workspace: add a root subcommand to print the workspace root path

CHANGELOG.md

@@ -81,6 +81,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   by a "␛" character. That prevents them from interfering with the ANSI escapes
   jj itself writes.
 
+* `jj workspace root` prints the root path of the current workspace.
+
 ### Fixed bugs
 
 * When sharing the working copy with a Git repo, we used to forget to export

docs/working-copy.md

@@ -70,7 +70,8 @@ directory together is called a "workspace". Each workspace can have a different
 commit checked out.
 
 Having multiple workspaces can be useful for running long-running tests in a one
-while you continue developing in another, for example.
+while you continue developing in another, for example. If needed,
+`jj workspace root` prints the root path of the current workspace.
 
 When you're done using a workspace, use `jj workspace forget` to make the repo
 forget about it. The files can be deleted from disk separately (either before or

src/commands/mod.rs

@@ -743,6 +743,7 @@ enum WorkspaceCommands {
     Add(WorkspaceAddArgs),
     Forget(WorkspaceForgetArgs),
     List(WorkspaceListArgs),
+    Root(WorkspaceRootArgs),
     UpdateStale(WorkspaceUpdateStaleArgs),
 }
 
@@ -773,6 +774,10 @@ struct WorkspaceForgetArgs {
 #[derive(clap::Args, Clone, Debug)]
 struct WorkspaceListArgs {}
 
+/// Show the current workspace root directory
+#[derive(clap::Args, Clone, Debug)]
+struct WorkspaceRootArgs {}
+
 /// Update a workspace that has become stale
 ///
 /// For information about stale working copies, see
@@ -3013,6 +3018,9 @@ fn cmd_workspace(
         WorkspaceCommands::List(command_matches) => {
             cmd_workspace_list(ui, command, command_matches)
         }
+        WorkspaceCommands::Root(command_matches) => {
+            cmd_workspace_root(ui, command, command_matches)
+        }
         WorkspaceCommands::UpdateStale(command_matches) => {
             cmd_workspace_update_stale(ui, command, command_matches)
         }
@@ -3142,6 +3150,24 @@ fn cmd_workspace_list(
     Ok(())
 }
 
+fn cmd_workspace_root(
+    ui: &mut Ui,
+    command: &CommandHelper,
+    _args: &WorkspaceRootArgs,
+) -> Result<(), CommandError> {
+    let workspace_command = command.workspace_helper(ui)?;
+    let root =
+        workspace_command
+            .workspace_root()
+            .to_str()
+            .ok_or_else(|| CommandError::UserError {
+                message: String::from("The workspace root is not valid UTF-8"),
+                hint: None,
+            })?;
+    writeln!(ui, "{root}")?;
+    Ok(())
+}
+
 fn cmd_workspace_update_stale(
     ui: &mut Ui,
     command: &CommandHelper,

tests/test_workspaces.rs

@@ -244,6 +244,41 @@ fn test_list_workspaces_template() {
     "###);
 }
 
+/// Test getting the workspace root from primary and secondary workspaces
+#[test]
+fn test_workspaces_root() {
+    let test_env = TestEnvironment::default();
+    test_env.jj_cmd_success(test_env.env_root(), &["init", "--git", "main"]);
+    let main_path = test_env.env_root().join("main");
+    let secondary_path = test_env.env_root().join("secondary");
+
+    let stdout = test_env.jj_cmd_success(&main_path, &["workspace", "root"]);
+    insta::assert_snapshot!(stdout, @r###"
+    $TEST_ENV/main
+    "###);
+    let main_subdir_path = main_path.join("subdir");
+    std::fs::create_dir(&main_subdir_path).unwrap();
+    let stdout = test_env.jj_cmd_success(&main_subdir_path, &["workspace", "root"]);
+    insta::assert_snapshot!(stdout, @r###"
+    $TEST_ENV/main
+    "###);
+
+    test_env.jj_cmd_success(
+        &main_path,
+        &["workspace", "add", "--name", "secondary", "../secondary"],
+    );
+    let stdout = test_env.jj_cmd_success(&secondary_path, &["workspace", "root"]);
+    insta::assert_snapshot!(stdout, @r###"
+    $TEST_ENV/secondary
+    "###);
+    let secondary_subdir_path = secondary_path.join("subdir");
+    std::fs::create_dir(&secondary_subdir_path).unwrap();
+    let stdout = test_env.jj_cmd_success(&secondary_subdir_path, &["workspace", "root"]);
+    insta::assert_snapshot!(stdout, @r###"
+    $TEST_ENV/secondary
+    "###);
+}
+
 fn get_log_output(test_env: &TestEnvironment, cwd: &Path) -> String {
     test_env.jj_cmd_success(
         cwd,