Return error instead of printing to stderr when words is too short

src/main.rs

@@ -27,11 +27,9 @@ fn main() -> Result<()> {
  let mut words: Vec<String> = words::list(args.dict_path)?;
  let mut rng = rand::thread_rng();
 
- print!(
- "{}",
- passphrase::new(&mut rng, &mut words, args.num_words, &args.separator)
- );
+ let passphrase = passphrase::new(&mut rng, &mut words, args.num_words, &args.separator)?;
 
+ print!("{}", passphrase);
  if std::io::stdout().is_terminal() {
  println!();
  }

src/passphrase.rs

@@ -1,24 +1,29 @@
+use eyre::{eyre, Result};
 use rand::Rng;
 
-pub fn new<T: Rng>(mut rng: T, words: &mut [String], num_words: usize, separator: &str) -> String {
+pub fn new<T: Rng>(
+ mut rng: T,
+ words: &mut [String],
+ num_words: usize,
+ separator: &str,
+) -> Result<String> {
  if words.len() < num_words {
- eprintln!(
+ return Err(eyre!(
  "Your dictionary only has {} suitable words, but you asked for {} words.",
  words.len(),
  num_words
- );
- return String::new();
+ ));
  }
 
  (0..num_words).for_each(|i| {
  let j = rng.gen_range(i..words.len());
  words.swap(i, j);
  });
 
- (0..num_words)
+ Ok((0..num_words)
  .map(|i| words[i].clone())
- .collect::<Vec<String>>()
- .join(separator)
+ .collect::<Vec<_>>()
+ .join(separator))
 }
 
 mod test {
@@ -66,7 +71,7 @@ mod test {
  let mut rng = ChaCha8Rng::seed_from_u64(seed);
  rng.set_stream(*i as u64);
  let mut words = words.clone();
- let s = passphrase::new(&mut rng, &mut words, W, " ");
+ let s = passphrase::new(&mut rng, &mut words, W, " ").unwrap();
  *acc.entry(s).or_insert(0) += 1_usize;
  acc
  })