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Add migration lint for 2024 prelude additions
This adds the migration lint for the newly ambiguous methods `poll` and `into_future`. When these methods are used on types implementing the respective traits, it will be ambiguous in the future, which can lead to hard errors or behavior changes depending on the exact circumstances.
1 parent a83cf56 commit 0f46870

15 files changed

+266
-1
lines changed

‎compiler/rustc_hir/src/lang_items.rs

+1
Original file line numberDiff line numberDiff line change
@@ -239,6 +239,7 @@ language_item_table! {
239239

240240
Iterator, sym::iterator, iterator_trait, Target::Trait, GenericRequirement::Exact(0);
241241
FusedIterator, sym::fused_iterator, fused_iterator_trait, Target::Trait, GenericRequirement::Exact(0);
242+
IntoFuture, sym::into_future_trait, into_future_trait, Target::Trait, GenericRequirement::None;
242243
Future, sym::future_trait, future_trait, Target::Trait, GenericRequirement::Exact(0);
243244
FutureOutput, sym::future_output, future_output, Target::AssocTy, GenericRequirement::Exact(0);
244245
AsyncIterator, sym::async_iterator, async_iterator_trait, Target::Trait, GenericRequirement::Exact(0);

‎compiler/rustc_hir_typeck/src/method/prelude_edition_lints.rs

+21-1
Original file line numberDiff line numberDiff line change
@@ -9,7 +9,7 @@ use rustc_hir as hir;
99
use rustc_lint::{ARRAY_INTO_ITER, BOXED_SLICE_INTO_ITER};
1010
use rustc_middle::span_bug;
1111
use rustc_middle::ty::{self, Ty};
12-
use rustc_session::lint::builtin::RUST_2021_PRELUDE_COLLISIONS;
12+
use rustc_session::lint::builtin::{RUST_2021_PRELUDE_COLLISIONS, RUST_2024_PRELUDE_COLLISIONS};
1313
use rustc_span::symbol::kw::{Empty, Underscore};
1414
use rustc_span::symbol::{sym, Ident};
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use rustc_span::Span;
@@ -35,6 +35,26 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
3535
let (prelude_or_array_lint, edition) = match segment.ident.name {
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// `try_into` was added to the prelude in Rust 2021.
3737
sym::try_into if !span.at_least_rust_2021() => (RUST_2021_PRELUDE_COLLISIONS, "2021"),
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sym::poll
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if !span.at_least_rust_2024()
40+
&& let Some(future) = self.tcx.lang_items().future_trait()
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&& self
42+
.infcx
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.type_implements_trait(future, [self_ty], self.param_env)
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.may_apply() =>
45+
{
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(RUST_2024_PRELUDE_COLLISIONS, "2024")
47+
}
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sym::into_future
49+
if !span.at_least_rust_2024()
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&& let Some(into_future) = self.tcx.lang_items().into_future_trait()
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&& self
52+
.infcx
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.type_implements_trait(into_future, [self_ty], self.param_env)
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.may_apply() =>
55+
{
56+
(RUST_2024_PRELUDE_COLLISIONS, "2024")
57+
}
3858
// `into_iter` wasn't added to the prelude,
3959
// but `[T; N].into_iter()` doesn't resolve to IntoIterator::into_iter
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// before Rust 2021, which results in the same problem.

‎compiler/rustc_lint_defs/src/builtin.rs

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@@ -89,6 +89,7 @@ declare_lint_pass! {
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RUST_2021_PREFIXES_INCOMPATIBLE_SYNTAX,
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RUST_2021_PRELUDE_COLLISIONS,
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RUST_2024_INCOMPATIBLE_PAT,
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RUST_2024_PRELUDE_COLLISIONS,
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SELF_CONSTRUCTOR_FROM_OUTER_ITEM,
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SEMICOLON_IN_EXPRESSIONS_FROM_MACROS,
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SINGLE_USE_LIFETIMES,
@@ -3841,6 +3842,46 @@ declare_lint! {
38413842
};
38423843
}
38433844

3845+
declare_lint! {
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/// The `rust_2024_prelude_collisions` lint detects the usage of trait methods which are ambiguous
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/// with traits added to the prelude in future editions.
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///
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/// ### Example
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///
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/// ```rust,edition2021,compile_fail
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/// #![deny(rust_2024_prelude_collisions)]
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/// trait Meow {
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/// fn poll(&self) {}
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/// }
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/// impl<T> Meow for T {}
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///
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/// fn main() {
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/// core::pin::pin!(async {}).poll();
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/// // ^^^^^^^^
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/// // This call to try_into matches both Future::poll and Meow::poll as
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/// // `Future` has been added to the Rust prelude in 2024 edition.
3863+
/// }
3864+
/// ```
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///
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/// {{produces}}
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///
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/// ### Explanation
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///
3870+
/// Rust 2024, introduces two new additions to the standard library's prelude,
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/// `Future` and `IntoFuture`. This results in an ambiguity as to which method/function
3872+
/// to call when an existing `poll`/`into_future` method is called via dot-call syntax or
3873+
/// a `poll`/`into_future` associated function is called directly on a type.
3874+
///
3875+
pub RUST_2024_PRELUDE_COLLISIONS,
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Allow,
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"detects the usage of trait methods which are ambiguous with traits added to the \
3878+
prelude in future editions",
3879+
@future_incompatible = FutureIncompatibleInfo {
3880+
reason: FutureIncompatibilityReason::EditionError(Edition::Edition2024),
3881+
reference: "<https://doc.rust-lang.org/nightly/edition-guide/rust-2024/prelude.html>",
3882+
};
3883+
}
3884+
38443885
declare_lint! {
38453886
/// The `rust_2021_prefixes_incompatible_syntax` lint detects identifiers that will be parsed as a
38463887
/// prefix instead in Rust 2021.

‎compiler/rustc_span/src/symbol.rs

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@@ -1023,6 +1023,7 @@ symbols! {
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integral,
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into_async_iter_into_iter,
10251025
into_future,
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into_future_trait,
10261027
into_iter,
10271028
intra_doc_pointers,
10281029
intrinsics,

‎library/core/src/future/into_future.rs

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@@ -105,6 +105,7 @@ use crate::future::Future;
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message = "`{Self}` is not a future",
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note = "{Self} must be a future or must implement `IntoFuture` to be awaited"
107107
)]
108+
#[cfg_attr(not(bootstrap), lang = "into_future_trait")]
108109
pub trait IntoFuture {
109110
/// The output that the future will produce on completion.
110111
#[stable(feature = "into_future", since = "1.64.0")]

‎tests/ui/rust-2024/prelude-migration/future-poll-already-future.rs

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@@ -0,0 +1,17 @@
1+
//@ revisions: e2021 e2024
2+
//@[e2021] edition: 2021
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//@[e2024] edition: 2024
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//@[e2024] compile-flags: -Zunstable-options
5+
//@ check-pass
6+
7+
#![deny(rust_2024_prelude_collisions)]
8+
9+
use std::future::Future;
10+
11+
fn main() {
12+
core::pin::pin!(async {}).poll(&mut context());
13+
}
14+
15+
fn context() -> core::task::Context<'static> {
16+
loop {}
17+
}

‎tests/ui/rust-2024/prelude-migration/future-poll-async-block.e2021.fixed

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@@ -0,0 +1,21 @@
1+
//@ revisions: e2021 e2024
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//@[e2021] edition: 2021
3+
//@[e2021] run-rustfix
4+
//@[e2024] edition: 2024
5+
//@[e2024] compile-flags: -Zunstable-options
6+
//@[e2024] check-pass
7+
8+
#![deny(rust_2024_prelude_collisions)]
9+
trait Meow {
10+
fn poll(&self, _ctx: &mut core::task::Context<'_>) {}
11+
}
12+
impl<T> Meow for T {}
13+
fn main() {
14+
Meow::poll(&core::pin::pin!(async {}), &mut context());
15+
//[e2021]~^ ERROR trait method `poll` will become ambiguous in Rust 2024
16+
//[e2021]~| WARN this is accepted in the current edition (Rust 2021) but is a hard error in Rust 2024!
17+
}
18+
19+
fn context() -> core::task::Context<'static> {
20+
loop {}
21+
}

‎tests/ui/rust-2024/prelude-migration/future-poll-async-block.e2021.stderr

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@@ -0,0 +1,16 @@
1+
error: trait method `poll` will become ambiguous in Rust 2024
2+
--> $DIR/future-poll-async-block.rs:14:5
3+
|
4+
LL | core::pin::pin!(async {}).poll(&mut context());
5+
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: disambiguate the associated function: `Meow::poll(&core::pin::pin!(async {}), &mut context())`
6+
|
7+
= warning: this is accepted in the current edition (Rust 2021) but is a hard error in Rust 2024!
8+
= note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2024/prelude.html>
9+
note: the lint level is defined here
10+
--> $DIR/future-poll-async-block.rs:8:9
11+
|
12+
LL | #![deny(rust_2024_prelude_collisions)]
13+
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
14+
15+
error: aborting due to 1 previous error
16+

‎tests/ui/rust-2024/prelude-migration/future-poll-async-block.rs

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@@ -0,0 +1,21 @@
1+
//@ revisions: e2021 e2024
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//@[e2021] edition: 2021
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//@[e2021] run-rustfix
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//@[e2024] edition: 2024
5+
//@[e2024] compile-flags: -Zunstable-options
6+
//@[e2024] check-pass
7+
8+
#![deny(rust_2024_prelude_collisions)]
9+
trait Meow {
10+
fn poll(&self, _ctx: &mut core::task::Context<'_>) {}
11+
}
12+
impl<T> Meow for T {}
13+
fn main() {
14+
core::pin::pin!(async {}).poll(&mut context());
15+
//[e2021]~^ ERROR trait method `poll` will become ambiguous in Rust 2024
16+
//[e2021]~| WARN this is accepted in the current edition (Rust 2021) but is a hard error in Rust 2024!
17+
}
18+
19+
fn context() -> core::task::Context<'static> {
20+
loop {}
21+
}

‎tests/ui/rust-2024/prelude-migration/future-poll-not-future.rs

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@@ -0,0 +1,14 @@
1+
//@ revisions: e2021 e2024
2+
//@[e2021] edition: 2021
3+
//@[e2024] edition: 2024
4+
//@[e2024] compile-flags: -Zunstable-options
5+
//@ check-pass
6+
7+
#![deny(rust_2024_prelude_collisions)]
8+
trait Meow {
9+
fn poll(&self) {}
10+
}
11+
impl<T> Meow for T {}
12+
fn main() {
13+
core::pin::pin!(()).poll();
14+
}

‎tests/ui/rust-2024/prelude-migration/into-future-adt.e2021.fixed

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Original file line numberDiff line numberDiff line change
@@ -0,0 +1,29 @@
1+
//@ revisions: e2021 e2024
2+
//@[e2021] edition: 2021
3+
//@[e2021] run-rustfix
4+
//@[e2024] edition: 2024
5+
//@[e2024] compile-flags: -Zunstable-options
6+
//@[e2024] check-pass
7+
8+
#![deny(rust_2024_prelude_collisions)]
9+
trait Meow {
10+
fn into_future(&self) {}
11+
}
12+
impl Meow for Cat {}
13+
14+
struct Cat;
15+
16+
impl core::future::IntoFuture for Cat {
17+
type Output = ();
18+
type IntoFuture = core::future::Ready<()>;
19+
20+
fn into_future(self) -> Self::IntoFuture {
21+
core::future::ready(())
22+
}
23+
}
24+
25+
fn main() {
26+
Meow::into_future(&Cat);
27+
//[e2021]~^ ERROR trait method `into_future` will become ambiguous in Rust 2024
28+
//[e2021]~| WARN this is accepted in the current edition (Rust 2021) but is a hard error in Rust 2024!
29+
}

‎tests/ui/rust-2024/prelude-migration/into-future-adt.e2021.stderr

+16
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@@ -0,0 +1,16 @@
1+
error: trait method `into_future` will become ambiguous in Rust 2024
2+
--> $DIR/into-future-adt.rs:26:5
3+
|
4+
LL | Cat.into_future();
5+
| ^^^^^^^^^^^^^^^^^ help: disambiguate the associated function: `Meow::into_future(&Cat)`
6+
|
7+
= warning: this is accepted in the current edition (Rust 2021) but is a hard error in Rust 2024!
8+
= note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2024/prelude.html>
9+
note: the lint level is defined here
10+
--> $DIR/into-future-adt.rs:8:9
11+
|
12+
LL | #![deny(rust_2024_prelude_collisions)]
13+
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
14+
15+
error: aborting due to 1 previous error
16+

‎tests/ui/rust-2024/prelude-migration/into-future-adt.rs

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@@ -0,0 +1,29 @@
1+
//@ revisions: e2021 e2024
2+
//@[e2021] edition: 2021
3+
//@[e2021] run-rustfix
4+
//@[e2024] edition: 2024
5+
//@[e2024] compile-flags: -Zunstable-options
6+
//@[e2024] check-pass
7+
8+
#![deny(rust_2024_prelude_collisions)]
9+
trait Meow {
10+
fn into_future(&self) {}
11+
}
12+
impl Meow for Cat {}
13+
14+
struct Cat;
15+
16+
impl core::future::IntoFuture for Cat {
17+
type Output = ();
18+
type IntoFuture = core::future::Ready<()>;
19+
20+
fn into_future(self) -> Self::IntoFuture {
21+
core::future::ready(())
22+
}
23+
}
24+
25+
fn main() {
26+
Cat.into_future();
27+
//[e2021]~^ ERROR trait method `into_future` will become ambiguous in Rust 2024
28+
//[e2021]~| WARN this is accepted in the current edition (Rust 2021) but is a hard error in Rust 2024!
29+
}

‎tests/ui/rust-2024/prelude-migration/into-future-already-into-future.rs

+24
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@@ -0,0 +1,24 @@
1+
//@ revisions: e2021 e2024
2+
//@[e2021] edition: 2021
3+
//@[e2024] edition: 2024
4+
//@[e2024] compile-flags: -Zunstable-options
5+
//@ check-pass
6+
7+
#![deny(rust_2024_prelude_collisions)]
8+
9+
use core::future::IntoFuture;
10+
11+
struct Cat;
12+
13+
impl IntoFuture for Cat {
14+
type Output = ();
15+
type IntoFuture = core::future::Ready<()>;
16+
17+
fn into_future(self) -> Self::IntoFuture {
18+
core::future::ready(())
19+
}
20+
}
21+
22+
fn main() {
23+
let _ = Cat.into_future();
24+
}

‎tests/ui/rust-2024/prelude-migration/into-future-not-into-future.rs

+14
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@@ -0,0 +1,14 @@
1+
//@ revisions: e2021 e2024
2+
//@[e2021] edition: 2021
3+
//@[e2024] edition: 2024
4+
//@[e2024] compile-flags: -Zunstable-options
5+
//@ check-pass
6+
7+
#![deny(rust_2024_prelude_collisions)]
8+
trait Meow {
9+
fn poll(&self) {}
10+
}
11+
impl<T> Meow for T {}
12+
fn main() {
13+
core::pin::pin!(()).poll();
14+
}

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