fix(pgwire): TruncatedFmt should respect utf8 char boundary (#14292)

src/utils/pgwire/src/lib.rs

@@ -18,6 +18,7 @@
 #![feature(trusted_len)]
 #![feature(lazy_cell)]
 #![feature(buf_read_has_data_left)]
+#![feature(round_char_boundary)]
 #![expect(clippy::doc_markdown, reason = "FIXME: later")]
 
 pub mod error;

src/utils/pgwire/src/pg_protocol.rs

@@ -1139,8 +1139,9 @@ pub mod truncated_fmt {
             }
 
             if self.remaining < s.len() {
-                self.f.write_str(&s[0..self.remaining])?;
-                self.remaining = 0;
+                let actual = s.floor_char_boundary(self.remaining);
+                self.f.write_str(&s[0..actual])?;
+                self.remaining -= actual;
                 self.f.write_str("...(truncated)")?;
                 self.finished = true; // so that ...(truncated) is printed exactly once
             } else {
@@ -1180,4 +1181,17 @@ pub mod truncated_fmt {
             .write_fmt(format_args!("{}", self.0))
         }
     }
+
+    #[cfg(test)]
+    mod tests {
+        use super::*;
+
+        #[test]
+        fn test_trunc_utf8() {
+            assert_eq!(
+                format!("{}", TruncatedFmt(&"select '🌊';", 10)),
+                "select '...(truncated)",
+            );
+        }
+    }
 }