add function single generic type support

[uraneko]

PR Type

Other(improvement)

PR Checklist

• Tests for the changes have been added / updated.
• Documentation comments have been added / updated.
• A changelog entry has been made for the appropriate packages.
• Format code with the latest stable rustfmt.
• (Team) Label with affected crates and semver status.

Overview

Closes #2866

[JohnTitor]

Thanks for the PR! I've tweaked to support more generics and have better test suite.
But the current implementation has technically breaking change around Default impl although I think the current is one of good form to land.
If you have a good idea here, I'm happy to hear and see it :)

[uraneko]

Thanks for the tweaks, I think the current pr state looks pretty good.

But the current implementation has technically breaking change around Default impl

I'm not very familiar with the code base, so I may be missing something obvious, but, what's the technically breaking change?

My understanding is that app.route(...) can still be used with the same syntax, while the method macro + app.service(...) pattern is now extended to support generics by registering service_function::<Generics>::default(). Or is the breaking change around something else?

Could you show me an example user code that would break due to this change?

By the way. should I add a function to the test file to clarify that lifetimes are also supported? Something like this:

// actix-web-codegen/tests/trybuild/route-generic-ok.rs

- trait UserRepository {                 
-     fn get_user(&self) -> u64;
- }                                      

- impl UserRepository for UserClient { 
-     fn get_user(&self) -> u64 {     
-         99
-     }
- }

+ trait UserRepository {
+    fn get_user(&self) -> &str;
+ }

+ impl UserRepository for UserClient { 
+     fn get_user(&self) -> &str {     
+        "99"                         
+     }                                
+ }

//...

+ #[get("/lifetime")]                                                      
+ async fn with_lifetime<'a, T>(client: web::Data<&'a T>) -> &'a str       
+ where                                                            
+    T: UserRepository + Send + Sync + 'static,                   
+ {                                                                
+    client.get_ref().get_user()                                  
+ }                                                              

//...

+ .app_data(web::Data::new(&UserClient))
+ .service(with_lifetime::<UserClient>::default())