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

[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.