users: Avoid > /dev/full panic

Author: oech3

src/uu/users/src/users.rs

@@ -6,6 +6,7 @@
 // spell-checker:ignore (paths) wtmp
 
 use std::ffi::OsString;
+use std::io::{Write, stdout};
 use std::path::Path;
 
 use clap::builder::ValueParser;
@@ -73,7 +74,7 @@ pub fn uumain(args: impl uucore::Args) -> UResult<()> {
 
     if !users.is_empty() {
         users.sort();
-        println!("{}", users.join(" "));
+        writeln!(stdout().lock(), "{}", users.join(" "))?;
     }
 
     Ok(())

tests/by-util/test_users.rs

@@ -6,6 +6,20 @@ use uutests::new_ucmd;
 #[cfg(any(target_vendor = "apple", target_os = "linux"))]
 use uutests::{util::TestScenario, util_name};
 
+#[test]
+#[cfg(target_os = "linux")]
+fn test_full_panic() {
+    let full = std::fs::OpenOptions::new()
+        .write(true)
+        .open("/dev/full")
+        .unwrap();
+
+    new_ucmd!()
+        .set_stdout(full)
+        .fails()
+        .stderr_contains("No space");
+}
+
 #[test]
 fn test_invalid_arg() {
     new_ucmd!().arg("--definitely-invalid").fails_with_code(1);