Support injection for generators. (#187)

* Initial implementation of generator injection for async functions.

* Added injection for sync generators.

* Added tests.

* Added additional type info to typing.Generator.

* Added additional type info to typing.AsyncGenerator.

* Added receive, send & return tests for sync generators.

* Added remaining tests for generators with context-resources.

* Added test for context resources with different scope.

* Added generator injection documentation.

* Cleaned up after review.

Author: alexanderlazarev0

docs/integrations/fastapi.md

@@ -98,7 +98,7 @@ and the global context will be set.
 
 ## Integrating with FastAPI Using DIContextMiddleware
 
-The `DIContextMiddleware` is can be used to manage context, but its features overlap with the [custom router class](#using-the-a-custom-router-class).
+The `DIContextMiddleware` can be used to manage context, but its features overlap with the [custom router class](#using-a-custom-router-class).
 The main advantage of using middleware is that you can set it up for your entire `FastAPI` application.
 
 > **Note:** If you want to use both the `DIContextMiddleware` and the custom router class, you should not pass any arguments to `create_fastapi_route_class()`.

docs/introduction/application-settings.md

@@ -0,0 +1,144 @@
+# Injection into Generator Functions
+
+
+`that-depends` supports dependency injections into generator functions. However, this comes
+with some minor limitations compared to regular functions.
+
+
+## Quickstart
+
+You can use the `@inject` decorator to inject dependencies into generator functions:
+
+=== "async generator"
+
+    ```python
+    @inject
+    async def my_generator(value: str = Provide[Container.factory]) -> typing.AsyncGenerator[str, None]:
+        yield value
+    ```
+
+=== "sync generator"
+
+    ```python
+    @inject
+    def my_generator(value: str = Provide[Container.factory]) -> typing.Generator[str, None, None]:
+        yield value
+    ```
+
+=== "async iterator"
+
+    ```python
+    @contextlib.asynccontextmanager
+    @inject
+    async def my_generator(value: str = Provide[Container.factory]) -> typing.AsyncIterator[str]:
+        yield value
+    ```
+
+=== "sync iterator"
+
+    ```python
+    @contextlib.contextmanager
+    @inject
+    def my_generator(value: str = Provide[Container.factory]) -> typing.Iterator[str]:
+        yield value
+    ```
+
+## Supported Generators
+
+### Synchronous Generators
+
+`that-depends` supports injection into sync generator functions with the following signature:
+
+```python
+Callable[P, Generator[<YieldType>, <SendType>, <ReturnType>]]
+```
+
+This means that wrapping a sync generator with `@inject` will always preserve all the behaviour of the wrapped generator:
+
+- It will yield as expected
+- It will accept sending values via `send()`
+- It will raise `StopIteration` when the generator is exhausted or otherwise returns.
+
+
+### Asynchronous Generators
+
+`that-depends` supports injection into async generator functions with the following signature:
+
+```python
+Callable[P, AsyncGenerator[<YieldType>, None]]
+```
+
+This means that wrapping an async generator with `@inject` will have the following effects:
+
+- The generator will yield as expected
+- The generator will **not** accept values via `asend()`
+
+If you need to send values to an async generator, you can simply resolve dependencies in the generator body:
+
+```python
+
+async def my_generator() -> typing.AsyncGenerator[float, float]:
+    value = await Container.factory.resolve()
+    receive = yield value # (1)!
+    yield receive + value
+
+```
+
+1. This receive will always be `None` if you would wrap this generator with @inject.
+
+
+
+## ContextResources
+
+`that-depends` will **not** allow context initialization for [ContextResource](../providers/context-resources.md) providers 
+as part of dependency injection into a generator.
+
+This is the case for both async and sync injection.
+
+**For example:**
+```python
+def sync_resource() -> typing.Iterator[float]:
+    yield random.random() 
+
+class Container(BaseContainer):
+    sync_provider = providers.ContextResource(sync_resource).with_config(scope=ContextScopes.INJECT)
+    dependent_provider = providers.Factory(lambda x: x, sync_provider.cast)
+
+@inject(scope=ContextScopes.INJECT) # (1)!
+def injected(val: float = Provide[Container.dependent_provider]) -> typing.Generator[float, None, None]:
+    yield val 
+
+# This will raise a `ContextProviderError`!
+next(_injected())
+```
+
+1. Matches context scope of `sync_provider` provider, which is a dependency of the `dependent_provider` provider.
+
+
+When calling `next(injected())`, `that-depends` will try to initialize a new context for the `sync_provider`,
+however, this is not permitted for generators, thus it will raise a `ContextProviderError`.
+
+
+Keep in mind that if context does not need to be initialized, the generator injection will work as expected:
+
+```python
+def sync_resource() -> typing.Iterator[float]:
+    yield random.random() 
+
+class Container(BaseContainer):
+    sync_provider = providers.ContextResource(sync_resource).with_config(scope=ContextScopes.REQUEST)
+    dependent_provider = providers.Factory(lambda x: x, sync_provider.cast)
+
+@inject(scope=ContextScopes.INJECT) # (1)!
+def injected(val: float = Provide[Container.dependent_provider]) -> typing.Generator[float, None, None]:
+    yield val 
+
+
+with container_context(scope=ContextScopes.REQUEST):
+    # This will resolve as expected
+    next(_injected())
+```
+
+Since no context initialization was needed, the generator will work as expected.
+
+1. Scope provided to `@inject` no longer matches scope of the `sync_provider`

docs/introduction/generator-injection.md

@@ -7,11 +7,12 @@ nav:
   - Introduction:
       - Containers: introduction/ioc-container.md
       - Dependency Injection: introduction/injection.md
-      - Scopes: introduction/scopes.md
+      - Generator Injection: introduction/generator-injection.md
       - String Injection: introduction/string-injection.md
-      - Multiple Containers: introduction/multiple-containers.md
-      - Application Settings: introduction/application-settings.md
+      - Scopes: introduction/scopes.md
       - Tear-down: introduction/tear-down.md
+      - Multiple Containers: introduction/multiple-containers.md
+
   - Providers:
       - Collections: providers/collections.md
       - Context-Resources: providers/context-resources.md