Can't use reexported function with same name as file in route!. Is this intended?

[arctic-alpaca]

Hello,

I'm trying to use a reexported function, with the same name as the file it is contained in, in a route! and for some reason it doesn't compile. The same usecase seems to work with actix so I'm not sure whether there is a mistake in my code or if this is a bug in Rocket or maybe a limitation of the rust compiler.

I have a function health_check in src/routes/health_check.rs and reexport it in src/routes/mod.rs/ with pub use health_check::*;. I then import it with use crate::routes::health_check; in src/startup.rs and try to use it with routes![health_check].

The compiler show this error message:

error[E0574]: expected struct, variant or union type, found function `health_check`
  --> src/startup.rs:22:41
   |
22 |         .mount("/health_check", routes![health_check])
   |                                         ^^^^^^^^^^^^ not a struct, variant or union type
   |
help: consider importing this struct instead
   |
1  | use crate::routes::health_check::health_check;
   |

If I do that, it works (after changing the visibility of mod health_check; in src/routes/mod.rs/.

Changing the name of the function to something that's different from the .rs file it is contained in also makes the code compile.

This is the code: https://github.com/arctic-alpaca/zero2prod_rocket
This CI run also shows the error: https://github.com/arctic-alpaca/zero2prod_rocket/runs/3210343077?check_suite_focus=true

This is the similar actix code: https://github.com/LukeMathWalker/zero-to-production/tree/root-chapter-03-part1
In the actix code, the subscribe function body can be replaced with HttpResponse::InternalServerError().finish() to allow for it to compile without sqlx issues / a running database.

I'd appreciate any input why this doesn't compile.

[jebrosen]

No, it's not intentional. But I'm also not sure if it's too easily avoidable.

The problem does have to do with the name clash:

I have a function health_check in src/routes/health_check.rs and reexport it in src/routes/mod.rs/ with pub use health_check::*;.

At this point you would have a module, routes, with these items in it: mod health_check;, fn health_check, and struct health_check. (struct health_check was generated by rocket). But because that struct has the same name as the module health_check, pub use health_check::*; does not reexport it. You can see this behavior in this playground example: https://play.rust-lang.org/?version=stable&mode=debug&edition=2018&gist=2ba98a811cf614dd722c9391143ec161 .

Incidentally, this is one of a few reasons in favor of avoiding * imports - rustc emits an error explaining the name conflict at this point, if you use pub use health_check::health_check;.

I then import it with use crate::routes::health_check; in src/startup.rs and try to use it with routes![health_check].

routes! wanted the struct health_check, but it wasn't actually reexported - and then you get a less good error message.

This is the similar actix code: https://github.com/LukeMathWalker/zero-to-production/tree/root-chapter-03-part1

In this actix-web version, it looks like you attach the routes in a way that does not use any macros. In Rocket's case, several important features (including error messages for route handlers) depend a lot on the macros and I don't think we could readily provide a similar option.

IIRC actix-web also has #[get] decorators as an option, and it may or may not have similar limitations.

---

For what it's worth I generally recommend not repeating names like health_check::health_check even when there is not a clash. In this case, I would probably have put the fn health_check() in src/routes/mod.rs without its own dedicated module because it is small, or in a utils.rs or general.rs with other routes in the same category.

[arctic-alpaca]

Thank you for your in depth answer!