Added support for generics in server fns

[rakshith-ravi]

I'm still getting the following error when compiling server_fn_axum:

error[E0283]: type annotations needed: cannot satisfy `S: app::_::_serde::Deserialize<'_>`
   --> src/app.rs:787:14
    |
787 | pub async fn test_fn<S>(
    |              ^^^^^^^^^^
    |
note: multiple `impl`s or `where` clauses satisfying `S: app::_::_serde::Deserialize<'_>` found
   --> src/app.rs:786:1
    |
786 | #[server]
    | ^^^^^^^^^
...
792 |     S: Display + Send + DeserializeOwned + Serialize + 'static,
    |                         ^^^^^^^^^^^^^^^^
note: required for `TestFn<S>` to implement `app::_::_serde::Deserialize<'de>`
   --> src/app.rs:786:1
    |
786 | #[server]
    | ^--------
    | |
    | unsatisfied trait bound introduced here
787 | pub async fn test_fn<S>(
    |              ^^^^^^^^^^
    = note: this error originates in the derive macro `::leptos::server_fn::serde::Deserialize` which comes from the expansion of the attribute macro `server` (in Nightly builds, run with -Z macro-backtrace for more info)

error[E0283]: type annotations needed: cannot satisfy `S: app::_::_serde::Deserialize<'de>`
   --> src/app.rs:786:1
    |
786 | #[server]
    | ^^^^^^^^^
    |
note: multiple `impl`s or `where` clauses satisfying `S: app::_::_serde::Deserialize<'de>` found
   --> src/app.rs:786:1
    |
786 | #[server]
    | ^^^^^^^^^
...
792 |     S: Display + Send + DeserializeOwned + Serialize + 'static,
    |                         ^^^^^^^^^^^^^^^^
    = note: this error originates in the derive macro `::leptos::server_fn::serde::Deserialize` (in Nightly builds, run with -Z macro-backtrace for more info)

error[E0283]: type annotations needed: cannot satisfy `S: app::_::_serde::Deserialize<'_>`
   --> src/app.rs:786:1
    |
786 | #[server]
    | ^^^^^^^^^
    |
note: multiple `impl`s or `where` clauses satisfying `S: app::_::_serde::Deserialize<'_>` found
   --> src/app.rs:786:1
    |
786 | #[server]
    | ^^^^^^^^^
...
792 |     S: Display + Send + DeserializeOwned + Serialize + 'static,
    |                         ^^^^^^^^^^^^^^^^
note: required for `app::_::<impl app::_::_serde::Deserialize<'de> for TestFn<S>>::deserialize::__Visitor<'de, S>` to implement `Visitor<'de>`
   --> src/app.rs:786:1
    |
786 | #[server]
    | ^^^^^^^^^ unsatisfied trait bound introduced in this `derive` macro
    = note: this error originates in the derive macro `::leptos::server_fn::serde::Deserialize` (in Nightly builds, run with -Z macro-backtrace for more info)

error[E0283]: type annotations needed: cannot satisfy `S: app::_::_serde::Deserialize<'_>`
   --> src/app.rs:786:1
    |
786 | #[server]
    | ^^^^^^^^^
    |
note: multiple `impl`s or `where` clauses satisfying `S: app::_::_serde::Deserialize<'_>` found
   --> src/app.rs:786:1
    |
786 | #[server]
    | ^^^^^^^^^
...
792 |     S: Display + Send + DeserializeOwned + Serialize + 'static,
    |                         ^^^^^^^^^^^^^^^^
note: required by a bound in `app::_::<impl app::_::_serde::Deserialize<'de> for TestFn<S>>::deserialize::__Visitor`
   --> src/app.rs:786:1
    |
786 | #[server]
    | ^^^^^^^^^ required by this bound in `__Visitor`
    = note: this error originates in the derive macro `::leptos::server_fn::serde::Deserialize` (in Nightly builds, run with -Z macro-backtrace for more info)

error[E0283]: type annotations needed: cannot satisfy `S: app::_::_serde::Deserialize<'_>`
    --> src/app.rs:788:12
     |
788  |     first: S,
     |            ^
     |
note: multiple `impl`s or `where` clauses satisfying `S: app::_::_serde::Deserialize<'_>` found
    --> src/app.rs:786:1
     |
786  | #[server]
     | ^^^^^^^^^
...
792  |     S: Display + Send + DeserializeOwned + Serialize + 'static,
     |                         ^^^^^^^^^^^^^^^^
note: required by a bound in `next_element`
    --> /Users/rakshith/.cargo/registry/src/index.crates.io-6f17d22bba15001f/serde-1.0.209/src/de/mod.rs:1733:12
     |
1731 |     fn next_element<T>(&mut self) -> Result<Option<T>, Self::Error>
     |        ------------ required by a bound in this associated function
1732 |     where
1733 |         T: Deserialize<'de>,
     |            ^^^^^^^^^^^^^^^^ required by this bound in `SeqAccess::next_element`
     = note: this error originates in the derive macro `::leptos::server_fn::serde::Deserialize` (in Nightly builds, run with -Z macro-backtrace for more info)

error[E0283]: type annotations needed: cannot satisfy `S: app::_::_serde::Deserialize<'_>`
    --> src/app.rs:788:12
     |
788  |     first: S,
     |            ^
     |
note: multiple `impl`s or `where` clauses satisfying `S: app::_::_serde::Deserialize<'_>` found
    --> src/app.rs:786:1
     |
786  | #[server]
     | ^^^^^^^^^
...
792  |     S: Display + Send + DeserializeOwned + Serialize + 'static,
     |                         ^^^^^^^^^^^^^^^^
note: required by a bound in `next_value`
    --> /Users/rakshith/.cargo/registry/src/index.crates.io-6f17d22bba15001f/serde-1.0.209/src/de/mod.rs:1872:12
     |
1870 |     fn next_value<V>(&mut self) -> Result<V, Self::Error>
     |        ---------- required by a bound in this associated function
1871 |     where
1872 |         V: Deserialize<'de>,
     |            ^^^^^^^^^^^^^^^^ required by this bound in `MapAccess::next_value`
     = note: this error originates in the derive macro `::leptos::server_fn::serde::Deserialize` (in Nightly builds, run with -Z macro-backtrace for more info)

For more information about this error, try `rustc --explain E0283`.
error: could not compile `server_fns_axum` (lib) due to 9 previous errors
Error: Failed to build server_fns_axum

Stack backtrace:
   0: std::backtrace::Backtrace::create
   1: anyhow::error::<impl anyhow::Error>::msg
   2: cargo_leptos::run::{{closure}}
   3: tokio::runtime::park::CachedParkThread::block_on
   4: tokio::runtime::context::runtime::enter_runtime
   5: cargo_leptos::main
   6: std::sys::backtrace::__rust_begin_short_backtrace
   7: std::rt::lang_start::{{closure}}
   8: std::rt::lang_start_internal
   9: _main
Error while executing command, exit code: 1

For context, test_fn expands to this:

#[doc = "Serialized arguments for the [`test_fn`] server function.\n\n"]
#[derive(
    Debug,
    Clone,
    ::leptos::server_fn::serde::Serialize,
    ::leptos::server_fn::serde::Deserialize,
)]
#[serde(crate = "leptos::server_fn::serde")]
pub struct TestFn<S>
where
    S: Display + Send + DeserializeOwned + Serialize + 'static,
{
    pub first: S,
    pub second: S,
}
impl<S> ::leptos::server_fn::ServerFn for TestFn<S>
where
    S: Display + Send + DeserializeOwned + Serialize + 'static,
{
    const PATH: &'static str = if "".is_empty() {
        ::leptos::server_fn::const_format::concatcp!(
            "/api",
            "/",
            "test_fn",
            ::leptos::server_fn::xxhash_rust::const_xxh64::xxh64(
                concat!(
                    env!("CARGO_MANIFEST_DIR"),
                    ":",
                    file!(),
                    ":",
                    line!(),
                    ":",
                    column!()
                )
                .as_bytes(),
                0
            )
        )
    } else {
        ::leptos::server_fn::const_format::concatcp!("/api", "")
    };
    type Client = ::leptos::server_fn::client::browser::BrowserClient;
    type ServerRequest = ::leptos::server_fn::request::BrowserMockReq;
    type ServerResponse = ::leptos::server_fn::response::BrowserMockRes;
    type Output = WhyNotResult;
    type InputEncoding = ::leptos::server_fn::codec::PostUrl;
    type OutputEncoding = ::leptos::server_fn::codec::Json;
    type Error = ::leptos::server_fn::error::NoCustomError;
    fn middlewares() -> Vec<
        std::sync::Arc<
            dyn ::leptos::server_fn::middleware::Layer<
                ::leptos::server_fn::request::BrowserMockReq,
                ::leptos::server_fn::response::BrowserMockRes,
            >,
        >,
    > {
        vec![]
    }
    #[allow(unused_variables)]
    async fn run_body(self) -> Result<WhyNotResult, ServerFnError> {
        unreachable!()
    }
}
#[allow(unused_variables)]
pub async fn test_fn<S>(
    first: S,
    second: S,
) -> Result<WhyNotResult, ServerFnError>
where
    S: Display + Send + DeserializeOwned + Serialize + 'static,
{
    use ::leptos::server_fn::ServerFn;
    let data = TestFn::<S> { first, second };
    data.run_on_client().await
}

Not sure why this is happening. Any help on this would be appreciated

[rakshith-ravi]

I am aware of the bad example namings and the debug prints that are currently present. Once I am able to get this working, I'll remove those and mark this PR as ready to review

[rakshith-ravi]

Oh my god I'm so stupid. I think I found the issue. Serde derives add a where clause of their own. Let me fix it and put an update to this PR.

[rakshith-ravi]

Okay, almost everything works now. The only part that's left is the inventory::submit! invocation that doesn't have a generic parameter that is defined on it

[benwis]

@rakshith-ravi Are you trying to enable having generics as inputs to a server function?

[rakshith-ravi]

Yes, sir.

Basically, trying to enable this:

#[server]
async fn test<S>(input: S) -> Result<(), ServerFnError>
where
    S: Display {
// body
}

In my work (the parts that I haven't pushed yet) I also have made the code a bit more flexible to eventually allow us to implement #2938

[gbj]

I added a commit that fixes the middleware-related issues on the examples here.

One small note: this is broken with one-argument server functions right now.

EDIT: I just added this in e2f096d because it was a one-liner

If I do something like this

#[server]
pub async fn test_fn<S>(input: S) -> Result<String, ServerFnError>
where
    S: Display,
{
    // insert a simulated wait
    tokio::time::sleep(std::time::Duration::from_millis(250)).await;
    Ok(input.to_string())
}

I get the error:

error[E0210]: type parameter `S` must be covered by another type when it appears before the first local type (`TestFn<_>`)
  --> src/app.rs:80:22
   |
80 | pub async fn test_fn<S>(input: S) -> Result<String, ServerFnError>
   |                      ^ type parameter `S` must be covered by another type when it appears before the first local type (`TestFn<_>`)
   |
   = note: implementing a foreign trait is only possible if at least one of the types for which it is implemented is local, and no uncovered type parameters appear before that first local type
   = note: in this case, 'before' refers to the following order: `impl<..> ForeignTrait<T1, ..., Tn> for T0`, where `T0` is the first and `Tn` is the last

Expanding the macro, I see that this is the issue:

impl<S> From<TestFn<S>> for S
where
    S: Display
        + ::leptos::server_fn::serde::Serialize
        + for<'leptos_param_lifetime> ::leptos::server_fn::serde::Deserialize<
            'leptos_param_lifetime,
        > + Send
        + 'static,
{
    fn from(value: TestFn<S>) -> Self {
        let TestFn::<S> { input } = value;
        input
    }
}

We add a From<_> argument for server fns with only one argument to convert from that argument to the server fn type easily. I think you most likely just need to suppress that implementation in the case that there's a generic.

[gbj]

Okay, weirdly I now get a linker error with my generic example. Could someone else try building examples/server_fns_axum and see if it works for you? (It may need explicit registration for that test_fn too)

[rakshith-ravi]

Yeah I'm getting the same error too. Not sure what's going on. Will look into this further

[rakshith-ravi]

Slept on this and had an idea:

The inventory crate uses static linking to register the objects. Perhaps we aren't removing the auto registering properly? That could possibly cause problems with the linker

[benwis]

@rakshith-ravi Any update on this?

[rakshith-ravi]

No update yet. There seems to be this odd linker issue. If that is figured out then we're pretty much good to go

[rakshith-ravi]

I have no clue why CI is green now. All I did was a rebase.

Programming at it's peak: My code doesn't work and I don't know why; My code works and I don't know why

[benwis]

The autofix CI fixed some spacing too. Is this ready now?

[benwis]

Speaking of, it seems like the caveat here is that endpoint and prefix won't work here due to the multiple endpoints?