[Feature] New structural tag support (#10691)

python/sglang/srt/constrained/llguidance_backend.py

@@ -32,6 +32,7 @@ from sglang.srt.constrained.base_grammar_backend import (
     BaseGrammarBackend,
     BaseGrammarObject,
 )
+from sglang.srt.constrained.utils import is_legacy_structural_tag
 
 logger = logging.getLogger(__name__)
 
@@ -160,6 +161,7 @@ class GuidanceBackend(BaseGrammarBackend):
     def dispatch_structural_tag(self, key_string: str) -> Optional[GuidanceGrammar]:
         try:
             structural_tag = json.loads(key_string)
+            assert is_legacy_structural_tag(structural_tag)
             tags = [
                 StructTag(
                     begin=structure["begin"],

python/sglang/srt/constrained/utils.py

@@ -0,0 +1,12 @@
+from typing import Dict
+
+
+def is_legacy_structural_tag(obj: Dict) -> bool:
+    # test whether an object is a legacy structural tag
+    # see `StructuralTagResponseFormat` at `sglang.srt.entrypoints.openai.protocol`
+    if obj.get("structures", None) is not None:
+        assert obj.get("triggers", None) is not None
+        return True
+    else:
+        assert obj.get("format", None) is not None
+        return False

python/sglang/srt/constrained/xgrammar_backend.py

@@ -34,6 +34,7 @@ from sglang.srt.constrained.base_grammar_backend import (
     BaseGrammarObject,
     GrammarStats,
 )
+from sglang.srt.constrained.utils import is_legacy_structural_tag
 from sglang.srt.utils import is_hip
 
 _is_hip = is_hip()
@@ -241,18 +242,22 @@ class XGrammarGrammarBackend(BaseGrammarBackend):
 
     def dispatch_structural_tag(self, key_string: str) -> Optional[XGrammarGrammar]:
         try:
+            # TODO(dark): it's REALLY stupid to construct object from string and decode it again
             structural_tag = json.loads(key_string)
-            tags = [
-                StructuralTagItem(
-                    begin=structure["begin"],
-                    schema=json.dumps(structure["schema"]),
-                    end=structure["end"],
+            if is_legacy_structural_tag(structural_tag):
+                tags = [
+                    StructuralTagItem(
+                        begin=structure["begin"],
+                        schema=json.dumps(structure["schema"]),
+                        end=structure["end"],
+                    )
+                    for structure in structural_tag["structures"]
+                ]
+                ctx = self.grammar_compiler.compile_structural_tag(
+                    tags, structural_tag["triggers"]
                 )
-                for structure in structural_tag["structures"]
-            ]
-            ctx = self.grammar_compiler.compile_structural_tag(
-                tags, structural_tag["triggers"]
-            )
+            else:
+                ctx = self.grammar_compiler.compile_structural_tag(key_string)
         except (RuntimeError, json.decoder.JSONDecodeError) as e:
             logging.error(f"Hit invalid structural_tag: {key_string=}, {e=}")
             return INVALID_GRAMMAR_OBJ