Raise error for incorrect JSON serialization (#7273)

Co-authored-by: Varad Bhatnagar <[email protected]>

Author: varadhbhatnagar

src/datasets/io/json.py

@@ -104,6 +104,11 @@ def write(self) -> int:
         if compression not in [None, "infer", "gzip", "bz2", "xz"]:
             raise NotImplementedError(f"`datasets` currently does not support {compression} compression")
 
+        if not lines and self.batch_size < self.dataset.num_rows:
+            raise NotImplementedError(
+                "Output JSON will not be formatted correctly when lines = False and batch_size < number of rows in the dataset. Use pandas.DataFrame.to_json() instead."
+            )
+
         if isinstance(self.path_or_buf, (str, bytes, os.PathLike)):
             with fsspec.open(
                 self.path_or_buf, "wb", compression=compression, **(self.storage_options or {})