message: annotate some unwraps with better messages
diff: @@ -249,7 +249,10 @@ fn setup(ask_user: bool) {
  println!("Installing xargo: `cargo install xargo -f`");
  }
  - if !cargo().args(&["install", "xargo", "-f"]).status().unwrap().success() {
  + if !cargo().args(&["install", "xargo", "-f"]).status()
  + .expect("failed to install xargo")
  + .success()
  + {
  show_error(format!("Failed to install xargo"));
  }
  }
  @@ -257,7 +260,9 @@ fn setup(ask_user: bool) {
  // Then, unless `XARGO_RUST_SRC` is set, we also need rust-src.
  // Let's see if it is already installed.
  if std::env::var("XARGO_RUST_SRC").is_err() {
  - let sysroot = Command::new("rustc").args(&["--print", "sysroot"]).output().unwrap().stdout;
  + let sysroot = Command::new("rustc").args(&["--print", "sysroot"]).output()
  + .expect("failed to get rustc sysroot")
  + .stdout;
  let sysroot = std::str::from_utf8(&sysroot).unwrap();
  let src = Path::new(sysroot.trim_end_matches('\n')).join("lib").join("rustlib").join("src");
  if !src.exists() {
  @@ -266,7 +271,10 @@ fn setup(ask_user: bool) {
  } else {
  println!("Installing rust-src component: `rustup component add rust-src`");
  }
  - if !Command::new("rustup").args(&["component", "add", "rust-src"]).status().unwrap().success() {
  + if !Command::new("rustup").args(&["component", "add", "rust-src"]).status()
  + .expect("failed to install rust-src component")
  + .success()
  + {
  show_error(format!("Failed to install rust-src component"));
  }
  }
  @@ -313,7 +321,9 @@ path = "lib.rs"
  if let Some(ref target) = target {
  command.arg("--target").arg(&target);
  }
  - if !command.status().unwrap().success()
  + if !command.status()
  + .expect("failed to run xargo")
  + .success()
  {
  show_error(format!("Failed to run xargo"));
  }
  