Parse failure using #[serde(flatten)] with Query Params

[epompeii]

When trying to use #[serde(flatten)] with query params, integers fail to parse with the following error when they are part of the nested, flattened struct:

Jul 07 23:10:58.044 INFO request completed, error_message_external: unable to parse query string: invalid type: string "8", expected u8, error_message_internal: unable to parse query string: invalid type: string "8", expected u8, response_code: 400, uri: /v0/projects/the-computer/branches?per_page=8&page=1, method: OPTIONS, req_id: 9fe8794e-d777-433a-8cb5-071c3ca69091, remote_addr: 127.0.0.1:64916, local_addr: 0.0.0.0:61016

Using flatten things look like this:

#[derive(Deserialize, JsonSchema)]
pub struct ProjBranchesQuery {
    pub name: Option<String>,
    #[serde(flatten)]
    pub pagination: JsonPagination<ProjBranchesSort>,
}

#[derive(Debug, Clone, Deserialize, Serialize)]
#[cfg_attr(feature = "schema", derive(JsonSchema))]
pub struct JsonPagination<T> {
    pub sort: Option<T>,
    pub direction: Option<JsonDirection>,
    pub per_page: Option<u8>,
    pub page: Option<u32>,
}

However in-lining things manually works just fine, no parse errors:

#[derive(Deserialize, JsonSchema)]
pub struct ProjBranchesQuery {
    pub name: Option<String>,
    pub sort: Option<ProjBranchesSort>,
    pub direction: Option<JsonDirection>,
    pub per_page: Option<u8>,
    pub page: Option<u32>,
}

Also inverting things works:

pub type ProjBranchesQuery = JsonPagination<ProjBranchesSort, ProjBranchesQueryParams>;

#[derive(Debug, Clone, Deserialize, Serialize)]
#[cfg_attr(feature = "schema", derive(JsonSchema))]
pub struct JsonPagination<S, Q> {
    pub sort: Option<S>,
    pub direction: Option<JsonDirection>,
    pub per_page: Option<u8>,
    pub page: Option<u32>,
    #[serde(flatten)]
    pub query: Q,
}

#[derive(Deserialize, JsonSchema)]
pub struct ProjBranchesQueryParams {
    pub name: Option<String>,
}

It is only when the integer field is in the nested, flattened struct that the error occurs.

[davepacheco]

Sorry for the slow response on this. Things have been pretty busy over here.

I believe this is the issue that's mentioned in the docs under https://docs.rs/dropshot/0.9.0/dropshot/index.html#advanced-usage-notes:

It’s possible to accept additional query parameters besides the pagination parameters by having your API endpoint handler function take two different arguments using Query, like this:
...
You might expect that instead of doing this, you could define your own structure that includes a PaginationParams using #[serde(flatten)], and this ought to work, but it currently doesn’t due to serde_urlencoded#33, which is really serde#1183.

I think this is the same issue as nox/serde_urlencoded#33, which is serde-rs/serde#1183. I'm not sure what we can do better here.

[epompeii]

No worries, @davepacheco. Congrats to you and the Oxide team for shipping your first rack!

I thought that, that limitation was just for the built-in PaginationParams, which I'm not using here.
Given how deep this limitation seems to run though, I'll just go the additional query parameters route.
Thanks for the pointer!