make rustc_allow_const_fn_unstable an actual rustc_attrs attribute

Author: cyrgani

compiler/rustc_feature/src/builtin_attrs.rs

@@ -1208,7 +1208,7 @@ pub static BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
         rustc_intrinsic_const_stable_indirect, Normal,
         template!(Word), WarnFollowing, EncodeCrossCrate::No,  "this is an internal implementation detail",
     ),
-    gated!(
+    rustc_attr!(
         rustc_allow_const_fn_unstable, Normal,
         template!(Word, List: &["feat1, feat2, ..."]), DuplicatesOk, EncodeCrossCrate::No,
         "rustc_allow_const_fn_unstable side-steps feature gating and stability checks"

compiler/rustc_feature/src/removed.rs

@@ -263,6 +263,7 @@ declare_features! (
      Some("removed in favor of `#![register_tool]`"), 66070),
     (removed, rust_2018_preview, "1.76.0", None,
      Some("2018 Edition preview is no longer relevant")),
+    (removed, rustc_allow_const_fn_unstable, "CURRENT_RUSTC_VERSION", Some(69399), Some("merged into `#![feature(rustc_attrs)]`")),
     /// Allows using the macros:
     /// + `__diagnostic_used`
     /// + `__register_diagnostic`

compiler/rustc_feature/src/unstable.rs

@@ -287,10 +287,6 @@ declare_features! (
     (internal, panic_runtime, "1.10.0", Some(32837)),
     /// Allows using pattern types.
     (internal, pattern_types, "1.79.0", Some(123646)),
-    /// Allows using `#[rustc_allow_const_fn_unstable]`.
-    /// This is an attribute on `const fn` for the same
-    /// purpose as `#[allow_internal_unstable]`.
-    (internal, rustc_allow_const_fn_unstable, "1.49.0", Some(69399)),
     /// Allows using compiler's own crates.
     (unstable, rustc_private, "1.0.0", Some(27812)),
     /// Allows using internal rustdoc features like `doc(keyword)`.

library/alloc/src/lib.rs

@@ -182,7 +182,6 @@
 #![feature(negative_impls)]
 #![feature(never_type)]
 #![feature(optimize_attribute)]
-#![feature(rustc_allow_const_fn_unstable)]
 #![feature(rustc_attrs)]
 #![feature(slice_internals)]
 #![feature(staged_api)]

library/core/src/lib.rs

@@ -159,7 +159,6 @@
 #![feature(pattern_types)]
 #![feature(prelude_import)]
 #![feature(repr_simd)]
-#![feature(rustc_allow_const_fn_unstable)]
 #![feature(rustc_attrs)]
 #![feature(rustdoc_internals)]
 #![feature(simd_ffi)]

tests/codegen-llvm/intrinsics/likely_assert.rs

@@ -1,5 +1,5 @@
 //@ compile-flags: -Copt-level=3
-#![feature(panic_internals, const_eval_select, rustc_allow_const_fn_unstable, core_intrinsics)]
+#![feature(panic_internals, const_eval_select, rustc_attrs, core_intrinsics)]
 #![crate_type = "lib"]
 
 // check that assert! and const_assert! emit branch weights

tests/ui/attributes/malformed-attrs.rs

@@ -2,7 +2,6 @@
 // We enable a bunch of features to not get feature-gate errs in this test.
 #![deny(invalid_doc_attributes)]
 #![feature(rustc_attrs)]
-#![feature(rustc_allow_const_fn_unstable)]
 #![feature(allow_internal_unstable)]
 // FIXME(#82232, #143834): temporarily renamed to mitigate `#[align]` nameres ambiguity
 #![feature(fn_align)]