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macros: allow temporary lifetime extension in select (#6722)
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@Darksonn
Darksonn authored Jul 26, 2024
1 parent ee8d4d1 commit 438def7
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211 changes: 210 additions & 1 deletion tokio/src/macros/select.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -489,13 +489,22 @@ doc! {macro_rules! select {
// Create a scope to separate polling from handling the output. This
// adds borrow checker flexibility when using the macro.
let mut output = {
// Store each future directly first (that is, without wrapping the future in a call to
// `IntoFuture::into_future`). This allows the `$fut` expression to make use of
// temporary lifetime extension.
//
// https://doc.rust-lang.org/1.58.1/reference/destructors.html#temporary-lifetime-extension
let futures_init = ($( $fut, )+);

// Safety: Nothing must be moved out of `futures`. This is to
// satisfy the requirement of `Pin::new_unchecked` called below.
//
// We can't use the `pin!` macro for this because `futures` is a
// tuple and the standard library provides no way to pin-project to
// the fields of a tuple.
let mut futures = ( $( $crate::macros::support::IntoFuture::into_future($fut) , )+ );
let mut futures = ($( $crate::macros::support::IntoFuture::into_future(
$crate::count_field!( futures_init.$($skip)* )
),)+);

// This assignment makes sure that the `poll_fn` closure only has a
// reference to the futures, instead of taking ownership of them.
Expand Down Expand Up @@ -854,6 +863,206 @@ macro_rules! count {
};
}

#[macro_export]
#[doc(hidden)]
macro_rules! count_field {
($var:ident. ) => {
$var.0
};
($var:ident. _) => {
$var.1
};
($var:ident. _ _) => {
$var.2
};
($var:ident. _ _ _) => {
$var.3
};
($var:ident. _ _ _ _) => {
$var.4
};
($var:ident. _ _ _ _ _) => {
$var.5
};
($var:ident. _ _ _ _ _ _) => {
$var.6
};
($var:ident. _ _ _ _ _ _ _) => {
$var.7
};
($var:ident. _ _ _ _ _ _ _ _) => {
$var.8
};
($var:ident. _ _ _ _ _ _ _ _ _) => {
$var.9
};
($var:ident. _ _ _ _ _ _ _ _ _ _) => {
$var.10
};
($var:ident. _ _ _ _ _ _ _ _ _ _ _) => {
$var.11
};
($var:ident. _ _ _ _ _ _ _ _ _ _ _ _) => {
$var.12
};
($var:ident. _ _ _ _ _ _ _ _ _ _ _ _ _) => {
$var.13
};
($var:ident. _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
$var.14
};
($var:ident. _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
$var.15
};
($var:ident. _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
$var.16
};
($var:ident. _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
$var.17
};
($var:ident. _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
$var.18
};
($var:ident. _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
$var.19
};
($var:ident. _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
$var.20
};
($var:ident. _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
$var.21
};
($var:ident. _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
$var.22
};
($var:ident. _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
$var.23
};
($var:ident. _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
$var.24
};
($var:ident. _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
$var.25
};
($var:ident. _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
$var.26
};
($var:ident. _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
$var.27
};
($var:ident. _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
$var.28
};
($var:ident. _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
$var.29
};
($var:ident. _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
$var.30
};
($var:ident. _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
$var.31
};
($var:ident. _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
$var.32
};
($var:ident. _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
$var.33
};
($var:ident. _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
$var.34
};
($var:ident. _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
$var.35
};
($var:ident. _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
$var.36
};
($var:ident. _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
$var.37
};
($var:ident. _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
$var.38
};
($var:ident. _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
$var.39
};
($var:ident. _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
$var.40
};
($var:ident. _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
$var.41
};
($var:ident. _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
$var.42
};
($var:ident. _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
$var.43
};
($var:ident. _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
$var.44
};
($var:ident. _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
$var.45
};
($var:ident. _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
$var.46
};
($var:ident. _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
$var.47
};
($var:ident. _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
$var.48
};
($var:ident. _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
$var.49
};
($var:ident. _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
$var.50
};
($var:ident. _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
$var.51
};
($var:ident. _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
$var.52
};
($var:ident. _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
$var.53
};
($var:ident. _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
$var.54
};
($var:ident. _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
$var.55
};
($var:ident. _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
$var.56
};
($var:ident. _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
$var.57
};
($var:ident. _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
$var.58
};
($var:ident. _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
$var.59
};
($var:ident. _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
$var.60
};
($var:ident. _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
$var.61
};
($var:ident. _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
$var.62
};
($var:ident. _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
$var.63
};
($var:ident. _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
$var.64
};
}

#[macro_export]
#[doc(hidden)]
macro_rules! select_variant {
Expand Down
8 changes: 8 additions & 0 deletions tokio/tests/macros_select.rs
View file
Original file line number Diff line number Diff line change
Expand Up @@ -709,3 +709,11 @@ async fn select_into_future() {
() = NotAFuture => {},
}
}

// regression test for https://github.com/tokio-rs/tokio/issues/6721
#[tokio::test]
async fn temporary_lifetime_extension() {
tokio::select! {
() = &mut std::future::ready(()) => {},
}
}

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