tests/test-sidedata.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

==========================================================
Test file dedicated to checking side-data related behavior
==========================================================

Check data can be written/read from sidedata
============================================

  $ cat << EOF >> $HGRCPATH
  > [extensions]
  > testsidedata=$TESTDIR/testlib/ext-sidedata.py
  > EOF

  $ hg init test-sidedata --config format.exp-use-side-data=yes
  $ cd test-sidedata
  $ echo aaa > a
  $ hg add a
  $ hg commit -m a --traceback
  $ echo aaa > b
  $ hg add b
  $ hg commit -m b
  $ echo xxx >> a
  $ hg commit -m aa

  $ hg debugsidedata -c 0
  2 sidedata entries
   entry-0001 size 4
   entry-0002 size 32
  $ hg debugsidedata -c 1 -v
  2 sidedata entries
   entry-0001 size 4
    '\x00\x00\x006'
   entry-0002 size 32
    '\x98\t\xf9\xc4v\xf0\xc5P\x90\xf7wRf\xe8\xe27e\xfc\xc1\x93\xa4\x96\xd0\x1d\x97\xaaG\x1d\xd7t\xfa\xde'
  $ hg debugsidedata -m 2
  2 sidedata entries
   entry-0001 size 4
   entry-0002 size 32
  $ hg debugsidedata a  1
  2 sidedata entries
   entry-0001 size 4
   entry-0002 size 32

Check upgrade behavior
======================

Right now, sidedata has not upgrade support

Check that we can upgrade to sidedata
-------------------------------------

  $ hg init up-no-side-data --config format.exp-use-side-data=no
  $ hg debugformat -v -R up-no-side-data
  format-variant     repo config default
  fncache:            yes    yes     yes
  dotencode:          yes    yes     yes
  generaldelta:       yes    yes     yes
  share-safe:          no     no      no
  sparserevlog:       yes    yes     yes
  persistent-nodemap:  no     no      no (no-rust !)
  persistent-nodemap: yes    yes      no (rust !)
  copies-sdc:          no     no      no
  revlog-v2:           no     no      no
  plain-cl-delta:     yes    yes     yes
  compression:        zlib   zlib    zlib (no-zstd !)
  compression:        zstd   zstd    zstd (zstd !)
  compression-level:  default default default
  $ hg debugformat -v -R up-no-side-data --config format.exp-use-side-data=yes
  format-variant     repo config default
  fncache:            yes    yes     yes
  dotencode:          yes    yes     yes
  generaldelta:       yes    yes     yes
  share-safe:          no     no      no
  sparserevlog:       yes    yes     yes
  persistent-nodemap:  no     no      no (no-rust !)
  persistent-nodemap: yes    yes      no (rust !)
  copies-sdc:          no     no      no
  revlog-v2:           no    yes      no
  plain-cl-delta:     yes    yes     yes
  compression:        zlib   zlib    zlib (no-zstd !)
  compression:        zstd   zstd    zstd (zstd !)
  compression-level:  default default default
  $ hg debugupgraderepo -R up-no-side-data --config format.exp-use-side-data=yes > /dev/null

Check that we can downgrade from sidedata
-----------------------------------------

  $ hg init up-side-data --config format.exp-use-side-data=yes
  $ hg debugformat -v -R up-side-data
  format-variant     repo config default
  fncache:            yes    yes     yes
  dotencode:          yes    yes     yes
  generaldelta:       yes    yes     yes
  share-safe:          no     no      no
  sparserevlog:       yes    yes     yes
  persistent-nodemap:  no     no      no (no-rust !)
  persistent-nodemap: yes    yes      no (rust !)
  copies-sdc:          no     no      no
  revlog-v2:          yes     no      no
  plain-cl-delta:     yes    yes     yes
  compression:        zlib   zlib    zlib (no-zstd !)
  compression:        zstd   zstd    zstd (zstd !)
  compression-level:  default default default
  $ hg debugformat -v -R up-side-data --config format.exp-use-side-data=no
  format-variant     repo config default
  fncache:            yes    yes     yes
  dotencode:          yes    yes     yes
  generaldelta:       yes    yes     yes
  share-safe:          no     no      no
  sparserevlog:       yes    yes     yes
  persistent-nodemap:  no     no      no (no-rust !)
  persistent-nodemap: yes    yes      no (rust !)
  copies-sdc:          no     no      no
  revlog-v2:          yes     no      no
  plain-cl-delta:     yes    yes     yes
  compression:        zlib   zlib    zlib (no-zstd !)
  compression:        zstd   zstd    zstd (zstd !)
  compression-level:  default default default
  $ hg debugupgraderepo -R up-side-data --config format.exp-use-side-data=no > /dev/null