truncate: add a division by zero error

Add an error for division by zero. Previously, running `truncate -s /0
file` or `-s %0` would panic due to division by zero. After this
change, it writes an error message "division by zero" to stderr and
terminates with an error code.

src/uu/truncate/src/truncate.rs

@@ -202,6 +202,9 @@ fn truncate_reference_and_size(
         }
         Ok(m) => m,
     };
+    if let TruncateMode::RoundDown(0) | TruncateMode::RoundUp(0) = mode {
+        return Err(USimpleError::new(1, "division by zero"));
+    }
     let metadata = metadata(rfilename).map_err(|e| match e.kind() {
         ErrorKind::NotFound => USimpleError::new(
             1,
@@ -271,6 +274,9 @@ fn truncate_reference_file_only(
 fn truncate_size_only(size_string: &str, filenames: Vec<String>, create: bool) -> UResult<()> {
     let mode = parse_mode_and_size(size_string)
         .map_err(|e| USimpleError::new(1, format!("Invalid number: {}", e)))?;
+    if let TruncateMode::RoundDown(0) | TruncateMode::RoundUp(0) = mode {
+        return Err(USimpleError::new(1, "division by zero"));
+    }
     for filename in &filenames {
         let fsize = match metadata(filename) {
             Ok(m) => m.len(),

tests/by-util/test_truncate.rs

@@ -346,3 +346,34 @@ fn test_new_file_no_create() {
         .no_stderr();
     assert!(!at.file_exists(filename));
 }
+
+#[test]
+fn test_division_by_zero_size_only() {
+    new_ucmd!()
+        .args(&["-s", "/0", "file"])
+        .fails()
+        .no_stdout()
+        .stderr_contains("division by zero");
+    new_ucmd!()
+        .args(&["-s", "%0", "file"])
+        .fails()
+        .no_stdout()
+        .stderr_contains("division by zero");
+}
+
+#[test]
+fn test_division_by_zero_reference_and_size() {
+    let (at, mut ucmd) = at_and_ucmd!();
+    at.make_file(FILE1);
+    ucmd.args(&["-r", FILE1, "-s", "/0", "file"])
+        .fails()
+        .no_stdout()
+        .stderr_contains("division by zero");
+
+    let (at, mut ucmd) = at_and_ucmd!();
+    at.make_file(FILE1);
+    ucmd.args(&["-r", FILE1, "-s", "%0", "file"])
+        .fails()
+        .no_stdout()
+        .stderr_contains("division by zero");
+}