Allow @validate_call to work on async methods

pydantic/_internal/_validate_call.py

@@ -3,7 +3,7 @@
 import inspect
 from dataclasses import dataclass
 from functools import partial
-from typing import Any, Callable
+from typing import Any, Awaitable, Callable
 
 import pydantic_core
 
@@ -80,7 +80,15 @@ def __init__(self, function: Callable[..., Any], config: ConfigDict | None, vali
             core_config = config_wrapper.core_config(self)
             schema = _discriminated_union.apply_discriminators(flatten_schema_defs(schema))
             simplified_schema = inline_schema_defs(schema)
-            self.__return_pydantic_validator__ = pydantic_core.SchemaValidator(simplified_schema, core_config)
+            validator = pydantic_core.SchemaValidator(simplified_schema, core_config)
+            if inspect.iscoroutinefunction(self.raw_function):
+
+                async def return_val_wrapper(aw: Awaitable[Any]) -> None:
+                    return validator.validate_python(await aw)
+
+                self.__return_pydantic_validator__ = return_val_wrapper
+            else:
+                self.__return_pydantic_validator__ = validator.validate_python
         else:
             self.__return_pydantic_core_schema__ = None
             self.__return_pydantic_validator__ = None
@@ -90,7 +98,7 @@ def __init__(self, function: Callable[..., Any], config: ConfigDict | None, vali
     def __call__(self, *args: Any, **kwargs: Any) -> Any:
         res = self.__pydantic_validator__.validate_python(pydantic_core.ArgsKwargs(args, kwargs))
         if self.__return_pydantic_validator__:
-            return self.__return_pydantic_validator__.validate_python(res)
+            return self.__return_pydantic_validator__(res)
         return res
 
     def __get__(self, obj: Any, objtype: type[Any] | None = None) -> ValidateCallWrapper:

tests/test_validate_call.py

@@ -4,7 +4,7 @@
 import sys
 from datetime import datetime, timezone
 from functools import partial
-from typing import List, Tuple
+from typing import Any, List, Tuple
 
 import pytest
 from pydantic_core import ArgsKwargs
@@ -703,3 +703,25 @@ class A:
             @decorator
             def method(self, x: int):
                 pass
+
+
+def test_async_func() -> None:
+    @validate_call(validate_return=True)
+    async def foo(a: Any) -> int:
+        return a
+
+    res = asyncio.run(foo(1))
+    assert res == 1
+
+    with pytest.raises(ValidationError) as exc_info:
+        asyncio.run(foo('x'))
+
+    # insert_assert(exc_info.value.errors(include_url=False))
+    assert exc_info.value.errors(include_url=False) == [
+        {
+            'type': 'int_parsing',
+            'loc': (),
+            'msg': 'Input should be a valid integer, unable to parse string as an integer',
+            'input': 'x',
+        }
+    ]