From e3d65507f9eccbf20a7de4b9c862661f0dc6df19 Mon Sep 17 00:00:00 2001
From: Henry Su <henrysu4707@gmail.com>
Date: Sun, 9 Aug 2026 11:43:06 -0500
Subject: [PATCH] fix(lib): apply strict JSON schema transform to tuple
 prefixItems

`_ensure_strict_json_schema` recursed into `items`, `anyOf`, `allOf`,
`properties` and `$defs` but not `prefixItems`, which pydantic v2 emits for
`tuple[...]` fields. As a result a tuple element carrying a `$ref` with
sibling keys (e.g. a field description) was left un-expanded, producing a
schema the API rejects, and nested objects inside tuples did not receive the
`additionalProperties: false` / `required` treatment.

Recurse into `prefixItems` just like `items`.
---
 src/openai/lib/_pydantic.py |  9 +++++
 tests/lib/test_pydantic.py  | 75 +++++++++++++++++++++++++++++++++++++
 2 files changed, 84 insertions(+)

diff --git a/src/openai/lib/_pydantic.py b/src/openai/lib/_pydantic.py
index 3cfe224cb1..3fd6ff4e19 100644
--- a/src/openai/lib/_pydantic.py
+++ b/src/openai/lib/_pydantic.py
@@ -66,6 +66,15 @@ def _ensure_strict_json_schema(
     if is_dict(items):
         json_schema["items"] = _ensure_strict_json_schema(items, path=(*path, "items"), root=root)
 
+    # tuples / positional arrays
+    # { 'type': 'array', 'prefixItems': [{...}, {...}] }
+    prefix_items = json_schema.get("prefixItems")
+    if is_list(prefix_items):
+        json_schema["prefixItems"] = [
+            _ensure_strict_json_schema(item, path=(*path, "prefixItems", str(i)), root=root)
+            for i, item in enumerate(prefix_items)
+        ]
+
     # unions
     any_of = json_schema.get("anyOf")
     if is_list(any_of):
diff --git a/tests/lib/test_pydantic.py b/tests/lib/test_pydantic.py
index 754a15151c..6ea5b1513c 100644
--- a/tests/lib/test_pydantic.py
+++ b/tests/lib/test_pydantic.py
@@ -1,7 +1,10 @@
 from __future__ import annotations
 
 from enum import Enum
+from typing import Tuple
+from typing_extensions import Annotated
 
+import pytest
 from pydantic import Field, BaseModel
 from inline_snapshot import snapshot
 
@@ -169,6 +172,78 @@ def test_most_types() -> None:
         )
 
 
+class Location(BaseModel):
+    lat: float
+    long: float
+
+
+class Route(BaseModel):
+    endpoints: Tuple[
+        Annotated[Location, Field(description="The starting point.")],
+        Annotated[Location, Field(description="The ending point.")],
+    ]
+
+
+@pytest.mark.skipif(PYDANTIC_V1, reason="`prefixItems` is only emitted by pydantic v2")
+def test_tuple_prefix_items_ref_expansion() -> None:
+    # tuple elements are emitted under `prefixItems`; the strict transform must
+    # recurse into them the same way it does for `items`, otherwise a `$ref` that
+    # carries sibling keys (e.g. a field description) is left un-expanded and the
+    # API rejects the resulting schema.
+    assert to_strict_json_schema(Route) == snapshot(
+        {
+            "$defs": {
+                "Location": {
+                    "properties": {
+                        "lat": {"title": "Lat", "type": "number"},
+                        "long": {"title": "Long", "type": "number"},
+                    },
+                    "required": ["lat", "long"],
+                    "title": "Location",
+                    "type": "object",
+                    "additionalProperties": False,
+                }
+            },
+            "properties": {
+                "endpoints": {
+                    "maxItems": 2,
+                    "minItems": 2,
+                    "prefixItems": [
+                        {
+                            "description": "The starting point.",
+                            "properties": {
+                                "lat": {"title": "Lat", "type": "number"},
+                                "long": {"title": "Long", "type": "number"},
+                            },
+                            "required": ["lat", "long"],
+                            "title": "Location",
+                            "type": "object",
+                            "additionalProperties": False,
+                        },
+                        {
+                            "description": "The ending point.",
+                            "properties": {
+                                "lat": {"title": "Lat", "type": "number"},
+                                "long": {"title": "Long", "type": "number"},
+                            },
+                            "required": ["lat", "long"],
+                            "title": "Location",
+                            "type": "object",
+                            "additionalProperties": False,
+                        },
+                    ],
+                    "title": "Endpoints",
+                    "type": "array",
+                }
+            },
+            "required": ["endpoints"],
+            "title": "Route",
+            "type": "object",
+            "additionalProperties": False,
+        }
+    )
+
+
 class Color(Enum):
     RED = "red"
     BLUE = "blue"