introduce crate rustc_feature and move active, accepted, and removed to it

9 files changed, 21 insertions, 1013 deletions

diff --git a/src/libsyntax/Cargo.toml b/src/libsyntax/Cargo.toml
index dff23076c82..085c1760c80 100644
--- a/src/libsyntax/Cargo.toml
+++ b/src/libsyntax/Cargo.toml
@@ -18,6 +18,7 @@ lazy_static = "1.0.0"
 syntax_pos = { path = "../libsyntax_pos" }
 errors = { path = "../librustc_errors", package = "rustc_errors" }
 rustc_data_structures = { path = "../librustc_data_structures" }
+rustc_feature = { path = "../librustc_feature" }
 rustc_index = { path = "../librustc_index" }
 rustc_lexer = { path = "../librustc_lexer" }
 rustc_macros = { path = "../librustc_macros" }
diff --git a/src/libsyntax/attr/builtin.rs b/src/libsyntax/attr/builtin.rs
index c10541c8c7e..eaa4a64025a 100644
--- a/src/libsyntax/attr/builtin.rs
+++ b/src/libsyntax/attr/builtin.rs
@@ -1,14 +1,15 @@
 //! Parsing and validation of builtin attributes
 
 use crate::ast::{self, Attribute, MetaItem, NestedMetaItem};
-use crate::feature_gate::{Features, GatedCfg};
 use crate::print::pprust;
+use crate::feature_gate::GatedCfg;
 use crate::sess::ParseSess;
 
 use errors::{Applicability, Handler};
 use std::num::NonZeroU32;
 use syntax_pos::hygiene::Transparency;
 use syntax_pos::{symbol::Symbol, symbol::sym, Span};
+use rustc_feature::Features;
 use rustc_macros::HashStable_Generic;
 
 use super::{mark_used, MetaItemKind};
diff --git a/src/libsyntax/feature_gate/accepted.rs b/src/libsyntax/feature_gate/accepted.rs
deleted file mode 100644
index dab83f48a03..00000000000
--- a/src/libsyntax/feature_gate/accepted.rs
+++ /dev/null
@@ -1,265 +0,0 @@
-//! List of the accepted feature gates.
-
-use crate::symbol::sym;
-use super::{State, Feature};
-
-macro_rules! declare_features {
-    ($(
-        $(#[doc = $doc:tt])* (accepted, $feature:ident, $ver:expr, $issue:expr, None),
-    )+) => {
-        /// Those language feature has since been Accepted (it was once Active)
-        pub const ACCEPTED_FEATURES: &[Feature] = &[
-            $(
-                Feature {
-                    state: State::Accepted,
-                    name: sym::$feature,
-                    since: $ver,
-                    issue: $issue,
-                    edition: None,
-                    description: concat!($($doc,)*),
-                }
-            ),+
-        ];
-    }
-}
-
-declare_features! (
-    // -------------------------------------------------------------------------
-    // feature-group-start: for testing purposes
-    // -------------------------------------------------------------------------
-
-    /// A temporary feature gate used to enable parser extensions needed
-    /// to bootstrap fix for #5723.
-    (accepted, issue_5723_bootstrap, "1.0.0", None, None),
-    /// These are used to test this portion of the compiler,
-    /// they don't actually mean anything.
-    (accepted, test_accepted_feature, "1.0.0", None, None),
-
-    // -------------------------------------------------------------------------
-    // feature-group-end: for testing purposes
-    // -------------------------------------------------------------------------
-
-    // -------------------------------------------------------------------------
-    // feature-group-start: accepted features
-    // -------------------------------------------------------------------------
-
-    /// Allows using associated `type`s in `trait`s.
-    (accepted, associated_types, "1.0.0", None, None),
-    /// Allows using assigning a default type to type parameters in algebraic data type definitions.
-    (accepted, default_type_params, "1.0.0", None, None),
-    // FIXME: explain `globs`.
-    (accepted, globs, "1.0.0", None, None),
-    /// Allows `macro_rules!` items.
-    (accepted, macro_rules, "1.0.0", None, None),
-    /// Allows use of `&foo[a..b]` as a slicing syntax.
-    (accepted, slicing_syntax, "1.0.0", None, None),
-    /// Allows struct variants `Foo { baz: u8, .. }` in enums (RFC 418).
-    (accepted, struct_variant, "1.0.0", None, None),
-    /// Allows indexing tuples.
-    (accepted, tuple_indexing, "1.0.0", None, None),
-    /// Allows the use of `if let` expressions.
-    (accepted, if_let, "1.0.0", None, None),
-    /// Allows the use of `while let` expressions.
-    (accepted, while_let, "1.0.0", None, None),
-    /// Allows using `#![no_std]`.
-    (accepted, no_std, "1.6.0", None, None),
-    /// Allows overloading augmented assignment operations like `a += b`.
-    (accepted, augmented_assignments, "1.8.0", Some(28235), None),
-    /// Allows empty structs and enum variants with braces.
-    (accepted, braced_empty_structs, "1.8.0", Some(29720), None),
-    /// Allows `#[deprecated]` attribute.
-    (accepted, deprecated, "1.9.0", Some(29935), None),
-    /// Allows macros to appear in the type position.
-    (accepted, type_macros, "1.13.0", Some(27245), None),
-    /// Allows use of the postfix `?` operator in expressions.
-    (accepted, question_mark, "1.13.0", Some(31436), None),
-    /// Allows `..` in tuple (struct) patterns.
-    (accepted, dotdot_in_tuple_patterns, "1.14.0", Some(33627), None),
-    /// Allows some increased flexibility in the name resolution rules,
-    /// especially around globs and shadowing (RFC 1560).
-    (accepted, item_like_imports, "1.15.0", Some(35120), None),
-    /// Allows using `Self` and associated types in struct expressions and patterns.
-    (accepted, more_struct_aliases, "1.16.0", Some(37544), None),
-    /// Allows elision of `'static` lifetimes in `static`s and `const`s.
-    (accepted, static_in_const, "1.17.0", Some(35897), None),
-    /// Allows field shorthands (`x` meaning `x: x`) in struct literal expressions.
-    (accepted, field_init_shorthand, "1.17.0", Some(37340), None),
-    /// Allows the definition recursive static items.
-    (accepted, static_recursion, "1.17.0", Some(29719), None),
-    /// Allows `pub(restricted)` visibilities (RFC 1422).
-    (accepted, pub_restricted, "1.18.0", Some(32409), None),
-    /// Allows `#![windows_subsystem]`.
-    (accepted, windows_subsystem, "1.18.0", Some(37499), None),
-    /// Allows `break {expr}` with a value inside `loop`s.
-    (accepted, loop_break_value, "1.19.0", Some(37339), None),
-    /// Allows numeric fields in struct expressions and patterns.
-    (accepted, relaxed_adts, "1.19.0", Some(35626), None),
-    /// Allows coercing non capturing closures to function pointers.
-    (accepted, closure_to_fn_coercion, "1.19.0", Some(39817), None),
-    /// Allows attributes on struct literal fields.
-    (accepted, struct_field_attributes, "1.20.0", Some(38814), None),
-    /// Allows the definition of associated constants in `trait` or `impl` blocks.
-    (accepted, associated_consts, "1.20.0", Some(29646), None),
-    /// Allows usage of the `compile_error!` macro.
-    (accepted, compile_error, "1.20.0", Some(40872), None),
-    /// Allows code like `let x: &'static u32 = &42` to work (RFC 1414).
-    (accepted, rvalue_static_promotion, "1.21.0", Some(38865), None),
-    /// Allows `Drop` types in constants (RFC 1440).
-    (accepted, drop_types_in_const, "1.22.0", Some(33156), None),
-    /// Allows the sysV64 ABI to be specified on all platforms
-    /// instead of just the platforms on which it is the C ABI.
-    (accepted, abi_sysv64, "1.24.0", Some(36167), None),
-    /// Allows `repr(align(16))` struct attribute (RFC 1358).
-    (accepted, repr_align, "1.25.0", Some(33626), None),
-    /// Allows '|' at beginning of match arms (RFC 1925).
-    (accepted, match_beginning_vert, "1.25.0", Some(44101), None),
-    /// Allows nested groups in `use` items (RFC 2128).
-    (accepted, use_nested_groups, "1.25.0", Some(44494), None),
-    /// Allows indexing into constant arrays.
-    (accepted, const_indexing, "1.26.0", Some(29947), None),
-    /// Allows using `a..=b` and `..=b` as inclusive range syntaxes.
-    (accepted, inclusive_range_syntax, "1.26.0", Some(28237), None),
-    /// Allows `..=` in patterns (RFC 1192).
-    (accepted, dotdoteq_in_patterns, "1.26.0", Some(28237), None),
-    /// Allows `fn main()` with return types which implements `Termination` (RFC 1937).
-    (accepted, termination_trait, "1.26.0", Some(43301), None),
-    /// Allows implementing `Clone` for closures where possible (RFC 2132).
-    (accepted, clone_closures, "1.26.0", Some(44490), None),
-    /// Allows implementing `Copy` for closures where possible (RFC 2132).
-    (accepted, copy_closures, "1.26.0", Some(44490), None),
-    /// Allows `impl Trait` in function arguments.
-    (accepted, universal_impl_trait, "1.26.0", Some(34511), None),
-    /// Allows `impl Trait` in function return types.
-    (accepted, conservative_impl_trait, "1.26.0", Some(34511), None),
-    /// Allows using the `u128` and `i128` types.
-    (accepted, i128_type, "1.26.0", Some(35118), None),
-    /// Allows default match binding modes (RFC 2005).
-    (accepted, match_default_bindings, "1.26.0", Some(42640), None),
-    /// Allows `'_` placeholder lifetimes.
-    (accepted, underscore_lifetimes, "1.26.0", Some(44524), None),
-    /// Allows attributes on lifetime/type formal parameters in generics (RFC 1327).
-    (accepted, generic_param_attrs, "1.27.0", Some(48848), None),
-    /// Allows `cfg(target_feature = "...")`.
-    (accepted, cfg_target_feature, "1.27.0", Some(29717), None),
-    /// Allows `#[target_feature(...)]`.
-    (accepted, target_feature, "1.27.0", None, None),
-    /// Allows using `dyn Trait` as a syntax for trait objects.
-    (accepted, dyn_trait, "1.27.0", Some(44662), None),
-    /// Allows `#[must_use]` on functions, and introduces must-use operators (RFC 1940).
-    (accepted, fn_must_use, "1.27.0", Some(43302), None),
-    /// Allows use of the `:lifetime` macro fragment specifier.
-    (accepted, macro_lifetime_matcher, "1.27.0", Some(34303), None),
-    /// Allows `#[test]` functions where the return type implements `Termination` (RFC 1937).
-    (accepted, termination_trait_test, "1.27.0", Some(48854), None),
-    /// Allows the `#[global_allocator]` attribute.
-    (accepted, global_allocator, "1.28.0", Some(27389), None),
-    /// Allows `#[repr(transparent)]` attribute on newtype structs.
-    (accepted, repr_transparent, "1.28.0", Some(43036), None),
-    /// Allows procedural macros in `proc-macro` crates.
-    (accepted, proc_macro, "1.29.0", Some(38356), None),
-    /// Allows `foo.rs` as an alternative to `foo/mod.rs`.
-    (accepted, non_modrs_mods, "1.30.0", Some(44660), None),
-    /// Allows use of the `:vis` macro fragment specifier
-    (accepted, macro_vis_matcher, "1.30.0", Some(41022), None),
-    /// Allows importing and reexporting macros with `use`,
-    /// enables macro modularization in general.
-    (accepted, use_extern_macros, "1.30.0", Some(35896), None),
-    /// Allows keywords to be escaped for use as identifiers.
-    (accepted, raw_identifiers, "1.30.0", Some(48589), None),
-    /// Allows attributes scoped to tools.
-    (accepted, tool_attributes, "1.30.0", Some(44690), None),
-    /// Allows multi-segment paths in attributes and derives.
-    (accepted, proc_macro_path_invoc, "1.30.0", Some(38356), None),
-    /// Allows all literals in attribute lists and values of key-value pairs.
-    (accepted, attr_literals, "1.30.0", Some(34981), None),
-    /// Allows inferring outlives requirements (RFC 2093).
-    (accepted, infer_outlives_requirements, "1.30.0", Some(44493), None),
-    /// Allows annotating functions conforming to `fn(&PanicInfo) -> !` with `#[panic_handler]`.
-    /// This defines the behavior of panics.
-    (accepted, panic_handler, "1.30.0", Some(44489), None),
-    /// Allows `#[used]` to preserve symbols (see llvm.used).
-    (accepted, used, "1.30.0", Some(40289), None),
-    /// Allows `crate` in paths.
-    (accepted, crate_in_paths, "1.30.0", Some(45477), None),
-    /// Allows resolving absolute paths as paths from other crates.
-    (accepted, extern_absolute_paths, "1.30.0", Some(44660), None),
-    /// Allows access to crate names passed via `--extern` through prelude.
-    (accepted, extern_prelude, "1.30.0", Some(44660), None),
-    /// Allows parentheses in patterns.
-    (accepted, pattern_parentheses, "1.31.0", Some(51087), None),
-    /// Allows the definition of `const fn` functions.
-    (accepted, min_const_fn, "1.31.0", Some(53555), None),
-    /// Allows scoped lints.
-    (accepted, tool_lints, "1.31.0", Some(44690), None),
-    /// Allows lifetime elision in `impl` headers. For example:
-    /// + `impl<I:Iterator> Iterator for &mut Iterator`
-    /// + `impl Debug for Foo<'_>`
-    (accepted, impl_header_lifetime_elision, "1.31.0", Some(15872), None),
-    /// Allows `extern crate foo as bar;`. This puts `bar` into extern prelude.
-    (accepted, extern_crate_item_prelude, "1.31.0", Some(55599), None),
-    /// Allows use of the `:literal` macro fragment specifier (RFC 1576).
-    (accepted, macro_literal_matcher, "1.32.0", Some(35625), None),
-    /// Allows use of `?` as the Kleene "at most one" operator in macros.
-    (accepted, macro_at_most_once_rep, "1.32.0", Some(48075), None),
-    /// Allows `Self` struct constructor (RFC 2302).
-    (accepted, self_struct_ctor, "1.32.0", Some(51994), None),
-    /// Allows `Self` in type definitions (RFC 2300).
-    (accepted, self_in_typedefs, "1.32.0", Some(49303), None),
-    /// Allows `use x::y;` to search `x` in the current scope.
-    (accepted, uniform_paths, "1.32.0", Some(53130), None),
-    /// Allows integer match exhaustiveness checking (RFC 2591).
-    (accepted, exhaustive_integer_patterns, "1.33.0", Some(50907), None),
-    /// Allows `use path as _;` and `extern crate c as _;`.
-    (accepted, underscore_imports, "1.33.0", Some(48216), None),
-    /// Allows `#[repr(packed(N))]` attribute on structs.
-    (accepted, repr_packed, "1.33.0", Some(33158), None),
-    /// Allows irrefutable patterns in `if let` and `while let` statements (RFC 2086).
-    (accepted, irrefutable_let_patterns, "1.33.0", Some(44495), None),
-    /// Allows calling `const unsafe fn` inside `unsafe` blocks in `const fn` functions.
-    (accepted, min_const_unsafe_fn, "1.33.0", Some(55607), None),
-    /// Allows let bindings, assignments and destructuring in `const` functions and constants.
-    /// As long as control flow is not implemented in const eval, `&&` and `||` may not be used
-    /// at the same time as let bindings.
-    (accepted, const_let, "1.33.0", Some(48821), None),
-    /// Allows `#[cfg_attr(predicate, multiple, attributes, here)]`.
-    (accepted, cfg_attr_multi, "1.33.0", Some(54881), None),
-    /// Allows top level or-patterns (`p | q`) in `if let` and `while let`.
-    (accepted, if_while_or_patterns, "1.33.0", Some(48215), None),
-    /// Allows `cfg(target_vendor = "...")`.
-    (accepted, cfg_target_vendor, "1.33.0", Some(29718), None),
-    /// Allows `extern crate self as foo;`.
-    /// This puts local crate root into extern prelude under name `foo`.
-    (accepted, extern_crate_self, "1.34.0", Some(56409), None),
-    /// Allows arbitrary delimited token streams in non-macro attributes.
-    (accepted, unrestricted_attribute_tokens, "1.34.0", Some(55208), None),
-    /// Allows paths to enum variants on type aliases including `Self`.
-    (accepted, type_alias_enum_variants, "1.37.0", Some(49683), None),
-    /// Allows using `#[repr(align(X))]` on enums with equivalent semantics
-    /// to wrapping an enum in a wrapper struct with `#[repr(align(X))]`.
-    (accepted, repr_align_enum, "1.37.0", Some(57996), None),
-    /// Allows `const _: TYPE = VALUE`.
-    (accepted, underscore_const_names, "1.37.0", Some(54912), None),
-    /// Allows free and inherent `async fn`s, `async` blocks, and `<expr>.await` expressions.
-    (accepted, async_await, "1.39.0", Some(50547), None),
-    /// Allows mixing bind-by-move in patterns and references to those identifiers in guards.
-    (accepted, bind_by_move_pattern_guards, "1.39.0", Some(15287), None),
-    /// Allows attributes in formal function parameters.
-    (accepted, param_attrs, "1.39.0", Some(60406), None),
-    /// Allows macro invocations in `extern {}` blocks.
-    (accepted, macros_in_extern, "1.40.0", Some(49476), None),
-    /// Allows future-proofing enums/structs with the `#[non_exhaustive]` attribute (RFC 2008).
-    (accepted, non_exhaustive, "1.40.0", Some(44109), None),
-    /// Allows calling constructor functions in `const fn`.
-    (accepted, const_constructor, "1.40.0", Some(61456), None),
-    /// Allows the use of `#[cfg(doctest)]`, set when rustdoc is collecting doctests.
-    (accepted, cfg_doctest, "1.40.0", Some(62210), None),
-    /// Allows the `!` type. Does not imply 'exhaustive_patterns' any more.
-    (accepted, never_type, "1.41.0", Some(35121), None),
-    /// Allows relaxing the coherence rules such that
-    /// `impl<T> ForeignTrait<LocalType> for ForeignType<T>` is permitted.
-    (accepted, re_rebalance_coherence, "1.41.0", Some(55437), None),
-
-    // -------------------------------------------------------------------------
-    // feature-group-end: accepted features
-    // -------------------------------------------------------------------------
-);
diff --git a/src/libsyntax/feature_gate/active.rs b/src/libsyntax/feature_gate/active.rs
deleted file mode 100644
index b04b30aa6bc..00000000000
--- a/src/libsyntax/feature_gate/active.rs
+++ /dev/null
@@ -1,554 +0,0 @@
-//! List of the active feature gates.
-
-use super::{State, Feature};
-
-use crate::edition::Edition;
-use crate::symbol::{Symbol, sym};
-
-use syntax_pos::Span;
-
-macro_rules! set {
-    ($field: ident) => {{
-        fn f(features: &mut Features, _: Span) {
-            features.$field = true;
-        }
-        f as fn(&mut Features, Span)
-    }}
-}
-
-macro_rules! declare_features {
-    ($(
-        $(#[doc = $doc:tt])* (active, $feature:ident, $ver:expr, $issue:expr, $edition:expr),
-    )+) => {
-        /// Represents active features that are currently being implemented or
-        /// currently being considered for addition/removal.
-        pub const ACTIVE_FEATURES:
-            &[Feature] =
-            &[$(
-                // (sym::$feature, $ver, $issue, $edition, set!($feature))
-                Feature {
-                    state: State::Active { set: set!($feature) },
-                    name: sym::$feature,
-                    since: $ver,
-                    issue: $issue,
-                    edition: $edition,
-                    description: concat!($($doc,)*),
-                }
-            ),+];
-
-        /// A set of features to be used by later passes.
-        #[derive(Clone)]
-        pub struct Features {
-            /// `#![feature]` attrs for language features, for error reporting.
-            pub declared_lang_features: Vec<(Symbol, Span, Option<Symbol>)>,
-            /// `#![feature]` attrs for non-language (library) features.
-            pub declared_lib_features: Vec<(Symbol, Span)>,
-            $(
-                $(#[doc = $doc])*
-                pub $feature: bool
-            ),+
-        }
-
-        impl Features {
-            pub fn new() -> Features {
-                Features {
-                    declared_lang_features: Vec::new(),
-                    declared_lib_features: Vec::new(),
-                    $($feature: false),+
-                }
-            }
-
-            pub fn walk_feature_fields<F>(&self, mut f: F)
-                where F: FnMut(&str, bool)
-            {
-                $(f(stringify!($feature), self.$feature);)+
-            }
-        }
-    };
-}
-
-impl Feature {
-    /// Sets this feature in `Features`. Panics if called on a non-active feature.
-    pub fn set(&self, features: &mut Features, span: Span) {
-        match self.state {
-            State::Active { set } => set(features, span),
-            _ => panic!("called `set` on feature `{}` which is not `active`", self.name)
-        }
-    }
-}
-
-// If you change this, please modify `src/doc/unstable-book` as well.
-//
-// Don't ever remove anything from this list; move them to `removed.rs`.
-//
-// The version numbers here correspond to the version in which the current status
-// was set. This is most important for knowing when a particular feature became
-// stable (active).
-//
-// Note that the features are grouped into internal/user-facing and then
-// sorted by version inside those groups. This is enforced with tidy.
-//
-// N.B., `tools/tidy/src/features.rs` parses this information directly out of the
-// source, so take care when modifying it.
-
-declare_features! (
-    // -------------------------------------------------------------------------
-    // feature-group-start: internal feature gates
-    // -------------------------------------------------------------------------
-
-    // no-tracking-issue-start
-
-    /// Allows using compiler's own crates.
-    (active, rustc_private, "1.0.0", Some(27812), None),
-
-    /// Allows using the `rust-intrinsic`'s "ABI".
-    (active, intrinsics, "1.0.0", None, None),
-
-    /// Allows using `#[lang = ".."]` attribute for linking items to special compiler logic.
-    (active, lang_items, "1.0.0", None, None),
-
-    /// Allows using the `#[stable]` and `#[unstable]` attributes.
-    (active, staged_api, "1.0.0", None, None),
-
-    /// Allows using `#[allow_internal_unstable]`. This is an
-    /// attribute on `macro_rules!` and can't use the attribute handling
-    /// below (it has to be checked before expansion possibly makes
-    /// macros disappear).
-    (active, allow_internal_unstable, "1.0.0", None, None),
-
-    /// Allows using `#[allow_internal_unsafe]`. This is an
-    /// attribute on `macro_rules!` and can't use the attribute handling
-    /// below (it has to be checked before expansion possibly makes
-    /// macros disappear).
-    (active, allow_internal_unsafe, "1.0.0", None, None),
-
-    /// Allows using `#[rustc_const_unstable(feature = "foo", ..)]` which
-    /// lets a function to be `const` when opted into with `#![feature(foo)]`.
-    (active, rustc_const_unstable, "1.0.0", None, None),
-
-    /// no-tracking-issue-end
-
-    /// Allows using `#[link_name="llvm.*"]`.
-    (active, link_llvm_intrinsics, "1.0.0", Some(29602), None),
-
-    /// Allows using `rustc_*` attributes (RFC 572).
-    (active, rustc_attrs, "1.0.0", Some(29642), None),
-
-    /// Allows using the `box $expr` syntax.
-    (active, box_syntax, "1.0.0", Some(49733), None),
-
-    /// Allows using `#[main]` to replace the entrypoint `#[lang = "start"]` calls.
-    (active, main, "1.0.0", Some(29634), None),
-
-    /// Allows using `#[start]` on a function indicating that it is the program entrypoint.
-    (active, start, "1.0.0", Some(29633), None),
-
-    /// Allows using the `#[fundamental]` attribute.
-    (active, fundamental, "1.0.0", Some(29635), None),
-
-    /// Allows using the `rust-call` ABI.
-    (active, unboxed_closures, "1.0.0", Some(29625), None),
-
-    /// Allows using the `#[linkage = ".."]` attribute.
-    (active, linkage, "1.0.0", Some(29603), None),
-
-    /// Allows features specific to OIBIT (auto traits).
-    (active, optin_builtin_traits, "1.0.0", Some(13231), None),
-
-    /// Allows using `box` in patterns (RFC 469).
-    (active, box_patterns, "1.0.0", Some(29641), None),
-
-    // no-tracking-issue-start
-
-    /// Allows using `#[prelude_import]` on glob `use` items.
-    (active, prelude_import, "1.2.0", None, None),
-
-    // no-tracking-issue-end
-
-    // no-tracking-issue-start
-
-    /// Allows using `#[omit_gdb_pretty_printer_section]`.
-    (active, omit_gdb_pretty_printer_section, "1.5.0", None, None),
-
-    /// Allows using the `vectorcall` ABI.
-    (active, abi_vectorcall, "1.7.0", None, None),
-
-    // no-tracking-issue-end
-
-    /// Allows using `#[structural_match]` which indicates that a type is structurally matchable.
-    (active, structural_match, "1.8.0", Some(31434), None),
-
-    /// Allows using the `may_dangle` attribute (RFC 1327).
-    (active, dropck_eyepatch, "1.10.0", Some(34761), None),
-
-    /// Allows using the `#![panic_runtime]` attribute.
-    (active, panic_runtime, "1.10.0", Some(32837), None),
-
-    /// Allows declaring with `#![needs_panic_runtime]` that a panic runtime is needed.
-    (active, needs_panic_runtime, "1.10.0", Some(32837), None),
-
-    // no-tracking-issue-start
-
-    /// Allows identifying the `compiler_builtins` crate.
-    (active, compiler_builtins, "1.13.0", None, None),
-
-    /// Allows using the `unadjusted` ABI; perma-unstable.
-    (active, abi_unadjusted, "1.16.0", None, None),
-
-    /// Allows identifying crates that contain sanitizer runtimes.
-    (active, sanitizer_runtime, "1.17.0", None, None),
-
-    /// Used to identify crates that contain the profiler runtime.
-    (active, profiler_runtime, "1.18.0", None, None),
-
-    /// Allows using the `thiscall` ABI.
-    (active, abi_thiscall, "1.19.0", None, None),
-
-    /// Allows using `#![needs_allocator]`, an implementation detail of `#[global_allocator]`.
-    (active, allocator_internals, "1.20.0", None, None),
-
-    /// Added for testing E0705; perma-unstable.
-    (active, test_2018_feature, "1.31.0", None, Some(Edition::Edition2018)),
-
-    // no-tracking-issue-end
-
-    // -------------------------------------------------------------------------
-    // feature-group-end: internal feature gates
-    // -------------------------------------------------------------------------
-
-    // -------------------------------------------------------------------------
-    // feature-group-start: actual feature gates (target features)
-    // -------------------------------------------------------------------------
-
-    // FIXME: Document these and merge with the list below.
-
-    // Unstable `#[target_feature]` directives.
-    (active, arm_target_feature, "1.27.0", Some(44839), None),
-    (active, aarch64_target_feature, "1.27.0", Some(44839), None),
-    (active, hexagon_target_feature, "1.27.0", Some(44839), None),
-    (active, powerpc_target_feature, "1.27.0", Some(44839), None),
-    (active, mips_target_feature, "1.27.0", Some(44839), None),
-    (active, avx512_target_feature, "1.27.0", Some(44839), None),
-    (active, mmx_target_feature, "1.27.0", Some(44839), None),
-    (active, sse4a_target_feature, "1.27.0", Some(44839), None),
-    (active, tbm_target_feature, "1.27.0", Some(44839), None),
-    (active, wasm_target_feature, "1.30.0", Some(44839), None),
-    (active, adx_target_feature, "1.32.0", Some(44839), None),
-    (active, cmpxchg16b_target_feature, "1.32.0", Some(44839), None),
-    (active, movbe_target_feature, "1.34.0", Some(44839), None),
-    (active, rtm_target_feature, "1.35.0", Some(44839), None),
-    (active, f16c_target_feature, "1.36.0", Some(44839), None),
-
-    // -------------------------------------------------------------------------
-    // feature-group-end: actual feature gates (target features)
-    // -------------------------------------------------------------------------
-
-    // -------------------------------------------------------------------------
-    // feature-group-start: actual feature gates
-    // -------------------------------------------------------------------------
-
-    /// Allows using the `#[link_args]` attribute.
-    (active, link_args, "1.0.0", Some(29596), None),
-
-    /// Allows defining identifiers beyond ASCII.
-    (active, non_ascii_idents, "1.0.0", Some(55467), None),
-
-    /// Allows using `#[plugin_registrar]` on functions.
-    (active, plugin_registrar, "1.0.0", Some(29597), None),
-
-    /// Allows using `#![plugin(myplugin)]`.
-    (active, plugin, "1.0.0", Some(29597), None),
-
-    /// Allows using `#[thread_local]` on `static` items.
-    (active, thread_local, "1.0.0", Some(29594), None),
-
-    /// Allows the use of SIMD types in functions declared in `extern` blocks.
-    (active, simd_ffi, "1.0.0", Some(27731), None),
-
-    /// Allows using non lexical lifetimes (RFC 2094).
-    (active, nll, "1.0.0", Some(43234), None),
-
-    /// Allows using slice patterns.
-    (active, slice_patterns, "1.0.0", Some(62254), None),
-
-    /// Allows the definition of `const` functions with some advanced features.
-    (active, const_fn, "1.2.0", Some(57563), None),
-
-    /// Allows associated type defaults.
-    (active, associated_type_defaults, "1.2.0", Some(29661), None),
-
-    /// Allows `#![no_core]`.
-    (active, no_core, "1.3.0", Some(29639), None),
-
-    /// Allows default type parameters to influence type inference.
-    (active, default_type_parameter_fallback, "1.3.0", Some(27336), None),
-
-    /// Allows `repr(simd)` and importing the various simd intrinsics.
-    (active, repr_simd, "1.4.0", Some(27731), None),
-
-    /// Allows `extern "platform-intrinsic" { ... }`.
-    (active, platform_intrinsics, "1.4.0", Some(27731), None),
-
-    /// Allows `#[unwind(..)]`.
-    ///
-    /// Permits specifying whether a function should permit unwinding or abort on unwind.
-    (active, unwind_attributes, "1.4.0", Some(58760), None),
-
-    /// Allows `#[no_debug]`.
-    (active, no_debug, "1.5.0", Some(29721), None),
-
-    /// Allows attributes on expressions and non-item statements.
-    (active, stmt_expr_attributes, "1.6.0", Some(15701), None),
-
-    /// Allows the use of type ascription in expressions.
-    (active, type_ascription, "1.6.0", Some(23416), None),
-
-    /// Allows `cfg(target_thread_local)`.
-    (active, cfg_target_thread_local, "1.7.0", Some(29594), None),
-
-    /// Allows specialization of implementations (RFC 1210).
-    (active, specialization, "1.7.0", Some(31844), None),
-
-    /// Allows using `#[naked]` on functions.
-    (active, naked_functions, "1.9.0", Some(32408), None),
-
-    /// Allows `cfg(target_has_atomic = "...")`.
-    (active, cfg_target_has_atomic, "1.9.0", Some(32976), None),
-
-    /// Allows `X..Y` patterns.
-    (active, exclusive_range_pattern, "1.11.0", Some(37854), None),
-
-    /// Allows exhaustive pattern matching on types that contain uninhabited types.
-    (active, exhaustive_patterns, "1.13.0", Some(51085), None),
-
-    /// Allows `union`s to implement `Drop`. Moreover, `union`s may now include fields
-    /// that don't implement `Copy` as long as they don't have any drop glue.
-    /// This is checked recursively. On encountering type variable where no progress can be made,
-    /// `T: Copy` is used as a substitute for "no drop glue".
-    ///
-    /// NOTE: A limited form of `union U { ... }` was accepted in 1.19.0.
-    (active, untagged_unions, "1.13.0", Some(55149), None),
-
-    /// Allows `#[link(..., cfg(..))]`.
-    (active, link_cfg, "1.14.0", Some(37406), None),
-
-    /// Allows `extern "ptx-*" fn()`.
-    (active, abi_ptx, "1.15.0", Some(38788), None),
-
-    /// Allows the `#[repr(i128)]` attribute for enums.
-    (active, repr128, "1.16.0", Some(35118), None),
-
-    /// Allows `#[link(kind="static-nobundle"...)]`.
-    (active, static_nobundle, "1.16.0", Some(37403), None),
-
-    /// Allows `extern "msp430-interrupt" fn()`.
-    (active, abi_msp430_interrupt, "1.16.0", Some(38487), None),
-
-    /// Allows declarative macros 2.0 (`macro`).
-    (active, decl_macro, "1.17.0", Some(39412), None),
-
-    /// Allows `extern "x86-interrupt" fn()`.
-    (active, abi_x86_interrupt, "1.17.0", Some(40180), None),
-
-    /// Allows overlapping impls of marker traits.
-    (active, overlapping_marker_traits, "1.18.0", Some(29864), None),
-
-    /// Allows a test to fail without failing the whole suite.
-    (active, allow_fail, "1.19.0", Some(46488), None),
-
-    /// Allows unsized tuple coercion.
-    (active, unsized_tuple_coercion, "1.20.0", Some(42877), None),
-
-    /// Allows defining generators.
-    (active, generators, "1.21.0", Some(43122), None),
-
-    /// Allows `#[doc(cfg(...))]`.
-    (active, doc_cfg, "1.21.0", Some(43781), None),
-
-    /// Allows `#[doc(masked)]`.
-    (active, doc_masked, "1.21.0", Some(44027), None),
-
-    /// Allows `#[doc(spotlight)]`.
-    (active, doc_spotlight, "1.22.0", Some(45040), None),
-
-    /// Allows `#[doc(include = "some-file")]`.
-    (active, external_doc, "1.22.0", Some(44732), None),
-
-    /// Allows using `crate` as visibility modifier, synonymous with `pub(crate)`.
-    (active, crate_visibility_modifier, "1.23.0", Some(53120), None),
-
-    /// Allows defining `extern type`s.
-    (active, extern_types, "1.23.0", Some(43467), None),
-
-    /// Allows trait methods with arbitrary self types.
-    (active, arbitrary_self_types, "1.23.0", Some(44874), None),
-
-    /// Allows in-band quantification of lifetime bindings (e.g., `fn foo(x: &'a u8) -> &'a u8`).
-    (active, in_band_lifetimes, "1.23.0", Some(44524), None),
-
-    /// Allows associated types to be generic, e.g., `type Foo<T>;` (RFC 1598).
-    (active, generic_associated_types, "1.23.0", Some(44265), None),
-
-    /// Allows defining `trait X = A + B;` alias items.
-    (active, trait_alias, "1.24.0", Some(41517), None),
-
-    /// Allows infering `'static` outlives requirements (RFC 2093).
-    (active, infer_static_outlives_requirements, "1.26.0", Some(54185), None),
-
-    /// Allows accessing fields of unions inside `const` functions.
-    (active, const_fn_union, "1.27.0", Some(51909), None),
-
-    /// Allows casting raw pointers to `usize` during const eval.
-    (active, const_raw_ptr_to_usize_cast, "1.27.0", Some(51910), None),
-
-    /// Allows dereferencing raw pointers during const eval.
-    (active, const_raw_ptr_deref, "1.27.0", Some(51911), None),
-
-    /// Allows comparing raw pointers during const eval.
-    (active, const_compare_raw_pointers, "1.27.0", Some(53020), None),
-
-    /// Allows `#[doc(alias = "...")]`.
-    (active, doc_alias, "1.27.0", Some(50146), None),
-
-    /// Allows inconsistent bounds in where clauses.
-    (active, trivial_bounds, "1.28.0", Some(48214), None),
-
-    /// Allows `'a: { break 'a; }`.
-    (active, label_break_value, "1.28.0", Some(48594), None),
-
-    /// Allows using `#[doc(keyword = "...")]`.
-    (active, doc_keyword, "1.28.0", Some(51315), None),
-
-    /// Allows reinterpretation of the bits of a value of one type as another
-    /// type during const eval.
-    (active, const_transmute, "1.29.0", Some(53605), None),
-
-    /// Allows using `try {...}` expressions.
-    (active, try_blocks, "1.29.0", Some(31436), None),
-
-    /// Allows defining an `#[alloc_error_handler]`.
-    (active, alloc_error_handler, "1.29.0", Some(51540), None),
-
-    /// Allows using the `amdgpu-kernel` ABI.
-    (active, abi_amdgpu_kernel, "1.29.0", Some(51575), None),
-
-    /// Allows panicking during const eval (producing compile-time errors).
-    (active, const_panic, "1.30.0", Some(51999), None),
-
-    /// Allows `#[marker]` on certain traits allowing overlapping implementations.
-    (active, marker_trait_attr, "1.30.0", Some(29864), None),
-
-    /// Allows macro invocations on modules expressions and statements and
-    /// procedural macros to expand to non-items.
-    (active, proc_macro_hygiene, "1.30.0", Some(54727), None),
-
-    /// Allows unsized rvalues at arguments and parameters.
-    (active, unsized_locals, "1.30.0", Some(48055), None),
-
-    /// Allows custom test frameworks with `#![test_runner]` and `#[test_case]`.
-    (active, custom_test_frameworks, "1.30.0", Some(50297), None),
-
-    /// Allows non-builtin attributes in inner attribute position.
-    (active, custom_inner_attributes, "1.30.0", Some(54726), None),
-
-    /// Allows `impl Trait` in bindings (`let`, `const`, `static`).
-    (active, impl_trait_in_bindings, "1.30.0", Some(63065), None),
-
-    /// Allows using `reason` in lint attributes and the `#[expect(lint)]` lint check.
-    (active, lint_reasons, "1.31.0", Some(54503), None),
-
-    /// Allows exhaustive integer pattern matching on `usize` and `isize`.
-    (active, precise_pointer_size_matching, "1.32.0", Some(56354), None),
-
-    /// Allows using `#[ffi_returns_twice]` on foreign functions.
-    (active, ffi_returns_twice, "1.34.0", Some(58314), None),
-
-    /// Allows const generic types (e.g. `struct Foo<const N: usize>(...);`).
-    (active, const_generics, "1.34.0", Some(44580), None),
-
-    /// Allows using `#[optimize(X)]`.
-    (active, optimize_attribute, "1.34.0", Some(54882), None),
-
-    /// Allows using C-variadics.
-    (active, c_variadic, "1.34.0", Some(44930), None),
-
-    /// Allows the user of associated type bounds.
-    (active, associated_type_bounds, "1.34.0", Some(52662), None),
-
-    /// Allows `if/while p && let q = r && ...` chains.
-    (active, let_chains, "1.37.0", Some(53667), None),
-
-    /// Allows #[repr(transparent)] on enums (RFC 2645).
-    (active, transparent_enums, "1.37.0", Some(60405), None),
-
-    /// Allows #[repr(transparent)] on unions (RFC 2645).
-    (active, transparent_unions, "1.37.0", Some(60405), None),
-
-    /// Allows explicit discriminants on non-unit enum variants.
-    (active, arbitrary_enum_discriminant, "1.37.0", Some(60553), None),
-
-    /// Allows `impl Trait` with multiple unrelated lifetimes.
-    (active, member_constraints, "1.37.0", Some(61977), None),
-
-    /// Allows `async || body` closures.
-    (active, async_closure, "1.37.0", Some(62290), None),
-
-    /// Allows `[x; N]` where `x` is a constant (RFC 2203).
-    (active, const_in_array_repeat_expressions, "1.37.0", Some(49147), None),
-
-    /// Allows `impl Trait` to be used inside type aliases (RFC 2515).
-    (active, type_alias_impl_trait, "1.38.0", Some(63063), None),
-
-    /// Allows the use of or-patterns (e.g., `0 | 1`).
-    (active, or_patterns, "1.38.0", Some(54883), None),
-
-    /// Allows the definition of `const extern fn` and `const unsafe extern fn`.
-    (active, const_extern_fn, "1.40.0", Some(64926), None),
-
-    /// Allows the use of raw-dylibs (RFC 2627).
-    (active, raw_dylib, "1.40.0", Some(58713), None),
-
-    /// Allows `#[track_caller]` to be used which provides
-    /// accurate caller location reporting during panic (RFC 2091).
-    (active, track_caller, "1.40.0", Some(47809), None),
-
-    /// Allows making `dyn Trait` well-formed even if `Trait` is not object safe.
-    /// In that case, `dyn Trait: Trait` does not hold. Moreover, coercions and
-    /// casts in safe Rust to `dyn Trait` for such a `Trait` is also forbidden.
-    (active, object_safe_for_dispatch, "1.40.0", Some(43561), None),
-
-    /// Allows using the `efiapi` ABI.
-    (active, abi_efiapi, "1.40.0", Some(65815), None),
-
-    /// Allows `&raw const $place_expr` and `&raw mut $place_expr` expressions.
-    (active, raw_ref_op, "1.41.0", Some(64490), None),
-
-    /// Allows diverging expressions to fall back to `!` rather than `()`.
-    (active, never_type_fallback, "1.41.0", Some(65992), None),
-
-    /// Allows using the `#[register_attr]` attribute.
-    (active, register_attr, "1.41.0", Some(66080), None),
-
-    /// Allows using the `#[register_tool]` attribute.
-    (active, register_tool, "1.41.0", Some(66079), None),
-
-    /// Allows the use of `if` and `match` in constants.
-    (active, const_if_match, "1.41.0", Some(49146), None),
-
-    // -------------------------------------------------------------------------
-    // feature-group-end: actual feature gates
-    // -------------------------------------------------------------------------
-);
-
-/// Some features are known to be incomplete and using them is likely to have
-/// unanticipated results, such as compiler crashes. We warn the user about these
-/// to alert them.
-pub const INCOMPLETE_FEATURES: &[Symbol] = &[
-    sym::impl_trait_in_bindings,
-    sym::generic_associated_types,
-    sym::const_generics,
-    sym::or_patterns,
-    sym::let_chains,
-    sym::raw_dylib,
-    sym::track_caller,
-];
diff --git a/src/libsyntax/feature_gate/builtin_attrs.rs b/src/libsyntax/feature_gate/builtin_attrs.rs
index a9f41633f30..e6f61e8fcbe 100644
--- a/src/libsyntax/feature_gate/builtin_attrs.rs
+++ b/src/libsyntax/feature_gate/builtin_attrs.rs
@@ -5,13 +5,13 @@ use AttributeGate::*;
 
 use super::check::{emit_feature_err, GateIssue};
 use super::check::{Stability, EXPLAIN_ALLOW_INTERNAL_UNSAFE, EXPLAIN_ALLOW_INTERNAL_UNSTABLE};
-use super::active::Features;
+use rustc_feature::Features;
 
 use crate::ast;
 use crate::attr::AttributeTemplate;
 use crate::sess::ParseSess;
-use crate::symbol::{Symbol, sym};
 
+use syntax_pos::symbol::{Symbol, sym};
 use syntax_pos::Span;
 use rustc_data_structures::fx::FxHashMap;
 use lazy_static::lazy_static;
diff --git a/src/libsyntax/feature_gate/check.rs b/src/libsyntax/feature_gate/check.rs
index ec0eaa56812..7d959756f23 100644
--- a/src/libsyntax/feature_gate/check.rs
+++ b/src/libsyntax/feature_gate/check.rs
@@ -1,6 +1,5 @@
-use super::{active::{ACTIVE_FEATURES, Features}, Feature, State as FeatureState};
-use super::accepted::ACCEPTED_FEATURES;
-use super::removed::{REMOVED_FEATURES, STABLE_REMOVED_FEATURES};
+use rustc_feature::{ACCEPTED_FEATURES, ACTIVE_FEATURES, Features, Feature, State as FeatureState};
+use rustc_feature::{REMOVED_FEATURES, STABLE_REMOVED_FEATURES};
 use super::builtin_attrs::{AttributeGate, BUILTIN_ATTRIBUTE_MAP};
 
 use crate::ast::{self, AssocTyConstraint, AssocTyConstraintKind, NodeId};
diff --git a/src/libsyntax/feature_gate/mod.rs b/src/libsyntax/feature_gate/mod.rs
deleted file mode 100644
index c4418c0f0f6..00000000000
--- a/src/libsyntax/feature_gate/mod.rs
+++ /dev/null
@@ -1,71 +0,0 @@
-//! # Feature gating
-//!
-//! This module implements the gating necessary for preventing certain compiler
-//! features from being used by default. This module will crawl a pre-expanded
-//! AST to ensure that there are no features which are used that are not
-//! enabled.
-//!
-//! Features are enabled in programs via the crate-level attributes of
-//! `#![feature(...)]` with a comma-separated list of features.
-//!
-//! For the purpose of future feature-tracking, once code for detection of feature
-//! gate usage is added, *do not remove it again* even once the feature
-//! becomes stable.
-
-mod accepted;
-mod removed;
-mod active;
-mod builtin_attrs;
-mod check;
-
-use crate::{edition::Edition, symbol::Symbol};
-use std::fmt;
-use std::num::NonZeroU32;
-use syntax_pos::Span;
-
-#[derive(Clone, Copy)]
-pub enum State {
-    Accepted,
-    Active { set: fn(&mut Features, Span) },
-    Removed { reason: Option<&'static str> },
-    Stabilized { reason: Option<&'static str> },
-}
-
-impl fmt::Debug for State {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        match self {
-            State::Accepted { .. } => write!(f, "accepted"),
-            State::Active { .. } => write!(f, "active"),
-            State::Removed { .. } => write!(f, "removed"),
-            State::Stabilized { .. } => write!(f, "stabilized"),
-        }
-    }
-}
-
-#[derive(Debug, Clone)]
-pub struct Feature {
-    state: State,
-    name: Symbol,
-    since: &'static str,
-    issue: Option<u32>,  // FIXME: once #58732 is done make this an Option<NonZeroU32>
-    edition: Option<Edition>,
-    description: &'static str,
-}
-
-impl Feature {
-    fn issue(&self) -> Option<NonZeroU32> {
-        self.issue.and_then(|i| NonZeroU32::new(i))
-    }
-}
-
-pub use active::{Features, INCOMPLETE_FEATURES};
-pub use builtin_attrs::{
-    AttributeGate, AttributeType, GatedCfg,
-    BuiltinAttribute, BUILTIN_ATTRIBUTES, BUILTIN_ATTRIBUTE_MAP,
-    deprecated_attributes, is_builtin_attr,  is_builtin_attr_name,
-};
-pub use check::{
-    check_crate, check_attribute, get_features, feature_err, emit_feature_err,
-    Stability, GateIssue, UnstableFeatures,
-    EXPLAIN_STMT_ATTR_SYNTAX, EXPLAIN_UNSIZED_TUPLE_COERCION,
-};
diff --git a/src/libsyntax/feature_gate/removed.rs b/src/libsyntax/feature_gate/removed.rs
deleted file mode 100644
index f0aa74c65df..00000000000
--- a/src/libsyntax/feature_gate/removed.rs
+++ /dev/null
@@ -1,116 +0,0 @@
-//! List of the removed feature gates.
-
-use crate::symbol::sym;
-use super::{State, Feature};
-
-macro_rules! declare_features {
-    ($(
-        $(#[doc = $doc:tt])* (removed, $feature:ident, $ver:expr, $issue:expr, None, $reason:expr),
-    )+) => {
-        /// Represents unstable features which have since been removed (it was once Active)
-        pub const REMOVED_FEATURES: &[Feature] = &[
-            $(
-                Feature {
-                    state: State::Removed { reason: $reason },
-                    name: sym::$feature,
-                    since: $ver,
-                    issue: $issue,
-                    edition: None,
-                    description: concat!($($doc,)*),
-                }
-            ),+
-        ];
-    };
-
-    ($(
-        $(#[doc = $doc:tt])* (stable_removed, $feature:ident, $ver:expr, $issue:expr, None),
-    )+) => {
-        /// Represents stable features which have since been removed (it was once Accepted)
-        pub const STABLE_REMOVED_FEATURES: &[Feature] = &[
-            $(
-                Feature {
-                    state: State::Stabilized { reason: None },
-                    name: sym::$feature,
-                    since: $ver,
-                    issue: $issue,
-                    edition: None,
-                    description: concat!($($doc,)*),
-                }
-            ),+
-        ];
-    };
-}
-
-declare_features! (
-    // -------------------------------------------------------------------------
-    // feature-group-start: removed features
-    // -------------------------------------------------------------------------
-
-    (removed, import_shadowing, "1.0.0", None, None, None),
-    (removed, managed_boxes, "1.0.0", None, None, None),
-    /// Allows use of unary negate on unsigned integers, e.g., -e for e: u8
-    (removed, negate_unsigned, "1.0.0", Some(29645), None, None),
-    (removed, reflect, "1.0.0", Some(27749), None, None),
-    /// A way to temporarily opt out of opt in copy. This will *never* be accepted.
-    (removed, opt_out_copy, "1.0.0", None, None, None),
-    (removed, quad_precision_float, "1.0.0", None, None, None),
-    (removed, struct_inherit, "1.0.0", None, None, None),
-    (removed, test_removed_feature, "1.0.0", None, None, None),
-    (removed, visible_private_types, "1.0.0", None, None, None),
-    (removed, unsafe_no_drop_flag, "1.0.0", None, None, None),
-    /// Allows using items which are missing stability attributes
-    (removed, unmarked_api, "1.0.0", None, None, None),
-    (removed, allocator, "1.0.0", None, None, None),
-    (removed, simd, "1.0.0", Some(27731), None,
-     Some("removed in favor of `#[repr(simd)]`")),
-    (removed, advanced_slice_patterns, "1.0.0", Some(62254), None,
-     Some("merged into `#![feature(slice_patterns)]`")),
-    (removed, macro_reexport, "1.0.0", Some(29638), None,
-     Some("subsumed by `pub use`")),
-    /// Allows using custom attributes (RFC 572).
-    (removed, custom_attribute, "1.0.0", Some(29642), None,
-     Some("removed in favor of `#![register_tool]` and `#![register_attr]`")),
-    (removed, pushpop_unsafe, "1.2.0", None, None, None),
-    (removed, needs_allocator, "1.4.0", Some(27389), None,
-     Some("subsumed by `#![feature(allocator_internals)]`")),
-    (removed, proc_macro_mod, "1.27.0", Some(54727), None,
-     Some("subsumed by `#![feature(proc_macro_hygiene)]`")),
-    (removed, proc_macro_expr, "1.27.0", Some(54727), None,
-     Some("subsumed by `#![feature(proc_macro_hygiene)]`")),
-    (removed, proc_macro_non_items, "1.27.0", Some(54727), None,
-     Some("subsumed by `#![feature(proc_macro_hygiene)]`")),
-    (removed, proc_macro_gen, "1.27.0", Some(54727), None,
-     Some("subsumed by `#![feature(proc_macro_hygiene)]`")),
-    (removed, panic_implementation, "1.28.0", Some(44489), None,
-     Some("subsumed by `#[panic_handler]`")),
-    /// Allows the use of `#[derive(Anything)]` as sugar for `#[derive_Anything]`.
-    (removed, custom_derive, "1.32.0", Some(29644), None,
-     Some("subsumed by `#[proc_macro_derive]`")),
-    /// Paths of the form: `extern::foo::bar`
-    (removed, extern_in_paths, "1.33.0", Some(55600), None,
-     Some("subsumed by `::foo::bar` paths")),
-    (removed, quote, "1.33.0", Some(29601), None, None),
-    /// Allows using `#[unsafe_destructor_blind_to_params]` (RFC 1238).
-    (removed, dropck_parametricity, "1.38.0", Some(28498), None, None),
-    (removed, await_macro, "1.38.0", Some(50547), None,
-     Some("subsumed by `.await` syntax")),
-    /// Allows defining `existential type`s.
-    (removed, existential_type, "1.38.0", Some(63063), None,
-     Some("removed in favor of `#![feature(type_alias_impl_trait)]`")),
-    /// Allows using the macros:
-    /// + `__diagnostic_used`
-    /// + `__register_diagnostic`
-    /// +`__build_diagnostic_array`
-    (removed, rustc_diagnostic_macros, "1.38.0", None, None, None),
-    /// Allows using `#[on_unimplemented(..)]` on traits.
-    /// (Moved to `rustc_attrs`.)
-    (removed, on_unimplemented, "1.40.0", None, None, None),
-
-    // -------------------------------------------------------------------------
-    // feature-group-end: removed features
-    // -------------------------------------------------------------------------
-);
-
-declare_features! (
-    (stable_removed, no_stack_check, "1.0.0", None, None),
-);
diff --git a/src/libsyntax/lib.rs b/src/libsyntax/lib.rs
index 22b49862f49..f0d857673e7 100644
--- a/src/libsyntax/lib.rs
+++ b/src/libsyntax/lib.rs
@@ -92,7 +92,20 @@ pub mod attr;
 pub mod expand;
 pub use syntax_pos::source_map;
 pub mod entry;
-pub mod feature_gate;
+pub mod feature_gate {
+    mod check;
+    pub use check::{
+        check_crate, check_attribute, get_features, feature_err, emit_feature_err,
+        Stability, GateIssue, UnstableFeatures,
+        EXPLAIN_STMT_ATTR_SYNTAX, EXPLAIN_UNSIZED_TUPLE_COERCION,
+    };
+    mod builtin_attrs;
+    pub use builtin_attrs::{
+        AttributeGate, AttributeType, GatedCfg,
+        BuiltinAttribute, BUILTIN_ATTRIBUTES, BUILTIN_ATTRIBUTE_MAP,
+        deprecated_attributes, is_builtin_attr,  is_builtin_attr_name,
+    };
+}
 pub mod mut_visit;
 pub mod ptr;
 pub mod show_span;