Restrict strings beginning with quote should also ending with quote.

It adds an additional check inside `parse_string`, and returns `unbalanced quote` if input string is unbalanced

crates/nu-parser/src/parser.rs

@@ -2831,6 +2831,17 @@ pub fn parse_string(working_set: &mut StateWorkingSet, span: Span) -> Expression
     if bytes[0] != b'\'' && bytes[0] != b'"' && bytes[0] != b'`' && bytes.contains(&b'(') {
         return parse_string_interpolation(working_set, span);
     }
+    // Check for unbalanced quotes:
+   {
+        if bytes.starts_with(b"\"") && (bytes.len() == 1 || !bytes.ends_with(b"\"")) {
+            working_set.error(ParseError::Unclosed("\"".into(), span));
+            return garbage(working_set, span);
+        }
+        if bytes.starts_with(b"\'") && (bytes.len() == 1 || !bytes.ends_with(b"\'")) {
+            working_set.error(ParseError::Unclosed("\'".into(), span));
+            return garbage(working_set, span);
+        }
+    }
 
     let (s, err) = unescape_unquote_string(bytes, span);
     if let Some(err) = err {

tests/repl/test_strings.rs

@@ -36,6 +36,12 @@ fn non_string_in_record() -> TestResult {
     )
 }
 
+#[test]
+fn unbalance_string() -> TestResult {
+    fail_test(r#""aaaab"cc"#, "unclosed \"")?;
+    fail_test(r#"'aaaab'cc"#, "unclosed '")
+}
+
 #[test]
 fn string_in_valuestream() -> TestResult {
     run_test(