status: prefer relative paths in Rust code … when the repository root is under the current directory, so the kernel needs to traverse fewer directory in every call to `read_dir` or `symlink_metadata`. Better yet would be to use libc functions like `openat` and `fstatat` to remove such repeated traversals entirely, but the standard library does not provide APIs based on those. Maybe with a crate like https://crates.io/crates/openat instead? Benchmarks of `rhg status` show that this patch is neutral in some configurations, and makes the command up to ~20% faster in others. Below is semi-arbitrary subset of results. The four numeric columns are: time (in seconds) with this changeset’s parent, time with this changeset, time difference (negative is better), time ratio (less than 1 is better). ``` mercurial-dirstate-v1 | default-plain-clean.no-iu.pbr | 0.0061 -> 0.0059: -0.0002 (0.97) mercurial-dirstate-v2 | default-plain-clean.no-iu.pbr | 0.0029 -> 0.0028: -0.0001 (0.97) mozilla-dirstate-v1 | default-plain-clean.no-iu.pbr | 0.2110 -> 0.2102: -0.0007 (1.00) mozilla-dirstate-v2 | default-copies-clean.ignored.pbr | 0.0489 -> 0.0401: -0.0088 (0.82) mozilla-dirstate-v2 | default-copies-clean.no-iu.pbr | 0.0479 -> 0.0393: -0.0085 (0.82) mozilla-dirstate-v2 | default-copies-large.all.pbr | 0.1262 -> 0.1210: -0.0051 (0.96) mozilla-dirstate-v2 | default-copies-small.ignored-unknown.pbr | 0.1262 -> 0.1200: -0.0062 (0.95) mozilla-dirstate-v2 | default-copies-small.ignored.pbr | 0.0536 -> 0.0417: -0.0119 (0.78) mozilla-dirstate-v2 | default-copies-small.no-iu.pbr | 0.0482 -> 0.0393: -0.0089 (0.81) mozilla-dirstate-v2 | default-plain-clean.ignored.pbr | 0.0518 -> 0.0402: -0.0116 (0.78) mozilla-dirstate-v2 | default-plain-clean.no-iu.pbr | 0.0481 -> 0.0392: -0.0088 (0.82) mozilla-dirstate-v2 | default-plain-large.all.pbr | 0.1271 -> 0.1218: -0.0052 (0.96) mozilla-dirstate-v2 | default-plain-small.ignored-unknown.pbr | 0.1225 -> 0.1202: -0.0022 (0.98) mozilla-dirstate-v2 | default-plain-small.ignored.pbr | 0.0510 -> 0.0418: -0.0092 (0.82) mozilla-dirstate-v2 | default-plain-small.no-iu.pbr | 0.0480 -> 0.0394: -0.0086 (0.82) netbeans-dirstate-v1 | default-plain-clean.no-iu.pbr | 0.1442 -> 0.1422: -0.0020 (0.99) netbeans-dirstate-v2 | default-plain-clean.no-iu.pbr | 0.0325 -> 0.0282: -0.0043 (0.87) ``` Differential Revision: https://phab.mercurial-scm.org/D12175

==========================================================
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 experimental.revlogv2=enable-unstable-format-and-corrupt-my-data
  $ 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 experimental.revlogv2=no
  $ hg debugformat -v -R up-no-side-data | egrep 'changelog-v2|revlog-v2'
  revlog-v2:           no     no      no
  changelog-v2:        no     no      no
  $ hg debugformat -v -R up-no-side-data --config experimental.revlogv2=enable-unstable-format-and-corrupt-my-data | egrep 'changelog-v2|revlog-v2'
  revlog-v2:           no    yes      no
  changelog-v2:        no     no      no
  $ hg debugupgraderepo -R up-no-side-data --config experimental.revlogv2=enable-unstable-format-and-corrupt-my-data > /dev/null

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

  $ hg init up-side-data --config experimental.revlogv2=enable-unstable-format-and-corrupt-my-data
  $ hg debugformat -v -R up-side-data | egrep 'changelog-v2|revlog-v2'
  revlog-v2:          yes     no      no
  changelog-v2:        no     no      no
  $ hg debugformat -v -R up-side-data --config experimental.revlogv2=no | egrep 'changelog-v2|revlog-v2'
  revlog-v2:          yes     no      no
  changelog-v2:        no     no      no
  $ hg debugupgraderepo -R up-side-data --config experimental.revlogv2=no > /dev/null