Fix: make solve_dependencies re-raise RuntimeError

If an async generator dependency raises RuntimeError:
generator didn't yield, make solve_dependencies catch
and re-raise it, to more easily identify the dependency
responsible for the error, and to provide more information
on how to fix the dependency

docs/en/docs/tutorial/dependencies/dependencies-with-yield.md

@@ -117,6 +117,10 @@ If you catch an exception using `except` in a dependency with `yield` and you do
 
 {* ../../docs_src/dependencies/tutorial008c_an_py39.py hl[15:16] *}
 
+The same applies for an `async` dependency with `yield`:
+
+{* ../../docs_src/dependencies/tutorial008e_an_py39.py hl[13:14] *}
+
 In this case, the client will see an *HTTP 500 Internal Server Error* response as it should, given that we are not raising an `HTTPException` or similar, but the server will **not have any logs** or any other indication of what was the error. 😱
 
 ### Always `raise` in Dependencies with `yield` and `except`
@@ -127,7 +131,11 @@ You can re-raise the same exception using `raise`:
 
 {* ../../docs_src/dependencies/tutorial008d_an_py39.py hl[17] *}
 
-Now the client will get the same *HTTP 500 Internal Server Error* response, but the server will have our custom `InternalError` in the logs. 😎
+The same applies for an `async` dependency with `yield`:
+
+{* ../../docs_src/dependencies/tutorial008f_an_py39.py hl[15] *}
+
+Now the client will get the same *HTTP 500 Internal Server Error* response, but the server will have our custom `InternalError` or `OSError` in the logs. 😎
 
 ## Execution of dependencies with `yield`
 

docs_src/dependencies/tutorial008e.py

@@ -0,0 +1,17 @@
+from anyio import open_file
+from fastapi import Depends, FastAPI
+
+app = FastAPI()
+
+
+async def get_username():
+    try:
+        async with await open_file("/path/to/sanchez.txt", "r") as f:
+            yield await f.read()  # pragma: no cover
+    except OSError:
+        print("We didn't re-raise, wubba lubba dub dub!")
+
+
+@app.get("/me")
+def get_me(username: str = Depends(get_username)):
+    return username  # pragma: no cover

docs_src/dependencies/tutorial008e_an.py

@@ -0,0 +1,18 @@
+from anyio import open_file
+from fastapi import Depends, FastAPI
+from typing_extensions import Annotated
+
+app = FastAPI()
+
+
+async def get_username():
+    try:
+        async with await open_file("/path/to/sanchez.txt", "r") as f:
+            yield await f.read()  # pragma: no cover
+    except OSError:
+        print("We didn't re-raise, wubba lubba dub dub!")
+
+
+@app.get("/me")
+def get_me(username: Annotated[str, Depends(get_username)]):
+    return username  # pragma: no cover

docs_src/dependencies/tutorial008e_an_py39.py

@@ -0,0 +1,19 @@
+from typing import Annotated
+
+from anyio import open_file
+from fastapi import Depends, FastAPI
+
+app = FastAPI()
+
+
+async def get_username():
+    try:
+        async with await open_file("/path/to/sanchez.txt", "r") as f:
+            yield await f.read()  # pragma: no cover
+    except OSError:
+        print("We didn't re-raise, wubba lubba dub dub!")
+
+
+@app.get("/me")
+def get_me(username: Annotated[str, Depends(get_username)]):
+    return username  # pragma: no cover

docs_src/dependencies/tutorial008f.py

@@ -0,0 +1,18 @@
+from anyio import open_file
+from fastapi import Depends, FastAPI
+
+app = FastAPI()
+
+
+async def get_username():
+    try:
+        async with await open_file("/path/to/sanchez.txt", "r") as f:
+            yield await f.read()  # pragma: no cover
+    except OSError:
+        print("We don't swallow the OS error here, we raise again 😎")
+        raise
+
+
+@app.get("/me")
+def get_me(username: str = Depends(get_username)):
+    return username  # pragma: no cover

docs_src/dependencies/tutorial008f_an.py

@@ -0,0 +1,19 @@
+from anyio import open_file
+from fastapi import Depends, FastAPI
+from typing_extensions import Annotated
+
+app = FastAPI()
+
+
+async def get_username():
+    try:
+        async with await open_file("/path/to/sanchez.txt", "r") as f:
+            yield await f.read()  # pragma: no cover
+    except OSError:
+        print("We don't swallow the OS error here, we raise again 😎")
+        raise
+
+
+@app.get("/me")
+def get_me(username: Annotated[str, Depends(get_username)]):
+    return username  # pragma: no cover

docs_src/dependencies/tutorial008f_an_py39.py

@@ -0,0 +1,20 @@
+from typing import Annotated
+
+from anyio import open_file
+from fastapi import Depends, FastAPI
+
+app = FastAPI()
+
+
+async def get_username():
+    try:
+        async with await open_file("/path/to/sanchez.txt", "r") as f:
+            yield await f.read()  # pragma: no cover
+    except OSError:
+        print("We don't swallow the OS error here, we raise again 😎")
+        raise
+
+
+@app.get("/me")
+def get_me(username: Annotated[str, Depends(get_username)]):
+    return username  # pragma: no cover

fastapi/dependencies/utils.py

@@ -52,6 +52,7 @@ from fastapi.concurrency import (
     contextmanager_in_threadpool,
 )
 from fastapi.dependencies.models import Dependant, SecurityRequirement
+from fastapi.exceptions import FastAPIError
 from fastapi.logger import logger
 from fastapi.security.base import SecurityBase
 from fastapi.security.oauth2 import OAuth2, SecurityScopes
@@ -557,7 +558,24 @@ async def solve_generator(
         cm = contextmanager_in_threadpool(contextmanager(call)(**sub_values))
     elif is_async_gen_callable(call):
         cm = asynccontextmanager(call)(**sub_values)
-    return await stack.enter_async_context(cm)
+
+    try:
+        solved = await stack.enter_async_context(cm)
+    except RuntimeError as ex:
+        if "generator didn't yield" not in f"{ex}":
+            raise ex
+
+        dependency_name = getattr(call, "__name__", "(unknown)")
+        raise FastAPIError(
+            f"Dependency {dependency_name} raised: {ex}. There's a high chance that "
+            "this is a dependency with yield that has a block with a bare except, or a "
+            "block with except Exception, and is not raising the exception again. Read "
+            "more about it in the docs: "
+            "https://fastapi.tiangolo.com/tutorial/dependencies/dependencies-with-yield"
+            "/#dependencies-with-yield-and-except"
+        ) from ex
+
+    return solved
 
 
 @dataclass

tests/test_dependency_runtime_errors.py

@@ -0,0 +1,29 @@
+import pytest
+from anyio import open_file
+from fastapi import Depends, FastAPI
+from fastapi.testclient import TestClient
+
+app = FastAPI()
+
+
+async def get_username():
+    try:
+        async with await open_file("/path/to/sanchez.txt", "r") as f:
+            yield await f.read()  # pragma: no cover
+    except OSError as ex:
+        raise RuntimeError("File something something, wubba lubba dub dub!") from ex
+
+
+@app.get("/me")
+def get_me(username: str = Depends(get_username)):
+    return username  # pragma: no cover
+
+
+client = TestClient(app)
+
+
+@pytest.mark.anyio
+def test_runtime_error():
+    with pytest.raises(RuntimeError) as exc_info:
+        client.get("/me")
+    assert "File something something" in exc_info.value.args[0]

tests/test_tutorial/test_dependencies/test_tutorial008e.py

@@ -0,0 +1,41 @@
+import importlib
+from types import ModuleType
+
+import pytest
+from fastapi.exceptions import FastAPIError
+from fastapi.testclient import TestClient
+
+from ...utils import needs_py39
+
+
+@pytest.fixture(
+    name="mod",
+    params=[
+        "tutorial008e",
+        "tutorial008e_an",
+        pytest.param("tutorial008e_an_py39", marks=needs_py39),
+    ],
+)
+def get_mod(request: pytest.FixtureRequest):
+    mod = importlib.import_module(f"docs_src.dependencies.{request.param}")
+
+    return mod
+
+
+@pytest.mark.anyio
+def test_fastapi_error(mod: ModuleType):
+    client = TestClient(mod.app)
+    with pytest.raises(FastAPIError) as exc_info:
+        client.get("/me")
+    assert (
+        "Dependency get_username raised: generator didn't yield"
+        in exc_info.value.args[0]
+    )
+
+
+@pytest.mark.anyio
+def test_internal_server_error(mod: ModuleType):
+    client = TestClient(mod.app, raise_server_exceptions=False)
+    response = client.get("/me")
+    assert response.status_code == 500, response.text
+    assert response.text == "Internal Server Error"

tests/test_tutorial/test_dependencies/test_tutorial008f.py

@@ -0,0 +1,37 @@
+import importlib
+from types import ModuleType
+
+import pytest
+from fastapi.testclient import TestClient
+
+from ...utils import needs_py39
+
+
+@pytest.fixture(
+    name="mod",
+    params=[
+        "tutorial008f",
+        "tutorial008f_an",
+        pytest.param("tutorial008f_an_py39", marks=needs_py39),
+    ],
+)
+def get_mod(request: pytest.FixtureRequest):
+    mod = importlib.import_module(f"docs_src.dependencies.{request.param}")
+
+    return mod
+
+
+@pytest.mark.anyio
+def test_os_error(mod: ModuleType):
+    client = TestClient(mod.app)
+    with pytest.raises(OSError) as exc_info:
+        client.get("/me")
+    assert "No such file or directory" in str(exc_info.value)
+
+
+@pytest.mark.anyio
+def test_internal_server_error(mod: ModuleType):
+    client = TestClient(mod.app, raise_server_exceptions=False)
+    response = client.get("/me")
+    assert response.status_code == 500, response.text
+    assert response.text == "Internal Server Error"