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    //! Server-side traits.

    use super::*;

    // FIXME(eddyb) generate the definition of `HandleStore` in `server.rs`.
    use super::client::HandleStore;

    /// Declare an associated item of one of the traits below, optionally
    /// adjusting it (i.e., adding bounds to types and default bodies to methods).
    macro_rules! associated_item {
        (type FreeFunctions) =>
            (type FreeFunctions: 'static;);
        (type TokenStream) =>
            (type TokenStream: 'static + Clone;);
        (type TokenStreamBuilder) =>
            (type TokenStreamBuilder: 'static;);
        (type TokenStreamIter) =>
            (type TokenStreamIter: 'static + Clone;);
        (type Group) =>
            (type Group: 'static + Clone;);
        (type Punct) =>
            (type Punct: 'static + Copy + Eq + Hash;);
        (type Ident) =>
            (type Ident: 'static + Copy + Eq + Hash;);
        (type Literal) =>
            (type Literal: 'static + Clone;);
        (type SourceFile) =>
            (type SourceFile: 'static + Clone;);
        (type MultiSpan) =>
            (type MultiSpan: 'static;);
        (type Diagnostic) =>
            (type Diagnostic: 'static;);
        (type Span) =>
            (type Span: 'static + Copy + Eq + Hash;);
        (fn drop(&mut self, $arg:ident: $arg_ty:ty)) =>
            (fn drop(&mut self, $arg: $arg_ty) { mem::drop($arg) });
        (fn clone(&mut self, $arg:ident: $arg_ty:ty) -> $ret_ty:ty) =>
            (fn clone(&mut self, $arg: $arg_ty) -> $ret_ty { $arg.clone() });
        ($($item:tt)*) => ($($item)*;)
    }

    macro_rules! declare_server_traits {
        ($($name:ident {
            $(fn $method:ident($($arg:ident: $arg_ty:ty),* $(,)?) $(-> $ret_ty:ty)?;)*
        }),* $(,)?) => {
            pub trait Types {
                $(associated_item!(type $name);)*
            }

            $(pub trait $name: Types {
                $(associated_item!(fn $method(&mut self, $($arg: $arg_ty),*) $(-> $ret_ty)?);)*
            })*

            pub trait Server: Types $(+ $name)* {}
            impl<S: Types $(+ $name)*> Server for S {}
        }
    }
    with_api!(Self, self_, declare_server_traits);

    pub(super) struct MarkedTypes<S: Types>(S);

    macro_rules! define_mark_types_impls {
        ($($name:ident {
            $(fn $method:ident($($arg:ident: $arg_ty:ty),* $(,)?) $(-> $ret_ty:ty)?;)*
        }),* $(,)?) => {
            impl<S: Types> Types for MarkedTypes<S> {
                $(type $name = Marked<S::$name, client::$name>;)*
            }

            $(impl<S: $name> $name for MarkedTypes<S> {
                $(fn $method(&mut self, $($arg: $arg_ty),*) $(-> $ret_ty)? {
                    <_>::mark($name::$method(&mut self.0, $($arg.unmark()),*))
                })*
            })*
        }
    }
    with_api!(Self, self_, define_mark_types_impls);

    struct Dispatcher<S: Types> {
        handle_store: HandleStore<S>,
        server: S,
    }

    macro_rules! define_dispatcher_impl {
        ($($name:ident {
            $(fn $method:ident($($arg:ident: $arg_ty:ty),* $(,)?) $(-> $ret_ty:ty)?;)*
        }),* $(,)?) => {
            // FIXME(eddyb) `pub` only for `ExecutionStrategy` below.
            pub trait DispatcherTrait {
                // HACK(eddyb) these are here to allow `Self::$name` to work below.
                $(type $name;)*
                fn dispatch(&mut self, b: Buffer<u8>) -> Buffer<u8>;
            }

            impl<S: Server> DispatcherTrait for Dispatcher<MarkedTypes<S>> {
                $(type $name = <MarkedTypes<S> as Types>::$name;)*
                fn dispatch(&mut self, mut b: Buffer<u8>) -> Buffer<u8> {
                    let Dispatcher { handle_store, server } = self;

                    let mut reader = &b[..];
                    match api_tags::Method::decode(&mut reader, &mut ()) {
                        $(api_tags::Method::$name(m) => match m {
                            $(api_tags::$name::$method => {
                                let mut call_method = || {
                                    reverse_decode!(reader, handle_store; $($arg: $arg_ty),*);
                                    $name::$method(server, $($arg),*)
                                };
                                // HACK(eddyb) don't use `panic::catch_unwind` in a panic.
                                // If client and server happen to use the same `libstd`,
                                // `catch_unwind` asserts that the panic counter was 0,
                                // even when the closure passed to it didn't panic.
                                let r = if thread::panicking() {
                                    Ok(call_method())
                                } else {
                                    panic::catch_unwind(panic::AssertUnwindSafe(call_method))
                                        .map_err(PanicMessage::from)
                                };

                                b.clear();
                                r.encode(&mut b, handle_store);
                            })*
                        }),*
                    }
                    b
                }
            }
        }
    }
    with_api!(Self, self_, define_dispatcher_impl);

    pub trait ExecutionStrategy {
        fn run_bridge_and_client<D: Copy + Send + 'static>(
            &self,
            dispatcher: &mut impl DispatcherTrait,
            input: Buffer<u8>,
            run_client: extern "C" fn(Bridge<'_>, D) -> Buffer<u8>,
            client_data: D,
            force_show_panics: bool,
        ) -> Buffer<u8>;
    }

    pub struct SameThread;

    impl ExecutionStrategy for SameThread {
        fn run_bridge_and_client<D: Copy + Send + 'static>(
            &self,
            dispatcher: &mut impl DispatcherTrait,
            input: Buffer<u8>,
            run_client: extern "C" fn(Bridge<'_>, D) -> Buffer<u8>,
            client_data: D,
            force_show_panics: bool,
        ) -> Buffer<u8> {
            let mut dispatch = |b| dispatcher.dispatch(b);

            run_client(
                Bridge { cached_buffer: input, dispatch: (&mut dispatch).into(), force_show_panics },
                client_data,
            )
        }
    }

    // NOTE(eddyb) Two implementations are provided, the second one is a bit
    // faster but neither is anywhere near as fast as same-thread execution.

    pub struct CrossThread1;

    impl ExecutionStrategy for CrossThread1 {
        fn run_bridge_and_client<D: Copy + Send + 'static>(
            &self,
            dispatcher: &mut impl DispatcherTrait,
            input: Buffer<u8>,
            run_client: extern "C" fn(Bridge<'_>, D) -> Buffer<u8>,
            client_data: D,
            force_show_panics: bool,
        ) -> Buffer<u8> {
            use std::sync::mpsc::channel;

            let (req_tx, req_rx) = channel();
            let (res_tx, res_rx) = channel();

            let join_handle = thread::spawn(move || {
                let mut dispatch = |b| {
                    req_tx.send(b).unwrap();
                    res_rx.recv().unwrap()
                };

                run_client(
                    Bridge {
                        cached_buffer: input,
                        dispatch: (&mut dispatch).into(),
                        force_show_panics,
                    },
                    client_data,
                )
            });

            for b in req_rx {
                res_tx.send(dispatcher.dispatch(b)).unwrap();
            }

            join_handle.join().unwrap()
        }
    }

    pub struct CrossThread2;

    impl ExecutionStrategy for CrossThread2 {
        fn run_bridge_and_client<D: Copy + Send + 'static>(
            &self,
            dispatcher: &mut impl DispatcherTrait,
            input: Buffer<u8>,
            run_client: extern "C" fn(Bridge<'_>, D) -> Buffer<u8>,
            client_data: D,
            force_show_panics: bool,
        ) -> Buffer<u8> {
            use std::sync::{Arc, Mutex};

            enum State<T> {
                Req(T),
                Res(T),
            }

            let mut state = Arc::new(Mutex::new(State::Res(Buffer::new())));

            let server_thread = thread::current();
            let state2 = state.clone();
            let join_handle = thread::spawn(move || {
                let mut dispatch = |b| {
                    *state2.lock().unwrap() = State::Req(b);
                    server_thread.unpark();
                    loop {
                        thread::park();
                        if let State::Res(b) = &mut *state2.lock().unwrap() {
                            break b.take();
                        }
                    }
                };

                let r = run_client(
                    Bridge {
                        cached_buffer: input,
                        dispatch: (&mut dispatch).into(),
                        force_show_panics,
                    },
                    client_data,
                );

                // Wake up the server so it can exit the dispatch loop.
                drop(state2);
                server_thread.unpark();

                r
            });

            // Check whether `state2` was dropped, to know when to stop.
            while Arc::get_mut(&mut state).is_none() {
                thread::park();
                let mut b = match &mut *state.lock().unwrap() {
                    State::Req(b) => b.take(),
                    _ => continue,
                };
                b = dispatcher.dispatch(b.take());
                *state.lock().unwrap() = State::Res(b);
                join_handle.thread().unpark();
            }

            join_handle.join().unwrap()
        }
    }

    fn run_server<
        S: Server,
        I: Encode<HandleStore<MarkedTypes<S>>>,
        O: for<'a, 's> DecodeMut<'a, 's, HandleStore<MarkedTypes<S>>>,
        D: Copy + Send + 'static,
    >(
        strategy: &impl ExecutionStrategy,
        handle_counters: &'static client::HandleCounters,
        server: S,
        input: I,
        run_client: extern "C" fn(Bridge<'_>, D) -> Buffer<u8>,
        client_data: D,
        force_show_panics: bool,
    ) -> Result<O, PanicMessage> {
        let mut dispatcher =
            Dispatcher { handle_store: HandleStore::new(handle_counters), server: MarkedTypes(server) };

        let mut b = Buffer::new();
        input.encode(&mut b, &mut dispatcher.handle_store);

        b = strategy.run_bridge_and_client(
            &mut dispatcher,
            b,
            run_client,
            client_data,
            force_show_panics,
        );

        Result::decode(&mut &b[..], &mut dispatcher.handle_store)
    }

    impl client::Client<fn(crate::TokenStream) -> crate::TokenStream> {
        pub fn run<S: Server>(
            &self,
            strategy: &impl ExecutionStrategy,
            server: S,
            input: S::TokenStream,
            force_show_panics: bool,
        ) -> Result<S::TokenStream, PanicMessage> {
            let client::Client { get_handle_counters, run, f } = *self;
            run_server(
                strategy,
                get_handle_counters(),
                server,
                <MarkedTypes<S> as Types>::TokenStream::mark(input),
                run,
                f,
                force_show_panics,
            )
            .map(<MarkedTypes<S> as Types>::TokenStream::unmark)
        }
    }

    impl client::Client<fn(crate::TokenStream, crate::TokenStream) -> crate::TokenStream> {
        pub fn run<S: Server>(
            &self,
            strategy: &impl ExecutionStrategy,
            server: S,
            input: S::TokenStream,
            input2: S::TokenStream,
            force_show_panics: bool,
        ) -> Result<S::TokenStream, PanicMessage> {
            let client::Client { get_handle_counters, run, f } = *self;
            run_server(
                strategy,
                get_handle_counters(),
                server,
                (
                    <MarkedTypes<S> as Types>::TokenStream::mark(input),
                    <MarkedTypes<S> as Types>::TokenStream::mark(input2),
                ),
                run,
                f,
                force_show_panics,
            )
            .map(<MarkedTypes<S> as Types>::TokenStream::unmark)
        }
    }