Handle non-ascii chars in query context summary

Author: parthchandra

native/spark-expr/src/query_context.rs

@@ -80,6 +80,15 @@ impl QueryContext {
         }
     }
 
+    /// Convert a character index to a byte offset in the SQL text.
+    /// Returns None if the character index is out of range.
+    fn char_index_to_byte_offset(&self, char_index: usize) -> Option<usize> {
+        self.sql_text
+            .char_indices()
+            .nth(char_index)
+            .map(|(byte_offset, _)| byte_offset)
+    }
+
     /// Generate a summary string showing SQL fragment with error location.
     /// (From SQLQueryContext.summary)
     ///
@@ -90,14 +99,23 @@ impl QueryContext {
     ///        ^^^
     /// ```
     pub fn format_summary(&self) -> String {
-        let start_idx = self.start_index.max(0) as usize;
-        let stop_idx = (self.stop_index + 1).max(0) as usize;
-
-        // Extract the problematic fragment
-        let fragment = if start_idx < self.sql_text.len() && stop_idx <= self.sql_text.len() {
-            &self.sql_text[start_idx..stop_idx]
-        } else {
-            ""
+        let start_char = self.start_index.max(0) as usize;
+        // stop_index is inclusive; fragment covers [start, stop]
+        let stop_char = (self.stop_index + 1).max(0) as usize;
+
+        let fragment = match (
+            self.char_index_to_byte_offset(start_char),
+            // stop_char may equal sql_text.chars().count() (one past the end)
+            self.char_index_to_byte_offset(stop_char).or_else(|| {
+                if stop_char == self.sql_text.chars().count() {
+                    Some(self.sql_text.len())
+                } else {
+                    None
+                }
+            }),
+        ) {
+            (Some(start_byte), Some(stop_byte)) => &self.sql_text[start_byte..stop_byte],
+            _ => "",
         };
 
         // Build the header line
@@ -130,20 +148,29 @@ impl QueryContext {
         // Add caret pointer
         let caret_position = self.start_position.max(0) as usize;
         summary.push_str(&" ".repeat(caret_position));
-        summary.push_str(&"^".repeat(fragment.len().max(1)));
+        // fragment.chars().count() gives the correct display width for non-ASCII
+        summary.push_str(&"^".repeat(fragment.chars().count().max(1)));
 
         summary
     }
 
     /// Returns the SQL fragment that caused the error.
     pub fn fragment(&self) -> String {
-        let start_idx = self.start_index.max(0) as usize;
-        let stop_idx = (self.stop_index + 1).max(0) as usize;
-
-        if start_idx < self.sql_text.len() && stop_idx <= self.sql_text.len() {
-            self.sql_text[start_idx..stop_idx].to_string()
-        } else {
-            String::new()
+        let start_char = self.start_index.max(0) as usize;
+        let stop_char = (self.stop_index + 1).max(0) as usize;
+
+        match (
+            self.char_index_to_byte_offset(start_char),
+            self.char_index_to_byte_offset(stop_char).or_else(|| {
+                if stop_char == self.sql_text.chars().count() {
+                    Some(self.sql_text.len())
+                } else {
+                    None
+                }
+            }),
+        ) {
+            (Some(start_byte), Some(stop_byte)) => self.sql_text[start_byte..stop_byte].to_string(),
+            _ => String::new(),
         }
     }
 }
@@ -357,4 +384,19 @@ mod tests {
         assert_eq!(map.len(), 0);
         assert!(map.is_empty());
     }
+
+    // Verify that fragment() and format_summary() correctly handle SQL text that
+    // contains multi-byte characters
+
+    #[test]
+    fn test_fragment_non_ascii_accented() {
+        // "é" is a 2-byte UTF-8 sequence (U+00E9).
+        // SQL: "SELECT café FROM t"
+        //       0123456789...
+        // char indices: c=7, a=8, f=9, é=10, ' '=11 ...  FROM = 12..
+        // start_index=7, stop_index=10 should yield "café"
+        let sql = "SELECT café FROM t".to_string();
+        let ctx = QueryContext::new(sql, 7, 10, None, None, 1, 7);
+        assert_eq!(ctx.fragment(), "café");
+    }
 }