[GPT-OSS] Structure_Tag support for gpt-oss tool-call in cot (#25515)

Signed-off-by: Hanchenli <lihanc2002@gmail.com>
Signed-off-by: Hanchenli <61769611+Hanchenli@users.noreply.github.com>
Signed-off-by: Wei Wei <wwei6@meta.com>
Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>
Co-authored-by: Wei Wei <wwei6@meta.com>
Co-authored-by: Wei Wei <weiweinpu@gmail.com>
Co-authored-by: Cyrus Leung <tlleungac@connect.ust.hk>

vllm/sampling_params.py

@@ -58,6 +58,7 @@ class StructuredOutputsParams:
                 self.choice is not None,
                 self.grammar is not None,
                 self.json_object is not None,
+                self.structural_tag is not None,
             ]
         )
         if count > 1:
@@ -66,6 +67,37 @@ class StructuredOutputsParams:
                 f"but multiple are specified: {self.__dict__}"
             )
 
+    def all_constraints_none(self) -> bool:
+        """
+        Returns True if all structured-output constraint fields are None.
+        """
+        return all(
+            getattr(self, field) is None
+            for field in (
+                "json",
+                "regex",
+                "choice",
+                "grammar",
+                "json_object",
+                "structural_tag",
+            )
+        )
+
+    def all_non_structural_tag_constraints_none(self) -> bool:
+        """
+        Returns True if all structured-output constraint fields are None.
+        """
+        return all(
+            getattr(self, field) is None
+            for field in (
+                "json",
+                "regex",
+                "choice",
+                "grammar",
+                "json_object",
+            )
+        )
+
 
 @dataclass
 class GuidedDecodingParams(StructuredOutputsParams):