Fixing NormalizedString append when normalized is empty. (#1717)

Co-authored-by: Anantha Kandrapu <[email protected]>

tokenizers/src/tokenizer/normalizer.rs

@@ -517,6 +517,9 @@ impl NormalizedString {
         if let Some((b, prev)) = self.normalized.char_indices().last() {
             let transformations = std::iter::once((prev, 0)).chain(s.chars().map(|c| (c, 1)));
             self.transform_range(Range::Normalized(b..), transformations, 0);
+        } else {
+            let transformations = s.chars().map(|c| (c, 1));
+            self.transform_range(Range::Normalized(..), transformations, 0);
         }
         self
     }
@@ -2284,4 +2287,24 @@ mod tests {
         s.lowercase();
         assert_eq!(s.get(), "a...");
     }
+
+    #[test]
+    fn test_append_after_clear() {
+        let mut n = NormalizedString::from("Hello");
+        assert_eq!(n.get(), "Hello");
+
+        n.clear();
+        assert_eq!(n.get(), "");
+
+        n.append(" World");
+        assert_eq!(n.get(), " World");
+
+        assert_eq!(n.len_original(), 5);
+        assert_eq!(n.len(), 6);
+
+        assert_eq!(n.get_range_original(Range::Original(0..5)), Some("Hello"));
+        assert_eq!(n.get_range_original(Range::Normalized(0..6)), Some(""));
+
+        assert_eq!(n.get_range(Range::Normalized(0..6)), Some(" World"));
+    }
 }