chroot-realpath: Add error context (#410360)

pkgs/by-name/ch/chroot-realpath/src/Cargo.lock

···
 # This file is automatically @generated by Cargo.
 # It is not intended for manual editing.
-version = 3
+version = 4
+
+[[package]]
+name = "anyhow"
+version = "1.0.98"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e16d2d3311acee920a9eb8d33b8cbc1787ce4a264e85f964c2404b969bdcd487"
 
 [[package]]
 name = "chroot-realpath"
 version = "0.1.0"
+dependencies = [
+ "anyhow",
+]

pkgs/by-name/ch/chroot-realpath/src/Cargo.toml

···
 edition = "2021"
 
 [dependencies]
+anyhow = "1.0.98"
 
 [profile.release]
 opt-level = "z"

pkgs/by-name/ch/chroot-realpath/src/src/main.rs

···
 use std::env;
-use std::io::{stdout, Error, ErrorKind, Write};
+use std::io::{stdout, Write};
 use std::os::unix::ffi::OsStrExt;
 use std::os::unix::fs;
 
-fn main() -> std::io::Result<()> {
+use anyhow::{bail, Context, Result};
+
+fn main() -> Result<()> {
     let args: Vec<String> = env::args().collect();
 
     if args.len() != 3 {
-        return Err(Error::new(
-            ErrorKind::InvalidInput,
-            format!("Usage: {} <chroot> <path>", args[0]),
-        ));
+        bail!("Usage: {} <chroot> <path>", args[0]);
     }
 
-    fs::chroot(&args[1])?;
-    std::env::set_current_dir("/")?;
+    fs::chroot(&args[1]).context("Failed to chroot")?;
+    std::env::set_current_dir("/").context("Failed to change directory")?;
 
-    let path = std::fs::canonicalize(&args[2])?;
+    let path = std::fs::canonicalize(&args[2])
+        .with_context(|| format!("Failed to canonicalize {}", args[2]))?;
 
-    stdout().write_all(path.into_os_string().as_bytes())?;
+    stdout()
+        .write_all(path.into_os_string().as_bytes())
+        .context("Failed to write output")?;
 
     Ok(())
 }