Fix prompt assembly for llama (#952)

* start at index 0

* add test to check for missing turns

* apply black

* Update test_prompt_tokenizers.py

* Update src/axolotl/monkeypatch/fastchat_conversation_turns.py

Co-authored-by: Motoki Wu <tokestermw@gmail.com>

* fix linting

* apply black

* add more tests for llama/sharegpt

* make logic clearer

---------

Co-authored-by: Motoki Wu <tokestermw@gmail.com>

src/axolotl/monkeypatch/fastchat_conversation_turns.py

@@ -83,14 +83,21 @@ def get_turns(  # pylint: disable=too-many-return-statements
                 yield role + ":", ""
         return
     if self.sep_style == SeparatorStyle.LLAMA2:
-        seps = [self.sep, self.sep2]
         if self.system_message:
+            if self.messages:
+                # For llama, the system message is incorporated into the first human instruction
+                first_role, first_msg = self.messages[0]
+                if first_role == self.roles[0]:
+                    system_prompt += first_msg
+                    self.messages.pop(0)
             yield "", system_prompt
-        else:
-            yield "", "[INST] "
-        for i, (role, message) in enumerate(self.messages[1:]):
+        for i, (role, message) in enumerate(self.messages):
             if message:
-                yield role + " ", message + seps[i % 2]
+                if (i % 2 == 0 and not self.system_message) or (
+                    i % 2 != 0 and self.system_message
+                ):
+                    role = "<s> " + role
+                yield role + " ", message
             else:
                 yield role, ""
         return

tests/test_prompt_tokenizers.py

@@ -114,6 +114,76 @@ class TestPromptTokenizationStrategies(unittest.TestCase):
                 in self._caplog.records[0].message
             )
 
+    def test_sharegpt_llama(self):
+        "Make sure the sharegpt/llama is tokenized and formatted correctly."
+        prompter = ShareGPTPrompterV2(conversation="llama-2")
+        strat = ShareGPTPromptTokenizingStrategy(
+            prompter,
+            self.tokenizer,
+            False,
+            2048,
+        )
+
+        def tokenize(conv):
+            return strat.tokenize_prompt(conv)["input_ids"]
+
+        def decode(ids):
+            return strat.tokenizer.decode(ids)
+
+        # Multi-turn conversations
+        multi_turn_conv = {
+            "conversations": [
+                {"from": "system", "value": "lorem"},
+                {"from": "human", "value": "abc"},
+                {"from": "gpt", "value": "ipsum"},
+                {"from": "human", "value": "123"},
+                {"from": "gpt", "value": "sit"},
+            ]
+        }
+        # fmt: off
+        mt_ids = tokenize(multi_turn_conv)
+        assert decode(mt_ids) == '<s> [INST] <<SYS>>\nlorem\n<</SYS>>\n\nabc [/INST] ipsum</s><s> [INST] 123 [/INST] sit</s>'
+        assert mt_ids == [1, 518, 25580, 29962, 3532, 14816, 29903, 6778, 13, 29880, 3668, 13, 29966, 829, 14816, 29903, 6778, 13, 13, 10736, 518, 29914, 25580, 29962, 23421, 2, 1, 518, 25580, 29962, 29871, 29896, 29906, 29941, 518, 29914, 25580, 29962, 7845, 2]
+
+        # Single-turn conversations
+        single_turn_conv = {
+            "conversations": [
+                {"from": "system", "value": "lorem"},
+                {"from": "human", "value": "abc"},
+                {"from": "gpt", "value": "ipsum"},
+            ]
+        }
+
+        st_ids = tokenize(single_turn_conv)
+        assert decode(st_ids) == '<s> [INST] <<SYS>>\nlorem\n<</SYS>>\n\nabc [/INST] ipsum</s>'
+        assert st_ids == [1, 518, 25580, 29962, 3532, 14816, 29903, 6778, 13, 29880, 3668, 13, 29966, 829, 14816, 29903, 6778, 13, 13, 10736, 518, 29914, 25580, 29962, 23421, 2]
+
+        # No system message, single-turn
+        no_sys_conv = {
+            "conversations": [
+                {"from": "human", "value": "abc"},
+                {"from": "gpt", "value": "ipsum"},
+            ]
+        }
+
+        ns_ids = tokenize(no_sys_conv)
+        assert decode(ns_ids) == '<s> [INST] abc [/INST] ipsum</s>'
+        assert ns_ids == [1, 518, 25580, 29962, 25638, 518, 29914, 25580, 29962, 23421, 2]
+
+        # No system message, multi-turn
+        no_sys_mt_conv = {
+            "conversations": [
+                {"from": "human", "value": "abc"},
+                {"from": "gpt", "value": "ipsum"},
+                {"from": "human", "value": "123"},
+                {"from": "gpt", "value": "sit"},
+            ]
+        }
+        ns_mt_ids = tokenize(no_sys_mt_conv)
+        assert decode(ns_mt_ids) == '<s> [INST] abc [/INST] ipsum</s><s> [INST] 123 [/INST] sit</s>'
+        assert ns_mt_ids == [1, 518, 25580, 29962, 25638, 518, 29914, 25580, 29962, 23421, 2, 1, 518, 25580, 29962, 29871, 29896, 29906, 29941, 518, 29914, 25580, 29962, 7845, 2]
+        # fmt: on
+
     def test_sharegpt_changes_roles(self):
         conversation = {
             "roles": ["USER", "CHARACTER"],