Summary

Fixes #14444

Since FastAPI 0.123.5 (PR #14434), using functools.wraps on an async wrapper around a sync function causes FastAPI to incorrectly treat the handler as sync, resulting in:

ValueError: [TypeError("'coroutine' object is not iterable"), TypeError('vars() argument must have __dict__ attribute')]

Root Cause

The is_coroutine_callable, is_gen_callable, and is_async_gen_callable properties in Dependant use _unwrapped_call (which uses inspect.unwrap()) to determine if a function is async/generator. When a decorator uses @wraps(func), it sets __wrapped__ pointing to the original function, so inspect.unwrap() follows that chain back to the original sync function instead of checking the actual async wrapper.

Fix

Check the actual callable first (not the unwrapped version) to correctly detect if the wrapper itself is async/generator, and only fall back to the unwrapped version for cases like partial.

Example that was broken

from functools import wraps
from fastapi import FastAPI

app = FastAPI()

def my_decorator(func):
    @wraps(func)
    async def wrapper():
        func()
        return 'OK'
    return wrapper

@app.get('/')
@my_decorator
def index():
    print('Hello!')

Test plan

• Added test case tests/test_async_wrapper_sync_function.py that reproduces the issue
• Verified existing tests/test_dependency_wrapped.py tests still pass
• Ran 128 dependency-related tests - all pass