[inference] check for unsupported model generate args (#2627)

deepspeed/inference/engine.py

@@ -49,6 +49,10 @@ def __init__(self, model, config):
 
         self._get_model_config_generate(config)  # keep for weird backward compatibility
 
+        # patch model generate with ours if model uses it
+        if hasattr(self.module, "generate"):
+            self.generate = self._generate
+
         if hasattr(self.module, "config"):
             DSPolicy.hf_model_config = self.module.config
 
@@ -148,8 +152,6 @@ def _get_model_config_generate(self, config):
         self.config = getattr(self.module,
                               'config',
                               None) if config.config is None else config.config
-        # todo: clarify with Reza if this gets used anywhere
-        self.generate = getattr(self.module, 'generate', None)
 
     def remove_mask_prepare_for_bloom(self):
         if hasattr(self.module, 'transformer'):
@@ -518,3 +520,19 @@ def forward(self, *inputs, **kwargs):
             self._model_times.append(duration)
 
         return outputs
+
+    def _generate(self, *inputs, **kwargs):
+        num_beams = 1
+        if "generation_config" in kwargs:
+            gen_config = kwargs["generation_config"]
+            num_beams = getattr(gen_config, "num_beams", 1)
+        if "num_beams" in kwargs:
+            num_beams = kwargs["num_beams"]
+
+        if num_beams > 1:
+            raise NotImplementedError(
+                "DeepSpeed does not support `num_beams` > 1, if this is important to you please "
+                "add your request to: https://github.com/microsoft/DeepSpeed/issues/2506"
+            )
+
+        return self.module.generate(*inputs, **kwargs)