v0.9.0

### Breaking changes

* The minimum supported Rust version (MSRV) is now 1.71.0.

* The storage format of branches, tags, and git refs has changed. Newly-stored
  repository data will no longer be loadable by older binaries.

* The `:` revset operator is deprecated. Use `::` instead. We plan to delete the
  `:` form in jj 0.15+.

* The `--allow-large-revsets` flag for `jj rebase` and `jj new` was replaced by
  a `all:` before the revset. For example, use `jj rebase -d 'all:foo-'`
  instead of `jj rebase --allow-large-revsets -d 'foo-'`.

* The `--allow-large-revsets` flag for `jj rebase` and `jj new` can no longer be
  used for allowing duplicate destinations. Include the potential duplicates
  in a single expression instead (e.g. `jj new 'all:x|y'`).

* The `push.branch-prefix` option was renamed to `git.push-branch-prefix`.

* The default editor on Windows is now `Notepad` instead of `pico`.

* `jj` will fail attempts to snapshot new files larger than 1MiB by default. This behavior
  can be customized with the `snapshot.max-new-file-size` config option.

* Author and committer signatures now use empty strings to represent unset
  names and email addresses. The `author`/`committer` template keywords and
  methods also return empty strings.
  Older binaries may not warn user when attempting to `git push` commits
  with such signatures.

* In revsets, the working-copy or remote symbols (such as `@`, `workspace_id@`,
  and `branch@remote`) can no longer be quoted as a unit. If a workspace or
  branch name contains whitespace, quote the name like `"branch name"@remote`.
  Also, these symbols will not be resolved as revset aliases or function
  parameters. For example, `author(foo@)` is now an error, and the revset alias
  `'revset-aliases.foo@' = '@'` will be failed to parse.

* The `root` revset symbol has been converted to function `root()`.

* The `..x` revset is now evaluated to `root()..x`, which means the root commit
  is no longer included.

* `jj git push` will now push all branches in the range `remote_branches()..@`
  instead of only branches pointing to `@` or `@-`.

* It's no longer allowed to create a Git remote named "git". Use `jj git remote
  rename` to rename the existing remote.
  [#1690](https://github.com/martinvonz/jj/issues/1690)

* Revset expression like `origin/main` will no longer resolve to a
  remote-tracking branch. Use `main@origin` instead.

### New features

* Default template for `jj log` now does not show irrelevant information
  (timestamp, empty, message placeholder etc.) about the root commit.

* Commit templates now support the `root` keyword, which is `true` for the root
  commit and `false` for every other commit.

* `jj init --git-repo` now works with bare repositories.

* `jj config edit --user` and `jj config set --user` will now pick a default
  config location if no existing file is found, potentially creating parent directories.

* `jj log` output is now topologically grouped.
  [#242](https://github.com/martinvonz/jj/issues/242)

* `jj git clone` now supports the `--colocate` flag to create the git repo
  in the same directory as the jj repo.

* `jj restore` gained a new option `--changes-in` to restore files
  from a merge revision's parents. This undoes the changes that `jj diff -r`
  would show.

* `jj diff`/`log` now supports `--tool <name>` option to generate diffs by
  external program. For configuration, see [the documentation](docs/config.md).
  [#1886](https://github.com/martinvonz/jj/issues/1886)

* A new experimental diff editor `meld-3` is introduced that sets up Meld to
  allow you to see both sides of the original diff while editing. This can be
  used with `jj split`, `jj move -i`, etc.

* `jj log`/`obslog`/`op log` now supports `--limit N` option to show the first
  `N` entries.

* Added the `ui.paginate` option to enable/disable pager usage in commands

* `jj checkout`/`jj describe`/`jj commit`/`jj new`/`jj squash` can take repeated
  `-m/--message` arguments. Each passed message will be combined into paragraphs
  (separated by a blank line)

* It is now possible to set a default description using the new
  `ui.default-description` option, to use when describing changes with an empty
  description.

* `jj split` will now leave the description empty on the second part if the
  description was empty on the input commit.

* `branches()`/`remote_branches()`/`author()`/`committer()`/`description()`
  revsets now support exact matching. For example, `branch(exact:main)`
  selects the branch named "main", but not "maint". `description(exact:"")`
  selects commits whose description is empty.

* Revsets gained a new function `mine()` that aliases `author(exact:"your_email")`.

* Added support for `::` and `..` revset operators with both left and right
  operands omitted. These expressions are equivalent to `all()` and `~root()`
  respectively.

* `jj log` timestamp format now accepts `.utc()` to convert a timestamp to UTC.
 
* templates now support additional string methods `.starts_with(x)`, `.ends_with(x)`
  `.remove_prefix(x)`, `.remove_suffix(x)`, and `.substr(start, end)`.

* `jj next` and `jj prev` are added, these allow you to traverse the history
  in a linear style. For people coming from Sapling and `git-branchles`
  see [#2126](https://github.com/martinvonz/jj/issues/2126) for 
  further pending improvements.

* `jj diff --stat` has been implemented. It shows a histogram of the changes,
  same as `git diff --stat`. Fixes [#2066](https://github.com/martinvonz/jj/issues/2066)

* `jj git fetch --all-remotes` has been implemented. It fetches all remotes
  instead of just the default remote

### Fixed bugs

* Fix issues related to .gitignore handling of untracked directories
  [#2051](https://github.com/martinvonz/jj/issues/2051).

* `jj config set --user` and `jj config edit --user` can now be used outside of any repository.

* SSH authentication could hang when ssh-agent couldn't be reached
  [#1970](https://github.com/martinvonz/jj/issues/1970)

* SSH authentication can now use ed25519 and ed25519-sk keys. They still need
  to be password-less.

* Git repository managed by the repo tool can now be detected as a "colocated"
  repository.
  [#2011](https://github.com/martinvonz/jj/issues/2011)

### Contributors

Thanks to the people who made this release happen!

* Alexander Potashev (@aspotashev)
* Anton Bulakh (@necauqua)
* Austin Seipp (@thoughtpolice)
* Benjamin Brittain (@benbrittain)
* Benjamin Saunders (@Ralith)
* Christophe Poucet (@poucet)
* Emily Kyle Fox (@emilykfox)
* Glen Choo (@chooglen)
* Ilya Grigoriev (@ilyagr)
* Kevin Liao (@kevincliao)
* Linus Arver (@listx)
* Martin Clausen (@maacl)
* Martin von Zweigbergk (@martinvonz)
* Matt Freitas-Stavola (@mbStavola)
* Oscar Bonilla (@ob)
* Philip Metzger (@PhilipMetzger)
* Piotr Kufel (@qfel)
* Preston Van Loon (@prestonvanloon)
* Tal Pressman (@talpr)
* Vamsi Avula (@avamsi)
* Vincent Breitmoser (@Valodim)
* Vladimir (@0xdeafbeef)
* Waleed Khan (@arxanas)
* Yuya Nishihara (@yuja)
* Zachary Dremann (@Dr-Emann)