{syntax -> rustc_ast_passes}::feature_gate

2 files changed, 0 insertions, 734 deletions

diff --git a/src/libsyntax/feature_gate/check.rs b/src/libsyntax/feature_gate/check.rs
deleted file mode 100644
index 46a22f12678..00000000000
--- a/src/libsyntax/feature_gate/check.rs
+++ /dev/null
@@ -1,730 +0,0 @@
-use crate::ast::{self, AssocTyConstraint, AssocTyConstraintKind, NodeId};
-use crate::ast::{GenericParam, GenericParamKind, PatKind, RangeEnd, VariantData};
-use crate::attr;
-use crate::sess::{feature_err, leveled_feature_err, GateStrength, ParseSess};
-use crate::visit::{self, FnKind, Visitor};
-
-use rustc_error_codes::*;
-use rustc_errors::{struct_span_err, Handler};
-use rustc_feature::{AttributeGate, BUILTIN_ATTRIBUTE_MAP};
-use rustc_feature::{Features, GateIssue, UnstableFeatures};
-use rustc_span::source_map::Spanned;
-use rustc_span::symbol::sym;
-use rustc_span::Span;
-
-use log::debug;
-
-macro_rules! gate_feature_fn {
-    ($cx: expr, $has_feature: expr, $span: expr, $name: expr, $explain: expr, $level: expr) => {{
-        let (cx, has_feature, span, name, explain, level) =
-            (&*$cx, $has_feature, $span, $name, $explain, $level);
-        let has_feature: bool = has_feature(&$cx.features);
-        debug!("gate_feature(feature = {:?}, span = {:?}); has? {}", name, span, has_feature);
-        if !has_feature && !span.allows_unstable($name) {
-            leveled_feature_err(cx.parse_sess, name, span, GateIssue::Language, explain, level)
-                .emit();
-        }
-    }};
-}
-
-macro_rules! gate_feature {
-    ($cx: expr, $feature: ident, $span: expr, $explain: expr) => {
-        gate_feature_fn!(
-            $cx,
-            |x: &Features| x.$feature,
-            $span,
-            sym::$feature,
-            $explain,
-            GateStrength::Hard
-        )
-    };
-    ($cx: expr, $feature: ident, $span: expr, $explain: expr, $level: expr) => {
-        gate_feature_fn!($cx, |x: &Features| x.$feature, $span, sym::$feature, $explain, $level)
-    };
-}
-
-pub fn check_attribute(attr: &ast::Attribute, parse_sess: &ParseSess, features: &Features) {
-    PostExpansionVisitor { parse_sess, features }.visit_attribute(attr)
-}
-
-struct PostExpansionVisitor<'a> {
-    parse_sess: &'a ParseSess,
-    features: &'a Features,
-}
-
-macro_rules! gate_feature_post {
-    ($cx: expr, $feature: ident, $span: expr, $explain: expr) => {{
-        let (cx, span) = ($cx, $span);
-        if !span.allows_unstable(sym::$feature) {
-            gate_feature!(cx, $feature, span, $explain)
-        }
-    }};
-    ($cx: expr, $feature: ident, $span: expr, $explain: expr, $level: expr) => {{
-        let (cx, span) = ($cx, $span);
-        if !span.allows_unstable(sym::$feature) {
-            gate_feature!(cx, $feature, span, $explain, $level)
-        }
-    }};
-}
-
-impl<'a> PostExpansionVisitor<'a> {
-    fn check_abi(&self, abi: ast::StrLit) {
-        let ast::StrLit { symbol_unescaped, span, .. } = abi;
-
-        match &*symbol_unescaped.as_str() {
-            // Stable
-            "Rust" | "C" | "cdecl" | "stdcall" | "fastcall" | "aapcs" | "win64" | "sysv64"
-            | "system" => {}
-            "rust-intrinsic" => {
-                gate_feature_post!(&self, intrinsics, span, "intrinsics are subject to change");
-            }
-            "platform-intrinsic" => {
-                gate_feature_post!(
-                    &self,
-                    platform_intrinsics,
-                    span,
-                    "platform intrinsics are experimental and possibly buggy"
-                );
-            }
-            "vectorcall" => {
-                gate_feature_post!(
-                    &self,
-                    abi_vectorcall,
-                    span,
-                    "vectorcall is experimental and subject to change"
-                );
-            }
-            "thiscall" => {
-                gate_feature_post!(
-                    &self,
-                    abi_thiscall,
-                    span,
-                    "thiscall is experimental and subject to change"
-                );
-            }
-            "rust-call" => {
-                gate_feature_post!(
-                    &self,
-                    unboxed_closures,
-                    span,
-                    "rust-call ABI is subject to change"
-                );
-            }
-            "ptx-kernel" => {
-                gate_feature_post!(
-                    &self,
-                    abi_ptx,
-                    span,
-                    "PTX ABIs are experimental and subject to change"
-                );
-            }
-            "unadjusted" => {
-                gate_feature_post!(
-                    &self,
-                    abi_unadjusted,
-                    span,
-                    "unadjusted ABI is an implementation detail and perma-unstable"
-                );
-            }
-            "msp430-interrupt" => {
-                gate_feature_post!(
-                    &self,
-                    abi_msp430_interrupt,
-                    span,
-                    "msp430-interrupt ABI is experimental and subject to change"
-                );
-            }
-            "x86-interrupt" => {
-                gate_feature_post!(
-                    &self,
-                    abi_x86_interrupt,
-                    span,
-                    "x86-interrupt ABI is experimental and subject to change"
-                );
-            }
-            "amdgpu-kernel" => {
-                gate_feature_post!(
-                    &self,
-                    abi_amdgpu_kernel,
-                    span,
-                    "amdgpu-kernel ABI is experimental and subject to change"
-                );
-            }
-            "efiapi" => {
-                gate_feature_post!(
-                    &self,
-                    abi_efiapi,
-                    span,
-                    "efiapi ABI is experimental and subject to change"
-                );
-            }
-            abi => self
-                .parse_sess
-                .span_diagnostic
-                .delay_span_bug(span, &format!("unrecognized ABI not caught in lowering: {}", abi)),
-        }
-    }
-
-    fn check_extern(&self, ext: ast::Extern) {
-        if let ast::Extern::Explicit(abi) = ext {
-            self.check_abi(abi);
-        }
-    }
-
-    fn maybe_report_invalid_custom_discriminants(&self, variants: &[ast::Variant]) {
-        let has_fields = variants.iter().any(|variant| match variant.data {
-            VariantData::Tuple(..) | VariantData::Struct(..) => true,
-            VariantData::Unit(..) => false,
-        });
-
-        let discriminant_spans = variants
-            .iter()
-            .filter(|variant| match variant.data {
-                VariantData::Tuple(..) | VariantData::Struct(..) => false,
-                VariantData::Unit(..) => true,
-            })
-            .filter_map(|variant| variant.disr_expr.as_ref().map(|c| c.value.span))
-            .collect::<Vec<_>>();
-
-        if !discriminant_spans.is_empty() && has_fields {
-            let mut err = feature_err(
-                self.parse_sess,
-                sym::arbitrary_enum_discriminant,
-                discriminant_spans.clone(),
-                "custom discriminant values are not allowed in enums with tuple or struct variants",
-            );
-            for sp in discriminant_spans {
-                err.span_label(sp, "disallowed custom discriminant");
-            }
-            for variant in variants.iter() {
-                match &variant.data {
-                    VariantData::Struct(..) => {
-                        err.span_label(variant.span, "struct variant defined here");
-                    }
-                    VariantData::Tuple(..) => {
-                        err.span_label(variant.span, "tuple variant defined here");
-                    }
-                    VariantData::Unit(..) => {}
-                }
-            }
-            err.emit();
-        }
-    }
-
-    fn check_gat(&self, generics: &ast::Generics, span: Span) {
-        if !generics.params.is_empty() {
-            gate_feature_post!(
-                &self,
-                generic_associated_types,
-                span,
-                "generic associated types are unstable"
-            );
-        }
-        if !generics.where_clause.predicates.is_empty() {
-            gate_feature_post!(
-                &self,
-                generic_associated_types,
-                span,
-                "where clauses on associated types are unstable"
-            );
-        }
-    }
-
-    /// Feature gate `impl Trait` inside `type Alias = $type_expr;`.
-    fn check_impl_trait(&self, ty: &ast::Ty) {
-        struct ImplTraitVisitor<'a> {
-            vis: &'a PostExpansionVisitor<'a>,
-        }
-        impl Visitor<'_> for ImplTraitVisitor<'_> {
-            fn visit_ty(&mut self, ty: &ast::Ty) {
-                if let ast::TyKind::ImplTrait(..) = ty.kind {
-                    gate_feature_post!(
-                        &self.vis,
-                        type_alias_impl_trait,
-                        ty.span,
-                        "`impl Trait` in type aliases is unstable"
-                    );
-                }
-                visit::walk_ty(self, ty);
-            }
-        }
-        ImplTraitVisitor { vis: self }.visit_ty(ty);
-    }
-}
-
-impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
-    fn visit_attribute(&mut self, attr: &ast::Attribute) {
-        let attr_info =
-            attr.ident().and_then(|ident| BUILTIN_ATTRIBUTE_MAP.get(&ident.name)).map(|a| **a);
-        // Check feature gates for built-in attributes.
-        if let Some((.., AttributeGate::Gated(_, name, descr, has_feature))) = attr_info {
-            gate_feature_fn!(self, has_feature, attr.span, name, descr, GateStrength::Hard);
-        }
-        // Check unstable flavors of the `#[doc]` attribute.
-        if attr.check_name(sym::doc) {
-            for nested_meta in attr.meta_item_list().unwrap_or_default() {
-                macro_rules! gate_doc { ($($name:ident => $feature:ident)*) => {
-                    $(if nested_meta.check_name(sym::$name) {
-                        let msg = concat!("`#[doc(", stringify!($name), ")]` is experimental");
-                        gate_feature!(self, $feature, attr.span, msg);
-                    })*
-                }}
-
-                gate_doc!(
-                    include => external_doc
-                    cfg => doc_cfg
-                    masked => doc_masked
-                    spotlight => doc_spotlight
-                    alias => doc_alias
-                    keyword => doc_keyword
-                );
-            }
-        }
-    }
-
-    fn visit_name(&mut self, sp: Span, name: ast::Name) {
-        if !name.as_str().is_ascii() {
-            gate_feature_post!(
-                &self,
-                non_ascii_idents,
-                self.parse_sess.source_map().def_span(sp),
-                "non-ascii idents are not fully supported"
-            );
-        }
-    }
-
-    fn visit_item(&mut self, i: &'a ast::Item) {
-        match i.kind {
-            ast::ItemKind::ForeignMod(ref foreign_module) => {
-                if let Some(abi) = foreign_module.abi {
-                    self.check_abi(abi);
-                }
-            }
-
-            ast::ItemKind::Fn(..) => {
-                if attr::contains_name(&i.attrs[..], sym::plugin_registrar) {
-                    gate_feature_post!(
-                        &self,
-                        plugin_registrar,
-                        i.span,
-                        "compiler plugins are experimental and possibly buggy"
-                    );
-                }
-                if attr::contains_name(&i.attrs[..], sym::start) {
-                    gate_feature_post!(
-                        &self,
-                        start,
-                        i.span,
-                        "`#[start]` functions are experimental \
-                                       and their signature may change \
-                                       over time"
-                    );
-                }
-                if attr::contains_name(&i.attrs[..], sym::main) {
-                    gate_feature_post!(
-                        &self,
-                        main,
-                        i.span,
-                        "declaration of a non-standard `#[main]` \
-                                        function may change over time, for now \
-                                        a top-level `fn main()` is required"
-                    );
-                }
-            }
-
-            ast::ItemKind::Struct(..) => {
-                for attr in attr::filter_by_name(&i.attrs[..], sym::repr) {
-                    for item in attr.meta_item_list().unwrap_or_else(Vec::new) {
-                        if item.check_name(sym::simd) {
-                            gate_feature_post!(
-                                &self,
-                                repr_simd,
-                                attr.span,
-                                "SIMD types are experimental and possibly buggy"
-                            );
-                        }
-                    }
-                }
-            }
-
-            ast::ItemKind::Enum(ast::EnumDef { ref variants, .. }, ..) => {
-                for variant in variants {
-                    match (&variant.data, &variant.disr_expr) {
-                        (ast::VariantData::Unit(..), _) => {}
-                        (_, Some(disr_expr)) => gate_feature_post!(
-                            &self,
-                            arbitrary_enum_discriminant,
-                            disr_expr.value.span,
-                            "discriminants on non-unit variants are experimental"
-                        ),
-                        _ => {}
-                    }
-                }
-
-                let has_feature = self.features.arbitrary_enum_discriminant;
-                if !has_feature && !i.span.allows_unstable(sym::arbitrary_enum_discriminant) {
-                    self.maybe_report_invalid_custom_discriminants(&variants);
-                }
-            }
-
-            ast::ItemKind::Impl(_, polarity, defaultness, ..) => {
-                if polarity == ast::ImplPolarity::Negative {
-                    gate_feature_post!(
-                        &self,
-                        optin_builtin_traits,
-                        i.span,
-                        "negative trait bounds are not yet fully implemented; \
-                                        use marker types for now"
-                    );
-                }
-
-                if let ast::Defaultness::Default = defaultness {
-                    gate_feature_post!(&self, specialization, i.span, "specialization is unstable");
-                }
-            }
-
-            ast::ItemKind::Trait(ast::IsAuto::Yes, ..) => {
-                gate_feature_post!(
-                    &self,
-                    optin_builtin_traits,
-                    i.span,
-                    "auto traits are experimental and possibly buggy"
-                );
-            }
-
-            ast::ItemKind::TraitAlias(..) => {
-                gate_feature_post!(&self, trait_alias, i.span, "trait aliases are experimental");
-            }
-
-            ast::ItemKind::MacroDef(ast::MacroDef { legacy: false, .. }) => {
-                let msg = "`macro` is experimental";
-                gate_feature_post!(&self, decl_macro, i.span, msg);
-            }
-
-            ast::ItemKind::TyAlias(ref ty, ..) => self.check_impl_trait(&ty),
-
-            _ => {}
-        }
-
-        visit::walk_item(self, i);
-    }
-
-    fn visit_foreign_item(&mut self, i: &'a ast::ForeignItem) {
-        match i.kind {
-            ast::ForeignItemKind::Fn(..) | ast::ForeignItemKind::Static(..) => {
-                let link_name = attr::first_attr_value_str_by_name(&i.attrs, sym::link_name);
-                let links_to_llvm = match link_name {
-                    Some(val) => val.as_str().starts_with("llvm."),
-                    _ => false,
-                };
-                if links_to_llvm {
-                    gate_feature_post!(
-                        &self,
-                        link_llvm_intrinsics,
-                        i.span,
-                        "linking to LLVM intrinsics is experimental"
-                    );
-                }
-            }
-            ast::ForeignItemKind::Ty => {
-                gate_feature_post!(&self, extern_types, i.span, "extern types are experimental");
-            }
-            ast::ForeignItemKind::Macro(..) => {}
-        }
-
-        visit::walk_foreign_item(self, i)
-    }
-
-    fn visit_ty(&mut self, ty: &'a ast::Ty) {
-        match ty.kind {
-            ast::TyKind::BareFn(ref bare_fn_ty) => {
-                self.check_extern(bare_fn_ty.ext);
-            }
-            ast::TyKind::Never => {
-                gate_feature_post!(&self, never_type, ty.span, "The `!` type is experimental");
-            }
-            _ => {}
-        }
-        visit::walk_ty(self, ty)
-    }
-
-    fn visit_fn_ret_ty(&mut self, ret_ty: &'a ast::FunctionRetTy) {
-        if let ast::FunctionRetTy::Ty(ref output_ty) = *ret_ty {
-            if let ast::TyKind::Never = output_ty.kind {
-                // Do nothing.
-            } else {
-                self.visit_ty(output_ty)
-            }
-        }
-    }
-
-    fn visit_expr(&mut self, e: &'a ast::Expr) {
-        match e.kind {
-            ast::ExprKind::Box(_) => {
-                gate_feature_post!(
-                    &self,
-                    box_syntax,
-                    e.span,
-                    "box expression syntax is experimental; you can call `Box::new` instead"
-                );
-            }
-            ast::ExprKind::Type(..) => {
-                // To avoid noise about type ascription in common syntax errors, only emit if it
-                // is the *only* error.
-                if self.parse_sess.span_diagnostic.err_count() == 0 {
-                    gate_feature_post!(
-                        &self,
-                        type_ascription,
-                        e.span,
-                        "type ascription is experimental"
-                    );
-                }
-            }
-            ast::ExprKind::TryBlock(_) => {
-                gate_feature_post!(&self, try_blocks, e.span, "`try` expression is experimental");
-            }
-            ast::ExprKind::Block(_, opt_label) => {
-                if let Some(label) = opt_label {
-                    gate_feature_post!(
-                        &self,
-                        label_break_value,
-                        label.ident.span,
-                        "labels on blocks are unstable"
-                    );
-                }
-            }
-            _ => {}
-        }
-        visit::walk_expr(self, e)
-    }
-
-    fn visit_arm(&mut self, arm: &'a ast::Arm) {
-        visit::walk_arm(self, arm)
-    }
-
-    fn visit_pat(&mut self, pattern: &'a ast::Pat) {
-        match &pattern.kind {
-            PatKind::Slice(pats) => {
-                for pat in &*pats {
-                    let span = pat.span;
-                    let inner_pat = match &pat.kind {
-                        PatKind::Ident(.., Some(pat)) => pat,
-                        _ => pat,
-                    };
-                    if inner_pat.is_rest() {
-                        gate_feature_post!(
-                            &self,
-                            slice_patterns,
-                            span,
-                            "subslice patterns are unstable"
-                        );
-                    }
-                }
-            }
-            PatKind::Box(..) => {
-                gate_feature_post!(
-                    &self,
-                    box_patterns,
-                    pattern.span,
-                    "box pattern syntax is experimental"
-                );
-            }
-            PatKind::Range(_, _, Spanned { node: RangeEnd::Excluded, .. }) => {
-                gate_feature_post!(
-                    &self,
-                    exclusive_range_pattern,
-                    pattern.span,
-                    "exclusive range pattern syntax is experimental"
-                );
-            }
-            _ => {}
-        }
-        visit::walk_pat(self, pattern)
-    }
-
-    fn visit_fn(
-        &mut self,
-        fn_kind: FnKind<'a>,
-        fn_decl: &'a ast::FnDecl,
-        span: Span,
-        _node_id: NodeId,
-    ) {
-        if let Some(header) = fn_kind.header() {
-            // Stability of const fn methods are covered in
-            // `visit_trait_item` and `visit_impl_item` below; this is
-            // because default methods don't pass through this point.
-            self.check_extern(header.ext);
-        }
-
-        if fn_decl.c_variadic() {
-            gate_feature_post!(&self, c_variadic, span, "C-variadic functions are unstable");
-        }
-
-        visit::walk_fn(self, fn_kind, fn_decl, span)
-    }
-
-    fn visit_generic_param(&mut self, param: &'a GenericParam) {
-        match param.kind {
-            GenericParamKind::Const { .. } => gate_feature_post!(
-                &self,
-                const_generics,
-                param.ident.span,
-                "const generics are unstable"
-            ),
-            _ => {}
-        }
-        visit::walk_generic_param(self, param)
-    }
-
-    fn visit_assoc_ty_constraint(&mut self, constraint: &'a AssocTyConstraint) {
-        match constraint.kind {
-            AssocTyConstraintKind::Bound { .. } => gate_feature_post!(
-                &self,
-                associated_type_bounds,
-                constraint.span,
-                "associated type bounds are unstable"
-            ),
-            _ => {}
-        }
-        visit::walk_assoc_ty_constraint(self, constraint)
-    }
-
-    fn visit_trait_item(&mut self, ti: &'a ast::AssocItem) {
-        match ti.kind {
-            ast::AssocItemKind::Fn(ref sig, ref block) => {
-                if block.is_none() {
-                    self.check_extern(sig.header.ext);
-                }
-                if sig.header.constness.node == ast::Constness::Const {
-                    gate_feature_post!(&self, const_fn, ti.span, "const fn is unstable");
-                }
-            }
-            ast::AssocItemKind::TyAlias(_, ref default) => {
-                if let Some(_) = default {
-                    gate_feature_post!(
-                        &self,
-                        associated_type_defaults,
-                        ti.span,
-                        "associated type defaults are unstable"
-                    );
-                }
-            }
-            _ => {}
-        }
-        visit::walk_trait_item(self, ti)
-    }
-
-    fn visit_assoc_item(&mut self, ii: &'a ast::AssocItem) {
-        if ii.defaultness == ast::Defaultness::Default {
-            gate_feature_post!(&self, specialization, ii.span, "specialization is unstable");
-        }
-
-        match ii.kind {
-            ast::AssocItemKind::Fn(ref sig, _) => {
-                if sig.decl.c_variadic() {
-                    gate_feature_post!(
-                        &self,
-                        c_variadic,
-                        ii.span,
-                        "C-variadic functions are unstable"
-                    );
-                }
-            }
-            ast::AssocItemKind::TyAlias(_, ref ty) => {
-                if let Some(ty) = ty {
-                    self.check_impl_trait(ty);
-                }
-                self.check_gat(&ii.generics, ii.span);
-            }
-            _ => {}
-        }
-        visit::walk_assoc_item(self, ii)
-    }
-
-    fn visit_vis(&mut self, vis: &'a ast::Visibility) {
-        if let ast::VisibilityKind::Crate(ast::CrateSugar::JustCrate) = vis.node {
-            gate_feature_post!(
-                &self,
-                crate_visibility_modifier,
-                vis.span,
-                "`crate` visibility modifier is experimental"
-            );
-        }
-        visit::walk_vis(self, vis)
-    }
-}
-
-pub fn check_crate(
-    krate: &ast::Crate,
-    parse_sess: &ParseSess,
-    features: &Features,
-    unstable: UnstableFeatures,
-) {
-    maybe_stage_features(&parse_sess.span_diagnostic, krate, unstable);
-    let mut visitor = PostExpansionVisitor { parse_sess, features };
-
-    let spans = parse_sess.gated_spans.spans.borrow();
-    macro_rules! gate_all {
-        ($gate:ident, $msg:literal) => {
-            for span in spans.get(&sym::$gate).unwrap_or(&vec![]) {
-                gate_feature!(&visitor, $gate, *span, $msg);
-            }
-        };
-    }
-    gate_all!(let_chains, "`let` expressions in this position are experimental");
-    gate_all!(async_closure, "async closures are unstable");
-    gate_all!(generators, "yield syntax is experimental");
-    gate_all!(or_patterns, "or-patterns syntax is experimental");
-    gate_all!(const_extern_fn, "`const extern fn` definitions are unstable");
-    gate_all!(raw_ref_op, "raw address of syntax is experimental");
-    gate_all!(const_trait_bound_opt_out, "`?const` on trait bounds is experimental");
-    gate_all!(const_trait_impl, "const trait impls are experimental");
-    gate_all!(half_open_range_patterns, "half-open range patterns are unstable");
-
-    // All uses of `gate_all!` below this point were added in #65742,
-    // and subsequently disabled (with the non-early gating readded).
-    macro_rules! gate_all {
-        ($gate:ident, $msg:literal) => {
-            // FIXME(eddyb) do something more useful than always
-            // disabling these uses of early feature-gatings.
-            if false {
-                for span in spans.get(&sym::$gate).unwrap_or(&vec![]) {
-                    gate_feature!(&visitor, $gate, *span, $msg);
-                }
-            }
-        };
-    }
-
-    gate_all!(trait_alias, "trait aliases are experimental");
-    gate_all!(associated_type_bounds, "associated type bounds are unstable");
-    gate_all!(crate_visibility_modifier, "`crate` visibility modifier is experimental");
-    gate_all!(const_generics, "const generics are unstable");
-    gate_all!(decl_macro, "`macro` is experimental");
-    gate_all!(box_patterns, "box pattern syntax is experimental");
-    gate_all!(exclusive_range_pattern, "exclusive range pattern syntax is experimental");
-    gate_all!(try_blocks, "`try` blocks are unstable");
-    gate_all!(label_break_value, "labels on blocks are unstable");
-    gate_all!(box_syntax, "box expression syntax is experimental; you can call `Box::new` instead");
-    // To avoid noise about type ascription in common syntax errors,
-    // only emit if it is the *only* error. (Also check it last.)
-    if parse_sess.span_diagnostic.err_count() == 0 {
-        gate_all!(type_ascription, "type ascription is experimental");
-    }
-
-    visit::walk_crate(&mut visitor, krate);
-}
-
-fn maybe_stage_features(span_handler: &Handler, krate: &ast::Crate, unstable: UnstableFeatures) {
-    if !unstable.is_nightly_build() {
-        for attr in krate.attrs.iter().filter(|attr| attr.check_name(sym::feature)) {
-            struct_span_err!(
-                span_handler,
-                attr.span,
-                E0554,
-                "`#![feature]` may not be used on the {} release channel",
-                option_env!("CFG_RELEASE_CHANNEL").unwrap_or("(unknown)")
-            )
-            .emit();
-        }
-    }
-}
diff --git a/src/libsyntax/lib.rs b/src/libsyntax/lib.rs
index 75c647f2daa..fcefe3d2a02 100644
--- a/src/libsyntax/lib.rs
+++ b/src/libsyntax/lib.rs
@@ -75,10 +75,6 @@ pub mod ast;
 pub mod attr;
 pub mod entry;
 pub mod expand;
-pub mod feature_gate {
-    mod check;
-    pub use check::{check_attribute, check_crate};
-}
 pub mod mut_visit;
 pub mod ptr;
 pub mod show_span;