routes macro allowing multiple paths per handler (#2718)

* WIP: basic implementation for `routes` macro

* chore: changelog, docs, tests

* error on missing methods

* Apply suggestions from code review

Co-authored-by: Igor Aleksanov <popzxc@yandex.ru>

* update test stderr expectation

* add additional tests

* fix stderr output

* remove useless ResourceType

this is dead code from back when .to and .to_async were different ways to add a service

Co-authored-by: Igor Aleksanov <popzxc@yandex.ru>
Co-authored-by: Rob Ede <robjtede@icloud.com>

actix-web-codegen/tests/trybuild/routes-missing-args-fail.rs

@@ -0,0 +1,14 @@
+use actix_web_codegen::*;
+
+#[routes]
+#[get]
+async fn index() -> String {
+    "Hello World!".to_owned()
+}
+
+#[actix_web::main]
+async fn main() {
+    use actix_web::App;
+
+    let srv = actix_test::start(|| App::new().service(index));
+}

actix-web-codegen/tests/trybuild/routes-missing-args-fail.stderr

@@ -0,0 +1,21 @@
+error: invalid service definition, expected #[get("<path>")]
+ --> tests/trybuild/routes-missing-args-fail.rs:4:1
+  |
+4 | #[get]
+  | ^^^^^^
+  |
+  = note: this error originates in the attribute macro `get` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error: Invalid input for macro
+ --> tests/trybuild/routes-missing-args-fail.rs:4:1
+  |
+4 | #[get]
+  | ^^^^^^
+
+error[E0277]: the trait bound `fn() -> impl std::future::Future {index}: HttpServiceFactory` is not satisfied
+  --> tests/trybuild/routes-missing-args-fail.rs:13:55
+   |
+13 |     let srv = actix_test::start(|| App::new().service(index));
+   |                                               ------- ^^^^^ the trait `HttpServiceFactory` is not implemented for `fn() -> impl std::future::Future {index}`
+   |                                               |
+   |                                               required by a bound introduced by this call

actix-web-codegen/tests/trybuild/routes-missing-method-fail.rs

@@ -0,0 +1,13 @@
+use actix_web_codegen::*;
+
+#[routes]
+async fn index() -> String {
+    "Hello World!".to_owned()
+}
+
+#[actix_web::main]
+async fn main() {
+    use actix_web::App;
+
+    let srv = actix_test::start(|| App::new().service(index));
+}

actix-web-codegen/tests/trybuild/routes-missing-method-fail.stderr

@@ -0,0 +1,15 @@
+error: The #[routes] macro requires at least one `#[<method>(..)]` attribute.
+ --> tests/trybuild/routes-missing-method-fail.rs:3:1
+  |
+3 | #[routes]
+  | ^^^^^^^^^
+  |
+  = note: this error originates in the attribute macro `routes` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the trait bound `fn() -> impl std::future::Future {index}: HttpServiceFactory` is not satisfied
+  --> tests/trybuild/routes-missing-method-fail.rs:12:55
+   |
+12 |     let srv = actix_test::start(|| App::new().service(index));
+   |                                               ------- ^^^^^ the trait `HttpServiceFactory` is not implemented for `fn() -> impl std::future::Future {index}`
+   |                                               |
+   |                                               required by a bound introduced by this call

actix-web-codegen/tests/trybuild/routes-ok.rs

@@ -0,0 +1,23 @@
+use actix_web_codegen::*;
+
+#[routes]
+#[get("/")]
+#[post("/")]
+async fn index() -> String {
+    "Hello World!".to_owned()
+}
+
+#[actix_web::main]
+async fn main() {
+    use actix_web::App;
+
+    let srv = actix_test::start(|| App::new().service(index));
+
+    let request = srv.get("/");
+    let response = request.send().await.unwrap();
+    assert!(response.status().is_success());
+
+    let request = srv.post("/");
+    let response = request.send().await.unwrap();
+    assert!(response.status().is_success());
+}