Fix type confusion in some scenarios (#3348)

* Fix type confusion in some scenarios

When the feature for rustls 0.22 is enabled, and rustls 0.23 is also
present in a project, there suddently exist multiple paths for errors
when building middleware chains due to the use of two consecutive `?`
operators without specifying the intermediate error type.

This commit addresses the issue by removing the first `?`, so that the
first error type will always be known, and the second `?` always has a
well defined implementation.

* Add CHANGES entry about type confusion

---------

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

actix-web/CHANGES.md

@@ -9,6 +9,7 @@
 ### Changed
 
 - Minimum supported Rust version (MSRV) is now 1.72.
+- Avoid type confusion in rare circumstances
 
 ## 4.5.1
 

actix-web/src/app_service.rs

@@ -263,8 +263,9 @@ impl ServiceFactory<ServiceRequest> for AppRoutingFactory {
             let guards = guards.borrow_mut().take().unwrap_or_default();
             let factory_fut = factory.new_service(());
             async move {
-                let service = factory_fut.await?;
+                factory_fut
-                Ok((path, guards, service))
+                    .await
+                    .map(move |service| (path, guards, service))
             }
         }));
 

actix-web/src/scope.rs

@@ -470,8 +470,9 @@ impl ServiceFactory<ServiceRequest> for ScopeFactory {
             let guards = guards.borrow_mut().take().unwrap_or_default();
             let factory_fut = factory.new_service(());
             async move {
-                let service = factory_fut.await?;
+                factory_fut
-                Ok((path, guards, service))
+                    .await
+                    .map(move |service| (path, guards, service))
             }
         }));