rhg: simplify `FindRootError` handling

Differential Revision: https://phab.mercurial-scm.org/D8867

rust/rhg/src/commands/root.rs

@@ -1,7 +1,7 b''
 use crate::commands::Command;
-use crate::error::{CommandError, CommandErrorKind};
+use crate::error::CommandError;
 use crate::ui::Ui;
-use hg::operations::{FindRoot, FindRootErrorKind};
+use hg::operations::FindRoot;
 use hg::utils::files::get_bytes_from_path;
 
 pub const HELP_TEXT: &str = "
@@ -22,15 +22,7 b" impl<'a> RootCommand<'a> {"
 
 impl<'a> Command<'a> for RootCommand<'a> {
     fn run(&self) -> Result<(), CommandError> {
-        let path_buf =
-            FindRoot::new().run().map_err(|err| match err.kind {
-                FindRootErrorKind::RootNotFound(path) => {
-                    CommandErrorKind::RootNotFound(path)
-                }
-                FindRootErrorKind::GetCurrentDirError(e) => {
-                    CommandErrorKind::CurrentDirNotFound(e)
-                }
-            })?;
+        let path_buf = FindRoot::new().run()?;
 
         let bytes = get_bytes_from_path(path_buf);
 

rust/rhg/src/error.rs

@@ -1,5 +1,6 b''
 use crate::exitcode;
 use crate::ui::UiError;
+use hg::operations::{FindRootError, FindRootErrorKind};
 use hg::utils::files::get_bytes_from_path;
 use std::convert::From;
 use std::path::PathBuf;
@@ -90,3 +91,16 b' impl From<UiError> for CommandError {'
         }
     }
 }
+
+impl From<FindRootError> for CommandError {
+    fn from(err: FindRootError) -> Self {
+        match err.kind {
+            FindRootErrorKind::RootNotFound(path) => CommandError {
+                kind: CommandErrorKind::RootNotFound(path),
+            },
+            FindRootErrorKind::GetCurrentDirError(e) => CommandError {
+                kind: CommandErrorKind::CurrentDirNotFound(e),
+            },
+        }
+    }
+}