[poem-openapi] Define Custom Response with generic will compile error

[umaYnit]

Steps to Reproduce the Problem

use poem_openapi::{ApiResponse, Object, payload::Json};

#[derive(Object)]
pub struct SuccessResponses<T> {
    status: i32,
    data: T,
}

#[derive(Object)]
pub struct ErrorMessage {
    code: i32,
    reason: String,
}


#[derive(ApiResponse)]
pub enum CustomApiResponse<T> {
    #[oai(status = 200)]
    Ok(Json<SuccessResponses<T>>),
    /// Returns when the BadRequest.
    #[oai(status = 400)]
    BadRequest,
}

this is error message:

error[E0412]: cannot find type `T` in this scope
 --> src\main.rs:6:11
  |
6 |     data: T,
  |           ^ not found in this scope

error[E0412]: cannot find type `T` in this scope
  --> src\main.rs:19:30
   |
19 |     Ok(Json<SuccessResponses<T>>),
   |                              ^ not found in this scope

error[E0107]: missing generics for struct `SuccessResponses`
 --> src\main.rs:4:12
  |
4 | pub struct SuccessResponses<T> {
  |            ^^^^^^^^^^^^^^^^ expected 1 generic argument
  |
note: struct defined here, with 1 generic parameter: `T`
 --> src\main.rs:4:12
  |
4 | pub struct SuccessResponses<T> {
  |            ^^^^^^^^^^^^^^^^ -
help: add missing generic argument
  |
4 | pub struct SuccessResponses<T><T> {
  |            ~~~~~~~~~~~~~~~~~~~

error[E0107]: missing generics for enum `CustomApiResponse`
  --> src\main.rs:17:10
   |
17 | pub enum CustomApiResponse<T> {
   |          ^^^^^^^^^^^^^^^^^ expected 1 generic argument
   |
note: enum defined here, with 1 generic parameter: `T`
  --> src\main.rs:17:10
   |
17 | pub enum CustomApiResponse<T> {
   |          ^^^^^^^^^^^^^^^^^ -
help: add missing generic argument
   |
17 | pub enum CustomApiResponse<T><T> {
   |          ~~~~~~~~~~~~~~~~~~~~

Specifications

• Version: latest
• Platform: Windows

[sunli829]

There are two ways.

Use concrete type

1. First, generic objects need to specify the name of each concrete type.

#[derive(Object)]
#[oai(concrete(name = "SuccessResponsesI32", params(i32)))]
pub struct SuccessResponses<T> {
    status: i32,
    data: T,
}

2. But it still fails to compile here.

#[derive(ApiResponse)]
pub enum CustomApiResponse<T> {
    #[oai(status = 200)]
    Ok(Json<SuccessResponses<T>>),
    /// Returns when the BadRequest.
    #[oai(status = 400)]
    BadRequest,
}

Because Object macro only implements the poem::types::Type trait for SuccessResponses<i32>.

3. So, you can do it like the following.

#[derive(ApiResponse)]
pub enum CustomApiResponse {
    #[oai(status = 200)]
    Ok(Json<SuccessResponses<i32>>),
    /// Returns when the BadRequest.
    #[oai(status = 400)]
    BadRequest,
}

Inline SuccessResponses

    #[derive(Object)]
    #[oai(inline)]
    pub struct SuccessResponses<T: ParseFromJSON + ToJSON> {
        status: i32,
        data: T,
    }

    #[derive(ApiResponse)]
    pub enum CustomApiResponse<T: ParseFromJSON + ToJSON> {
        #[oai(status = 200)]
        Ok(poem_openapi::payload::Json<SuccessResponses<T>>),
        /// Returns when the BadRequest.
        #[oai(status = 400)]
        BadRequest,
    }

Inline objects must avoid circular dependencies.