Different Extractor Order May Cause an Error

[dupeiran001]

• I have looked for existing issues (including closed) about this

Bug Report

Version

├── axum v0.6.20
│ ├── axum-core v0.3.4
│ ├── axum v0.6.20 ()
│ │ │ ├── axum v0.6.20 ()

Platform

Linux LAPTOP-0F8O2SNI 5.15.90.1-microsoft-standard-WSL2 #1 SMP Fri Jan 27 02:56:13 UTC 2023 x86_64 x86_64 x86_64 GNU/Linux

Description

I have a State<_> extractor and a Json<_> extractor, and it cause an error when I place State<_> after Json<_>, it works well when these two are reversed.

I tried this code:

this works:

pub async fn demo_server(
    State(app): State<App>,
    Json(vo): Json<Vo>,
) -> String {
    todo!()
}

and this not:

pub async fn demo_server(
    Json(vo): Json<Vo>,
    State(app): State<App>,
) -> String {
    todo!()
}

App is my custom state, and Vo is an input parameter from request, which has implemented Deserialize

in the wrong code snippt, it has the following error message when add the function to router:

error[E0277]: the trait bound `fn(axum::Json<vo::pdf_convert::PdfConvertVo>, axum::extract::State<ryplat::app::App>) -> impl futures_util::Future<Output = ryplat::api::common::ResultDTO<std::string::String>> {service::file_convert::pdf_convert::pdf_to_image}: axum::handler::Handler<_, _, _>` is not satisfied
   --> src/main.rs:18:48
    |
18  |         .route("/a/convert/pdf/to/image", post(pdf_to_image))
    |                                           ---- ^^^^^^^^^^^^ the trait `axum::handler::Handler<_, _, _>` is not implemented for fn item `fn(axum::Json<vo::pdf_convert::PdfConvertVo>, axum::extract::State<ryplat::app::App>) -> impl futures_util::Future<Output = ryplat::api::common::ResultDTO<std::string::String>> {service::file_convert::pdf_convert::pdf_to_image}`
    |                                           |
    |                                           required by a bound introduced by this call
    |
    = help: the following other types implement trait `axum::handler::Handler<T, S, B>`:
              <axum::handler::Layered<L, H, T, S, B, B2> as axum::handler::Handler<T, S, B2>>
              <axum::routing::MethodRouter<S, B> as axum::handler::Handler<(), S, B>>
note: required by a bound in `axum::routing::post`
   --> /home/dpr/.cargo/registry/src/crates.obei.com.cn-8e030f22a0aa026e/axum-0.6.20/src/routing/method_routing.rs:407:1
    |
407 | top_level_handler_fn!(post, POST);
    | ^^^^^^^^^^^^^^^^^^^^^^----^^^^^^^
    | |                     |
    | |                     required by a bound in this function
    | required by this bound in `post`
    = note: this error originates in the macro `top_level_handler_fn` (in Nightly builds, run with -Z macro-backtrace for more info)

[jplatte]

This is intentional: https://docs.rs/axum/latest/axum/extract/index.html#the-order-of-extractors