Allow specifying serde path and avoid injecting extern crate serde as _serde.

[carllerche]

tower-web provides a #[derive(Response)] macro. This macro is a shim on top of serde's derive(Serialize). It works by catching HTTP specific attributes and leaving any serde attributes. It then generates a "shadow" version of the struct that has the actual derive(Serialize).

The problem is that the user must add serde to their Cargo.toml even if they do not interact with any serde APIs directly.

tower-web re-exports serde in the crate. I propose to have a serde attribute that allows specifying the path to serde. If this attribute is set, the extern crate serde as _serde is omitted.

This gist illustrates the problem. hello.rs is very basic. I also included the expanded code.

In short, I would like this line omitted and all references to _serde replaced with __tw::codegen::serde.

One way to expose the API is as an attribute:

#[derive(Serialize)]
#[serde(serde_path = "__tw::codegen::serde")]
struct Routes {
// ....
}

If you like this strategy, I could attempt a PR.

[dtolnay]

Seems reasonable. Please send a PR.

You will need to decide whether the given path is a use path or a relative path i.e. whether the expanded code is:

use __tw::codegen::serde;
impl serde::Serialize for T

or this:

impl __tw::codegen::serde::Serialize for T

Those would have different behavior in 2015 edition.

[carllerche]

I'm pretty sure use doesn't work in the anon const scope thing. Since tower-web generates in a const scope, it cannot do option 1.

My thought is that whatever is set in #[serde(serde_path = "__tw::codegen::serde")] is used verbatim in the generated code. i.e. option 2.

Do you have thoughts on this? Also, do you have thoughts on what the attr should be?

[carllerche]

Gentle ping :)

When you are +1 on the path, I can try to put together a PR (since it will probably be non-trivial, I'm hoping to get approval on the direction first).

[dtolnay]

Thanks for the reminder. I would accept a PR for option 2 using:

#[serde(crate = "__tw::codegen::serde")]

as the attribute.