fix(core): Address UTF-8 character boundary issues in LineBreaker

Cargo.toml

@@ -175,6 +175,7 @@ tailcall-valid = { workspace = true }
 dashmap = "6.1.0"
 urlencoding = "2.1.3"
 tailcall-chunk = "0.3.0"
+unicode-segmentation = "1.12.0"
 
 # to build rquickjs bindings on systems without builtin bindings
 [target.'cfg(all(target_os = "windows", target_arch = "x86"))'.dependencies]

src/core/document.rs

@@ -4,6 +4,7 @@ use std::fmt::Display;
 use async_graphql::parser::types::*;
 use async_graphql::Positioned;
 use async_graphql_value::ConstValue;
+use unicode_segmentation::UnicodeSegmentation;
 
 use super::jit::Directive as JitDirective;
 use super::json::JsonLikeOwned;
@@ -28,19 +29,35 @@ impl<'a> Iterator for LineBreaker<'a> {
             return None;
         }
 
-        let end_index = self
-            .string
-            .chars()
-            .skip(self.index + self.break_at)
-            .enumerate()
-            .find(|(_, ch)| ch.is_whitespace())
-            .map(|(index, _)| self.index + self.break_at + index + 1)
-            .unwrap_or(self.string.len());
+        let graphemes = self.string[self.index..].graphemes(true).peekable();
+        let mut iter = graphemes;
+        let mut current_len = 0;
+        let mut last_valid_index = self.index;
+
+        while let Some(grapheme) = iter.peek() {
+            let grapheme_len = grapheme.len();
+
+            if current_len + grapheme_len > self.break_at {
+                break;
+            }
+
+            iter.next();
+            current_len += grapheme_len;
+            last_valid_index += grapheme_len;
+        }
+
+        for grapheme in iter {
+            if grapheme.chars().any(|ch| ch.is_whitespace()) {
+                last_valid_index += grapheme.len();
+                break;
+            }
+            last_valid_index += grapheme.len();
+        }
 
         let start_index = self.index;
-        self.index = end_index;
+        self.index = last_valid_index;
 
-        Some(&self.string[start_index..end_index])
+        Some(&self.string[start_index..self.index])
     }
 }
 
@@ -456,3 +473,38 @@ impl<'a, Input: JsonLikeOwned + Display> From<&'a JitDirective<Input>> for Direc
         }
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::get_formatted_docs;
+
+    #[test]
+    fn test_get_formatted_docs() {
+        let input = Some(String::from(
+            "This is a test string for get_formatted_docs function. You are typing a long sentence for testing. What a nice, long sentence!",
+        ));
+        let indent = 4;
+
+        let result = get_formatted_docs(input, indent);
+        let expected = String::from(
+            "    \"\"\"\n    This is a test string for get_formatted_docs function. You are typing a long sentence \n    for testing. What a nice, long sentence!\n    \"\"\"\n",
+        );
+
+        assert_eq!(result, expected)
+    }
+
+    #[test]
+    fn test_get_formatted_docs_utf8() {
+        let input = Some(String::from(
+            "get_formatted_docs 함수 테스트를 위한 문장입니다. 테스트를 위해 긴 문장을 입력하는 중 입니다. テストのために長い文章を入力しているところです。なんて素敵な長文です！",
+        ));
+        let indent = 4;
+
+        let result = get_formatted_docs(input, indent);
+        let expected = String::from(
+            "    \"\"\"\n    get_formatted_docs 함수 테스트를 위한 문장입니다. 테스트를 위해 \n    긴 문장을 입력하는 중 입니다. テストのために長い文章を入力しているところです。なんて素敵な長文です！\n    \"\"\"\n",
+        );
+
+        assert_eq!(result, expected)
+    }
+}