Generate: assistant should be greedy in assisted decoding (#30778)

* assistant should be greedy

* better comment

* Update src/transformers/generation/candidate_generator.py
Co-authored-by: amyeroberts <22614925+amyeroberts@users.noreply.github.com>

---------
Co-authored-by: amyeroberts <22614925+amyeroberts@users.noreply.github.com>

src/transformers/generation/candidate_generator.py

@@ -150,6 +150,12 @@ class AssistedCandidateGenerator(CandidateGenerator):
         self.generation_config.return_dict_in_generate = True
         self.generation_config.output_scores = True
 
+        # Disable sampling -- this implementation of assisted generation/speculative decoding uses the assistant
+        # greedily to maximize matches. Disables sampling-related flags to prevent warnings
+        self.generation_config.do_sample = False
+        for attr in ("temperature", "top_p", "min_p", "typical_p", "top_k", "epsilon_cutoff", "eta_cutoff"):
+            setattr(self.generation_config, attr, None)
+
         # avoid unnecessary warnings that min_length is larger than max_new_tokens
         # remove the `MinLengthLogitsProcessor` if exists (NOTE: no need to check for `MinNewTokensLogitsProcessor`)
         self.main_model_min_length = self.generation_config.min_length

src/transformers/generation/configuration_utils.py

@@ -496,6 +496,11 @@ class GenerationConfig(PushToHubMixin):
                     greedy_wrong_parameter_msg.format(flag_name="top_p", flag_value=self.top_p),
                     UserWarning,
                 )
+            if self.min_p is not None:
+                warnings.warn(
+                    greedy_wrong_parameter_msg.format(flag_name="min_p", flag_value=self.min_p),
+                    UserWarning,
+                )
             if self.typical_p is not None and self.typical_p != 1.0:
                 warnings.warn(
                     greedy_wrong_parameter_msg.format(flag_name="typical_p", flag_value=self.typical_p),