[Frontend] Support override generation config in args (#12409)

Signed-off-by: liuyanyi <wolfsonliu@163.com>

tests/test_config.py

@@ -281,3 +281,73 @@ def test_uses_mrope(model_id, uses_mrope):
     )
 
     assert config.uses_mrope == uses_mrope
+
+
+def test_generation_config_loading():
+    model_id = "Qwen/Qwen2.5-1.5B-Instruct"
+
+    # When set generation_config to None, the default generation config
+    # will not be loaded.
+    model_config = ModelConfig(model_id,
+                               task="auto",
+                               tokenizer=model_id,
+                               tokenizer_mode="auto",
+                               trust_remote_code=False,
+                               seed=0,
+                               dtype="float16",
+                               generation_config=None)
+    assert model_config.get_diff_sampling_param() == {}
+
+    # When set generation_config to "auto", the default generation config
+    # should be loaded.
+    model_config = ModelConfig(model_id,
+                               task="auto",
+                               tokenizer=model_id,
+                               tokenizer_mode="auto",
+                               trust_remote_code=False,
+                               seed=0,
+                               dtype="float16",
+                               generation_config="auto")
+
+    correct_generation_config = {
+        "repetition_penalty": 1.1,
+        "temperature": 0.7,
+        "top_p": 0.8,
+        "top_k": 20,
+    }
+
+    assert model_config.get_diff_sampling_param() == correct_generation_config
+
+    # The generation config could be overridden by the user.
+    override_generation_config = {"temperature": 0.5, "top_k": 5}
+
+    model_config = ModelConfig(
+        model_id,
+        task="auto",
+        tokenizer=model_id,
+        tokenizer_mode="auto",
+        trust_remote_code=False,
+        seed=0,
+        dtype="float16",
+        generation_config="auto",
+        override_generation_config=override_generation_config)
+
+    override_result = correct_generation_config.copy()
+    override_result.update(override_generation_config)
+
+    assert model_config.get_diff_sampling_param() == override_result
+
+    # When generation_config is set to None and override_generation_config
+    # is set, the override_generation_config should be used directly.
+    model_config = ModelConfig(
+        model_id,
+        task="auto",
+        tokenizer=model_id,
+        tokenizer_mode="auto",
+        trust_remote_code=False,
+        seed=0,
+        dtype="float16",
+        generation_config=None,
+        override_generation_config=override_generation_config)
+
+    assert model_config.get_diff_sampling_param() == override_generation_config