relnotes/6.6

update: add a Rust fast-path when updating from null (and clean)

This case is easy to detect and we have all we need to generate a valid
working copy and dirstate entirely in Rust, which speeds things up
considerably:

On my machine updating a repo of ~300k files goes from 10.00s down to 4.2s,
all while consuming 50% less system time, with all caches hot.
Something to note is that further improvements will probably happen
with the upcoming `InnerRevlog` series that does smarter
mmap hanlding, especially for filelogs.

Here are benchmark numbers on a machine with only 4 cores (and no SMT enabled)

```
### data-env-vars.name               = heptapod-public-2024-03-25-ds2-pnm
  # benchmark.name                   = hg.command.update
  # bin-env-vars.hg.py-re2-module    = default
  # bin-env-vars.hg.changeset.node   = <this change>
  # benchmark.variants.atomic-update = no
  # benchmark.variants.scenario      = null-to-tip
  # benchmark.variants.worker        = default
default: 5.328762  ~~~~~
rust: 1.308654  (-75.44%, -4.02)
### data-env-vars.name               = mercurial-devel-2024-03-22-ds2-pnm
  # benchmark.name                   = hg.command.update
  # bin-env-vars.hg.py-re2-module    = default
  # bin-env-vars.hg.changeset.node   = <this change>
  # benchmark.variants.atomic-update = no
  # benchmark.variants.scenario      = null-to-tip
  # benchmark.variants.worker        = default
default: 1.693271  ~~~~~
rust: 1.151053  (-32.02%, -0.54)
### data-env-vars.name               = mozilla-unified-2024-03-22-ds2-pnm
  # benchmark.name                   = hg.command.update
  # bin-env-vars.hg.py-re2-module    = default
  # bin-env-vars.hg.changeset.node   = <this change>
  # benchmark.variants.atomic-update = no
  # benchmark.variants.scenario      = null-to-tip
  # benchmark.variants.worker        = default
default: 38.901613  ~~~~~
rust: 11.637880 (-70.08%, -27.26)
### data-env-vars.name               = netbsd-xsrc-public-2024-09-19-ds2-pnm
  # benchmark.name                   = hg.command.update
  # bin-env-vars.hg.py-re2-module    = default
  # bin-env-vars.hg.changeset.node   = <this change>
  # benchmark.variants.atomic-update = no
  # benchmark.variants.scenario      = null-to-tip
  # benchmark.variants.worker        = default
default: 4.793727  ~~~~~
rust: 1.505905  (-68.59%, -3.29)
```

= Mercurial 6.6.3 =

 * tests: don't use "status" operand of dd in test-censor.t (issue6858)
 * tests: make sha256line.py available for all tests
 * tests: use sha256line.py instead of /dev/random in test-censor.t (issue6858)
 * tests: fix nondeterministic test failure in test-contrib-perf.t
 * rust-changelog: don't panic on empty file lists
 * grep: restore usage of --include/--exclude options

 = Mercurial 6.6.2 =

 * histedit: remove superfluous echo() and endwin() calls (issue6859)
 * persistent-nodemap: avoid writing nodemap for empty revlog
 * persistent-nodemap: respect the mmap setting when refreshing data
 * bundle: do not detect --base argument that match nothing as lack of argument
 * narrow: prevent removal of ACL-defined excludes
 * pycompat: fix bytestr(bytes) in Python 3.11

= Mercurial 6.6.1 =

The first two patches fix aborted transactions that could happen since 6.6.

 * revlog: avoid exposing delayed index entry too widely in non-inline revlog
 * revlog: avoid wrongly updating the data file location on "divert"
 * tests: do not fail tests in a state with uncommitted .py file removal
 * perf-tags: fix the --clear-fnode-cache-rev code
 * perf-tags: fix clear_cache_fnodes to actually clear that cache
 * censor: fix things around inlining
 * Various Python 3 cleanups
 * Various Windows test suite fixes

= Mercurial 6.6 =

As usual, a *lot* of patches don't make it to this list.

== New Features ==
 * rust-config: add support for default config items
 * rhg: add config defaults to configitems.toml
 * rhg: support "status FILE"
 * rhg: support rhg files [FILE]
 * commands: add admin namespace
 * admin-command: add verify command
 * debug-delta-chain: add options to control what we compute
 * Added some caching for uncompressed revlog chunks that speed up some operations

== New Experimental Features ==

== Bug Fixes ==
 * Improve OpenVMS support
 * byteify-strings: passe sysstr to attr function and wrapper
 * journal: track bookmark deletion
 * transaction: actually delete file created during the transaction on rollback
 * pull: avoid referencing a variable before it is initialized
 * rust-filepatterns: also normalize RelPath
 * narrow: hoist a variable to a higher level to avoid use-before-init warning
 * convert: stabilize subversion date sorter
 * run-tests: detect HGWITHRUSTEXT value
 * censor: accept censored revision during upgrade
 * rust-matchers: fix quadratic complexity in `FileMatcher`
 * unstable: do not consider internal phases when computing unstable
 * Still a whole bunch of Python 2 -> 3 migration leftovers

== Backwards Compatibility Changes ==
 * perf: display all timing by default
 * infinitepush: drop the extension
 * debug-delta-chain: print less data by default

== Internal API Changes ==

 * The revlog interface has been significantly cleaned up.
 * configitems: add `documentation` field
 * configitems: declare items in a TOML file
 * configitems: move blackbox's config items to the new configitems.toml
 * path-suboption: deprecated specifying the attributes as bytes
 * pycompat: deprecate using bytes
 * check-code: drop the `safehasattr` rule
 * safehasattr: drop usage in favor of hasattr
 * rust: add `UncheckedRevision` type
 * rust: implement the `Graph` trait for all revlogs
 * rust: make `Revision` a newtype
 * perf: change the way we approach revlog reading
 * perf: ensure all readlog's reading is done within a `reading` context
 * delta-chain: move the debugdeltachain command in revlogutils

== Miscellaneous ==