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Rewrite join! and try_join! as procedural macros #1783
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[package] | ||
name = "futures-join-macro-preview" | ||
edition = "2018" | ||
version = "0.3.0-alpha.17" | ||
authors = ["Taiki Endo <te316e89@gmail.com>"] | ||
license = "MIT OR Apache-2.0" | ||
repository = "https://github.com/rust-lang-nursery/futures-rs" | ||
homepage = "https://rust-lang-nursery.github.io/futures-rs" | ||
documentation = "https://rust-lang-nursery.github.io/futures-api-docs/0.3.0-alpha.17/futures_join_macro" | ||
description = """ | ||
Definition of the `join!` macro and the `try_join!` macro. | ||
""" | ||
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[lib] | ||
name = "futures_join_macro" | ||
proc-macro = true | ||
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[features] | ||
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[dependencies] | ||
proc-macro2 = "0.4" | ||
proc-macro-hack = "0.5.3" | ||
quote = "0.6" | ||
syn = { version = "0.15.25", features = ["full"] } |
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../LICENSE-APACHE |
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../LICENSE-MIT |
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//! The futures-rs `join! macro implementation. | ||
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#![recursion_limit = "128"] | ||
#![warn(rust_2018_idioms, unreachable_pub)] | ||
// It cannot be included in the published code because this lints have false positives in the minimum required version. | ||
#![cfg_attr(test, warn(single_use_lifetimes))] | ||
#![warn(clippy::all)] | ||
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extern crate proc_macro; | ||
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use proc_macro::TokenStream; | ||
use proc_macro2::{Span, TokenStream as TokenStream2}; | ||
use proc_macro_hack::proc_macro_hack; | ||
use quote::quote; | ||
use syn::parse::{Parse, ParseStream}; | ||
use syn::{parenthesized, parse_quote, Expr, Ident, Token}; | ||
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mod kw { | ||
syn::custom_keyword!(futures_crate_path); | ||
} | ||
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#[derive(Default)] | ||
struct Join { | ||
futures_crate_path: Option<syn::Path>, | ||
fut_exprs: Vec<Expr>, | ||
} | ||
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impl Parse for Join { | ||
fn parse(input: ParseStream<'_>) -> syn::Result<Self> { | ||
let mut join = Join::default(); | ||
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// When `futures_crate_path(::path::to::futures::lib)` is provided, | ||
// it sets the path through which futures library functions will be | ||
// accessed. | ||
if input.peek(kw::futures_crate_path) { | ||
input.parse::<kw::futures_crate_path>()?; | ||
let content; | ||
parenthesized!(content in input); | ||
join.futures_crate_path = Some(content.parse()?); | ||
} | ||
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while !input.is_empty() { | ||
join.fut_exprs.push(input.parse::<Expr>()?); | ||
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if !input.is_empty() { | ||
input.parse::<Token![,]>()?; | ||
} | ||
} | ||
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Ok(join) | ||
} | ||
} | ||
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fn bind_futures( | ||
futures_crate: &syn::Path, | ||
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 = Ident::new(&format!("_fut{}", i), 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); | ||
}); | ||
name | ||
}) | ||
.collect(); | ||
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(future_let_bindings, future_names) | ||
} | ||
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/// The `join!` macro. | ||
#[proc_macro_hack] | ||
pub fn join(input: TokenStream) -> TokenStream { | ||
let parsed = syn::parse_macro_input!(input as Join); | ||
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let futures_crate = parsed | ||
.futures_crate_path | ||
.unwrap_or_else(|| parse_quote!(::futures_util)); | ||
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// should be def_site, but that's unstable | ||
let span = Span::call_site(); | ||
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let (future_let_bindings, future_names) = bind_futures(&futures_crate, parsed.fut_exprs, span); | ||
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let poll_futures = future_names.iter().map(|fut| { | ||
quote! { | ||
__all_done &= #futures_crate::core_reexport::future::Future::poll( | ||
unsafe { #futures_crate::core_reexport::pin::Pin::new_unchecked(&mut #fut) }, __cx).is_ready(); | ||
} | ||
}); | ||
let take_outputs = future_names.iter().map(|fut| { | ||
quote! { | ||
unsafe { #futures_crate::core_reexport::pin::Pin::new_unchecked(&mut #fut) }.take_output().unwrap(), | ||
} | ||
}); | ||
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TokenStream::from(quote! { { | ||
#( #future_let_bindings )* | ||
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#futures_crate::future::poll_fn(move |__cx: &mut #futures_crate::task::Context<'_>| { | ||
let mut __all_done = true; | ||
#( #poll_futures )* | ||
if __all_done { | ||
#futures_crate::core_reexport::task::Poll::Ready(( | ||
#( #take_outputs )* | ||
)) | ||
} else { | ||
#futures_crate::core_reexport::task::Poll::Pending | ||
} | ||
}).await | ||
} }) | ||
} | ||
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/// The `try_join!` macro. | ||
#[proc_macro_hack] | ||
pub fn try_join(input: TokenStream) -> TokenStream { | ||
let parsed = syn::parse_macro_input!(input as Join); | ||
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let futures_crate = parsed | ||
.futures_crate_path | ||
.unwrap_or_else(|| parse_quote!(::futures_util)); | ||
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// should be def_site, but that's unstable | ||
let span = Span::call_site(); | ||
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let (future_let_bindings, future_names) = bind_futures(&futures_crate, parsed.fut_exprs, span); | ||
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let poll_futures = future_names.iter().map(|fut| { | ||
quote! { | ||
if #futures_crate::core_reexport::future::Future::poll( | ||
unsafe { #futures_crate::core_reexport::pin::Pin::new_unchecked(&mut #fut) }, __cx).is_pending() | ||
{ | ||
__all_done = false; | ||
} else if unsafe { #futures_crate::core_reexport::pin::Pin::new_unchecked(&mut #fut) }.output_mut().unwrap().is_err() { | ||
// `.err().unwrap()` rather than `.unwrap_err()` so that we don't introduce | ||
// a `T: Debug` bound. | ||
return #futures_crate::core_reexport::task::Poll::Ready( | ||
#futures_crate::core_reexport::result::Result::Err( | ||
unsafe { #futures_crate::core_reexport::pin::Pin::new_unchecked(&mut #fut) }.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. | ||
unsafe { #futures_crate::core_reexport::pin::Pin::new_unchecked(&mut #fut) }.take_output().unwrap().ok().unwrap(), | ||
} | ||
}); | ||
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TokenStream::from(quote! { { | ||
#( #future_let_bindings )* | ||
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#futures_crate::future::poll_fn(move |__cx: &mut #futures_crate::task::Context<'_>| { | ||
let mut __all_done = true; | ||
#( #poll_futures )* | ||
if __all_done { | ||
#futures_crate::core_reexport::task::Poll::Ready( | ||
#futures_crate::core_reexport::result::Result::Ok(( | ||
#( #take_outputs )* | ||
)) | ||
) | ||
} else { | ||
#futures_crate::core_reexport::task::Poll::Pending | ||
} | ||
}).await | ||
} }) | ||
} |
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For almost the same reason as
select!
, this is optional infutures_util
(see #1701).