cp: don't panic on verbose/debug write errors

src/uu/cp/src/cp.rs

@@ -1666,7 +1666,7 @@
         match self {
             Self::NoClobber => {
                 if debug {
-                    println!("{}", translate!("cp-debug-skipped", "path" => path.quote()));
+                    print_stdout_line(translate!("cp-debug-skipped", "path" => path.quote()))?;
                 }
                 Err(CpError::Skipped(false))
             }
@@ -2100,7 +2100,7 @@
 
     if options.update == UpdateMode::None {
         if options.debug {
-            println!("skipped {}", dest.quote());
+            print_stdout_line(format!("skipped {}", dest.quote()))?;
         }
         return Err(CpError::Skipped(false));
     }
@@ -2205,10 +2205,7 @@
     match fs::remove_file(path) {
         Ok(()) => {
             if options.verbose {
-                println!(
-                    "{}",
-                    translate!("cp-verbose-removed", "path" => path.quote())
-                );
+                print_stdout_line(translate!("cp-verbose-removed", "path" => path.quote()))?;
             }
         }
         Err(err) if err.kind() == io::ErrorKind::NotFound => {
@@ -2299,6 +2296,21 @@
     Ok(())
 }
 
+/// Print a single `--verbose`/`--debug` line to stdout, surfacing a write
+/// failure (e.g. stdout redirected to a full disk, or a closed pipe) as a
+/// normal error instead of panicking inside `println!`. Mirrors the buffered
+/// write approach of [`print_paths`] so every user-facing verbose/debug line
+/// shares the same non-panicking behaviour. See #10554.
+fn print_stdout_line(line: impl Display) -> CopyResult<()> {
+    use std::io::Write;
+
+    let mut out = io::BufWriter::new(io::stdout().lock());
+    let write_err = |e| CpError::IoErrContext(e, translate!("cp-error-write"));
+    writeln!(out, "{line}").map_err(write_err)?;
+    out.flush().map_err(write_err)?;
+    Ok(())
+}
+
 /// Handles the copy mode for a file copy operation.
 ///
 /// This function determines how to copy a file based on the provided options.
@@ -2382,7 +2394,7 @@
                     }
                     UpdateMode::None => {
                         if options.debug {
-                            println!("skipped {}", dest.quote());
+                            print_stdout_line(format!("skipped {}", dest.quote()))?;
                         }
 
                         return Ok(PerformedAction::Skipped);

tests/by-util/test_cp.rs

@@ -120,6 +120,46 @@
     assert!(at.file_exists("dest_file"));
 }
 
+// https://github.com/uutils/coreutils/issues/10554
+// #13310 made the `'src' -> 'dest'` verbose line non-panicking, but the
+// remaining `--verbose`/`--debug` lines still used `println!` and panicked on a
+// stdout write error (e.g. `> /dev/full`). Verify each of those paths now
+// reports the write error instead of crashing, matching the `'src' -> 'dest'`
+// behaviour fixed by `test_cp_verbose_write_error_is_reported`.
+#[test]
+#[cfg(target_os = "linux")]
+fn test_cp_verbose_removed_write_error_is_reported_issue10554() {
+    let (at, mut ucmd) = at_and_ucmd!();
+    at.touch("source_file");
+    at.touch("dest_file");
+    // `--remove-destination` always unlinks the existing dest first, emitting
+    // the `removed 'dest_file'` verbose line before the copy begins.
+    ucmd.arg("--remove-destination")
+        .arg("--verbose")
+        .arg("source_file")
+        .arg("dest_file")
+        .set_stdout(std::fs::File::create("/dev/full").unwrap())
+        .fails()
+        .stderr_is("cp: write error: No space left on device\n");
+}
+
+#[test]
+#[cfg(target_os = "linux")]
+fn test_cp_debug_skipped_write_error_is_reported_issue10554() {
+    let (at, mut ucmd) = at_and_ucmd!();
+    at.touch("source_file");
+    at.touch("dest_file");
+    // `--no-clobber --debug` against an existing dest emits the debug
+    // `skipped 'dest_file'` line via the same `print_stdout_line` helper.
+    ucmd.arg("--debug")
+        .arg("--no-clobber")
+        .arg("source_file")
+        .arg("dest_file")
+        .set_stdout(std::fs::File::create("/dev/full").unwrap())
+        .fails()
+        .stderr_is("cp: write error: No space left on device\n");
+}
+
 #[test]
 fn test_cp_cp() {
     let (at, mut ucmd) = at_and_ucmd!();