diff -r dd3050227a84 -r 513b3ef277a3 rust/rhg/src/commands/root.rs
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/rust/rhg/src/commands/root.rs	Fri Jun 05 09:01:35 2020 +0200
@@ -0,0 +1,76 @@
+use crate::commands::Command;
+use crate::error::{CommandError, CommandErrorKind};
+use crate::ui::Ui;
+use hg::operations::{FindRoot, FindRootError, FindRootErrorKind, Operation};
+use hg::utils::files::get_bytes_from_path;
+use std::path::PathBuf;
+
+pub const HELP_TEXT: &str = "
+Print the root directory of the current repository.
+
+Returns 0 on success.
+";
+
+pub struct RootCommand {
+    ui: Ui,
+}
+
+impl RootCommand {
+    pub fn new() -> Self {
+        RootCommand { ui: Ui::new() }
+    }
+
+    fn display_found_path(
+        &self,
+        path_buf: PathBuf,
+    ) -> Result<(), CommandError> {
+        let bytes = get_bytes_from_path(path_buf);
+
+        // TODO use formating macro
+        self.ui.write_stdout(&[bytes.as_slice(), b"\n"].concat())?;
+
+        Err(CommandErrorKind::Ok.into())
+    }
+
+    fn display_error(&self, error: FindRootError) -> Result<(), CommandError> {
+        match error.kind {
+            FindRootErrorKind::RootNotFound(path) => {
+                let bytes = get_bytes_from_path(path);
+
+                // TODO use formating macro
+                self.ui.write_stderr(
+                    &[
+                        b"abort: no repository found in '",
+                        bytes.as_slice(),
+                        b"' (.hg not found)!\n",
+                    ]
+                    .concat(),
+                )?;
+
+                Err(CommandErrorKind::RootNotFound.into())
+            }
+            FindRootErrorKind::GetCurrentDirError(e) => {
+                // TODO use formating macro
+                self.ui.write_stderr(
+                    &[
+                        b"abort: error getting current working directory: ",
+                        e.to_string().as_bytes(),
+                        b"\n",
+                    ]
+                    .concat(),
+                )?;
+
+                Err(CommandErrorKind::CurrentDirNotFound.into())
+            }
+        }
+    }
+}
+
+impl Command for RootCommand {
+    fn run(&self) -> Result<(), CommandError> {
+        match FindRoot::new().run() {
+            Ok(path_buf) => self.display_found_path(path_buf),
+            Err(e) => self.display_error(e),
+        }
+    }
+}