[model] add smollm2 support (#8220)

src/llamafactory/data/template.py

@@ -1693,6 +1693,22 @@ register_template(
 )
 
 
+register_template(
+    name="smollm2",
+    format_system=StringFormatter(
+        slots=["<|im_start|>system\n{{content}}<|im_end|>\n"]
+    ),
+    format_user=StringFormatter(
+        slots=["<|im_start|>user\n{{content}}<|im_end|>\n<|im_start|>assistant\n"]
+    ),
+    format_assistant=StringFormatter(
+        slots=["{{content}}<|im_end|>\n"]
+    ),
+    stop_words=["<|im_end|>"],
+    default_system="You are a helpful AI assistant named SmolLM, trained by Hugging Face.",
+)
+
+
 register_template(
     name="solar",
     format_user=StringFormatter(slots=["### User:\n{{content}}\n\n### Assistant:\n"]),