🔓 Remove lm_head check in AutoModelForCausalLMWithValueHead (#2398)

* Remove lm_head check in `AutoModelForCausalLMWithValueHead`

* Style

* Remove test

tests/test_modeling_value_head.py

@@ -265,14 +265,6 @@ def test_generate(self, model_name):
         # Just check if the generation works
         _ = model.generate(input_ids, generation_config=generation_config)
 
-    def test_raise_error_not_causallm(self):
-        # Test with a model without a LM head
-        model_id = "trl-internal-testing/tiny-GPT2LMHeadModel"
-        # This should raise a ValueError
-        with self.assertRaises(ValueError):
-            pretrained_model = AutoModelForCausalLM.from_pretrained(model_id)
-            _ = AutoModelForCausalLMWithValueHead.from_pretrained(pretrained_model.transformer)
-
     def test_transformers_bf16_kwargs(self):
         r"""
         Test if the transformers kwargs are correctly passed
@@ -283,10 +275,11 @@ def test_transformers_bf16_kwargs(self):
         for model_name in self.all_model_names:
             trl_model = self.trl_model_class.from_pretrained(model_name, torch_dtype=torch.bfloat16)
 
-            lm_head_namings = self.trl_model_class.lm_head_namings
+            lm_head_namings = ["lm_head", "embed_out", "output_layer"]
 
             self.assertTrue(
-                any(hasattr(trl_model.pretrained_model, lm_head_naming) for lm_head_naming in lm_head_namings)
+                any(hasattr(trl_model.pretrained_model, lm_head_naming) for lm_head_naming in lm_head_namings),
+                "Can't test the model because it doesn't have any of the expected lm_head namings",
             )
 
             for lm_head_naming in lm_head_namings:

trl/models/modeling_value_head.py

@@ -69,9 +69,6 @@ class AutoModelForCausalLMWithValueHead(PreTrainedModelWrapper):
     Class attributes:
         - **transformers_parent_class** (`transformers.PreTrainedModel`) -- The parent class of the wrapped model. This
             should be set to `transformers.AutoModelForCausalLM` for this class.
-        - **lm_head_namings** (`tuple`) -- A tuple of strings that are used to identify the language model head of the
-            wrapped model. This is set to `("lm_head", "embed_out", "output_layer")` for this class but can be changed
-            for other models in the future
         - **supported_args** (`tuple`) -- A tuple of strings that are used to identify the arguments that are supported
             by the `ValueHead` class. Currently, the supported args are:
             - **summary_dropout_prob** (`float`, `optional`, defaults to `None`) -- The dropout probability for the
@@ -86,7 +83,6 @@ class AutoModelForCausalLMWithValueHead(PreTrainedModelWrapper):
     """
 
     transformers_parent_class = AutoModelForCausalLM
-    lm_head_namings = ["lm_head", "embed_out", "output_layer"]
     supported_args = (
         "summary_dropout_prob",
         "v_head_initializer_range",
@@ -106,12 +102,7 @@ def __init__(self, pretrained_model, **kwargs):
         """
         super().__init__(pretrained_model, **kwargs)
         v_head_kwargs, _, _ = self._split_kwargs(kwargs)
-
-        if not any(hasattr(self.pretrained_model, attribute) for attribute in self.lm_head_namings):
-            raise ValueError("The model does not have a language model head, please use a model that has one.")
-
         self.v_head = ValueHead(self.pretrained_model.config, **v_head_kwargs)
-
         self._init_weights(**v_head_kwargs)
 
     def _init_weights(self, **kwargs):