fix(parser): Correctly bind 'char' boundaries

Fixes #553

crates/core/src/parser/parser.rs

@@ -649,7 +649,10 @@ impl<'a> InvalidLiquidToken<'a> {
         let invalid_token_position = invalid_token_span.start_pos();
         let (offset_l, offset_c) = invalid_token_position.line_col();
         let offset_l = offset_l - 1;
-        let offset_c = offset_c - 1;
+        let offset_c = (0..offset_c)
+            .rev()
+            .find(|i| invalid_token_position.line_of().is_char_boundary(*i))
+            .unwrap_or(0);
 
         let end_position = match next_elements.last() {
             Some(element) => element.as_span().end_pos(),

tests/errors.rs

@@ -1,8 +1,22 @@
+use snapbox::assert_data_eq;
+use snapbox::str;
+
 #[test]
-#[should_panic]
 fn test_fuzz() {
-    let _ = liquid::ParserBuilder::with_stdlib()
+    match liquid::ParserBuilder::with_stdlib()
         .build()
         .unwrap()
-        .parse("˄{%");
+        .parse("˄{%")
+    {
+        Ok(_) => panic!("should fail"),
+        Err(err) => assert_data_eq!(err.to_string(), str![[r#"
+liquid:  --> 1:3
+  |
+1 | {%
+  |   ^---
+  |
+  = expected Identifier
+
+"#]]),
+    }
 }