From cfdb9476d4e863f722f5c23f792caf7566eccafd Mon Sep 17 00:00:00 2001
From: Tamir Duberstein <tamird@gmail.com>
Date: Sat, 30 Nov 2024 09:06:18 -0500
Subject: [PATCH] Refine dataclass check

Change the `dataclasses.is_dataclass` overload used from
```
@overload
def is_dataclass(obj: object) -> TypeIs[DataclassInstance | type[DataclassInstance]]: ...
```
to
```
@overload
def is_dataclass(obj: type) -> TypeIs[type[DataclassInstance]]: ...
```

This fixes the following mypy errors:
```
fastapi/encoders.py:244: error: Argument 1 to "asdict" has incompatible type "DataclassInstance | type[DataclassInstance]"; expected "DataclassInstance"  [arg-type]
fastapi/routing.py:122: error: Argument 1 to "asdict" has incompatible type "DataclassInstance | type[DataclassInstance]"; expected "DataclassInstance"  [arg-type]
Found 2 errors in 2 files (checked 44 source files)
```
---
 fastapi/encoders.py | 2 +-
 fastapi/routing.py  | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/fastapi/encoders.py b/fastapi/encoders.py
index 451ea0760..c416abbcb 100644
--- a/fastapi/encoders.py
+++ b/fastapi/encoders.py
@@ -240,7 +240,7 @@ def jsonable_encoder(
             custom_encoder=encoders,
             sqlalchemy_safe=sqlalchemy_safe,
         )
-    if dataclasses.is_dataclass(obj):
+    if dataclasses.is_dataclass(type(obj)):
         obj_dict = dataclasses.asdict(obj)
         return jsonable_encoder(
             obj_dict,
diff --git a/fastapi/routing.py b/fastapi/routing.py
index 8ea4bb219..c0d9c821a 100644
--- a/fastapi/routing.py
+++ b/fastapi/routing.py
@@ -118,7 +118,7 @@ def _prepare_response_content(
             )
             for k, v in res.items()
         }
-    elif dataclasses.is_dataclass(res):
+    elif dataclasses.is_dataclass(type(res)):
         return dataclasses.asdict(res)
     return res