rust-lang · compiler-errors · Mar 12, 2025 · Mar 12, 2025 · Mar 12, 2025
diff --git a/compiler/rustc_ast_lowering/src/lib.rs b/compiler/rustc_ast_lowering/src/lib.rs
@@ -954,17 +954,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                                 }
                             }
                         };
-                        let mut err = self.dcx().create_err(err);
-                        if !self.tcx.features().return_type_notation()
-                            && self.tcx.sess.is_nightly_build()
-                        {
-                            add_feature_diagnostics(
-                                &mut err,
-                                &self.tcx.sess,
-                                sym::return_type_notation,
-                            );
-                        }
-                        err.emit();
+                        self.dcx().emit_err(err);
                         GenericArgsCtor {
                             args: Default::default(),
                             constraints: &[],

diff --git a/compiler/rustc_ast_lowering/src/path.rs b/compiler/rustc_ast_lowering/src/path.rs
@@ -6,7 +6,6 @@ use rustc_hir::GenericArg;
 use rustc_hir::def::{DefKind, PartialRes, Res};
 use rustc_hir::def_id::DefId;
 use rustc_middle::span_bug;
-use rustc_session::parse::add_feature_diagnostics;
 use rustc_span::{BytePos, DUMMY_SP, DesugaringKind, Ident, Span, Symbol, kw, sym};
 use smallvec::{SmallVec, smallvec};
 use tracing::{debug, instrument};
@@ -287,17 +286,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                                 }
                             }
                         };
-                        let mut err = self.dcx().create_err(err);
-                        if !self.tcx.features().return_type_notation()
-                            && self.tcx.sess.is_nightly_build()
-                        {
-                            add_feature_diagnostics(
-                                &mut err,
-                                &self.tcx.sess,
-                                sym::return_type_notation,
-                            );
-                        }
-                        err.emit();
+                        self.dcx().emit_err(err);
                         (
                             GenericArgsCtor {
                                 args: Default::default(),

diff --git a/compiler/rustc_ast_passes/src/feature_gate.rs b/compiler/rustc_ast_passes/src/feature_gate.rs
@@ -498,7 +498,6 @@ pub fn check_crate(krate: &ast::Crate, sess: &Session, features: &Features) {
     gate_all!(postfix_match, "postfix match is experimental");
     gate_all!(mut_ref, "mutable by-reference bindings are experimental");
     gate_all!(global_registration, "global registration is experimental");
-    gate_all!(return_type_notation, "return type notation is experimental");
     gate_all!(pin_ergonomics, "pinned reference syntax is experimental");
     gate_all!(unsafe_fields, "`unsafe` fields are experimental");
     gate_all!(unsafe_binders, "unsafe binder types are experimental");

diff --git a/compiler/rustc_feature/src/accepted.rs b/compiler/rustc_feature/src/accepted.rs
@@ -364,6 +364,8 @@ declare_features! (
     (accepted, result_ffi_guarantees, "1.84.0", Some(110503)),
     /// Allows return-position `impl Trait` in traits.
     (accepted, return_position_impl_trait_in_trait, "1.75.0", Some(91611)),
+    /// Allows bounding the return type of AFIT/RPITIT.
+    (accepted, return_type_notation, "CURRENT_RUSTC_VERSION", Some(109417)),
     /// Allows code like `let x: &'static u32 = &42` to work (RFC 1414).
     (accepted, rvalue_static_promotion, "1.21.0", Some(38865)),
     /// Allows `Self` in type definitions (RFC 2300).

diff --git a/compiler/rustc_feature/src/unstable.rs b/compiler/rustc_feature/src/unstable.rs
@@ -616,8 +616,6 @@ declare_features! (
     (incomplete, repr128, "1.16.0", Some(56071)),
     /// Allows `repr(simd)` and importing the various simd intrinsics.
     (unstable, repr_simd, "1.4.0", Some(27731)),
-    /// Allows bounding the return type of AFIT/RPITIT.
-    (unstable, return_type_notation, "1.70.0", Some(109417)),
     /// Allows `extern "rust-cold"`.
     (unstable, rust_cold_cc, "1.63.0", Some(97544)),
     /// Allows use of x86 SHA512, SM3 and SM4 target-features and intrinsics

diff --git a/compiler/rustc_hir_analysis/src/check/compare_impl_item.rs b/compiler/rustc_hir_analysis/src/check/compare_impl_item.rs
@@ -13,6 +13,7 @@ use rustc_infer::infer::{self, InferCtxt, TyCtxtInferExt};
 use rustc_infer::traits::util;
 use rustc_middle::ty::error::{ExpectedFound, TypeError};
 use rustc_middle::ty::fold::BottomUpFolder;
+use rustc_middle::ty::print::with_types_for_signature;
 use rustc_middle::ty::util::ExplicitSelf;
 use rustc_middle::ty::{
     self, GenericArgs, GenericParamDefKind, Ty, TyCtxt, TypeFoldable, TypeFolder,
@@ -1058,11 +1059,12 @@ fn report_trait_method_mismatch<'tcx>(
                     let ap = Applicability::MachineApplicable;
                     match sig.decl.output {
                         hir::FnRetTy::DefaultReturn(sp) => {
-                            let sugg = format!(" -> {}", trait_sig.output());
+                            let sugg =
+                                with_types_for_signature!(format!(" -> {}", trait_sig.output()));
                             diag.span_suggestion_verbose(sp, msg, sugg, ap);
                         }
                         hir::FnRetTy::Return(hir_ty) => {
-                            let sugg = trait_sig.output();
+                            let sugg = with_types_for_signature!(trait_sig.output().to_string());
                             diag.span_suggestion_verbose(hir_ty.span, msg, sugg, ap);
                         }
                     };

diff --git a/compiler/rustc_hir_analysis/src/check/compare_impl_item/refine.rs b/compiler/rustc_hir_analysis/src/check/compare_impl_item/refine.rs
@@ -6,6 +6,7 @@ use rustc_infer::infer::TyCtxtInferExt;
 use rustc_lint_defs::builtin::{REFINING_IMPL_TRAIT_INTERNAL, REFINING_IMPL_TRAIT_REACHABLE};
 use rustc_middle::span_bug;
 use rustc_middle::traits::ObligationCause;
+use rustc_middle::ty::print::with_types_for_signature;
 use rustc_middle::ty::{
     self, Ty, TyCtxt, TypeFoldable, TypeFolder, TypeSuperVisitable, TypeVisitable,
     TypeVisitableExt, TypeVisitor, TypingMode,
@@ -333,7 +334,7 @@ fn report_mismatched_rpitit_signature<'tcx>(
         });
 
     let span = unmatched_bound.unwrap_or(span);
-    tcx.emit_node_span_lint(
+    with_types_for_signature!(tcx.emit_node_span_lint(
         if is_internal { REFINING_IMPL_TRAIT_INTERNAL } else { REFINING_IMPL_TRAIT_REACHABLE },
         tcx.local_def_id_to_hir_id(impl_m_def_id.expect_local()),
         span,
@@ -345,7 +346,7 @@ fn report_mismatched_rpitit_signature<'tcx>(
             return_ty,
             unmatched_bound,
         },
-    );
+    ));
 }
 
 fn type_visibility<'tcx>(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>) -> Option<ty::Visibility<DefId>> {

diff --git a/compiler/rustc_hir_analysis/src/check/mod.rs b/compiler/rustc_hir_analysis/src/check/mod.rs
@@ -84,6 +84,7 @@ use rustc_infer::infer::{self, TyCtxtInferExt as _};
 use rustc_infer::traits::ObligationCause;
 use rustc_middle::query::Providers;
 use rustc_middle::ty::error::{ExpectedFound, TypeError};
+use rustc_middle::ty::print::with_types_for_signature;
 use rustc_middle::ty::{self, GenericArgs, GenericArgsRef, Ty, TyCtxt, TypingMode};
 use rustc_middle::{bug, span_bug};
 use rustc_session::parse::feature_err;
@@ -240,11 +241,11 @@ fn missing_items_err(
         (Vec::new(), Vec::new(), Vec::new());
 
     for &trait_item in missing_items {
-        let snippet = suggestion_signature(
+        let snippet = with_types_for_signature!(suggestion_signature(
             tcx,
             trait_item,
             tcx.impl_trait_ref(impl_def_id).unwrap().instantiate_identity(),
-        );
+        ));
         let code = format!("{padding}{snippet}\n{padding}");
         if let Some(span) = tcx.hir().span_if_local(trait_item.def_id) {
             missing_trait_item_label
@@ -474,7 +475,11 @@ fn fn_sig_suggestion<'tcx>(
         ""
     };
 
-    let output = if !output.is_unit() { format!(" -> {output}") } else { String::new() };
+    let output = if !output.is_unit() {
+        with_types_for_signature!(format!(" -> {output}"))
+    } else {
+        String::new()
+    };
 
     let safety = sig.safety.prefix_str();
     let (generics, where_clauses) = bounds_from_generic_predicates(tcx, predicates);

diff --git a/compiler/rustc_lint/messages.ftl b/compiler/rustc_lint/messages.ftl
@@ -21,10 +21,6 @@ lint_associated_const_elided_lifetime = {$elided ->
     .suggestion = use the `'static` lifetime
     .note = cannot automatically infer `'static` because of other lifetimes in scope
 
-lint_async_fn_in_trait = use of `async fn` in public traits is discouraged as auto trait bounds cannot be specified
-    .note = you can suppress this lint if you plan to use the trait only in your own code, or do not care about auto traits like `Send` on the `Future`
-    .suggestion = you can alternatively desugar to a normal `fn` that returns `impl Future` and add any desired bounds such as `Send`, but these cannot be relaxed without a breaking API change
-
 lint_atomic_ordering_fence = memory fences cannot have `Relaxed` ordering
     .help = consider using ordering modes `Acquire`, `Release`, `AcqRel` or `SeqCst`
 

diff --git a/compiler/rustc_lint/src/async_fn_in_trait.rs b/compiler/rustc_lint/src/async_fn_in_trait.rs
diff --git a/compiler/rustc_lint/src/lib.rs b/compiler/rustc_lint/src/lib.rs
@@ -36,7 +36,6 @@
 // tidy-alphabetical-end
 
 mod async_closures;
-mod async_fn_in_trait;
 pub mod builtin;
 mod context;
 mod dangling;
@@ -82,7 +81,6 @@ mod unqualified_local_imports;
 mod unused;
 
 use async_closures::AsyncClosureUsage;
-use async_fn_in_trait::AsyncFnInTrait;
 use builtin::*;
 use dangling::*;
 use default_could_be_derived::DefaultCouldBeDerived;
@@ -238,7 +236,6 @@ late_lint_methods!(
             MissingDebugImplementations: MissingDebugImplementations,
             MissingDoc: MissingDoc,
             AsyncClosureUsage: AsyncClosureUsage,
-            AsyncFnInTrait: AsyncFnInTrait,
             NonLocalDefinitions: NonLocalDefinitions::default(),
             ImplTraitOvercaptures: ImplTraitOvercaptures,
             IfLetRescope: IfLetRescope::default(),
@@ -604,6 +601,11 @@ fn register_builtins(store: &mut LintStore) {
         "converted into hard error, see issue #127323 \
          <https://github.com/rust-lang/rust/issues/127323> for more information",
     );
+    store.register_removed(
+        "async_fn_in_trait",
+        "lint was relaxed since return-type notation is stabilized; \
+        see <https://github.com/rust-lang/rust/pull/138424> for more information",
+    )
 }
 
 fn register_internals(store: &mut LintStore) {

diff --git a/compiler/rustc_lint/src/lints.rs b/compiler/rustc_lint/src/lints.rs
@@ -2100,20 +2100,6 @@ pub(crate) struct UnusedAllocationDiag;
 #[diag(lint_unused_allocation_mut)]
 pub(crate) struct UnusedAllocationMutDiag;
 
-pub(crate) struct AsyncFnInTraitDiag {
-    pub sugg: Option<Vec<(Span, String)>>,
-}
-
-impl<'a> LintDiagnostic<'a, ()> for AsyncFnInTraitDiag {
-    fn decorate_lint<'b>(self, diag: &'b mut Diag<'a, ()>) {
-        diag.primary_message(fluent::lint_async_fn_in_trait);
-        diag.note(fluent::lint_note);
-        if let Some(sugg) = self.sugg {
-            diag.multipart_suggestion(fluent::lint_suggestion, sugg, Applicability::MaybeIncorrect);
-        }
-    }
-}
-
 #[derive(LintDiagnostic)]
 #[diag(lint_unit_bindings)]
 pub(crate) struct UnitBindingsDiag {