From 535d5b3f9f1546ccb5cc8370e51fcf06f149761e Mon Sep 17 00:00:00 2001
From: Motov Yurii <109919500+YuriiMotov@users.noreply.github.com>
Date: Tue, 17 Jun 2025 09:46:27 +0200
Subject: [PATCH] =?UTF-8?q?=F0=9F=90=9B=20Fix=20truncating=20the=20model's?=
 =?UTF-8?q?=20description=20with=20form=20feed=20(`\f`)=20character=20for?=
 =?UTF-8?q?=20Pydantic=20V2=20(#13698)?=
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Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
---
 fastapi/_compat.py                            |  5 +++
 ...napi_model_description_trim_on_formfeed.py | 31 +++++++++++++++++++
 2 files changed, 36 insertions(+)
 create mode 100644 tests/test_openapi_model_description_trim_on_formfeed.py

diff --git a/fastapi/_compat.py b/fastapi/_compat.py
index c07e4a3b0..227ad837d 100644
--- a/fastapi/_compat.py
+++ b/fastapi/_compat.py
@@ -16,6 +16,7 @@ from typing import (
     Tuple,
     Type,
     Union,
+    cast,
 )
 
 from fastapi.exceptions import RequestErrorModel
@@ -231,6 +232,10 @@ if PYDANTIC_V2:
         field_mapping, definitions = schema_generator.generate_definitions(
             inputs=inputs
         )
+        for item_def in cast(Dict[str, Dict[str, Any]], definitions).values():
+            if "description" in item_def:
+                item_description = cast(str, item_def["description"]).split("\f")[0]
+                item_def["description"] = item_description
         return field_mapping, definitions  # type: ignore[return-value]
 
     def is_scalar_field(field: ModelField) -> bool:
diff --git a/tests/test_openapi_model_description_trim_on_formfeed.py b/tests/test_openapi_model_description_trim_on_formfeed.py
new file mode 100644
index 000000000..e18d4f6b2
--- /dev/null
+++ b/tests/test_openapi_model_description_trim_on_formfeed.py
@@ -0,0 +1,31 @@
+from fastapi import FastAPI
+from fastapi.testclient import TestClient
+from pydantic import BaseModel
+
+app = FastAPI()
+
+
+class MyModel(BaseModel):
+    """
+    A model with a form feed character in the title.
+    \f
+    Text after form feed character.
+    """
+
+
+@app.get("/foo")
+def foo(v: MyModel):  # pragma: no cover
+    pass
+
+
+client = TestClient(app)
+
+
+def test_openapi():
+    response = client.get("/openapi.json")
+    assert response.status_code == 200, response.text
+    openapi_schema = response.json()
+
+    assert openapi_schema["components"]["schemas"]["MyModel"]["description"] == (
+        "A model with a form feed character in the title.\n"
+    )