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.

17 files changed, 342 insertions, 0 deletions

diff --git a/tests/ui/rust-2024/prelude-migration/future-poll-already-future.rs b/tests/ui/rust-2024/prelude-migration/future-poll-already-future.rs
new file mode 100644
index 00000000000..7bf5118c340
--- /dev/null
+++ b/tests/ui/rust-2024/prelude-migration/future-poll-already-future.rs
@@ -0,0 +1,17 @@
+//@ revisions: e2021 e2024
+//@[e2021] edition: 2021
+//@[e2024] edition: 2024
+//@[e2024] compile-flags: -Zunstable-options
+//@ check-pass
+
+#![deny(rust_2024_prelude_collisions)]
+
+use std::future::Future;
+
+fn main() {
+    core::pin::pin!(async {}).poll(&mut context());
+}
+
+fn context() -> core::task::Context<'static> {
+    loop {}
+}
diff --git a/tests/ui/rust-2024/prelude-migration/future-poll-async-block.e2021.fixed b/tests/ui/rust-2024/prelude-migration/future-poll-async-block.e2021.fixed
new file mode 100644
index 00000000000..44850c8c45b
--- /dev/null
+++ b/tests/ui/rust-2024/prelude-migration/future-poll-async-block.e2021.fixed
@@ -0,0 +1,21 @@
+//@ revisions: e2021 e2024
+//@[e2021] edition: 2021
+//@[e2021] run-rustfix
+//@[e2024] edition: 2024
+//@[e2024] compile-flags: -Zunstable-options
+//@[e2024] check-pass
+
+#![deny(rust_2024_prelude_collisions)]
+trait Meow {
+    fn poll(&self, _ctx: &mut core::task::Context<'_>) {}
+}
+impl<T> Meow for T {}
+fn main() {
+    Meow::poll(&core::pin::pin!(async {}), &mut context());
+    //[e2021]~^ ERROR trait method `poll` will become ambiguous in Rust 2024
+    //[e2021]~| WARN this is accepted in the current edition (Rust 2021) but is a hard error in Rust 2024!
+}
+
+fn context() -> core::task::Context<'static> {
+    loop {}
+}
diff --git a/tests/ui/rust-2024/prelude-migration/future-poll-async-block.e2021.stderr b/tests/ui/rust-2024/prelude-migration/future-poll-async-block.e2021.stderr
new file mode 100644
index 00000000000..496b3197c34
--- /dev/null
+++ b/tests/ui/rust-2024/prelude-migration/future-poll-async-block.e2021.stderr
@@ -0,0 +1,16 @@
+error: trait method `poll` will become ambiguous in Rust 2024
+  --> $DIR/future-poll-async-block.rs:14:5
+   |
+LL |     core::pin::pin!(async {}).poll(&mut context());
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: disambiguate the associated function: `Meow::poll(&core::pin::pin!(async {}), &mut context())`
+   |
+   = warning: this is accepted in the current edition (Rust 2021) but is a hard error in Rust 2024!
+   = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2024/prelude.html>
+note: the lint level is defined here
+  --> $DIR/future-poll-async-block.rs:8:9
+   |
+LL | #![deny(rust_2024_prelude_collisions)]
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to 1 previous error
+
diff --git a/tests/ui/rust-2024/prelude-migration/future-poll-async-block.rs b/tests/ui/rust-2024/prelude-migration/future-poll-async-block.rs
new file mode 100644
index 00000000000..614e4c786c5
--- /dev/null
+++ b/tests/ui/rust-2024/prelude-migration/future-poll-async-block.rs
@@ -0,0 +1,21 @@
+//@ revisions: e2021 e2024
+//@[e2021] edition: 2021
+//@[e2021] run-rustfix
+//@[e2024] edition: 2024
+//@[e2024] compile-flags: -Zunstable-options
+//@[e2024] check-pass
+
+#![deny(rust_2024_prelude_collisions)]
+trait Meow {
+    fn poll(&self, _ctx: &mut core::task::Context<'_>) {}
+}
+impl<T> Meow for T {}
+fn main() {
+    core::pin::pin!(async {}).poll(&mut context());
+    //[e2021]~^ ERROR trait method `poll` will become ambiguous in Rust 2024
+    //[e2021]~| WARN this is accepted in the current edition (Rust 2021) but is a hard error in Rust 2024!
+}
+
+fn context() -> core::task::Context<'static> {
+    loop {}
+}
diff --git a/tests/ui/rust-2024/prelude-migration/future-poll-not-future-pinned.e2021.fixed b/tests/ui/rust-2024/prelude-migration/future-poll-not-future-pinned.e2021.fixed
new file mode 100644
index 00000000000..c96d1dcecc2
--- /dev/null
+++ b/tests/ui/rust-2024/prelude-migration/future-poll-not-future-pinned.e2021.fixed
@@ -0,0 +1,21 @@
+//@ revisions: e2021 e2024
+//@[e2021] edition: 2021
+//@[e2021] run-rustfix
+//@[e2024] edition: 2024
+//@[e2024] compile-flags: -Zunstable-options
+//@[e2024] check-pass
+
+#![deny(rust_2024_prelude_collisions)]
+trait Meow {
+    fn poll(&self) {}
+}
+impl<T> Meow for T {}
+fn main() {
+    // This is a deliberate false positive.
+    // While `()` does not implement `Future` and can therefore not be ambiguous, we
+    // do not check that in the lint, as that introduces additional complexities.
+    // Just checking whether the self type is `Pin<&mut _>` is enough.
+    Meow::poll(&core::pin::pin!(()));
+    //[e2021]~^ ERROR trait method `poll` will become ambiguous in Rust 2024
+    //[e2021]~| WARN this is accepted in the current edition (Rust 2021) but is a hard error in Rust 2024!
+}
diff --git a/tests/ui/rust-2024/prelude-migration/future-poll-not-future-pinned.e2021.stderr b/tests/ui/rust-2024/prelude-migration/future-poll-not-future-pinned.e2021.stderr
new file mode 100644
index 00000000000..020a00ccdec
--- /dev/null
+++ b/tests/ui/rust-2024/prelude-migration/future-poll-not-future-pinned.e2021.stderr
@@ -0,0 +1,16 @@
+error: trait method `poll` will become ambiguous in Rust 2024
+  --> $DIR/future-poll-not-future-pinned.rs:18:5
+   |
+LL |     core::pin::pin!(()).poll();
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^ help: disambiguate the associated function: `Meow::poll(&core::pin::pin!(()))`
+   |
+   = warning: this is accepted in the current edition (Rust 2021) but is a hard error in Rust 2024!
+   = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2024/prelude.html>
+note: the lint level is defined here
+  --> $DIR/future-poll-not-future-pinned.rs:8:9
+   |
+LL | #![deny(rust_2024_prelude_collisions)]
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to 1 previous error
+
diff --git a/tests/ui/rust-2024/prelude-migration/future-poll-not-future-pinned.rs b/tests/ui/rust-2024/prelude-migration/future-poll-not-future-pinned.rs
new file mode 100644
index 00000000000..21b170a5f1d
--- /dev/null
+++ b/tests/ui/rust-2024/prelude-migration/future-poll-not-future-pinned.rs
@@ -0,0 +1,21 @@
+//@ revisions: e2021 e2024
+//@[e2021] edition: 2021
+//@[e2021] run-rustfix
+//@[e2024] edition: 2024
+//@[e2024] compile-flags: -Zunstable-options
+//@[e2024] check-pass
+
+#![deny(rust_2024_prelude_collisions)]
+trait Meow {
+    fn poll(&self) {}
+}
+impl<T> Meow for T {}
+fn main() {
+    // This is a deliberate false positive.
+    // While `()` does not implement `Future` and can therefore not be ambiguous, we
+    // do not check that in the lint, as that introduces additional complexities.
+    // Just checking whether the self type is `Pin<&mut _>` is enough.
+    core::pin::pin!(()).poll();
+    //[e2021]~^ ERROR trait method `poll` will become ambiguous in Rust 2024
+    //[e2021]~| WARN this is accepted in the current edition (Rust 2021) but is a hard error in Rust 2024!
+}
diff --git a/tests/ui/rust-2024/prelude-migration/future-poll-not-future.rs b/tests/ui/rust-2024/prelude-migration/future-poll-not-future.rs
new file mode 100644
index 00000000000..899b69ebfc2
--- /dev/null
+++ b/tests/ui/rust-2024/prelude-migration/future-poll-not-future.rs
@@ -0,0 +1,15 @@
+//@ revisions: e2021 e2024
+//@[e2021] edition: 2021
+//@[e2024] edition: 2024
+//@[e2024] compile-flags: -Zunstable-options
+//@ check-pass
+
+#![deny(rust_2024_prelude_collisions)]
+trait Meow {
+    fn poll(&self) {}
+}
+impl<T> Meow for T {}
+fn main() {
+    // As the self type here is not `Pin<&mut _>`, the lint does not fire.
+    ().poll();
+}
diff --git a/tests/ui/rust-2024/prelude-migration/in_2024_compatibility.rs b/tests/ui/rust-2024/prelude-migration/in_2024_compatibility.rs
new file mode 100644
index 00000000000..b6a5d278720
--- /dev/null
+++ b/tests/ui/rust-2024/prelude-migration/in_2024_compatibility.rs
@@ -0,0 +1,17 @@
+//@ edition: 2021
+
+#![deny(rust_2024_compatibility)]
+
+trait Meow {
+    fn poll(&self, _ctx: &mut core::task::Context<'_>) {}
+}
+impl<T> Meow for T {}
+fn main() {
+    core::pin::pin!(async {}).poll(&mut context());
+    //~^ ERROR trait method `poll` will become ambiguous in Rust 2024
+    //~| WARN this is accepted in the current edition (Rust 2021) but is a hard error in Rust 2024!
+}
+
+fn context() -> core::task::Context<'static> {
+    loop {}
+}
diff --git a/tests/ui/rust-2024/prelude-migration/in_2024_compatibility.stderr b/tests/ui/rust-2024/prelude-migration/in_2024_compatibility.stderr
new file mode 100644
index 00000000000..5865029d65d
--- /dev/null
+++ b/tests/ui/rust-2024/prelude-migration/in_2024_compatibility.stderr
@@ -0,0 +1,17 @@
+error: trait method `poll` will become ambiguous in Rust 2024
+  --> $DIR/in_2024_compatibility.rs:10:5
+   |
+LL |     core::pin::pin!(async {}).poll(&mut context());
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: disambiguate the associated function: `Meow::poll(&core::pin::pin!(async {}), &mut context())`
+   |
+   = warning: this is accepted in the current edition (Rust 2021) but is a hard error in Rust 2024!
+   = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2024/prelude.html>
+note: the lint level is defined here
+  --> $DIR/in_2024_compatibility.rs:3:9
+   |
+LL | #![deny(rust_2024_compatibility)]
+   |         ^^^^^^^^^^^^^^^^^^^^^^^
+   = note: `#[deny(rust_2024_prelude_collisions)]` implied by `#[deny(rust_2024_compatibility)]`
+
+error: aborting due to 1 previous error
+
diff --git a/tests/ui/rust-2024/prelude-migration/into-future-adt.e2021.fixed b/tests/ui/rust-2024/prelude-migration/into-future-adt.e2021.fixed
new file mode 100644
index 00000000000..0b0873eb238
--- /dev/null
+++ b/tests/ui/rust-2024/prelude-migration/into-future-adt.e2021.fixed
@@ -0,0 +1,29 @@
+//@ revisions: e2021 e2024
+//@[e2021] edition: 2021
+//@[e2021] run-rustfix
+//@[e2024] edition: 2024
+//@[e2024] compile-flags: -Zunstable-options
+//@[e2024] check-pass
+
+#![deny(rust_2024_prelude_collisions)]
+trait Meow {
+    fn into_future(&self) {}
+}
+impl Meow for Cat {}
+
+struct Cat;
+
+impl core::future::IntoFuture for Cat {
+    type Output = ();
+    type IntoFuture = core::future::Ready<()>;
+
+    fn into_future(self) -> Self::IntoFuture {
+        core::future::ready(())
+    }
+}
+
+fn main() {
+    Meow::into_future(&Cat);
+    //[e2021]~^ ERROR trait method `into_future` will become ambiguous in Rust 2024
+    //[e2021]~| WARN this is accepted in the current edition (Rust 2021) but is a hard error in Rust 2024!
+}
diff --git a/tests/ui/rust-2024/prelude-migration/into-future-adt.e2021.stderr b/tests/ui/rust-2024/prelude-migration/into-future-adt.e2021.stderr
new file mode 100644
index 00000000000..b74e80e2a4a
--- /dev/null
+++ b/tests/ui/rust-2024/prelude-migration/into-future-adt.e2021.stderr
@@ -0,0 +1,16 @@
+error: trait method `into_future` will become ambiguous in Rust 2024
+  --> $DIR/into-future-adt.rs:26:5
+   |
+LL |     Cat.into_future();
+   |     ^^^^^^^^^^^^^^^^^ help: disambiguate the associated function: `Meow::into_future(&Cat)`
+   |
+   = warning: this is accepted in the current edition (Rust 2021) but is a hard error in Rust 2024!
+   = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2024/prelude.html>
+note: the lint level is defined here
+  --> $DIR/into-future-adt.rs:8:9
+   |
+LL | #![deny(rust_2024_prelude_collisions)]
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to 1 previous error
+
diff --git a/tests/ui/rust-2024/prelude-migration/into-future-adt.rs b/tests/ui/rust-2024/prelude-migration/into-future-adt.rs
new file mode 100644
index 00000000000..0db70930bc7
--- /dev/null
+++ b/tests/ui/rust-2024/prelude-migration/into-future-adt.rs
@@ -0,0 +1,29 @@
+//@ revisions: e2021 e2024
+//@[e2021] edition: 2021
+//@[e2021] run-rustfix
+//@[e2024] edition: 2024
+//@[e2024] compile-flags: -Zunstable-options
+//@[e2024] check-pass
+
+#![deny(rust_2024_prelude_collisions)]
+trait Meow {
+    fn into_future(&self) {}
+}
+impl Meow for Cat {}
+
+struct Cat;
+
+impl core::future::IntoFuture for Cat {
+    type Output = ();
+    type IntoFuture = core::future::Ready<()>;
+
+    fn into_future(self) -> Self::IntoFuture {
+        core::future::ready(())
+    }
+}
+
+fn main() {
+    Cat.into_future();
+    //[e2021]~^ ERROR trait method `into_future` will become ambiguous in Rust 2024
+    //[e2021]~| WARN this is accepted in the current edition (Rust 2021) but is a hard error in Rust 2024!
+}
diff --git a/tests/ui/rust-2024/prelude-migration/into-future-already-into-future.rs b/tests/ui/rust-2024/prelude-migration/into-future-already-into-future.rs
new file mode 100644
index 00000000000..6bc2ea31705
--- /dev/null
+++ b/tests/ui/rust-2024/prelude-migration/into-future-already-into-future.rs
@@ -0,0 +1,24 @@
+//@ revisions: e2021 e2024
+//@[e2021] edition: 2021
+//@[e2024] edition: 2024
+//@[e2024] compile-flags: -Zunstable-options
+//@ check-pass
+
+#![deny(rust_2024_prelude_collisions)]
+
+use core::future::IntoFuture;
+
+struct Cat;
+
+impl IntoFuture for Cat {
+    type Output = ();
+    type IntoFuture = core::future::Ready<()>;
+
+    fn into_future(self) -> Self::IntoFuture {
+        core::future::ready(())
+    }
+}
+
+fn main() {
+    let _ = Cat.into_future();
+}
diff --git a/tests/ui/rust-2024/prelude-migration/into-future-not-into-future.e2021.fixed b/tests/ui/rust-2024/prelude-migration/into-future-not-into-future.e2021.fixed
new file mode 100644
index 00000000000..a798014d93d
--- /dev/null
+++ b/tests/ui/rust-2024/prelude-migration/into-future-not-into-future.e2021.fixed
@@ -0,0 +1,23 @@
+//@ revisions: e2021 e2024
+//@[e2021] edition: 2021
+//@[e2021] run-rustfix
+//@[e2024] edition: 2024
+//@[e2024] compile-flags: -Zunstable-options
+//@[e2024] check-pass
+
+#![deny(rust_2024_prelude_collisions)]
+trait Meow {
+    fn into_future(&self) {}
+}
+impl Meow for Cat {}
+
+struct Cat;
+
+fn main() {
+    // This is a false positive, but it should be rare enough to not matter, and checking whether
+    // it implements the trait can have other nontrivial consequences, so it was decided to accept
+    // this.
+    Meow::into_future(&Cat);
+    //[e2021]~^ ERROR trait method `into_future` will become ambiguous in Rust 2024
+    //[e2021]~| WARN this is accepted in the current edition (Rust 2021) but is a hard error in Rust 2024!
+}
diff --git a/tests/ui/rust-2024/prelude-migration/into-future-not-into-future.e2021.stderr b/tests/ui/rust-2024/prelude-migration/into-future-not-into-future.e2021.stderr
new file mode 100644
index 00000000000..6ea4580ca72
--- /dev/null
+++ b/tests/ui/rust-2024/prelude-migration/into-future-not-into-future.e2021.stderr
@@ -0,0 +1,16 @@
+error: trait method `into_future` will become ambiguous in Rust 2024
+  --> $DIR/into-future-not-into-future.rs:20:5
+   |
+LL |     Cat.into_future();
+   |     ^^^^^^^^^^^^^^^^^ help: disambiguate the associated function: `Meow::into_future(&Cat)`
+   |
+   = warning: this is accepted in the current edition (Rust 2021) but is a hard error in Rust 2024!
+   = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2024/prelude.html>
+note: the lint level is defined here
+  --> $DIR/into-future-not-into-future.rs:8:9
+   |
+LL | #![deny(rust_2024_prelude_collisions)]
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to 1 previous error
+
diff --git a/tests/ui/rust-2024/prelude-migration/into-future-not-into-future.rs b/tests/ui/rust-2024/prelude-migration/into-future-not-into-future.rs
new file mode 100644
index 00000000000..23e81cfe6b4
--- /dev/null
+++ b/tests/ui/rust-2024/prelude-migration/into-future-not-into-future.rs
@@ -0,0 +1,23 @@
+//@ revisions: e2021 e2024
+//@[e2021] edition: 2021
+//@[e2021] run-rustfix
+//@[e2024] edition: 2024
+//@[e2024] compile-flags: -Zunstable-options
+//@[e2024] check-pass
+
+#![deny(rust_2024_prelude_collisions)]
+trait Meow {
+    fn into_future(&self) {}
+}
+impl Meow for Cat {}
+
+struct Cat;
+
+fn main() {
+    // This is a false positive, but it should be rare enough to not matter, and checking whether
+    // it implements the trait can have other nontrivial consequences, so it was decided to accept
+    // this.
+    Cat.into_future();
+    //[e2021]~^ ERROR trait method `into_future` will become ambiguous in Rust 2024
+    //[e2021]~| WARN this is accepted in the current edition (Rust 2021) but is a hard error in Rust 2024!
+}