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Replace Pin::new_unchecked with #[pin_project] in tuple_from_req! (#1293)

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Using some module trickery, we can generate a tuple struct for each
invocation of the macro. This allows us to use `pin_project` to project
through to the tuple fields, removing the need to use
`Pin::new_unchecked`

Co-authored-by: Yuki Okushi <huyuumi.dev@gmail.com>
This commit is contained in:
Aaron Hill 2020-01-27 20:45:26 -05:00 committed by Yuki Okushi
parent a2d4ff157e
commit d137a8635b
1 changed files with 67 additions and 41 deletions
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34
src/extract.rs
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@ -193,6 +193,30 @@ impl FromRequest for () {
macro_rules! tuple_from_req ({$fut_type:ident, $(($n:tt, $T:ident)),+} => {
// This module is a trick to get around the inability of
// `macro_rules!` macros to make new idents. We want to make
// a new `FutWrapper` struct for each distinct invocation of
// this macro. Ideally, we would name it something like
// `FutWrapper_$fut_type`, but this can't be done in a macro_rules
// macro.
//
// Instead, we put everything in a module named `$fut_type`, thus allowing
// us to use the name `FutWrapper` without worrying about conflicts.
// This macro only exists to generate trait impls for tuples - these
// are inherently global, so users don't have to care about this
// weird trick.
#[allow(non_snake_case)]
mod $fut_type {
// Bring everything into scope, so we don't need
// redundant imports
use super::*;
/// A helper struct to allow us to pin-project through
/// to individual fields
#[pin_project::pin_project]
struct FutWrapper<$($T: FromRequest),+>($(#[pin] $T::Future),+);
/// FromRequest implementation for tuple
#[doc(hidden)]
#[allow(unused_parens)]
@ -205,7 +229,7 @@ macro_rules! tuple_from_req ({$fut_type:ident, $(($n:tt, $T:ident)),+} => {
fn from_request(req: &HttpRequest, payload: &mut Payload) -> Self::Future {
$fut_type {
items: <($(Option<$T>,)+)>::default(),
futs: ($($T::from_request(req, payload),)+),
futs: FutWrapper($($T::from_request(req, payload),)+),
}
}
}
@ -214,7 +238,8 @@ macro_rules! tuple_from_req ({$fut_type:ident, $(($n:tt, $T:ident)),+} => {
#[pin_project::pin_project]
pub struct $fut_type<$($T: FromRequest),+> {
items: ($(Option<$T>,)+),
futs: ($($T::Future,)+),
#[pin]
futs: FutWrapper<$($T,)+>,
}
impl<$($T: FromRequest),+> Future for $fut_type<$($T),+>
@ -222,12 +247,12 @@ macro_rules! tuple_from_req ({$fut_type:ident, $(($n:tt, $T:ident)),+} => {
type Output = Result<($($T,)+), Error>;
fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
let this = self.project();
let mut this = self.project();
let mut ready = true;
$(
if this.items.$n.is_none() {
match unsafe { Pin::new_unchecked(&mut this.futs.$n) }.poll(cx) {
match this.futs.as_mut().project().$n.poll(cx) {
Poll::Ready(Ok(item)) => {
this.items.$n = Some(item);
}
@ -246,6 +271,7 @@ macro_rules! tuple_from_req ({$fut_type:ident, $(($n:tt, $T:ident)),+} => {
}
}
}
}
});
#[rustfmt::skip]