Support GLM-4.7 function calling via structural tags (#28149)

Co-authored-by: Xinyuan Tong <115166877+JustinTong0323@users.noreply.github.com>
Co-authored-by: Xinyuan Tong <xinyuantong.cs@gmail.com>

python/sglang/srt/function_call/glm47_moe_detector.py

@@ -3,10 +3,15 @@ import json
 import logging
 import re
 from enum import Enum
-from typing import Any, Dict, List, Optional, Tuple
+from functools import lru_cache
+from typing import Any, Dict, List, Literal, Optional, Tuple, Union
 
-from sglang.srt.entrypoints.openai.protocol import Tool
+from sglang.srt.entrypoints.openai.protocol import Tool, ToolChoice
-from sglang.srt.function_call.base_format_detector import BaseFormatDetector
+from sglang.srt.function_call.base_format_detector import (
+    BaseFormatDetector,
+    StructuralTag,
+    get_model_structural_tag,
+)
 from sglang.srt.function_call.core_types import (
     StreamingParseResult,
     ToolCallItem,
@@ -17,6 +22,21 @@ from sglang.srt.function_call.utils import infer_type_from_json_schema
 logger = logging.getLogger(__name__)
 
 
+@lru_cache(maxsize=1)
+def _glm47_native_structural_tag_available() -> bool:
+    # "glm_4_7" is only registered in newer xgrammar, so the import can succeed
+    # while the model name stays unknown. Probe once and fall back if absent.
+    if get_model_structural_tag is None:
+        return False
+    try:
+        get_model_structural_tag(
+            model="glm_4_7", tools=[], tool_choice="auto", reasoning=False
+        )
+        return True
+    except Exception:
+        return False
+
+
 class StreamState(str, Enum):
     """State machine states for XML to JSON streaming conversion."""
 
@@ -781,7 +801,22 @@ class Glm47MoeDetector(BaseFormatDetector):
         return arguments
 
     def supports_structural_tag(self) -> bool:
-        return False
+        return _glm47_native_structural_tag_available()
+
+    def get_structural_tag(
+        self,
+        tools: Union[List[Tool], None] = None,
+        tool_choice: Union[ToolChoice, Literal["auto", "required"]] = "auto",
+        thinking_mode: bool = False,
+    ) -> Optional[StructuralTag]:
+        if not self.supports_structural_tag():
+            return None
+        return super().get_structural_tag(
+            tools=tools, tool_choice=tool_choice, thinking_mode=thinking_mode
+        )
 
     def structure_info(self) -> _GetInfoFunc:
-        raise NotImplementedError()
+        raise NotImplementedError
+
+    def get_structural_tag_name(self) -> str:
+        return "glm_4_7"

test/registered/unit/function_call/test_function_call_parser.py

@@ -3360,6 +3360,69 @@ class TestGlm47MoeDetector(unittest.TestCase):
         self.assertEqual(params["old_string"], "    indented code")
         self.assertEqual(params["new_string"], "        also indented")
 
+    def test_get_model_structural_tag(self):
+        """GLM-4.7/GLM-5 use xgrammar's native "glm_4_7" structural tag."""
+        import xgrammar as xgr
+
+        self.assertTrue(self.detector.supports_structural_tag())
+        self.assertEqual(self.detector.get_structural_tag_name(), "glm_4_7")
+
+        # thinking_mode=True keeps the </think> reasoning prefix.
+        structural_tag = self.detector.get_structural_tag(
+            self.tools, thinking_mode=True
+        )
+        self.assertIsInstance(structural_tag, xgr.StructuralTag)
+        self.assertIsInstance(
+            xgr.Grammar.from_structural_tag(structural_tag), xgr.Grammar
+        )
+        serialized = structural_tag.model_dump_json()
+        self.assertIn("glm_xml", serialized)
+        self.assertIn("<tool_call>", serialized)
+        self.assertIn("</think>", serialized)
+
+        # thinking_mode=False drops the reasoning prefix (ReasonerGrammarBackend
+        # owns </think> when --reasoning-parser is configured).
+        structural_tag = self.detector.get_structural_tag(
+            self.tools, thinking_mode=False
+        )
+        self.assertIsInstance(structural_tag, xgr.StructuralTag)
+        self.assertIsInstance(
+            xgr.Grammar.from_structural_tag(structural_tag), xgr.Grammar
+        )
+        self.assertNotEqual("sequence", structural_tag.model_dump()["format"]["type"])
+
+        # tool_choice="required" must still compile to a grammar.
+        structural_tag = self.detector.get_structural_tag(
+            self.tools, thinking_mode=True, tool_choice="required"
+        )
+        self.assertIsInstance(structural_tag, xgr.StructuralTag)
+        self.assertIsInstance(
+            xgr.Grammar.from_structural_tag(structural_tag), xgr.Grammar
+        )
+
+    def test_required_tool_choice_falls_back_when_native_tag_is_unavailable(self):
+        from unittest.mock import patch
+
+        from sglang.srt.function_call.function_call_parser import FunctionCallParser
+        from sglang.srt.function_call.glm47_moe_detector import (
+            _glm47_native_structural_tag_available,
+        )
+
+        with patch(
+            "sglang.srt.function_call.glm47_moe_detector.get_model_structural_tag",
+            None,
+        ):
+            _glm47_native_structural_tag_available.cache_clear()
+            self.assertFalse(self.detector.supports_structural_tag())
+            self.assertIsNone(self.detector.get_structural_tag(self.tools))
+
+            parser = FunctionCallParser(self.tools, "glm47")
+            constraint = parser.get_structure_constraint("required")
+
+            self.assertIsNotNone(constraint)
+            self.assertEqual("json_schema", constraint[0])
+            _glm47_native_structural_tag_available.cache_clear()
+
 
 class TestJsonArrayParser(unittest.TestCase):
     def setUp(self):