cli: implement jj root

This is a convenient command when scripting around, for things like:
$ cd $(jj root) && do something

Currently this fails if the path to the repo contains non-utf8 bytes,
similarly to `jj status` failing on non-utf8 paths inside the repo.

CHANGELOG.md

@@ -19,6 +19,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 * `jj branch rename` will now warn if the renamed branch has a remote branch, since
   those will have to be manually renamed outside of `jj`.
 
+* `jj root` will print the path to the working copy root.
+
 ### Fixed bugs
 
 

cli/src/commands/mod.rs

@@ -43,6 +43,7 @@ mod prev;
 mod rebase;
 mod resolve;
 mod restore;
+mod root;
 mod run;
 mod show;
 mod sparse;
@@ -118,6 +119,7 @@ enum Command {
         help_template = "Not a real subcommand; consider `jj backout` or `jj restore`"
     )]
     Revert(DummyCommandArgs),
+    Root(root::RootArgs),
     #[command(hide = true)]
     // TODO: Flesh out.
     Run(run::RunArgs),
@@ -179,6 +181,7 @@ pub fn run_command(ui: &mut Ui, command_helper: &CommandHelper) -> Result<(), Co
         Command::Unsquash(sub_args) => unsquash::cmd_unsquash(ui, command_helper, sub_args),
         Command::Restore(sub_args) => restore::cmd_restore(ui, command_helper, sub_args),
         Command::Revert(_args) => revert(),
+        Command::Root(sub_args) => root::cmd_root(ui, command_helper, sub_args),
         Command::Run(sub_args) => run::cmd_run(ui, command_helper, sub_args),
         Command::Diffedit(sub_args) => diffedit::cmd_diffedit(ui, command_helper, sub_args),
         Command::Split(sub_args) => split::cmd_split(ui, command_helper, sub_args),

cli/src/commands/root.rs

@@ -0,0 +1,41 @@
+// Copyright 2024 The Jujutsu Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+use std::io::Write;
+
+use tracing::instrument;
+
+use crate::cli_util::{user_error, CommandError, CommandHelper};
+use crate::ui::Ui;
+
+#[derive(clap::Args, Clone, Debug)]
+pub(crate) struct RootArgs {}
+
+#[instrument(skip_all)]
+pub(crate) fn cmd_root(
+    ui: &mut Ui,
+    command: &CommandHelper,
+    RootArgs {}: &RootArgs,
+) -> Result<(), CommandError> {
+    let workspace_root = command.workspace_loader()?.workspace_root();
+    if let Some(p) = workspace_root.to_str() {
+        writeln!(ui.stdout(), "{}", p)?;
+        Ok(())
+    } else {
+        Err(user_error(format!(
+            "root path {:?} is not valid UTF-8",
+            workspace_root
+        )))
+    }
+}

cli/tests/test_root.rs

@@ -0,0 +1,30 @@
+// Copyright 2024 The Jujutsu Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+use crate::common::TestEnvironment;
+
+pub mod common;
+
+#[test]
+fn test_root() {
+    let test_env = TestEnvironment::default();
+    test_env.jj_cmd_ok(test_env.env_root(), &["init", ".", "--git"]);
+    let subdir = test_env.env_root().join("subdir");
+    std::fs::create_dir(&subdir).unwrap();
+    let stdout = test_env.jj_cmd_success(&subdir, &["root"]);
+    assert_eq!(
+        &stdout,
+        &[&*test_env.env_root().to_string_lossy(), "\n"].concat()
+    );
+}