Fix tiktoken add generation prompt (#890)

llmfoundry/tokenizers/tiktoken.py

@@ -198,7 +198,7 @@ def default_chat_template(self):
             '{% else %}'
             "{{ '\n' + '<|im_start|>' + message['role'] + '\n' + message['content'] + '<|im_end|>' }}"
             '{% endif %}'
-            '{% if (add_generation_prompt == true) %}'
+            '{% if (add_generation_prompt == true and loop.last) %}'
             "{{ '\n' + '<|im_start|>' + 'assistant' + '\n' }}"
             "{% elif (message['role'] == 'assistant') %}"
             '{{ eos_token }}'

tests/tokenizers/test_tiktoken.py

@@ -108,6 +108,12 @@
         'Please summarize the goals in this text:\n\nGoing outside has benefits include reducing stress and triggering the relaxation response, which can help us not only feel better mentally, but even heal faster from physical ailments.',
     'role':
         'user'
+}, {
+    'content': 'You should go outside and touch grass.',
+    'role': 'assistant'
+}, {
+    'content': 'What else can I do?',
+    'role': 'user'
 }]]
 
 MULTI_TURN_GENERATE_STRING = [
@@ -118,6 +124,10 @@
 
 Going outside has benefits include reducing stress and triggering the relaxation response, which can help us not only feel better mentally, but even heal faster from physical ailments.<|im_end|>
 <|im_start|>assistant
+You should go outside and touch grass.<|im_end|><|endoftext|>
+<|im_start|>user
+What else can I do?<|im_end|>
+<|im_start|>assistant
 """
 ]