Simplify (and fix) passing of guided decoding backend options (#17008)

Signed-off-by: Harry Mellor <19981378+hmellor@users.noreply.github.com>

vllm/sampling_params.py

@@ -8,6 +8,7 @@ from typing import Annotated, Any, Optional, Union
 
 import msgspec
 from pydantic import BaseModel
+from typing_extensions import deprecated
 
 from vllm.logger import init_logger
 from vllm.logits_process import LogitsProcessor
@@ -37,6 +38,10 @@ class GuidedDecodingParams:
     json_object: Optional[bool] = None
     """These are other options that can be set"""
     backend: Optional[str] = None
+    backend_was_auto: bool = False
+    disable_fallback: bool = False
+    disable_any_whitespace: bool = False
+    disable_additional_properties: bool = False
     whitespace_pattern: Optional[str] = None
     structural_tag: Optional[str] = None
 
@@ -68,36 +73,6 @@ class GuidedDecodingParams:
             structural_tag=structural_tag,
         )
 
-    @property
-    def backend_name(self) -> str:
-        """Return the backend name without any options.
-        
-        For example if the backend is "xgrammar:no-fallback", returns "xgrammar"
-        """
-        return (self.backend or "").split(":")[0]
-
-    def backend_options(self) -> list[str]:
-        """Return the backend options as a list of strings."""
-        if not self.backend or ":" not in self.backend:
-            return []
-        return self.backend.split(":")[1].split(",")
-
-    def add_option(self, opt_name: str) -> None:
-        """Adds an option to the backend options."""
-        if not self.backend:
-            self.backend = f":{opt_name}"
-        elif ":" not in self.backend:
-            self.backend += f":{opt_name}"
-        else:
-            options = set(self.backend_options())
-            options.add(opt_name)
-            self.backend = f"{self.backend_name}:{','.join(sorted(options))}"
-
-    def no_fallback(self) -> bool:
-        """Returns True if the "no-fallback" option is supplied for the guided
-        decoding backend"""
-        return "no-fallback" in self.backend_options()
-
     def __post_init__(self):
         """Validate that some fields are mutually exclusive."""
         guide_count = sum([
@@ -109,6 +84,27 @@ class GuidedDecodingParams:
                 "You can only use one kind of guided decoding but multiple are "
                 f"specified: {self.__dict__}")
 
+        if self.backend is not None and ":" in self.backend:
+            self._extract_backend_options()
+
+    @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."""
+        assert isinstance(self.backend, str)
+        self.backend, options = self.backend.split(":")
+        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
+
 
 class RequestOutputKind(Enum):
     # Return entire output so far in every RequestOutput