fix `add_special_tokens=False` in generate_until + decoding fixes

lm_eval/models/vllm_causallms.py

@@ -139,6 +139,11 @@ please install vllm via `pip install lm-eval[vllm]` or `pip install -e .[vllm]`"
         if "do_sample" in kwargs.keys():
             kwargs.pop("do_sample")
         if generate:
+            # hf defaults
+            kwargs["skip_special_tokens"] = kwargs.get("skip_special_tokens", False)
+            kwargs["spaces_between_special_tokens"] = kwargs.get(
+                "spaces_between_special_tokens", False
+            )
             sampling_params = SamplingParams(max_tokens=max_tokens, stop=stop, **kwargs)
         else:
             sampling_params = SamplingParams(
@@ -226,7 +231,7 @@ please install vllm via `pip install lm-eval[vllm]` or `pip install -e .[vllm]`"
 
         # batch tokenize contexts
         context, all_gen_kwargs = zip(*(req.args for req in requests))
-        context_encoding = self.tokenizer(context).input_ids
+        context_encoding = self.tokenizer(context, add_special_tokens=False).input_ids
         requests = [
             ((a, b), c) for a, b, c in zip(context, context_encoding, all_gen_kwargs)
         ]