rust-lang · BoxyUwU · Apr 4, 2025
diff --git a/compiler/rustc_ast_lowering/messages.ftl b/compiler/rustc_ast_lowering/messages.ftl
@@ -172,9 +172,6 @@ ast_lowering_template_modifier = template modifier
 
 ast_lowering_this_not_async = this is not `async`
 
-ast_lowering_underscore_array_length_unstable =
-    using `_` for array lengths is unstable
-
 ast_lowering_underscore_expr_lhs_assign =
     in expressions, `_` can only be used on the left-hand side of an assignment
     .label = `_` not allowed here

diff --git a/compiler/rustc_ast_lowering/src/lib.rs b/compiler/rustc_ast_lowering/src/lib.rs
@@ -50,7 +50,7 @@ use rustc_data_structures::sorted_map::SortedMap;
 use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
 use rustc_data_structures::sync::spawn;
 use rustc_data_structures::tagged_ptr::TaggedRef;
-use rustc_errors::{DiagArgFromDisplay, DiagCtxtHandle, StashKey};
+use rustc_errors::{DiagArgFromDisplay, DiagCtxtHandle};
 use rustc_hir::def::{DefKind, LifetimeRes, Namespace, PartialRes, PerNS, Res};
 use rustc_hir::def_id::{CRATE_DEF_ID, LOCAL_CRATE, LocalDefId};
 use rustc_hir::{
@@ -61,7 +61,7 @@ use rustc_index::{Idx, IndexSlice, IndexVec};
 use rustc_macros::extension;
 use rustc_middle::span_bug;
 use rustc_middle::ty::{ResolverAstLowering, TyCtxt};
-use rustc_session::parse::{add_feature_diagnostics, feature_err};
+use rustc_session::parse::add_feature_diagnostics;
 use rustc_span::symbol::{Ident, Symbol, kw, sym};
 use rustc_span::{DUMMY_SP, DesugaringKind, Span};
 use smallvec::{SmallVec, smallvec};
@@ -2068,15 +2068,6 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
         // `ExprKind::Paren(ExprKind::Underscore)` and should also be lowered to `GenericArg::Infer`
         match c.value.peel_parens().kind {
             ExprKind::Underscore => {
-                if !self.tcx.features().generic_arg_infer() {
-                    feature_err(
-                        &self.tcx.sess,
-                        sym::generic_arg_infer,
-                        c.value.span,
-                        fluent_generated::ast_lowering_underscore_array_length_unstable,
-                    )
-                    .stash(c.value.span, StashKey::UnderscoreForArrayLengths);
-                }
                 let ct_kind = hir::ConstArgKind::Infer(self.lower_span(c.value.span), ());
                 self.arena.alloc(hir::ConstArg { hir_id: self.lower_node_id(c.id), kind: ct_kind })
             }

diff --git a/compiler/rustc_feature/src/accepted.rs b/compiler/rustc_feature/src/accepted.rs
@@ -220,6 +220,8 @@ declare_features! (
     (accepted, fn_must_use, "1.27.0", Some(43302)),
     /// Allows capturing variables in scope using format_args!
     (accepted, format_args_capture, "1.58.0", Some(67984)),
+    /// Infer generic args for both consts and types.
+    (accepted, generic_arg_infer, "CURRENT_RUSTC_VERSION", Some(85077)),
     /// Allows associated types to be generic, e.g., `type Foo<T>;` (RFC 1598).
     (accepted, generic_associated_types, "1.65.0", Some(44265)),
     /// Allows attributes on lifetime/type formal parameters in generics (RFC 1327).

diff --git a/compiler/rustc_feature/src/unstable.rs b/compiler/rustc_feature/src/unstable.rs
@@ -514,8 +514,6 @@ declare_features! (
     (unstable, frontmatter, "1.88.0", Some(136889)),
     /// Allows defining gen blocks and `gen fn`.
     (unstable, gen_blocks, "1.75.0", Some(117078)),
-    /// Infer generic args for both consts and types.
-    (unstable, generic_arg_infer, "1.55.0", Some(85077)),
     /// Allows non-trivial generic constants which have to have wfness manually propagated to callers
     (incomplete, generic_const_exprs, "1.56.0", Some(76560)),
     /// Allows generic parameters and where-clauses on free & associated const items.

diff --git a/compiler/rustc_hir_analysis/src/collect/type_of.rs b/compiler/rustc_hir_analysis/src/collect/type_of.rs
@@ -452,13 +452,6 @@ fn infer_placeholder_type<'tcx>(
             if let Some(ty) = node.ty() {
                 visitor.visit_ty_unambig(ty);
             }
-            // If we have just one span, let's try to steal a const `_` feature error.
-            let try_steal_span = if !tcx.features().generic_arg_infer() && visitor.spans.len() == 1
-            {
-                visitor.spans.first().copied()
-            } else {
-                None
-            };
             // If we didn't find any infer tys, then just fallback to `span`.
             if visitor.spans.is_empty() {
                 visitor.spans.push(span);
@@ -489,15 +482,7 @@ fn infer_placeholder_type<'tcx>(
                 }
             }
 
-            if let Some(try_steal_span) = try_steal_span {
-                cx.dcx().try_steal_replace_and_emit_err(
-                    try_steal_span,
-                    StashKey::UnderscoreForArrayLengths,
-                    diag,
-                )
-            } else {
-                diag.emit()
-            }
+            diag.emit()
         });
     Ty::new_error(tcx, guar)
 }

diff --git a/compiler/rustc_hir_analysis/src/hir_ty_lowering/generics.rs b/compiler/rustc_hir_analysis/src/hir_ty_lowering/generics.rs
@@ -8,7 +8,7 @@ use rustc_middle::ty::{
     self, GenericArgsRef, GenericParamDef, GenericParamDefKind, IsSuggestable, Ty,
 };
 use rustc_session::lint::builtin::LATE_BOUND_LIFETIME_ARGUMENTS;
-use rustc_span::{kw, sym};
+use rustc_span::kw;
 use smallvec::SmallVec;
 use tracing::{debug, instrument};
 
@@ -258,19 +258,6 @@ pub fn lower_generic_args<'tcx: 'a, 'a>(
                             GenericParamDefKind::Const { .. },
                             _,
                         ) => {
-                            if let GenericParamDefKind::Const { .. } = param.kind
-                                && let GenericArg::Infer(inf) = arg
-                                && !tcx.features().generic_arg_infer()
-                            {
-                                rustc_session::parse::feature_err(
-                                    tcx.sess,
-                                    sym::generic_arg_infer,
-                                    inf.span,
-                                    "const arguments cannot yet be inferred with `_`",
-                                )
-                                .emit();
-                            }
-
                             // We lower to an infer even when the feature gate is not enabled
                             // as it is useful for diagnostics to be able to see a `ConstKind::Infer`
                             args.push(ctx.provided_kind(&args, param, arg));

diff --git a/library/core/src/lib.rs b/library/core/src/lib.rs
@@ -153,7 +153,6 @@
 #![feature(f16)]
 #![feature(freeze_impls)]
 #![feature(fundamental)]
-#![feature(generic_arg_infer)]
 #![feature(if_let_guard)]
 #![feature(intra_doc_pointers)]
 #![feature(intrinsics)]

diff --git a/src/tools/clippy/tests/ui/single_range_in_vec_init.rs b/src/tools/clippy/tests/ui/single_range_in_vec_init.rs
@@ -2,7 +2,6 @@
 //@no-rustfix: overlapping suggestions
 #![allow(clippy::no_effect, clippy::unnecessary_operation, clippy::useless_vec, unused)]
 #![warn(clippy::single_range_in_vec_init)]
-#![feature(generic_arg_infer)]
 
 #[macro_use]
 extern crate proc_macros;

diff --git a/src/tools/clippy/tests/ui/single_range_in_vec_init.stderr b/src/tools/clippy/tests/ui/single_range_in_vec_init.stderr
@@ -1,5 +1,5 @@
 error: an array of `Range` that is only one element
-  --> tests/ui/single_range_in_vec_init.rs:26:5
+  --> tests/ui/single_range_in_vec_init.rs:25:5
    |
 LL |     [0..200];
    |     ^^^^^^^^
@@ -18,7 +18,7 @@ LL +     [0; 200];
    |
 
 error: a `Vec` of `Range` that is only one element
-  --> tests/ui/single_range_in_vec_init.rs:28:5
+  --> tests/ui/single_range_in_vec_init.rs:27:5
    |
 LL |     vec![0..200];
    |     ^^^^^^^^^^^^
@@ -35,7 +35,7 @@ LL +     vec![0; 200];
    |
 
 error: an array of `Range` that is only one element
-  --> tests/ui/single_range_in_vec_init.rs:30:5
+  --> tests/ui/single_range_in_vec_init.rs:29:5
    |
 LL |     [0u8..200];
    |     ^^^^^^^^^^
@@ -52,7 +52,7 @@ LL +     [0u8; 200];
    |
 
 error: an array of `Range` that is only one element
-  --> tests/ui/single_range_in_vec_init.rs:32:5
+  --> tests/ui/single_range_in_vec_init.rs:31:5
    |
 LL |     [0usize..200];
    |     ^^^^^^^^^^^^^
@@ -69,7 +69,7 @@ LL +     [0usize; 200];
    |
 
 error: an array of `Range` that is only one element
-  --> tests/ui/single_range_in_vec_init.rs:34:5
+  --> tests/ui/single_range_in_vec_init.rs:33:5
    |
 LL |     [0..200usize];
    |     ^^^^^^^^^^^^^
@@ -86,7 +86,7 @@ LL +     [0; 200usize];
    |
 
 error: a `Vec` of `Range` that is only one element
-  --> tests/ui/single_range_in_vec_init.rs:36:5
+  --> tests/ui/single_range_in_vec_init.rs:35:5
    |
 LL |     vec![0u8..200];
    |     ^^^^^^^^^^^^^^
@@ -103,7 +103,7 @@ LL +     vec![0u8; 200];
    |
 
 error: a `Vec` of `Range` that is only one element
-  --> tests/ui/single_range_in_vec_init.rs:38:5
+  --> tests/ui/single_range_in_vec_init.rs:37:5
    |
 LL |     vec![0usize..200];
    |     ^^^^^^^^^^^^^^^^^
@@ -120,7 +120,7 @@ LL +     vec![0usize; 200];
    |
 
 error: a `Vec` of `Range` that is only one element
-  --> tests/ui/single_range_in_vec_init.rs:40:5
+  --> tests/ui/single_range_in_vec_init.rs:39:5
    |
 LL |     vec![0..200usize];
    |     ^^^^^^^^^^^^^^^^^
@@ -137,7 +137,7 @@ LL +     vec![0; 200usize];
    |
 
 error: an array of `Range` that is only one element
-  --> tests/ui/single_range_in_vec_init.rs:43:5
+  --> tests/ui/single_range_in_vec_init.rs:42:5
    |
 LL |     [0..200isize];
    |     ^^^^^^^^^^^^^
@@ -149,7 +149,7 @@ LL +     (0..200isize).collect::<std::vec::Vec<isize>>();
    |
 
 error: a `Vec` of `Range` that is only one element
-  --> tests/ui/single_range_in_vec_init.rs:45:5
+  --> tests/ui/single_range_in_vec_init.rs:44:5
    |
 LL |     vec![0..200isize];
    |     ^^^^^^^^^^^^^^^^^

diff --git a/tests/crashes/111419.rs b/tests/crashes/111419.rs
@@ -1,6 +1,6 @@
 //@ known-bug: #111419
 #![allow(incomplete_features)]
-#![feature(generic_const_exprs, generic_arg_infer)]
+#![feature(generic_const_exprs)]
 
 pub trait Example<const X: usize, const Y: usize, const Z: usize = { X + Y }>
 where

diff --git a/tests/ui/array-slice-vec/suggest-array-length.fixed b/tests/ui/array-slice-vec/suggest-array-length.fixed
@@ -10,14 +10,9 @@ fn main() {
     //~^ ERROR the placeholder `_` is not allowed within types on item signatures for static variables
     static REF_STATIK: &[u8; 1] = &[1];
     //~^ ERROR the placeholder `_` is not allowed within types on item signatures for static variables
-    let foo: [i32; 3] = [1, 2, 3];
-    //~^ ERROR using `_` for array lengths is unstable
-    let bar: [i32; 3] = [0; 3];
-    //~^ ERROR using `_` for array lengths is unstable
-    let ref_foo: &[i32; 3] = &[1, 2, 3];
-    //~^ ERROR using `_` for array lengths is unstable
-    let ref_bar: &[i32; 3] = &[0; 3];
-    //~^ ERROR using `_` for array lengths is unstable
-    let multiple_ref_foo: &&[i32; 3] = &&[1, 2, 3];
-    //~^ ERROR using `_` for array lengths is unstable
+    let foo: [i32; _] = [1, 2, 3];
+    let bar: [i32; _] = [0; 3];
+    let ref_foo: &[i32; _] = &[1, 2, 3];
+    let ref_bar: &[i32; _] = &[0; 3];
+    let multiple_ref_foo: &&[i32; _] = &&[1, 2, 3];
 }
diff --git a/tests/ui/array-slice-vec/suggest-array-length.rs b/tests/ui/array-slice-vec/suggest-array-length.rs
@@ -11,13 +11,8 @@ fn main() {
     static REF_STATIK: &[u8; _] = &[1];
     //~^ ERROR the placeholder `_` is not allowed within types on item signatures for static variables
     let foo: [i32; _] = [1, 2, 3];
-    //~^ ERROR using `_` for array lengths is unstable
     let bar: [i32; _] = [0; 3];
-    //~^ ERROR using `_` for array lengths is unstable
     let ref_foo: &[i32; _] = &[1, 2, 3];
-    //~^ ERROR using `_` for array lengths is unstable
     let ref_bar: &[i32; _] = &[0; 3];
-    //~^ ERROR using `_` for array lengths is unstable
     let multiple_ref_foo: &&[i32; _] = &&[1, 2, 3];
-    //~^ ERROR using `_` for array lengths is unstable
 }
diff --git a/tests/ui/array-slice-vec/suggest-array-length.stderr b/tests/ui/array-slice-vec/suggest-array-length.stderr
@@ -46,57 +46,6 @@ LL -     static REF_STATIK: &[u8; _] = &[1];
 LL +     static REF_STATIK: &[u8; 1] = &[1];
    |
 
-error[E0658]: using `_` for array lengths is unstable
-  --> $DIR/suggest-array-length.rs:13:20
-   |
-LL |     let foo: [i32; _] = [1, 2, 3];
-   |                    ^ help: consider specifying the array length: `3`
-   |
-   = note: see issue #85077 <https://github.com/rust-lang/rust/issues/85077> for more information
-   = help: add `#![feature(generic_arg_infer)]` to the crate attributes to enable
-   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
-
-error[E0658]: using `_` for array lengths is unstable
-  --> $DIR/suggest-array-length.rs:15:20
-   |
-LL |     let bar: [i32; _] = [0; 3];
-   |                    ^ help: consider specifying the array length: `3`
-   |
-   = note: see issue #85077 <https://github.com/rust-lang/rust/issues/85077> for more information
-   = help: add `#![feature(generic_arg_infer)]` to the crate attributes to enable
-   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
-
-error[E0658]: using `_` for array lengths is unstable
-  --> $DIR/suggest-array-length.rs:17:25
-   |
-LL |     let ref_foo: &[i32; _] = &[1, 2, 3];
-   |                         ^ help: consider specifying the array length: `3`
-   |
-   = note: see issue #85077 <https://github.com/rust-lang/rust/issues/85077> for more information
-   = help: add `#![feature(generic_arg_infer)]` to the crate attributes to enable
-   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
-
-error[E0658]: using `_` for array lengths is unstable
-  --> $DIR/suggest-array-length.rs:19:25
-   |
-LL |     let ref_bar: &[i32; _] = &[0; 3];
-   |                         ^ help: consider specifying the array length: `3`
-   |
-   = note: see issue #85077 <https://github.com/rust-lang/rust/issues/85077> for more information
-   = help: add `#![feature(generic_arg_infer)]` to the crate attributes to enable
-   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
-
-error[E0658]: using `_` for array lengths is unstable
-  --> $DIR/suggest-array-length.rs:21:35
-   |
-LL |     let multiple_ref_foo: &&[i32; _] = &&[1, 2, 3];
-   |                                   ^ help: consider specifying the array length: `3`
-   |
-   = note: see issue #85077 <https://github.com/rust-lang/rust/issues/85077> for more information
-   = help: add `#![feature(generic_arg_infer)]` to the crate attributes to enable
-   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
-
-error: aborting due to 9 previous errors
+error: aborting due to 4 previous errors
 
-Some errors have detailed explanations: E0121, E0658.
-For more information about an error, try `rustc --explain E0121`.
+For more information about this error, try `rustc --explain E0121`.
diff --git a/tests/ui/async-await/issues/issue-95307.rs b/tests/ui/async-await/issues/issue-95307.rs
@@ -6,7 +6,6 @@
 pub trait C {
     async fn new() -> [u8; _];
     //~^ ERROR: the placeholder `_` is not allowed within types on item signatures for functions
-    //~| ERROR using `_` for array lengths is unstable
 }
 
 fn main() {}
diff --git a/tests/ui/async-await/issues/issue-95307.stderr b/tests/ui/async-await/issues/issue-95307.stderr
@@ -4,17 +4,6 @@ error[E0121]: the placeholder `_` is not allowed within types on item signatures
 LL |     async fn new() -> [u8; _];
    |                            ^ not allowed in type signatures
 
-error[E0658]: using `_` for array lengths is unstable
-  --> $DIR/issue-95307.rs:7:28
-   |
-LL |     async fn new() -> [u8; _];
-   |                            ^
-   |
-   = note: see issue #85077 <https://github.com/rust-lang/rust/issues/85077> for more information
-   = help: add `#![feature(generic_arg_infer)]` to the crate attributes to enable
-   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
-
-error: aborting due to 2 previous errors
+error: aborting due to 1 previous error
 
-Some errors have detailed explanations: E0121, E0658.
-For more information about an error, try `rustc --explain E0121`.
+For more information about this error, try `rustc --explain E0121`.
diff --git a/tests/ui/closures/binder/forbid_ambig_const_infers.rs b/tests/ui/closures/binder/forbid_ambig_const_infers.rs
@@ -1,4 +1,4 @@
-#![feature(generic_arg_infer, closure_lifetime_binder)]
+#![feature(closure_lifetime_binder)]
 
 struct Foo<const N: usize>([u32; N]);
 

diff --git a/tests/ui/closures/binder/forbid_ambig_type_infers.rs b/tests/ui/closures/binder/forbid_ambig_type_infers.rs
@@ -1,4 +1,4 @@
-#![feature(generic_arg_infer, closure_lifetime_binder)]
+#![feature(closure_lifetime_binder)]
 
 struct Foo<T>(T);
 

diff --git a/tests/ui/closures/binder/forbid_const_infer.rs b/tests/ui/closures/binder/forbid_const_infer.rs
@@ -1,4 +1,4 @@
-#![feature(generic_arg_infer, closure_lifetime_binder)]
+#![feature(closure_lifetime_binder)]
 
 fn main() {
     let c = for<'a> |b: &'a [u32; _]| -> u32 { b[0] };

diff --git a/tests/ui/const-generics/associated_const_equality/equality_bound_with_infer.rs b/tests/ui/const-generics/associated_const_equality/equality_bound_with_infer.rs
@@ -1,4 +1,4 @@
-#![feature(generic_arg_infer, associated_const_equality, generic_const_items)]
+#![feature(associated_const_equality, generic_const_items)]
 #![expect(incomplete_features)]
 
 // Regression test for #133066 where we would try to evaluate `<() as Foo>::ASSOC<_>` even

diff --git a/tests/ui/const-generics/generic_arg_infer/array-repeat-expr-lib.rs b/tests/ui/const-generics/generic_arg_infer/array-repeat-expr-lib.rs
@@ -1,6 +1,5 @@
 //@ check-pass
 
-#![feature(generic_arg_infer)]
 #![crate_type = "lib"]
 
 // Test that encoding the hallucinated `DefId` for the `_` const argument doesn't

diff --git a/tests/ui/const-generics/generic_arg_infer/array-repeat-expr.rs b/tests/ui/const-generics/generic_arg_infer/array-repeat-expr.rs
@@ -1,7 +1,6 @@
 //@ run-pass
 
 // To avoid having to `or` gate `_` as an expr.
-#![feature(generic_arg_infer)]
 
 fn foo() -> [u8; 3] {
     let x: [u8; _] = [0; _];