Parser panic for signature with multibyte char for short flag #8821 (#8849)

Hey I'm a developer and I'm still new to nushell and rust but I would
like to learn more about both. This is my first PR for this project.

The intent of my change is to allow to use multibyte utf-8 characters in
commands short flags.

crates/nu-parser/src/parser.rs

@@ -32,6 +32,7 @@ use log::trace;
 use std::{
     collections::{HashMap, HashSet},
     num::ParseIntError,
+    str,
 };
 
 #[cfg(feature = "plugin")]
@@ -451,12 +452,13 @@ fn parse_short_flags(
 
     let arg_contents = working_set.get_span_contents(arg_span);
 
-    if arg_contents.starts_with(b"-") && arg_contents.len() > 1 {
+    if let Ok(arg_contents_uft8_ref) = str::from_utf8(arg_contents) {
-        let short_flags = &arg_contents[1..];
+        if arg_contents_uft8_ref.starts_with('-') && arg_contents_uft8_ref.len() > 1 {
+            let short_flags = &arg_contents_uft8_ref[1..];
             let mut found_short_flags = vec![];
             let mut unmatched_short_flags = vec![];
-        for short_flag in short_flags.iter().enumerate() {
+            for short_flag in short_flags.chars().enumerate() {
-            let short_flag_char = char::from(*short_flag.1);
+                let short_flag_char = short_flag.1;
                 let orig = arg_span;
                 let short_flag_span = Span::new(
                     orig.start + 1 + short_flag.0,
@@ -479,7 +481,9 @@ fn parse_short_flags(
 
                 // check to see if we have a negative number
                 if let Some(positional) = sig.get_positional(positional_idx) {
-                if positional.shape == SyntaxShape::Int || positional.shape == SyntaxShape::Number {
+                    if positional.shape == SyntaxShape::Int
+                        || positional.shape == SyntaxShape::Number
+                    {
                         if String::from_utf8_lossy(arg_contents).parse::<f64>().is_ok() {
                             return None;
                         } else if let Some(first) = unmatched_short_flags.first() {
@@ -525,6 +529,10 @@ fn parse_short_flags(
         } else {
             None
         }
+    } else {
+        working_set.error(ParseError::NonUtf8(arg_span));
+        None
+    }
 }
 
 fn first_kw_idx(

tests/parsing/mod.rs

@@ -237,3 +237,14 @@ fn numberlike_command_name() {
 
     assert!(actual.err.contains("backticks"));
 }
+
+#[test]
+fn call_command_with_non_ascii_argument() {
+    let actual = nu!(cwd: "tests/parsing/samples",
+        r#"
+            def nu-arg [--umlaut(-ö): int] {}
+            nu-arg -ö 42
+        "#);
+
+    assert_eq!(actual.err.len(), 0);
+}