Simplify (and fix) passing of guided decoding backend options

examples/online_serving/openai_chat_completion_structured_outputs.py

@@ -112,8 +112,8 @@ def extra_backend_options_completion(client: OpenAI, model: str):
               "alan.turing@enigma.com\n")
 
     try:
-        # The no-fallback option forces vLLM to use xgrammar, so when it fails
-        # you get a 400 with the reason why
+        # The guided_decoding_disable_fallback option forces vLLM to use
+        # xgrammar, so when it fails you get a 400 with the reason why
         completion = client.chat.completions.create(
             model=model,
             messages=[{
@@ -123,7 +123,8 @@ def extra_backend_options_completion(client: OpenAI, model: str):
             extra_body={
                 "guided_regex": r"\w+@\w+\.com\n",
                 "stop": ["\n"],
-                "guided_decoding_backend": "xgrammar:no-fallback"
+                "guided_decoding_backend": "xgrammar",
+                "guided_decoding_disable_fallback": True,
             },
         )
         return completion.choices[0].message.content

tests/model_executor/test_guided_processors.py

@@ -202,12 +202,15 @@ def test_multiple_guided_options_not_allowed(sample_json_schema, sample_regex):
 
 def test_guided_decoding_backend_options():
     """Test backend-specific options"""
-    params = GuidedDecodingParams(
-        backend="xgrammar:option-1,option-2,option-3")
-    assert params.backend_options() == ["option-1", "option-2", "option-3"]
-
-    no_fallback = GuidedDecodingParams(backend="xgrammar:option-1,no-fallback")
-    assert no_fallback.no_fallback()
+    with pytest.warns(DeprecationWarning):
+        guided_decoding_params = GuidedDecodingParams(
+            backend=
+            "xgrammar:no-fallback,disable-any-whitespace,no-additional-properties"
+        )
+    assert guided_decoding_params.backend == "xgrammar"
+    assert guided_decoding_params.disable_fallback
+    assert guided_decoding_params.disable_any_whitespace
+    assert guided_decoding_params.disable_additional_properties
 
 
 def test_pickle_xgrammar_tokenizer_data():

tests/v1/entrypoints/llm/test_struct_output_generate.py

@@ -17,15 +17,12 @@
 from vllm.sampling_params import GuidedDecodingParams, SamplingParams
 
 PARAMS_MODELS_BACKENDS_TOKENIZER_MODE = [
-    ("mistralai/Ministral-8B-Instruct-2410", "xgrammar:disable-any-whitespace",
-     "auto"),
-    ("mistralai/Ministral-8B-Instruct-2410", "guidance:disable-any-whitespace",
-     "auto"),
-    ("mistralai/Ministral-8B-Instruct-2410", "xgrammar:disable-any-whitespace",
-     "mistral"),
-    ("Qwen/Qwen2.5-1.5B-Instruct", "xgrammar:disable-any-whitespace", "auto"),
+    ("mistralai/Ministral-8B-Instruct-2410", "xgrammar", "auto"),
+    ("mistralai/Ministral-8B-Instruct-2410", "guidance", "auto"),
+    ("mistralai/Ministral-8B-Instruct-2410", "xgrammar", "mistral"),
+    ("Qwen/Qwen2.5-1.5B-Instruct", "xgrammar", "auto"),
     #FIXME: This test is flaky on CI thus disabled
-    #("Qwen/Qwen2.5-1.5B-Instruct", "guidance:disable-any-whitespace", "auto"),
+    #("Qwen/Qwen2.5-1.5B-Instruct", "guidance", "auto"),
 ]
 
 PARAMS_MODELS_TOKENIZER_MODE = [
@@ -73,6 +70,7 @@ def test_structured_output(
               enforce_eager=enforce_eager,
               max_model_len=1024,
               guided_decoding_backend=guided_decoding_backend,
+              guided_decoding_disable_any_whitespace=True,
               tokenizer_mode=tokenizer_mode)
 
     #
@@ -98,8 +96,7 @@ def test_structured_output(
 
         generated_text = output.outputs[0].text
         assert generated_text is not None
-        if 'disable-any-whitespace' in guided_decoding_backend:
-            assert "\n" not in generated_text
+        assert "\n" not in generated_text
         print(f"Prompt: {prompt!r}, Generated text: {generated_text!r}")
         output_json = json.loads(generated_text)
         jsonschema.validate(instance=output_json, schema=sample_json_schema)
@@ -520,10 +517,11 @@ def test_structured_output_auto_mode(
 def test_guidance_no_additional_properties(monkeypatch: pytest.MonkeyPatch):
     monkeypatch.setenv("VLLM_USE_V1", "1")
 
-    backend = 'guidance:no-additional-properties,disable-any-whitespace'
     llm = LLM(model="Qwen/Qwen2.5-1.5B-Instruct",
               max_model_len=1024,
-              guided_decoding_backend=backend)
+              guided_decoding_backend="guidance",
+              guided_decoding_disable_any_whitespace=True,
+              guided_decoding_disable_additional_properties=True)
 
     schema = {
         'type': 'object',
@@ -548,7 +546,11 @@ def test_guidance_no_additional_properties(monkeypatch: pytest.MonkeyPatch):
         "<|im_end|>\n<|im_start|>assistant\n")
 
     def generate_with_backend(backend):
-        guided_params = GuidedDecodingParams(json=schema, backend=backend)
+        guided_params = GuidedDecodingParams(
+            json=schema,
+            backend=backend,
+            disable_any_whitespace=True,
+            disable_additional_properties=True)
         sampling_params = SamplingParams(temperature=0,
                                          max_tokens=256,
                                          guided_decoding=guided_params)
@@ -562,8 +564,7 @@ def generate_with_backend(backend):
         jsonschema.validate(instance=parsed_json, schema=schema)
         return parsed_json
 
-    generated = generate_with_backend(
-        'guidance:no-additional-properties,disable-any-whitespace')
+    generated = generate_with_backend("guidance")
     assert "a1" in generated
     assert "a2" in generated
     assert "a3" in generated

tests/v1/test_oracle.py

@@ -57,7 +57,8 @@ def test_unsupported_configs(monkeypatch):
         with pytest.raises(NotImplementedError):
             AsyncEngineArgs(
                 model=MODEL,
-                guided_decoding_backend="lm-format-enforcer:no-fallback",
+                guided_decoding_backend="lm-format-enforcer",
+                guided_decoding_disable_fallback=True,
             ).create_engine_config()
 
         with pytest.raises(NotImplementedError):

vllm/config.py

@@ -17,12 +17,14 @@
 from importlib.util import find_spec
 from pathlib import Path
 from typing import (TYPE_CHECKING, Any, Callable, ClassVar, Final, Literal,
-                    Optional, Protocol, TypeVar, Union, get_args, get_origin)
+                    Optional, Protocol, TypeVar, Union, cast, get_args,
+                    get_origin)
 
 import torch
 from pydantic import BaseModel, Field, PrivateAttr
 from torch.distributed import ProcessGroup, ReduceOp
 from transformers import PretrainedConfig
+from typing_extensions import deprecated
 
 import vllm.envs as envs
 from vllm.compilation.inductor_pass import CallableInductorPass, InductorPass
@@ -32,7 +34,6 @@
                                                      get_quantization_config)
 from vllm.model_executor.models import ModelRegistry
 from vllm.platforms import CpuArchEnum, current_platform
-from vllm.sampling_params import GuidedDecodingParams
 from vllm.tracing import is_otel_available, otel_import_error_traceback
 from vllm.transformers_utils.config import (
     ConfigFormat, get_config, get_hf_image_processor_config,
@@ -344,7 +345,7 @@ def compute_hash(self) -> str:
     def __init__(
         self,
         model: str,
-        task: Union[TaskOption, Literal["draft"]],
+        task: Literal[TaskOption, Literal["draft"]],
         tokenizer: str,
         tokenizer_mode: str,
         trust_remote_code: bool,
@@ -701,7 +702,7 @@ def _get_preferred_task(
 
     def _resolve_task(
         self,
-        task_option: Union[TaskOption, Literal["draft"]],
+        task_option: Literal[TaskOption, Literal["draft"]],
     ) -> tuple[set[_ResolvedTask], _ResolvedTask]:
         if task_option == "draft":
             return {"draft"}, "draft"
@@ -3185,13 +3186,36 @@ def get_served_model_name(model: str,
 class DecodingConfig:
     """Dataclass which contains the decoding strategy of the engine."""
 
-    guided_decoding_backend: GuidedDecodingBackend = \
-        "auto" if envs.VLLM_USE_V1 else "xgrammar"
+    @property
+    @deprecated(
+        "`guided_decoding_backend` is deprecated and has been renamed to "
+        "`backend`. This will be removed in v0.10.0. Please use the "
+        "`backend` argument instead.")
+    def guided_decoding_backend(self) -> GuidedDecodingBackend:
+        return self.backend
+
+    @guided_decoding_backend.setter
+    def guided_decoding_backend(self, value: GuidedDecodingBackend):
+        self.backend = value
+
+    backend: GuidedDecodingBackend = "auto" if envs.VLLM_USE_V1 else "xgrammar"
     """Which engine will be used for guided decoding (JSON schema / regex etc)
     by default. With "auto", we will make opinionated choices based on request
     contents and what the backend libraries currently support, so the behavior
     is subject to change in each release."""
 
+    disable_fallback: bool = False
+    """If `True`, vLLM will not fallback to a different backend on error."""
+
+    disable_any_whitespace: bool = False
+    """If `True`, the model will not generate any whitespace during guided
+    decoding. This is only supported for xgrammar and guidance backends."""
+
+    disable_additional_properties: bool = False
+    """If `True`, the `guidance` backend will not use `additionalProperties`
+    in the JSON schema. This is only supported for the `guidance` backend and
+    is used to better align its behaviour with `outlines` and `xgrammar`."""
+
     reasoning_backend: Optional[str] = None
     """Select the reasoning parser depending on the model that you're using.
     This is used to parse the reasoning content into OpenAI API format.
@@ -3217,15 +3241,41 @@ def compute_hash(self) -> str:
         return hash_str
 
     def __post_init__(self):
-        backend = GuidedDecodingParams(
-            backend=self.guided_decoding_backend).backend_name
+        if ":" in self.backend:
+            self._extract_backend_options()
+
         if envs.VLLM_USE_V1:
             valid_guided_backends = get_args(GuidedDecodingBackendV1)
         else:
             valid_guided_backends = get_args(GuidedDecodingBackendV0)
-        if backend not in valid_guided_backends:
-            raise ValueError(f"Invalid guided_decoding_backend '{backend}',"
+        if self.backend not in valid_guided_backends:
+            raise ValueError(f"Invalid backend '{self.backend}',"
                              f" must be one of {valid_guided_backends}")
+        if (self.disable_any_whitespace
+                and self.backend not in ("xgrammar", "guidance")):
+            raise ValueError("disable_any_whitespace is only supported for "
+                             "xgrammar and guidance backends.")
+        if (self.disable_additional_properties and self.backend != "guidance"):
+            raise ValueError("disable_additional_properties is only supported "
+                             "for the guidance backend.")
+
+    @deprecated(
+        "Passing guided decoding backend options inside backend in the format "
+        "'backend:...' is deprecated. This will be removed in v0.10.0. Please "
+        "use the dedicated arguments '--disable-fallback', "
+        "'--disable-any-whitespace' and '--disable-additional-properties' "
+        "instead.")
+    def _extract_backend_options(self):
+        """Extract backend options from the backend string."""
+        backend, options = self.backend.split(":")
+        self.backend = cast(GuidedDecodingBackend, backend)
+        options_set = set(options.strip().split(","))
+        if "no-fallback" in options_set:
+            self.disable_fallback = True
+        if "disable-any-whitespace" in options_set:
+            self.disable_any_whitespace = True
+        if "no-additional-properties" in options_set:
+            self.disable_additional_properties = True
 
 
 @dataclass

vllm/engine/arg_utils.py

@@ -18,9 +18,9 @@
 from vllm.config import (BlockSize, CacheConfig, CacheDType, CompilationConfig,
                          ConfigFormat, ConfigType, DecodingConfig, Device,
                          DeviceConfig, DistributedExecutorBackend,
-                         GuidedDecodingBackendV1, HfOverrides,
-                         KVTransferConfig, LoadConfig, LoadFormat, LoRAConfig,
-                         ModelConfig, ModelImpl, MultiModalConfig,
+                         GuidedDecodingBackend, GuidedDecodingBackendV1,
+                         HfOverrides, KVTransferConfig, LoadConfig, LoadFormat,
+                         LoRAConfig, ModelConfig, ModelImpl, MultiModalConfig,
                          ObservabilityConfig, ParallelConfig, PoolerConfig,
                          PrefixCachingHashAlgo, PromptAdapterConfig,
                          SchedulerConfig, SchedulerPolicy, SpeculativeConfig,
@@ -317,7 +317,12 @@ class EngineArgs:
         bool] = SchedulerConfig.enable_chunked_prefill
     disable_chunked_mm_input: bool = SchedulerConfig.disable_chunked_mm_input
 
-    guided_decoding_backend: str = DecodingConfig.guided_decoding_backend
+    guided_decoding_backend: GuidedDecodingBackend = DecodingConfig.backend
+    guided_decoding_disable_fallback: bool = DecodingConfig.disable_fallback
+    guided_decoding_disable_any_whitespace: bool = \
+        DecodingConfig.disable_any_whitespace
+    guided_decoding_disable_additional_properties: bool = \
+        DecodingConfig.disable_additional_properties
     logits_processor_pattern: Optional[str] = None
 
     speculative_config: Optional[Dict[str, Any]] = None
@@ -498,9 +503,17 @@ def add_cli_args(parser: FlexibleArgumentParser) -> FlexibleArgumentParser:
             title="DecodingConfig",
             description=DecodingConfig.__doc__,
         )
+        guided_decoding_group.add_argument("--guided-decoding-backend",
+                                           **guided_decoding_kwargs["backend"])
         guided_decoding_group.add_argument(
-            '--guided-decoding-backend',
-            **guided_decoding_kwargs["guided_decoding_backend"])
+            "--guided-decoding-disable-fallback",
+            **guided_decoding_kwargs["disable_fallback"])
+        guided_decoding_group.add_argument(
+            "--guided-decoding-disable-any-whitespace",
+            **guided_decoding_kwargs["disable_any_whitespace"])
+        guided_decoding_group.add_argument(
+            "--guided-decoding-disable-additional-properties",
+            **guided_decoding_kwargs["disable_additional_properties"])
         guided_decoding_group.add_argument(
             "--reasoning-parser",
             # This choices is a special case because it's not static
@@ -1244,7 +1257,11 @@ def create_engine_config(
                                         if self.enable_prompt_adapter else None
 
         decoding_config = DecodingConfig(
-            guided_decoding_backend=self.guided_decoding_backend,
+            backend=self.guided_decoding_backend,
+            disable_fallback=self.guided_decoding_disable_fallback,
+            disable_any_whitespace=self.guided_decoding_disable_any_whitespace,
+            disable_additional_properties=\
+                self.guided_decoding_disable_additional_properties,
             reasoning_backend=self.reasoning_parser
             if self.enable_reasoning else None,
         )
@@ -1335,9 +1352,8 @@ def _is_v1_supported_oracle(self, model_config: ModelConfig) -> bool:
                                recommend_to_remove=True)
             return False
 
-        # remove backend options when doing this check
-        if self.guided_decoding_backend.split(':')[0] \
-            not in get_args(GuidedDecodingBackendV1):
+        if self.guided_decoding_backend not in get_args(
+                GuidedDecodingBackendV1):
             _raise_or_fallback(
                 feature_name=
                 f"--guided-decoding-backend={self.guided_decoding_backend}",

vllm/engine/llm_engine.py

@@ -2091,7 +2091,7 @@ def _build_logits_processors(
 
             tokenizer = self.get_tokenizer(lora_request=lora_request)
             guided_decoding.backend = guided_decoding.backend or \
-                self.decoding_config.guided_decoding_backend
+                self.decoding_config.backend
 
             if self.decoding_config.reasoning_backend is not None:
                 logger.debug("Building with reasoning backend %s",

vllm/engine/multiprocessing/client.py

@@ -615,9 +615,9 @@ async def _process_request(
                 build_guided_decoding_logits_processor_async(
                     sampling_params=params,
                     tokenizer=await self.get_tokenizer(lora_request),
-                    default_guided_backend=(self.decoding_config.guided_decoding_backend
+                    default_guided_backend=(self.decoding_config.backend
                         if self.decoding_config
-                        else DecodingConfig.guided_decoding_backend),
+                        else DecodingConfig.backend),
                     model_config=self.model_config,
                     reasoning_backend=self.decoding_config.reasoning_backend,
                 )