fix packing so that concatenated sequences reset the attention

tests/test_packed_dataset.py

@@ -0,0 +1,64 @@
+"""Module for testing dataset sequence packing"""
+
+import unittest
+from pathlib import Path
+
+from datasets import Dataset, load_dataset
+from transformers import AutoTokenizer
+
+from axolotl.datasets import ConstantLengthDataset, TokenizedPromptDataset
+from axolotl.prompt_tokenizers import AlpacaPromptTokenizingStrategy
+from axolotl.prompters import AlpacaPrompter
+
+
+class TestPacking(unittest.TestCase):
+    """
+    Test class for packing dataset sequences
+    """
+
+    def setUp(self) -> None:
+        self.tokenizer = AutoTokenizer.from_pretrained("huggyllama/llama-7b")
+        self.tokenizer.add_special_tokens(
+            {
+                "bos_token": "<s>",
+                "eos_token": "</s>",
+                "unk_token": "<unk>",
+            }
+        )
+
+    def test_resets_attention(self):
+        prompter = AlpacaPrompter("chat")
+        strat = AlpacaPromptTokenizingStrategy(
+            prompter,
+            self.tokenizer,
+            False,
+            2048,
+        )
+        dateset = load_dataset(
+            "json",
+            data_files=str(Path(__file__).parent / "fixtures/alpaca/alpaca.json"),
+        )["train"]
+        dataset = Dataset.from_list(list(TokenizedPromptDataset(strat, dateset)))
+
+        constant_len_dataset = ConstantLengthDataset(
+            self.tokenizer,
+            [dataset],
+            seq_length=2048,
+        )
+        packed_dataset = Dataset.from_list(list(constant_len_dataset))
+        example = packed_dataset[0]
+        next_bos_index = (
+            example["input_ids"][1:].index(self.tokenizer.bos_token_id) + 1
+        )  # add one since we sliced
+
+        # first example doesn't have mask reset
+        assert example["input_ids"][0] == self.tokenizer.bos_token_id
+        assert example["attention_mask"][0] == 1
+
+        # but subsequent one does
+        assert example["input_ids"][next_bos_index] == self.tokenizer.bos_token_id
+        assert example["attention_mask"][next_bos_index] == 0
+
+
+if __name__ == "__main__":
+    unittest.main()