  > do
  >   echo f$x rev3 > "f$x"
  >   echo d1/f$x rev3 > "d1/f$x"
  >   echo d2/f$x rev3 > "d2/f$x"
  >   hg commit -m "Commit rev3 of f$x, d1/f$x, d2/f$x"
  > done
  $ cd ..

pull new changes with --depth specified. There were 10 changes to the d2
directory but the shallow pull should only fetch 3.

  $ cd shallow
  $ hg pull --depth 2
  pulling from ssh://user@dummy/master
  searching for changes
  adding changesets
  adding manifests
  adding file changes
  added 4 changesets with 10 changes to 10 files
  new changesets *:* (glob)
  (run 'hg update' to get a working copy)
  $ hg log -T '{rev}{if(ellipsis,"...")}: {desc}\n'
  7: Commit rev3 of f10, d1/f10, d2/f10
  6: Commit rev3 of f9, d1/f9, d2/f9
  5: Commit rev3 of f8, d1/f8, d2/f8
  4...: Commit rev3 of f7, d1/f7, d2/f7
  3: Commit rev2 of f10, d1/f10, d2/f10
  2: Commit rev2 of f9, d1/f9, d2/f9
  1: Commit rev2 of f8, d1/f8, d2/f8
  0...: Commit rev2 of f7, d1/f7, d2/f7

  $ hg update 4
  10 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ cat d2/f7 d2/f8
  d2/f7 rev3
  d2/f8 rev2
  $ hg update 7
  3 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ cat d2/f10
  d2/f10 rev3

  $ cd ..

cannot clone with zero or negative depth

  $ hg clone --narrow ssh://user@dummy/master bad --include "d2" --depth 0
  requesting all changes
  remote: abort: depth must be positive, got 0
  abort: pull failed on remote
  [100]
  $ hg clone --narrow ssh://user@dummy/master bad --include "d2" --depth -1
  requesting all changes
  remote: abort: depth must be positive, got -1
  abort: pull failed on remote
  [100]