cli: deprecate jj split --siblings in favor of jj split --parallel

This better matches `jj parallelize`.

CHANGELOG.md

@@ -23,6 +23,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 * Replacing `-l` shorthand for `--limit` with `-n` in `jj log`, `jj op log` and `jj obslog`.
 
+* `jj split --siblings` is deprecated in favor of `jj split --parallel` (to
+  match `jj parallelize`).
+
 ### New features
 
 * Show paths to config files when configuration errors occur

cli/src/commands/split.rs

@@ -51,9 +51,11 @@ pub(crate) struct SplitArgs {
     /// The revision to split
     #[arg(long, short, default_value = "@")]
     revision: RevisionArg,
-    /// Split the revision into two siblings instead of a parent and child.
-    #[arg(long, short)]
-    siblings: bool,
+    /// Split the revision into two parallel revisions instead of a parent and
+    /// child.
+    // TODO: Delete `--siblings` alias in jj 0.25+
+    #[arg(long, short, alias = "siblings")]
+    parallel: bool,
     /// Put these paths in the first commit
     #[arg(value_hint = clap::ValueHint::AnyPath)]
     paths: Vec<String>,
@@ -137,15 +139,15 @@ the operation will be aborted.
 
     // Create the second commit, which includes everything the user didn't
     // select.
-    let (second_tree, second_base_tree) = if args.siblings {
+    let (second_tree, second_base_tree) = if args.parallel {
         // Merge the original commit tree with its parent using the tree
         // containing the user selected changes as the base for the merge.
         // This results in a tree with the changes the user didn't select.
         (end_tree.merge(&selected_tree, &base_tree)?, &base_tree)
     } else {
         (end_tree, &selected_tree)
     };
-    let second_commit_parents = if args.siblings {
+    let second_commit_parents = if args.parallel {
         commit.parent_ids().to_vec()
     } else {
         vec![first_commit.id().clone()]
@@ -189,11 +191,11 @@ the operation will be aborted.
         vec![commit.id().clone()],
         |mut rewriter| {
             num_rebased += 1;
-            if args.siblings {
+            if args.parallel {
                 rewriter
                     .replace_parent(second_commit.id(), [first_commit.id(), second_commit.id()]);
             }
-            // We don't need to do anything special for the non-siblings case
+            // We don't need to do anything special for the non-parallel case
             // since we already marked the original commit as rewritten.
             rewriter.rebase(command.settings())?.write()?;
             Ok(())

cli/tests/cli-reference@.md.snap

@@ -1771,7 +1771,7 @@ Splitting an empty commit is not supported because the same effect can be achiev
 * `-r`, `--revision <REVISION>` — The revision to split
 
   Default value: `@`
-* `-s`, `--siblings` — Split the revision into two siblings instead of a parent and child
+* `-p`, `--parallel` — Split the revision into two parallel revisions instead of a parent and child
 
   Possible values: `true`, `false`
 

cli/tests/test_split_command.rs

@@ -343,7 +343,7 @@ fn test_split_siblings_no_descendants() {
         ["dump editor1", "next invocation\n", "dump editor2"].join("\0"),
     )
     .unwrap();
-    let (stdout, stderr) = test_env.jj_cmd_ok(&workspace_path, &["split", "--siblings", "file1"]);
+    let (stdout, stderr) = test_env.jj_cmd_ok(&workspace_path, &["split", "--parallel", "file1"]);
     insta::assert_snapshot!(stdout, @"");
     insta::assert_snapshot!(stderr, @r###"
     First part: qpvuntsm 8d2b7558 TESTED=TODO
@@ -421,7 +421,7 @@ fn test_split_siblings_with_descendants() {
         .join("\0"),
     )
     .unwrap();
-    let (stdout, stderr) = test_env.jj_cmd_ok(&workspace_path, &["split", "--siblings", "file1"]);
+    let (stdout, stderr) = test_env.jj_cmd_ok(&workspace_path, &["split", "--parallel", "file1"]);
     insta::assert_snapshot!(stdout, @"");
     insta::assert_snapshot!(stderr, @r###"
     Rebased 2 descendant commits
@@ -500,7 +500,7 @@ fn test_split_siblings_with_merge_child() {
     .unwrap();
     let (stdout, stderr) = test_env.jj_cmd_ok(
         &workspace_path,
-        &["split", "-r", "description(a)", "--siblings", "file1"],
+        &["split", "-r", "description(a)", "--parallel", "file1"],
     );
     insta::assert_snapshot!(stdout, @"");
     insta::assert_snapshot!(stderr, @r###"