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|
//! The futures-rs `join! macro implementation.
use proc_macro::TokenStream;
use proc_macro2::{Span, TokenStream as TokenStream2};
use quote::{format_ident, quote};
use syn::parse::{Parse, ParseStream};
use syn::{Expr, Ident, Token};
#[derive(Default)]
struct Join {
fut_exprs: Vec<Expr>,
}
impl Parse for Join {
fn parse(input: ParseStream<'_>) -> syn::Result<Self> {
let mut join = Self::default();
while !input.is_empty() {
join.fut_exprs.push(input.parse::<Expr>()?);
if !input.is_empty() {
input.parse::<Token![,]>()?;
}
}
Ok(join)
}
}
fn bind_futures(fut_exprs: Vec<Expr>, span: Span) -> (Vec<TokenStream2>, Vec<Ident>) {
let mut future_let_bindings = Vec::with_capacity(fut_exprs.len());
let future_names: Vec<_> = fut_exprs
.into_iter()
.enumerate()
.map(|(i, expr)| {
let name = format_ident!("_fut{}", i, span = span);
future_let_bindings.push(quote! {
// Move future into a local so that it is pinned in one place and
// is no longer accessible by the end user.
let mut #name = __futures_crate::future::maybe_done(#expr);
let mut #name = unsafe { __futures_crate::Pin::new_unchecked(&mut #name) };
});
name
})
.collect();
(future_let_bindings, future_names)
}
/// The `join!` macro.
pub(crate) fn join(input: TokenStream) -> TokenStream {
let parsed = syn::parse_macro_input!(input as Join);
// should be def_site, but that's unstable
let span = Span::call_site();
let (future_let_bindings, future_names) = bind_futures(parsed.fut_exprs, span);
let poll_futures = future_names.iter().map(|fut| {
quote! {
__all_done &= __futures_crate::future::Future::poll(
#fut.as_mut(), __cx).is_ready();
}
});
let take_outputs = future_names.iter().map(|fut| {
quote! {
#fut.as_mut().take_output().unwrap(),
}
});
TokenStream::from(quote! { {
#( #future_let_bindings )*
__futures_crate::future::poll_fn(move |__cx: &mut __futures_crate::task::Context<'_>| {
let mut __all_done = true;
#( #poll_futures )*
if __all_done {
__futures_crate::task::Poll::Ready((
#( #take_outputs )*
))
} else {
__futures_crate::task::Poll::Pending
}
}).await
} })
}
/// The `try_join!` macro.
pub(crate) fn try_join(input: TokenStream) -> TokenStream {
let parsed = syn::parse_macro_input!(input as Join);
// should be def_site, but that's unstable
let span = Span::call_site();
let (future_let_bindings, future_names) = bind_futures(parsed.fut_exprs, span);
let poll_futures = future_names.iter().map(|fut| {
quote! {
if __futures_crate::future::Future::poll(
#fut.as_mut(), __cx).is_pending()
{
__all_done = false;
} else if #fut.as_mut().output_mut().unwrap().is_err() {
// `.err().unwrap()` rather than `.unwrap_err()` so that we don't introduce
// a `T: Debug` bound.
// Also, for an error type of ! any code after `err().unwrap()` is unreachable.
#[allow(unreachable_code)]
return __futures_crate::task::Poll::Ready(
__futures_crate::Err(
#fut.as_mut().take_output().unwrap().err().unwrap()
)
);
}
}
});
let take_outputs = future_names.iter().map(|fut| {
quote! {
// `.ok().unwrap()` rather than `.unwrap()` so that we don't introduce
// an `E: Debug` bound.
// Also, for an ok type of ! any code after `ok().unwrap()` is unreachable.
#[allow(unreachable_code)]
#fut.as_mut().take_output().unwrap().ok().unwrap(),
}
});
TokenStream::from(quote! { {
#( #future_let_bindings )*
#[allow(clippy::diverging_sub_expression)]
__futures_crate::future::poll_fn(move |__cx: &mut __futures_crate::task::Context<'_>| {
let mut __all_done = true;
#( #poll_futures )*
if __all_done {
__futures_crate::task::Poll::Ready(
__futures_crate::Ok((
#( #take_outputs )*
))
)
} else {
__futures_crate::task::Poll::Pending
}
}).await
} })
}
|
