Add type safe state extractor (#1155)

* begin threading the state through

* Pass state to extractors

* make state extractor work

* make sure nesting with different states work

* impl Service for MethodRouter<()>

* Fix some of axum-macro's tests

* Implement more traits for `State`

* Update examples to use `State`

* consistent naming of request body param

* swap type params

* Default the state param to ()

* fix docs references

* Docs and handler state refactoring

* docs clean ups

* more consistent naming

* when does MethodRouter implement Service?

* add missing docs

* use `Router`'s default state type param

* changelog

* don't use default type param for FromRequest and RequestParts

probably safer for library authors so you don't accidentally forget

* fix examples

* minor docs tweaks

* clarify how to convert handlers into services

* group methods in one impl block

* make sure merged `MethodRouter`s can access state

* fix docs link

* test merge with same state type

* Document how to access state from middleware

* Port cookie extractors to use state to extract keys (#1250)

* Updates ECOSYSTEM with a new sample project (#1252)

* Avoid unhelpful compiler suggestion (#1251)

* fix docs typo

* document how library authors should access state

* Add `RequestParts::with_state`

* fix example

* apply suggestions from review

* add relevant changes to axum-extra and axum-core changelogs

* Add `route_service_with_tsr`

* fix trybuild expectations

* make sure `SpaRouter` works with routers that have state

* Change order of type params on FromRequest and RequestParts

* reverse order of `RequestParts::with_state` args to match type params

* Add `FromRef` trait (#1268)

* Add `FromRef` trait

* Remove unnecessary type params

* format

* fix docs link

* format examples

* Avoid unnecessary `MethodRouter`

* apply suggestions from review

Co-authored-by: Dani Pardo <[email protected]>
Co-authored-by: Jonas Platte <[email protected]>

axum-core/src/extract/from_ref.rs

@@ -0,0 +1,23 @@
+/// Used to do reference-to-value conversions thus not consuming the input value.
+///
+/// This is mainly used with [`State`] to extract "substates" from a reference to main application
+/// state.
+///
+/// See [`State`] for more details on how library authors should use this trait.
+///
+/// [`State`]: https://docs.rs/axum/0.6/axum/extract/struct.State.html
+// NOTE: This trait is defined in axum-core, even though it is mainly used with `State` which is
+// defined in axum. That allows crate authors to use it when implementing extractors.
+pub trait FromRef<T> {
+    /// Converts to this type from a reference to the input type.
+    fn from_ref(input: &T) -> Self;
+}
+
+impl<T> FromRef<T> for T
+where
+    T: Clone,
+{
+    fn from_ref(input: &T) -> Self {
+        input.clone()
+    }
+}