find: reject a signed -maxdepth/-mindepth value to match GNU

src/find/matchers/mod.rs

@@ -308,8 +308,11 @@ fn convert_arg_to_number(
     option_name: &str,
     value_as_string: &str,
 ) -> Result<usize, Box<dyn Error>> {
+    // Only accept plain decimal digits. Rust's `usize::from_str` also accepts a
+    // leading '+', but GNU find rejects a signed value like "+1" here, which is
+    // consistent with the "positive decimal integer" wording below.
     match value_as_string.parse::<usize>() {
-        Ok(val) => Ok(val),
+        Ok(val) if value_as_string.bytes().all(|b| b.is_ascii_digit()) => Ok(val),
         _ => Err(From::from(format!(
             "Expected a positive decimal integer argument to {option_name}, but got \
              `{value_as_string}'"
@@ -1790,6 +1793,18 @@ mod tests {
         }
     }
 
+    #[test]
+    fn convert_arg_to_number_test() {
+        assert_eq!(convert_arg_to_number("-maxdepth", "12").unwrap(), 12);
+        assert_eq!(convert_arg_to_number("-maxdepth", "0").unwrap(), 0);
+        // A signed value is rejected, matching GNU find (Rust's parser would
+        // otherwise accept the leading '+').
+        assert!(convert_arg_to_number("-maxdepth", "+1").is_err());
+        assert!(convert_arg_to_number("-mindepth", "+2").is_err());
+        assert!(convert_arg_to_number("-maxdepth", "-1").is_err());
+        assert!(convert_arg_to_number("-maxdepth", "1a").is_err());
+    }
+
     #[test]
     fn convert_arg_to_comparable_value_test() {
         assert_eq!(