[V1] Add `disable-any-whitespace` option support for xgrammar (#15316)

Signed-off-by: Russell Bryant <rbryant@redhat.com>

tests/v1/entrypoints/llm/test_struct_output_generate.py

@@ -57,6 +57,50 @@ def test_guided_json_completion(
         jsonschema.validate(instance=output_json, schema=sample_json_schema)
 
 
+@pytest.mark.skip_global_cleanup
+@pytest.mark.parametrize("guided_decoding_backend",
+                         GUIDED_DECODING_BACKENDS_V1)
+@pytest.mark.parametrize("model_name", MODELS_TO_TEST)
+def test_guided_json_completion_disable_any_whitespace(
+    monkeypatch: pytest.MonkeyPatch,
+    sample_json_schema: dict[str, Any],
+    guided_decoding_backend: str,
+    model_name: str,
+):
+    if guided_decoding_backend != "xgrammar":
+        pytest.skip("disable-any-whitespace is only supported for xgrammar.")
+    guided_decoding_backend = 'xgrammar:disable-any-whitespace'
+
+    monkeypatch.setenv("VLLM_USE_V1", "1")
+    llm = LLM(model=model_name,
+              max_model_len=1024,
+              guided_decoding_backend=guided_decoding_backend)
+    sampling_params = SamplingParams(
+        temperature=1.0,
+        max_tokens=1000,
+        guided_decoding=GuidedDecodingParams(json=sample_json_schema))
+    outputs = llm.generate(prompts=[
+        f"Give an example JSON for an employee profile "
+        f"that fits this schema: {sample_json_schema}"
+    ] * 2,
+                           sampling_params=sampling_params,
+                           use_tqdm=True)
+
+    assert outputs is not None
+
+    for output in outputs:
+        assert output is not None
+        assert isinstance(output, RequestOutput)
+        prompt = output.prompt
+
+        generated_text = output.outputs[0].text
+        assert generated_text is not None
+        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)
+
+
 @pytest.mark.skip_global_cleanup
 @pytest.mark.parametrize("guided_decoding_backend",
                          GUIDED_DECODING_BACKENDS_V1)
@@ -301,7 +345,6 @@ def test_guided_choice_completion(
         prompts="The best language for type-safe systems programming is ",
         sampling_params=sampling_params,
         use_tqdm=True)
-
     assert outputs is not None
     for output in outputs:
         assert output is not None

vllm/engine/arg_utils.py

@@ -1486,7 +1486,9 @@ class EngineArgs:
             return False
 
         # Only support Xgrammar for guided decoding so far.
-        SUPPORTED_GUIDED_DECODING = ["xgrammar", "xgrammar:nofallback"]
+        SUPPORTED_GUIDED_DECODING = [
+            "xgrammar", "xgrammar:disable-any-whitespace"
+        ]
         if self.guided_decoding_backend not in SUPPORTED_GUIDED_DECODING:
             _raise_or_fallback(feature_name="--guided-decoding-backend",
                                recommend_to_remove=False)

vllm/v1/engine/processor.py

@@ -120,7 +120,7 @@ class Processor:
         if not params.guided_decoding or not self.decoding_config:
             return
 
-        supported_backends = ["xgrammar"]
+        supported_backends = ["xgrammar", "xgrammar:disable-any-whitespace"]
         engine_level_backend = self.decoding_config.guided_decoding_backend
         if engine_level_backend not in supported_backends:
             raise ValueError(f"Only {supported_backends} structured output is "

vllm/v1/structured_output/backend_xgrammar.py

@@ -26,6 +26,9 @@ class XgrammarBackend(StructuredOutputBackend):
 
     def __init__(self, vllm_config: VllmConfig):
         self.vllm_config = vllm_config
+        self.disable_any_whitespace = (
+            "disable-any-whitespace"
+            in vllm_config.decoding_config.guided_decoding_backend)
         tokenizer_group = init_tokenizer_from_configs(
             model_config=vllm_config.model_config,
             scheduler_config=vllm_config.scheduler_config,
@@ -74,8 +77,8 @@ class XgrammarBackend(StructuredOutputBackend):
     def compile_grammar(self, request_type: StructuredOutputOptions,
                         grammar_spec: str) -> StructuredOutputGrammar:
         if request_type == StructuredOutputOptions.JSON:
-            ctx = self.compiler.compile_json_schema(grammar_spec,
-                                                    any_whitespace=False)
+            ctx = self.compiler.compile_json_schema(
+                grammar_spec, any_whitespace=not self.disable_any_whitespace)
         elif request_type == StructuredOutputOptions.JSON_OBJECT:
             ctx = self.compiler.compile_builtin_json_grammar()
         elif request_type == StructuredOutputOptions.GRAMMAR: