Add a --siblings option to the jj split command

If the --siblings option is used, the target commit is split into two sibling
commits instead of parent and child commits. Any children of the original
commit will have both sibilings as their new parents.


ISSUE=#2274

CHANGELOG.md

@@ -24,14 +24,15 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### New features
 
-* Config now supports rgb hex colors (in the form `#rrggbb`) wherever existing color names are supported.
+* Config now supports rgb hex colors (in the form `#rrggbb`) wherever existing color names are
+  supported.
 
 * `ui.default-command` now accepts multiple string arguments, for more complex
   default `jj` commands.
 
 * Graph node symbols are now configurable via templates
-  * `templates.log_node`
-  * `templates.op_log_node`
+    * `templates.log_node`
+    * `templates.op_log_node`
 
 * `jj log` now includes synthetic nodes in the graph where some revisions were
   elided.
@@ -54,6 +55,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 * `jj duplicate` and `jj abandon` can now take more than a single `-r` argument,
   for consistency with other commands.
 
+* `jj split` now supports a `--siblings/-s` option that splits the target
+  revision into siblings with the same parents and children.
+
 ### Fixed bugs
 
 ## [0.15.1] - 2024-03-06
@@ -91,8 +95,8 @@ No code changes (fixing Rust `Cargo.toml` stuff).
   commits when they are created.
 
   This comes with out-of-the-box support for the following backends:
-  * GnuPG
-  * SSH
+    * GnuPG
+    * SSH
 
   Signature verification and an explicit sign command will hopefully come soon.
 
@@ -138,7 +142,7 @@ No code changes (fixing Rust `Cargo.toml` stuff).
 
 * `jj commit`/`diffedit`/`move`/`resolve`/`split`/`squash`/`unsquash` now accept
   `--tool=<NAME>` option to override the default.
-   [#2575](https://github.com/martinvonz/jj/issues/2575)
+  [#2575](https://github.com/martinvonz/jj/issues/2575)
 
 * Added completions for [Nushell](https://nushell.sh) to `jj util completion`
 
@@ -158,7 +162,7 @@ No code changes (fixing Rust `Cargo.toml` stuff).
   When symlink support is unavailable, they will be materialized as regular files in the
   working copy (instead of resulting in a crash).
   [#2](https://github.com/martinvonz/jj/issues/2)
-  
+
 * On Windows, the `:builtin` pager is now used by default, rather than being
   disabled entirely.
 
@@ -192,7 +196,6 @@ Thanks to the people who made this release happen!
 * Vladimir (@0xdeafbeef)
 * Yuya Nishihara (@yuja)
 
-
 ## [0.14.0] - 2024-02-07
 
 ### Deprecations
@@ -205,7 +208,7 @@ Thanks to the people who made this release happen!
   copy commit on top of a single specified revision, i.e. with one parent.
   `merge` creates a new working copy commit on top of *at least* two specified
   revisions, i.e. with two or more parents.
-  
+
   The only difference between these commands and `jj new`, which *also* creates
   a new working copy commit, is that `new` can create a working copy commit on
   top of any arbitrary number of revisions, so it can handle both the previous
@@ -226,7 +229,6 @@ Thanks to the people who made this release happen!
 
   Use `jj git init` instead.
 
-
 ### Breaking changes
 
 * (Minor) Diff summaries (e.g. `jj diff -s`) now use `D` for "Deleted" instead
@@ -318,7 +320,6 @@ Thanks to the people who made this release happen!
 * vwkd (@vwkd)
 * Yuya Nishihara (@yuja)
 
-
 ## [0.13.0] - 2024-01-03
 
 ### Breaking changes
@@ -352,7 +353,6 @@ Thanks to the people who made this release happen!
 * Waleed Khan (@arxanas)
 * Yuya Nishihara (@yuja)
 
-
 ## [0.12.0] - 2023-12-05
 
 ### Breaking changes
@@ -362,7 +362,7 @@ Thanks to the people who made this release happen!
 
 * `jj branch set` no longer creates a new branch. Use `jj branch create`
   instead.
-  
+
 * `jj init --git` in an existing Git repository now errors and exits rather than
   creating a second Git store.
 
@@ -413,7 +413,6 @@ Thanks to the people who made this release happen!
 * Waleed Khan (@arxanas)
 * Yuya Nishihara (@yuja)
 
-
 ## [0.11.0] - 2023-11-01
 
 ### Breaking changes
@@ -437,9 +436,9 @@ Thanks to the people who made this release happen!
   `git.auto-local-branch` setting is applied only to newly fetched remote
   branches. Existing remote branches are migrated as follows:
 
-  * If local branch exists, the corresponding remote branches are considered
-    tracking branches.
-  * Otherwise, the remote branches are non-tracking branches.
+    * If local branch exists, the corresponding remote branches are considered
+      tracking branches.
+    * Otherwise, the remote branches are non-tracking branches.
 
   If the deduced tracking flags are wrong, use `jj branch track`/`untrack`
   commands to fix them up.
@@ -461,7 +460,8 @@ Thanks to the people who made this release happen!
 
 ### New features
 
-* `jj`'s stable release can now be installed with [`cargo binstall jj-cli`](https://github.com/cargo-bins/cargo-binstall).
+* `jj`'s stable release can now be installed
+  with [`cargo binstall jj-cli`](https://github.com/cargo-bins/cargo-binstall).
 
 * `jj workspace add` now takes a `--revision` argument.
 
@@ -514,7 +514,6 @@ Thanks to the people who made this release happen!
 * Waleed Khan (@arxanas)
 * Yuya Nishihara (@yuja)
 
-
 ## [0.10.0] - 2023-10-04
 
 ### Breaking changes
@@ -526,8 +525,8 @@ Thanks to the people who made this release happen!
 
 ### New features
 
-* The `ancestors()` revset function now takes an optional `depth` argument 
-  to limit the depth of the ancestor set. For example, use `jj log -r 
+* The `ancestors()` revset function now takes an optional `depth` argument
+  to limit the depth of the ancestor set. For example, use `jj log -r
   'ancestors(@, 5)` to view the last 5 commits.
 
 * Support for the Watchman filesystem monitor is now bundled by default. Set
@@ -577,7 +576,6 @@ Thanks to the people who made this release happen!
 * Yuya Nishihara (@yuja)
 * Zachary Dremann (@Dr-Emann)
 
-
 ## [0.9.0] - 2023-09-06
 
 ### Breaking changes
@@ -692,13 +690,13 @@ Thanks to the people who made this release happen!
   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 
+  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,
@@ -754,7 +752,6 @@ Thanks to the people who made this release happen!
 * Yuya Nishihara (@yuja)
 * Zachary Dremann (@Dr-Emann)
 
-
 ## [0.8.0] - 2023-07-09
 
 ### Breaking changes
@@ -955,7 +952,6 @@ Thanks to the people who made this release happen!
 * Waleed Khan (@arxanas)
 * Yuya Nishihara (@yuja)
 
-
 ## [0.7.0] - 2023-02-16
 
 ### Breaking changes
@@ -1151,25 +1147,25 @@ Thanks to the people who made this release happen!
 
 Thanks to the people who made this release happen!
 
- * Aleksandr Mikhailov (@AM5800)
- * Augie Fackler (@durin42)
- * Benjamin Saunders (@Ralith)
- * Daniel Ploch (@torquestomp)
- * Danny Hooper (@hooper)
- * David Barnett (@dbarnett)
- * Glen Choo (@chooglen)
- * Herby Gillot (@herbygillot)
- * Ilya Grigoriev (@ilyagr)
- * Luke Granger-Brown (@lukegb)
- * Martin von Zweigbergk (@martinvonz)
- * Michael Forster (@MForster)
- * Philip Metzger (@PhilipMetzger)
- * Ruben Slabbert (@rslabbert)
- * Samuel Tardieu (@samueltardieu)
- * Tal Pressman (@talpr)
- * Vamsi Avula (@avamsi)
- * Waleed Khan (@arxanas)
- * Yuya Nishihara (@yuja)
+* Aleksandr Mikhailov (@AM5800)
+* Augie Fackler (@durin42)
+* Benjamin Saunders (@Ralith)
+* Daniel Ploch (@torquestomp)
+* Danny Hooper (@hooper)
+* David Barnett (@dbarnett)
+* Glen Choo (@chooglen)
+* Herby Gillot (@herbygillot)
+* Ilya Grigoriev (@ilyagr)
+* Luke Granger-Brown (@lukegb)
+* Martin von Zweigbergk (@martinvonz)
+* Michael Forster (@MForster)
+* Philip Metzger (@PhilipMetzger)
+* Ruben Slabbert (@rslabbert)
+* Samuel Tardieu (@samueltardieu)
+* Tal Pressman (@talpr)
+* Vamsi Avula (@avamsi)
+* Waleed Khan (@arxanas)
+* Yuya Nishihara (@yuja)
 
 ## [0.6.1] - 2022-12-05
 
@@ -1294,17 +1290,16 @@ No changes, only changed to a released version of the `thrift` crate dependency.
 
 Thanks to the people who made this release happen!
 
- * Martin von Zweigbergk (@martinvonz)
- * Benjamin Saunders (@Ralith)
- * Yuya Nishihara (@yuja)
- * Glen Choo (@chooglen)
- * Ilya Grigoriev (@ilyagr)
- * Ruben Slabbert (@rslabbert)
- * Waleed Khan (@arxanas)
- * Sean E. Russell (@xxxserxxx)
- * Pranay Sashank (@pranaysashank)
- * Luke Granger-Brown (@lukegb)
-
+* Martin von Zweigbergk (@martinvonz)
+* Benjamin Saunders (@Ralith)
+* Yuya Nishihara (@yuja)
+* Glen Choo (@chooglen)
+* Ilya Grigoriev (@ilyagr)
+* Ruben Slabbert (@rslabbert)
+* Waleed Khan (@arxanas)
+* Sean E. Russell (@xxxserxxx)
+* Pranay Sashank (@pranaysashank)
+* Luke Granger-Brown (@lukegb)
 
 ## [0.5.1] - 2022-10-17
 
@@ -1569,9 +1564,9 @@ No changes, only trying to get the automated build to work.
 
 ### Fixed bugs
 
- - Fixed crash when `core.excludesFile` pointed to nonexistent file, and made
-   leading `~/` in that config expand to `$HOME/`
-   [#131](https://github.com/martinvonz/jj/issues/131)
+- Fixed crash when `core.excludesFile` pointed to nonexistent file, and made
+  leading `~/` in that config expand to `$HOME/`
+  [#131](https://github.com/martinvonz/jj/issues/131)
 
 ## [0.3.0] - 2022-03-12