Adjust the method ambiguity lint too

compiler/rustc_hir_typeck/src/method/mod.rs

@@ -3,7 +3,7 @@
 //! [rustc dev guide]: https://rustc-dev-guide.rust-lang.org/method-lookup.html
 
 mod confirm;
-mod prelude2021;
+mod prelude_edition_lints;
 pub mod probe;
 mod suggest;
 
@@ -186,7 +186,9 @@ pub fn lookup_method(
         let pick =
             self.lookup_probe(segment.ident, self_ty, call_expr, ProbeScope::TraitsInScope)?;
 
-        self.lint_dot_call_from_2018(self_ty, segment, span, call_expr, self_expr, &pick, args);
+        self.lint_edition_dependent_dot_call(
+            self_ty, segment, span, call_expr, self_expr, &pick, args,
+        );
 
         for &import_id in &pick.import_ids {
             debug!("used_trait_import: {:?}", import_id);

compiler/rustc_hir_typeck/src/method/prelude_edition_lints.rs

@@ -1,12 +1,12 @@
-use crate::{
-    method::probe::{self, Pick},
-    FnCtxt,
-};
+use crate::method::probe::{self, Pick};
+use crate::FnCtxt;
+
 use hir::def_id::DefId;
 use hir::HirId;
 use hir::ItemKind;
 use rustc_errors::Applicability;
 use rustc_hir as hir;
+use rustc_lint::{ARRAY_INTO_ITER, BOXED_SLICE_INTO_ITER};
 use rustc_middle::span_bug;
 use rustc_middle::ty::{self, Ty};
 use rustc_session::lint::builtin::RUST_2021_PRELUDE_COLLISIONS;
@@ -17,7 +17,7 @@
 use std::fmt::Write;
 
 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
-    pub(super) fn lint_dot_call_from_2018(
+    pub(super) fn lint_edition_dependent_dot_call(
         &self,
         self_ty: Ty<'tcx>,
         segment: &hir::PathSegment<'_>,
@@ -32,22 +32,32 @@ pub(super) fn lint_dot_call_from_2018(
             segment.ident, self_ty, call_expr, self_expr
         );
 
-        // Rust 2021 and later is already using the new prelude
-        if span.at_least_rust_2021() {
-            return;
-        }
-
-        let prelude_or_array_lint = match segment.ident.name {
+        let (prelude_or_array_lint, edition) = match segment.ident.name {
             // `try_into` was added to the prelude in Rust 2021.
-            sym::try_into => RUST_2021_PRELUDE_COLLISIONS,
+            sym::try_into if !span.at_least_rust_2021() => (RUST_2021_PRELUDE_COLLISIONS, "2021"),
             // `into_iter` wasn't added to the prelude,
             // but `[T; N].into_iter()` doesn't resolve to IntoIterator::into_iter
             // before Rust 2021, which results in the same problem.
             // It is only a problem for arrays.
-            sym::into_iter if let ty::Array(..) = self_ty.kind() => {
-                // In this case, it wasn't really a prelude addition that was the problem.
-                // Instead, the problem is that the array-into_iter hack will no longer apply in Rust 2021.
-                rustc_lint::ARRAY_INTO_ITER
+            sym::into_iter => {
+                if let ty::Array(..) = self_ty.kind()
+                    && !span.at_least_rust_2021()
+                {
+                    // In this case, it wasn't really a prelude addition that was the problem.
+                    // Instead, the problem is that the array-into_iter hack will no longer
+                    // apply in Rust 2021.
+                    (ARRAY_INTO_ITER, "2021")
+                } else if self_ty.is_box()
+                    && self_ty.boxed_ty().is_slice()
+                    && !span.at_least_rust_2024()
+                {
+                    // In this case, it wasn't really a prelude addition that was the problem.
+                    // Instead, the problem is that the boxed-slice-into_iter hack will no
+                    // longer apply in Rust 2024.
+                    (BOXED_SLICE_INTO_ITER, "2024")
+                } else {
+                    return;
+                }
             }
             _ => return,
         };
@@ -81,7 +91,10 @@ pub(super) fn lint_dot_call_from_2018(
                 prelude_or_array_lint,
                 self_expr.hir_id,
                 self_expr.span,
-                format!("trait method `{}` will become ambiguous in Rust 2021", segment.ident.name),
+                format!(
+                    "trait method `{}` will become ambiguous in Rust {edition}",
+                    segment.ident.name
+                ),
                 |lint| {
                     let sp = self_expr.span;
 
@@ -131,7 +144,10 @@ pub(super) fn lint_dot_call_from_2018(
                 prelude_or_array_lint,
                 call_expr.hir_id,
                 call_expr.span,
-                format!("trait method `{}` will become ambiguous in Rust 2021", segment.ident.name),
+                format!(
+                    "trait method `{}` will become ambiguous in Rust {edition}",
+                    segment.ident.name
+                ),
                 |lint| {
                     let sp = call_expr.span;
                     let trait_name = self.trait_path_or_bare_name(

compiler/rustc_lint/src/lib.rs

@@ -81,7 +81,7 @@
 mod unit_bindings;
 mod unused;
 
-pub use shadowed_into_iter::ARRAY_INTO_ITER;
+pub use shadowed_into_iter::{ARRAY_INTO_ITER, BOXED_SLICE_INTO_ITER};
 
 use rustc_hir::def_id::LocalModDefId;
 use rustc_middle::query::Providers;

tests/ui/rust-2024/box-slice-into-iter-ambiguous.fixed

@@ -0,0 +1,27 @@
+// See https://github.com/rust-lang/rust/issues/88475
+//@ run-rustfix
+//@ edition:2021
+//@ check-pass
+#![warn(boxed_slice_into_iter)]
+#![allow(unused)]
+
+struct FooIter;
+
+trait MyIntoIter {
+    fn into_iter(self) -> FooIter;
+}
+
+impl<T> MyIntoIter for Box<[T]> {
+    fn into_iter(self) -> FooIter {
+        FooIter
+    }
+}
+
+struct Point;
+
+pub fn main() {
+    let points: Box<[_]> = vec![Point].into_boxed_slice();
+    let y = MyIntoIter::into_iter(points);
+    //~^ WARNING trait method `into_iter` will become ambiguous in Rust 2024
+    //~| WARNING this changes meaning in Rust 2024
+}

tests/ui/rust-2024/box-slice-into-iter-ambiguous.rs

@@ -0,0 +1,27 @@
+// See https://github.com/rust-lang/rust/issues/88475
+//@ run-rustfix
+//@ edition:2021
+//@ check-pass
+#![warn(boxed_slice_into_iter)]
+#![allow(unused)]
+
+struct FooIter;
+
+trait MyIntoIter {
+    fn into_iter(self) -> FooIter;
+}
+
+impl<T> MyIntoIter for Box<[T]> {
+    fn into_iter(self) -> FooIter {
+        FooIter
+    }
+}
+
+struct Point;
+
+pub fn main() {
+    let points: Box<[_]> = vec![Point].into_boxed_slice();
+    let y = points.into_iter();
+    //~^ WARNING trait method `into_iter` will become ambiguous in Rust 2024
+    //~| WARNING this changes meaning in Rust 2024
+}

tests/ui/rust-2024/box-slice-into-iter-ambiguous.stderr

@@ -0,0 +1,15 @@
+warning: trait method `into_iter` will become ambiguous in Rust 2024
+  --> $DIR/box-slice-into-iter-ambiguous.rs:24:13
+   |
+LL |     let y = points.into_iter();
+   |             ^^^^^^^^^^^^^^^^^^ help: disambiguate the associated function: `MyIntoIter::into_iter(points)`
+   |
+   = warning: this changes meaning in Rust 2024
+note: the lint level is defined here
+  --> $DIR/box-slice-into-iter-ambiguous.rs:5:9
+   |
+LL | #![warn(boxed_slice_into_iter)]
+   |         ^^^^^^^^^^^^^^^^^^^^^
+
+warning: 1 warning emitted
+