fix support for 12 extractors (#2582)

Co-authored-by: Rob Ede <robjtede@icloud.com>

CHANGES.md

@@ -7,10 +7,12 @@
 
 ### Changed
 - `HttpResponse` can now be used as a `Responder` with any body type. [#2567]
+- Maximim number of extractors has changed from 10 to 12. [#2582]
 
 [#1988]: https://github.com/actix/actix-web/pull/1988
 [#2567]: https://github.com/actix/actix-web/pull/2567
 [#2569]: https://github.com/actix/actix-web/pull/2569
+[#2582]: https://github.com/actix/actix-web/pull/2582
 
 
 ## 4.0.0-beta.19 - 2022-01-04

src/extract.rs

@@ -290,16 +290,6 @@ impl FromRequest for Method {
     }
 }
 
-#[doc(hidden)]
-impl FromRequest for () {
-    type Error = Infallible;
-    type Future = Ready<Result<Self, Self::Error>>;
-
-    fn from_request(_: &HttpRequest, _: &mut Payload) -> Self::Future {
-        ok(())
-    }
-}
-
 #[doc(hidden)]
 #[allow(non_snake_case)]
 mod tuple_from_req {
@@ -388,6 +378,15 @@ mod tuple_from_req {
         }
     }
 
+    impl FromRequest for () {
+        type Error = Infallible;
+        type Future = Ready<Result<Self, Self::Error>>;
+
+        fn from_request(_: &HttpRequest, _: &mut Payload) -> Self::Future {
+            ok(())
+        }
+    }
+
     tuple_from_req! { TupleFromRequest1; A }
     tuple_from_req! { TupleFromRequest2; A, B }
     tuple_from_req! { TupleFromRequest3; A, B, C }
@@ -398,6 +397,8 @@ mod tuple_from_req {
     tuple_from_req! { TupleFromRequest8; A, B, C, D, E, F, G, H }
     tuple_from_req! { TupleFromRequest9; A, B, C, D, E, F, G, H, I }
     tuple_from_req! { TupleFromRequest10; A, B, C, D, E, F, G, H, I, J }
+    tuple_from_req! { TupleFromRequest11; A, B, C, D, E, F, G, H, I, J, K }
+    tuple_from_req! { TupleFromRequest12; A, B, C, D, E, F, G, H, I, J, K, L }
 }
 
 #[cfg(test)]

src/handler.rs

@@ -12,17 +12,14 @@ use crate::{
 /// # What Is A Request Handler
 /// A request handler has three requirements:
 /// 1. It is an async function (or a function/closure that returns an appropriate future);
-/// 1. The function accepts zero or more parameters that implement [`FromRequest`];
+/// 1. The function parameters (up to 12) implement [`FromRequest`];
 /// 1. The async function (or future) resolves to a type that can be converted into an
 ///   [`HttpResponse`] (i.e., it implements the [`Responder`] trait).
 ///
 /// # Compiler Errors
 /// If you get the error `the trait Handler<_> is not implemented`, then your handler does not
-/// fulfill one or more of the above requirements.
-///
-/// Unfortunately we cannot provide a better compile error message (while keeping the trait's
-/// flexibility) unless a stable alternative to [`#[rustc_on_unimplemented]`][on_unimpl] is added
-/// to Rust.
+/// fulfill the _first_ of the above requirements. Missing other requirements manifest as errors on
+/// implementing [`FromRequest`] and [`Responder`], respectively.
 ///
 /// # How Do Handlers Receive Variable Numbers Of Arguments
 /// Rest assured there is no macro magic here; it's just traits.
@@ -62,13 +59,15 @@ use crate::{
 /// This is the source code for the 2-parameter implementation of `Handler` to help illustrate the
 /// bounds of the handler call after argument extraction:
 /// ```ignore
-/// impl<Func, Arg1, Arg2, R> Handler<(Arg1, Arg2), R> for Func
+/// impl<Func, Arg1, Arg2, Fut> Handler<(Arg1, Arg2)> for Func
 /// where
-///     Func: Fn(Arg1, Arg2) -> R + Clone + 'static,
-///     R: Future,
-///     R::Output: Responder,
+///     Func: Fn(Arg1, Arg2) -> Fut + Clone + 'static,
+///     Fut: Future,
 /// {
-///     fn call(&self, (arg1, arg2): (Arg1, Arg2)) -> R {
+///     type Output = Fut::Output;
+///     type Future = Fut;
+///
+///     fn call(&self, (arg1, arg2): (Arg1, Arg2)) -> Self::Future {
 ///         (self)(arg1, arg2)
 ///     }
 /// }
@@ -76,7 +75,6 @@ use crate::{
 ///
 /// [arity]: https://en.wikipedia.org/wiki/Arity
 /// [`from_request`]: FromRequest::from_request
-/// [on_unimpl]: https://github.com/rust-lang/rust/issues/29628
 pub trait Handler<Args>: Clone + 'static {
     type Output;
     type Future: Future<Output = Self::Output>;
@@ -121,7 +119,8 @@ where
 /// ```
 macro_rules! factory_tuple ({ $($param:ident)* } => {
     impl<Func, Fut, $($param,)*> Handler<($($param,)*)> for Func
-    where Func: Fn($($param),*) -> Fut + Clone + 'static,
+    where
+        Func: Fn($($param),*) -> Fut + Clone + 'static,
         Fut: Future,
     {
         type Output = Fut::Output;
@@ -148,3 +147,25 @@ factory_tuple! { A B C D E F G H I }
 factory_tuple! { A B C D E F G H I J }
 factory_tuple! { A B C D E F G H I J K }
 factory_tuple! { A B C D E F G H I J K L }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn assert_impl_handler<T: FromRequest>(_: impl Handler<T>) {}
+
+    #[test]
+    fn arg_number() {
+        async fn handler_min() {}
+
+        #[rustfmt::skip]
+        #[allow(clippy::too_many_arguments, clippy::just_underscores_and_digits)]
+        async fn handler_max(
+            _01: (), _02: (), _03: (), _04: (), _05: (), _06: (),
+            _07: (), _08: (), _09: (), _10: (), _11: (), _12: (),
+        ) {}
+
+        assert_impl_handler(handler_min);
+        assert_impl_handler(handler_max);
+    }
+}