From be2ad5f92060b66788740e2e8302a490fbd226f4 Mon Sep 17 00:00:00 2001
From: Andreas Karatzas <akaratza@amd.com>
Date: Thu, 18 Dec 2025 01:04:57 -0600
Subject: [PATCH] [ROCm][Bugfix] fix(structured_output): Skip guidance backend
 for schemas with patternProperties (#30730)

Signed-off-by: Andreas Karatzas <akaratza@amd.com>
---
 vllm/v1/engine/input_processor.py             | 21 +++++++++++++--
 vllm/v1/structured_output/backend_guidance.py | 26 +++++++++++++++++++
 2 files changed, 45 insertions(+), 2 deletions(-)

diff --git a/vllm/v1/engine/input_processor.py b/vllm/v1/engine/input_processor.py
index 65e0c845b0afa..29293877cb69d 100644
--- a/vllm/v1/engine/input_processor.py
+++ b/vllm/v1/engine/input_processor.py
@@ -24,7 +24,10 @@ from vllm.tokenizers.mistral import MistralTokenizer
 from vllm.utils import length_from_prompt_token_ids_or_embeds
 from vllm.v1.engine import EngineCoreRequest
 from vllm.v1.metrics.stats import MultiModalCacheStats
-from vllm.v1.structured_output.backend_guidance import validate_guidance_grammar
+from vllm.v1.structured_output.backend_guidance import (
+    has_guidance_unsupported_json_features,
+    validate_guidance_grammar,
+)
 from vllm.v1.structured_output.backend_lm_format_enforcer import (
     validate_structured_output_request_lm_format_enforcer,
 )
@@ -340,8 +343,22 @@ class InputProcessor:
                 # The request either failed validation
                 # or includes some jsonschema feature(s) that
                 # are not supported in xgrammar.
-                if isinstance(self.tokenizer, MistralTokenizer):
+
+                # Check if schema has features unsupported by guidance
+                so_params = params.structured_outputs
+                skip_guidance = False
+                if so_params.json:
+                    if isinstance(so_params.json, str):
+                        import json
+
+                        schema = json.loads(so_params.json)
+                    else:
+                        schema = so_params.json
+                    skip_guidance = has_guidance_unsupported_json_features(schema)
+
+                if isinstance(self.tokenizer, MistralTokenizer) or skip_guidance:
                     # Fall back to outlines if the tokenizer is Mistral
+                    # or if schema contains features unsupported by guidance
                     validate_structured_output_request_outlines(params)
                     params.structured_outputs._backend = "outlines"
                 else:
diff --git a/vllm/v1/structured_output/backend_guidance.py b/vllm/v1/structured_output/backend_guidance.py
index 2962a439dcb3e..727a67333bd71 100644
--- a/vllm/v1/structured_output/backend_guidance.py
+++ b/vllm/v1/structured_output/backend_guidance.py
@@ -44,6 +44,32 @@ def _walk_json_for_additional_properties(data: object):
             _walk_json_for_additional_properties(item)
 
 
+def has_guidance_unsupported_json_features(schema: dict[str, Any]) -> bool:
+    """Check if JSON schema contains features unsupported by guidance/llguidance."""
+
+    def check_object(obj: dict[str, Any]) -> bool:
+        if not isinstance(obj, dict):
+            return False
+
+        # patternProperties is not supported by llguidance
+        if "patternProperties" in obj:
+            return True
+
+        # Recursively check all nested objects and arrays
+        for value in obj.values():
+            if isinstance(value, dict):
+                if check_object(value):
+                    return True
+            elif isinstance(value, list):
+                for item in value:
+                    if isinstance(item, dict) and check_object(item):
+                        return True
+
+        return False
+
+    return check_object(schema)
+
+
 def process_for_additional_properties(
     guide_json: str | dict[str, Any],
 ) -> dict[str, Any]: