src/librustc_ast_passes/feature_gate.rs

   1 use rustc_error_codes::*;
   2 use rustc_errors::{struct_span_err, Handler};
   3 use rustc_feature::{AttributeGate, BUILTIN_ATTRIBUTE_MAP};
   4 use rustc_feature::{Features, GateIssue, UnstableFeatures};
   5 use rustc_span::source_map::Spanned;
   6 use rustc_span::symbol::sym;
   7 use rustc_span::Span;
   8 use syntax::ast::{self, AssocTyConstraint, AssocTyConstraintKind, NodeId};
   9 use syntax::ast::{GenericParam, GenericParamKind, PatKind, RangeEnd, VariantData};
  10 use syntax::attr;
  11 use syntax::sess::{feature_err, leveled_feature_err, GateStrength, ParseSess};
  12 use syntax::visit::{self, FnKind, Visitor};
  13
  14 use log::debug;
  15
  16 macro_rules! gate_feature_fn {
  17     ($cx: expr, $has_feature: expr, $span: expr, $name: expr, $explain: expr, $level: expr) => {{
  18         let (cx, has_feature, span, name, explain, level) =
  19             (&*$cx, $has_feature, $span, $name, $explain, $level);
  20         let has_feature: bool = has_feature(&$cx.features);
  21         debug!("gate_feature(feature = {:?}, span = {:?}); has? {}", name, span, has_feature);
  22         if !has_feature && !span.allows_unstable($name) {
  23             leveled_feature_err(cx.parse_sess, name, span, GateIssue::Language, explain, level)
  24                 .emit();
  25         }
  26     }};
  27 }
  28
  29 macro_rules! gate_feature {
  30     ($cx: expr, $feature: ident, $span: expr, $explain: expr) => {
  31         gate_feature_fn!(
  32             $cx,
  33             |x: &Features| x.$feature,
  34             $span,
  35             sym::$feature,
  36             $explain,
  37             GateStrength::Hard
  38         )
  39     };
  40     ($cx: expr, $feature: ident, $span: expr, $explain: expr, $level: expr) => {
  41         gate_feature_fn!($cx, |x: &Features| x.$feature, $span, sym::$feature, $explain, $level)
  42     };
  43 }
  44
  45 pub fn check_attribute(attr: &ast::Attribute, parse_sess: &ParseSess, features: &Features) {
  46     PostExpansionVisitor { parse_sess, features }.visit_attribute(attr)
  47 }
  48
  49 struct PostExpansionVisitor<'a> {
  50     parse_sess: &'a ParseSess,
  51     features: &'a Features,
  52 }
  53
  54 macro_rules! gate_feature_post {
  55     ($cx: expr, $feature: ident, $span: expr, $explain: expr) => {{
  56         let (cx, span) = ($cx, $span);
  57         if !span.allows_unstable(sym::$feature) {
  58             gate_feature!(cx, $feature, span, $explain)
  59         }
  60     }};
  61     ($cx: expr, $feature: ident, $span: expr, $explain: expr, $level: expr) => {{
  62         let (cx, span) = ($cx, $span);
  63         if !span.allows_unstable(sym::$feature) {
  64             gate_feature!(cx, $feature, span, $explain, $level)
  65         }
  66     }};
  67 }
  68
  69 impl<'a> PostExpansionVisitor<'a> {
  70     fn check_abi(&self, abi: ast::StrLit) {
  71         let ast::StrLit { symbol_unescaped, span, .. } = abi;
  72
  73         match &*symbol_unescaped.as_str() {
  74             // Stable
  75             "Rust" | "C" | "cdecl" | "stdcall" | "fastcall" | "aapcs" | "win64" | "sysv64"
  76             | "system" => {}
  77             "rust-intrinsic" => {
  78                 gate_feature_post!(&self, intrinsics, span, "intrinsics are subject to change");
  79             }
  80             "platform-intrinsic" => {
  81                 gate_feature_post!(
  82                     &self,
  83                     platform_intrinsics,
  84                     span,
  85                     "platform intrinsics are experimental and possibly buggy"
  86                 );
  87             }
  88             "vectorcall" => {
  89                 gate_feature_post!(
  90                     &self,
  91                     abi_vectorcall,
  92                     span,
  93                     "vectorcall is experimental and subject to change"
  94                 );
  95             }
  96             "thiscall" => {
  97                 gate_feature_post!(
  98                     &self,
  99                     abi_thiscall,
 100                     span,
 101                     "thiscall is experimental and subject to change"
 102                 );
 103             }
 104             "rust-call" => {
 105                 gate_feature_post!(
 106                     &self,
 107                     unboxed_closures,
 108                     span,
 109                     "rust-call ABI is subject to change"
 110                 );
 111             }
 112             "ptx-kernel" => {
 113                 gate_feature_post!(
 114                     &self,
 115                     abi_ptx,
 116                     span,
 117                     "PTX ABIs are experimental and subject to change"
 118                 );
 119             }
 120             "unadjusted" => {
 121                 gate_feature_post!(
 122                     &self,
 123                     abi_unadjusted,
 124                     span,
 125                     "unadjusted ABI is an implementation detail and perma-unstable"
 126                 );
 127             }
 128             "msp430-interrupt" => {
 129                 gate_feature_post!(
 130                     &self,
 131                     abi_msp430_interrupt,
 132                     span,
 133                     "msp430-interrupt ABI is experimental and subject to change"
 134                 );
 135             }
 136             "x86-interrupt" => {
 137                 gate_feature_post!(
 138                     &self,
 139                     abi_x86_interrupt,
 140                     span,
 141                     "x86-interrupt ABI is experimental and subject to change"
 142                 );
 143             }
 144             "amdgpu-kernel" => {
 145                 gate_feature_post!(
 146                     &self,
 147                     abi_amdgpu_kernel,
 148                     span,
 149                     "amdgpu-kernel ABI is experimental and subject to change"
 150                 );
 151             }
 152             "efiapi" => {
 153                 gate_feature_post!(
 154                     &self,
 155                     abi_efiapi,
 156                     span,
 157                     "efiapi ABI is experimental and subject to change"
 158                 );
 159             }
 160             abi => self
 161                 .parse_sess
 162                 .span_diagnostic
 163                 .delay_span_bug(span, &format!("unrecognized ABI not caught in lowering: {}", abi)),
 164         }
 165     }
 166
 167     fn check_extern(&self, ext: ast::Extern) {
 168         if let ast::Extern::Explicit(abi) = ext {
 169             self.check_abi(abi);
 170         }
 171     }
 172
 173     fn maybe_report_invalid_custom_discriminants(&self, variants: &[ast::Variant]) {
 174         let has_fields = variants.iter().any(|variant| match variant.data {
 175             VariantData::Tuple(..) | VariantData::Struct(..) => true,
 176             VariantData::Unit(..) => false,
 177         });
 178
 179         let discriminant_spans = variants
 180             .iter()
 181             .filter(|variant| match variant.data {
 182                 VariantData::Tuple(..) | VariantData::Struct(..) => false,
 183                 VariantData::Unit(..) => true,
 184             })
 185             .filter_map(|variant| variant.disr_expr.as_ref().map(|c| c.value.span))
 186             .collect::<Vec<_>>();
 187
 188         if !discriminant_spans.is_empty() && has_fields {
 189             let mut err = feature_err(
 190                 self.parse_sess,
 191                 sym::arbitrary_enum_discriminant,
 192                 discriminant_spans.clone(),
 193                 "custom discriminant values are not allowed in enums with tuple or struct variants",
 194             );
 195             for sp in discriminant_spans {
 196                 err.span_label(sp, "disallowed custom discriminant");
 197             }
 198             for variant in variants.iter() {
 199                 match &variant.data {
 200                     VariantData::Struct(..) => {
 201                         err.span_label(variant.span, "struct variant defined here");
 202                     }
 203                     VariantData::Tuple(..) => {
 204                         err.span_label(variant.span, "tuple variant defined here");
 205                     }
 206                     VariantData::Unit(..) => {}
 207                 }
 208             }
 209             err.emit();
 210         }
 211     }
 212
 213     fn check_gat(&self, generics: &ast::Generics, span: Span) {
 214         if !generics.params.is_empty() {
 215             gate_feature_post!(
 216                 &self,
 217                 generic_associated_types,
 218                 span,
 219                 "generic associated types are unstable"
 220             );
 221         }
 222         if !generics.where_clause.predicates.is_empty() {
 223             gate_feature_post!(
 224                 &self,
 225                 generic_associated_types,
 226                 span,
 227                 "where clauses on associated types are unstable"
 228             );
 229         }
 230     }
 231
 232     /// Feature gate `impl Trait` inside `type Alias = $type_expr;`.
 233     fn check_impl_trait(&self, ty: &ast::Ty) {
 234         struct ImplTraitVisitor<'a> {
 235             vis: &'a PostExpansionVisitor<'a>,
 236         }
 237         impl Visitor<'_> for ImplTraitVisitor<'_> {
 238             fn visit_ty(&mut self, ty: &ast::Ty) {
 239                 if let ast::TyKind::ImplTrait(..) = ty.kind {
 240                     gate_feature_post!(
 241                         &self.vis,
 242                         type_alias_impl_trait,
 243                         ty.span,
 244                         "`impl Trait` in type aliases is unstable"
 245                     );
 246                 }
 247                 visit::walk_ty(self, ty);
 248             }
 249         }
 250         ImplTraitVisitor { vis: self }.visit_ty(ty);
 251     }
 252 }
 253
 254 impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
 255     fn visit_attribute(&mut self, attr: &ast::Attribute) {
 256         let attr_info =
 257             attr.ident().and_then(|ident| BUILTIN_ATTRIBUTE_MAP.get(&ident.name)).map(|a| **a);
 258         // Check feature gates for built-in attributes.
 259         if let Some((.., AttributeGate::Gated(_, name, descr, has_feature))) = attr_info {
 260             gate_feature_fn!(self, has_feature, attr.span, name, descr, GateStrength::Hard);
 261         }
 262         // Check unstable flavors of the `#[doc]` attribute.
 263         if attr.check_name(sym::doc) {
 264             for nested_meta in attr.meta_item_list().unwrap_or_default() {
 265                 macro_rules! gate_doc { ($($name:ident => $feature:ident)*) => {
 266                     $(if nested_meta.check_name(sym::$name) {
 267                         let msg = concat!("`#[doc(", stringify!($name), ")]` is experimental");
 268                         gate_feature!(self, $feature, attr.span, msg);
 269                     })*
 270                 }}
 271
 272                 gate_doc!(
 273                     include => external_doc
 274                     cfg => doc_cfg
 275                     masked => doc_masked
 276                     spotlight => doc_spotlight
 277                     alias => doc_alias
 278                     keyword => doc_keyword
 279                 );
 280             }
 281         }
 282     }
 283
 284     fn visit_name(&mut self, sp: Span, name: ast::Name) {
 285         if !name.as_str().is_ascii() {
 286             gate_feature_post!(
 287                 &self,
 288                 non_ascii_idents,
 289                 self.parse_sess.source_map().def_span(sp),
 290                 "non-ascii idents are not fully supported"
 291             );
 292         }
 293     }
 294
 295     fn visit_item(&mut self, i: &'a ast::Item) {
 296         match i.kind {
 297             ast::ItemKind::ForeignMod(ref foreign_module) => {
 298                 if let Some(abi) = foreign_module.abi {
 299                     self.check_abi(abi);
 300                 }
 301             }
 302
 303             ast::ItemKind::Fn(..) => {
 304                 if attr::contains_name(&i.attrs[..], sym::plugin_registrar) {
 305                     gate_feature_post!(
 306                         &self,
 307                         plugin_registrar,
 308                         i.span,
 309                         "compiler plugins are experimental and possibly buggy"
 310                     );
 311                 }
 312                 if attr::contains_name(&i.attrs[..], sym::start) {
 313                     gate_feature_post!(
 314                         &self,
 315                         start,
 316                         i.span,
 317                         "`#[start]` functions are experimental \
 318                                        and their signature may change \
 319                                        over time"
 320                     );
 321                 }
 322                 if attr::contains_name(&i.attrs[..], sym::main) {
 323                     gate_feature_post!(
 324                         &self,
 325                         main,
 326                         i.span,
 327                         "declaration of a non-standard `#[main]` \
 328                                         function may change over time, for now \
 329                                         a top-level `fn main()` is required"
 330                     );
 331                 }
 332             }
 333
 334             ast::ItemKind::Struct(..) => {
 335                 for attr in attr::filter_by_name(&i.attrs[..], sym::repr) {
 336                     for item in attr.meta_item_list().unwrap_or_else(Vec::new) {
 337                         if item.check_name(sym::simd) {
 338                             gate_feature_post!(
 339                                 &self,
 340                                 repr_simd,
 341                                 attr.span,
 342                                 "SIMD types are experimental and possibly buggy"
 343                             );
 344                         }
 345                     }
 346                 }
 347             }
 348
 349             ast::ItemKind::Enum(ast::EnumDef { ref variants, .. }, ..) => {
 350                 for variant in variants {
 351                     match (&variant.data, &variant.disr_expr) {
 352                         (ast::VariantData::Unit(..), _) => {}
 353                         (_, Some(disr_expr)) => gate_feature_post!(
 354                             &self,
 355                             arbitrary_enum_discriminant,
 356                             disr_expr.value.span,
 357                             "discriminants on non-unit variants are experimental"
 358                         ),
 359                         _ => {}
 360                     }
 361                 }
 362
 363                 let has_feature = self.features.arbitrary_enum_discriminant;
 364                 if !has_feature && !i.span.allows_unstable(sym::arbitrary_enum_discriminant) {
 365                     self.maybe_report_invalid_custom_discriminants(&variants);
 366                 }
 367             }
 368
 369             ast::ItemKind::Impl(_, polarity, defaultness, ..) => {
 370                 if polarity == ast::ImplPolarity::Negative {
 371                     gate_feature_post!(
 372                         &self,
 373                         optin_builtin_traits,
 374                         i.span,
 375                         "negative trait bounds are not yet fully implemented; \
 376                                         use marker types for now"
 377                     );
 378                 }
 379
 380                 if let ast::Defaultness::Default = defaultness {
 381                     gate_feature_post!(&self, specialization, i.span, "specialization is unstable");
 382                 }
 383             }
 384
 385             ast::ItemKind::Trait(ast::IsAuto::Yes, ..) => {
 386                 gate_feature_post!(
 387                     &self,
 388                     optin_builtin_traits,
 389                     i.span,
 390                     "auto traits are experimental and possibly buggy"
 391                 );
 392             }
 393
 394             ast::ItemKind::TraitAlias(..) => {
 395                 gate_feature_post!(&self, trait_alias, i.span, "trait aliases are experimental");
 396             }
 397
 398             ast::ItemKind::MacroDef(ast::MacroDef { legacy: false, .. }) => {
 399                 let msg = "`macro` is experimental";
 400                 gate_feature_post!(&self, decl_macro, i.span, msg);
 401             }
 402
 403             ast::ItemKind::TyAlias(ref ty, ..) => self.check_impl_trait(&ty),
 404
 405             _ => {}
 406         }
 407
 408         visit::walk_item(self, i);
 409     }
 410
 411     fn visit_foreign_item(&mut self, i: &'a ast::ForeignItem) {
 412         match i.kind {
 413             ast::ForeignItemKind::Fn(..) | ast::ForeignItemKind::Static(..) => {
 414                 let link_name = attr::first_attr_value_str_by_name(&i.attrs, sym::link_name);
 415                 let links_to_llvm = match link_name {
 416                     Some(val) => val.as_str().starts_with("llvm."),
 417                     _ => false,
 418                 };
 419                 if links_to_llvm {
 420                     gate_feature_post!(
 421                         &self,
 422                         link_llvm_intrinsics,
 423                         i.span,
 424                         "linking to LLVM intrinsics is experimental"
 425                     );
 426                 }
 427             }
 428             ast::ForeignItemKind::Ty => {
 429                 gate_feature_post!(&self, extern_types, i.span, "extern types are experimental");
 430             }
 431             ast::ForeignItemKind::Macro(..) => {}
 432         }
 433
 434         visit::walk_foreign_item(self, i)
 435     }
 436
 437     fn visit_ty(&mut self, ty: &'a ast::Ty) {
 438         match ty.kind {
 439             ast::TyKind::BareFn(ref bare_fn_ty) => {
 440                 self.check_extern(bare_fn_ty.ext);
 441             }
 442             ast::TyKind::Never => {
 443                 gate_feature_post!(&self, never_type, ty.span, "The `!` type is experimental");
 444             }
 445             _ => {}
 446         }
 447         visit::walk_ty(self, ty)
 448     }
 449
 450     fn visit_fn_ret_ty(&mut self, ret_ty: &'a ast::FunctionRetTy) {
 451         if let ast::FunctionRetTy::Ty(ref output_ty) = *ret_ty {
 452             if let ast::TyKind::Never = output_ty.kind {
 453                 // Do nothing.
 454             } else {
 455                 self.visit_ty(output_ty)
 456             }
 457         }
 458     }
 459
 460     fn visit_expr(&mut self, e: &'a ast::Expr) {
 461         match e.kind {
 462             ast::ExprKind::Box(_) => {
 463                 gate_feature_post!(
 464                     &self,
 465                     box_syntax,
 466                     e.span,
 467                     "box expression syntax is experimental; you can call `Box::new` instead"
 468                 );
 469             }
 470             ast::ExprKind::Type(..) => {
 471                 // To avoid noise about type ascription in common syntax errors, only emit if it
 472                 // is the *only* error.
 473                 if self.parse_sess.span_diagnostic.err_count() == 0 {
 474                     gate_feature_post!(
 475                         &self,
 476                         type_ascription,
 477                         e.span,
 478                         "type ascription is experimental"
 479                     );
 480                 }
 481             }
 482             ast::ExprKind::TryBlock(_) => {
 483                 gate_feature_post!(&self, try_blocks, e.span, "`try` expression is experimental");
 484             }
 485             ast::ExprKind::Block(_, opt_label) => {
 486                 if let Some(label) = opt_label {
 487                     gate_feature_post!(
 488                         &self,
 489                         label_break_value,
 490                         label.ident.span,
 491                         "labels on blocks are unstable"
 492                     );
 493                 }
 494             }
 495             _ => {}
 496         }
 497         visit::walk_expr(self, e)
 498     }
 499
 500     fn visit_arm(&mut self, arm: &'a ast::Arm) {
 501         visit::walk_arm(self, arm)
 502     }
 503
 504     fn visit_pat(&mut self, pattern: &'a ast::Pat) {
 505         match &pattern.kind {
 506             PatKind::Slice(pats) => {
 507                 for pat in &*pats {
 508                     let span = pat.span;
 509                     let inner_pat = match &pat.kind {
 510                         PatKind::Ident(.., Some(pat)) => pat,
 511                         _ => pat,
 512                     };
 513                     if inner_pat.is_rest() {
 514                         gate_feature_post!(
 515                             &self,
 516                             slice_patterns,
 517                             span,
 518                             "subslice patterns are unstable"
 519                         );
 520                     }
 521                 }
 522             }
 523             PatKind::Box(..) => {
 524                 gate_feature_post!(
 525                     &self,
 526                     box_patterns,
 527                     pattern.span,
 528                     "box pattern syntax is experimental"
 529                 );
 530             }
 531             PatKind::Range(_, _, Spanned { node: RangeEnd::Excluded, .. }) => {
 532                 gate_feature_post!(
 533                     &self,
 534                     exclusive_range_pattern,
 535                     pattern.span,
 536                     "exclusive range pattern syntax is experimental"
 537                 );
 538             }
 539             _ => {}
 540         }
 541         visit::walk_pat(self, pattern)
 542     }
 543
 544     fn visit_fn(
 545         &mut self,
 546         fn_kind: FnKind<'a>,
 547         fn_decl: &'a ast::FnDecl,
 548         span: Span,
 549         _node_id: NodeId,
 550     ) {
 551         if let Some(header) = fn_kind.header() {
 552             // Stability of const fn methods are covered in
 553             // `visit_trait_item` and `visit_impl_item` below; this is
 554             // because default methods don't pass through this point.
 555             self.check_extern(header.ext);
 556         }
 557
 558         if fn_decl.c_variadic() {
 559             gate_feature_post!(&self, c_variadic, span, "C-variadic functions are unstable");
 560         }
 561
 562         visit::walk_fn(self, fn_kind, fn_decl, span)
 563     }
 564
 565     fn visit_generic_param(&mut self, param: &'a GenericParam) {
 566         match param.kind {
 567             GenericParamKind::Const { .. } => gate_feature_post!(
 568                 &self,
 569                 const_generics,
 570                 param.ident.span,
 571                 "const generics are unstable"
 572             ),
 573             _ => {}
 574         }
 575         visit::walk_generic_param(self, param)
 576     }
 577
 578     fn visit_assoc_ty_constraint(&mut self, constraint: &'a AssocTyConstraint) {
 579         match constraint.kind {
 580             AssocTyConstraintKind::Bound { .. } => gate_feature_post!(
 581                 &self,
 582                 associated_type_bounds,
 583                 constraint.span,
 584                 "associated type bounds are unstable"
 585             ),
 586             _ => {}
 587         }
 588         visit::walk_assoc_ty_constraint(self, constraint)
 589     }
 590
 591     fn visit_trait_item(&mut self, ti: &'a ast::AssocItem) {
 592         match ti.kind {
 593             ast::AssocItemKind::Fn(ref sig, ref block) => {
 594                 if block.is_none() {
 595                     self.check_extern(sig.header.ext);
 596                 }
 597                 if sig.header.constness.node == ast::Constness::Const {
 598                     gate_feature_post!(&self, const_fn, ti.span, "const fn is unstable");
 599                 }
 600             }
 601             ast::AssocItemKind::TyAlias(_, ref default) => {
 602                 if let Some(_) = default {
 603                     gate_feature_post!(
 604                         &self,
 605                         associated_type_defaults,
 606                         ti.span,
 607                         "associated type defaults are unstable"
 608                     );
 609                 }
 610             }
 611             _ => {}
 612         }
 613         visit::walk_trait_item(self, ti)
 614     }
 615
 616     fn visit_assoc_item(&mut self, ii: &'a ast::AssocItem) {
 617         if ii.defaultness == ast::Defaultness::Default {
 618             gate_feature_post!(&self, specialization, ii.span, "specialization is unstable");
 619         }
 620
 621         match ii.kind {
 622             ast::AssocItemKind::Fn(ref sig, _) => {
 623                 if sig.decl.c_variadic() {
 624                     gate_feature_post!(
 625                         &self,
 626                         c_variadic,
 627                         ii.span,
 628                         "C-variadic functions are unstable"
 629                     );
 630                 }
 631             }
 632             ast::AssocItemKind::TyAlias(_, ref ty) => {
 633                 if let Some(ty) = ty {
 634                     self.check_impl_trait(ty);
 635                 }
 636                 self.check_gat(&ii.generics, ii.span);
 637             }
 638             _ => {}
 639         }
 640         visit::walk_assoc_item(self, ii)
 641     }
 642
 643     fn visit_vis(&mut self, vis: &'a ast::Visibility) {
 644         if let ast::VisibilityKind::Crate(ast::CrateSugar::JustCrate) = vis.node {
 645             gate_feature_post!(
 646                 &self,
 647                 crate_visibility_modifier,
 648                 vis.span,
 649                 "`crate` visibility modifier is experimental"
 650             );
 651         }
 652         visit::walk_vis(self, vis)
 653     }
 654 }
 655
 656 pub fn check_crate(
 657     krate: &ast::Crate,
 658     parse_sess: &ParseSess,
 659     features: &Features,
 660     unstable: UnstableFeatures,
 661 ) {
 662     maybe_stage_features(&parse_sess.span_diagnostic, krate, unstable);
 663     let mut visitor = PostExpansionVisitor { parse_sess, features };
 664
 665     let spans = parse_sess.gated_spans.spans.borrow();
 666     macro_rules! gate_all {
 667         ($gate:ident, $msg:literal) => {
 668             for span in spans.get(&sym::$gate).unwrap_or(&vec![]) {
 669                 gate_feature!(&visitor, $gate, *span, $msg);
 670             }
 671         };
 672     }
 673     gate_all!(let_chains, "`let` expressions in this position are experimental");
 674     gate_all!(async_closure, "async closures are unstable");
 675     gate_all!(generators, "yield syntax is experimental");
 676     gate_all!(or_patterns, "or-patterns syntax is experimental");
 677     gate_all!(const_extern_fn, "`const extern fn` definitions are unstable");
 678     gate_all!(raw_ref_op, "raw address of syntax is experimental");
 679     gate_all!(const_trait_bound_opt_out, "`?const` on trait bounds is experimental");
 680     gate_all!(const_trait_impl, "const trait impls are experimental");
 681     gate_all!(half_open_range_patterns, "half-open range patterns are unstable");
 682
 683     // All uses of `gate_all!` below this point were added in #65742,
 684     // and subsequently disabled (with the non-early gating readded).
 685     macro_rules! gate_all {
 686         ($gate:ident, $msg:literal) => {
 687             // FIXME(eddyb) do something more useful than always
 688             // disabling these uses of early feature-gatings.
 689             if false {
 690                 for span in spans.get(&sym::$gate).unwrap_or(&vec![]) {
 691                     gate_feature!(&visitor, $gate, *span, $msg);
 692                 }
 693             }
 694         };
 695     }
 696
 697     gate_all!(trait_alias, "trait aliases are experimental");
 698     gate_all!(associated_type_bounds, "associated type bounds are unstable");
 699     gate_all!(crate_visibility_modifier, "`crate` visibility modifier is experimental");
 700     gate_all!(const_generics, "const generics are unstable");
 701     gate_all!(decl_macro, "`macro` is experimental");
 702     gate_all!(box_patterns, "box pattern syntax is experimental");
 703     gate_all!(exclusive_range_pattern, "exclusive range pattern syntax is experimental");
 704     gate_all!(try_blocks, "`try` blocks are unstable");
 705     gate_all!(label_break_value, "labels on blocks are unstable");
 706     gate_all!(box_syntax, "box expression syntax is experimental; you can call `Box::new` instead");
 707     // To avoid noise about type ascription in common syntax errors,
 708     // only emit if it is the *only* error. (Also check it last.)
 709     if parse_sess.span_diagnostic.err_count() == 0 {
 710         gate_all!(type_ascription, "type ascription is experimental");
 711     }
 712
 713     visit::walk_crate(&mut visitor, krate);
 714 }
 715
 716 fn maybe_stage_features(span_handler: &Handler, krate: &ast::Crate, unstable: UnstableFeatures) {
 717     if !unstable.is_nightly_build() {
 718         for attr in krate.attrs.iter().filter(|attr| attr.check_name(sym::feature)) {
 719             struct_span_err!(
 720                 span_handler,
 721                 attr.span,
 722                 E0554,
 723                 "`#![feature]` may not be used on the {} release channel",
 724                 option_env!("CFG_RELEASE_CHANNEL").unwrap_or("(unknown)")
 725             )
 726             .emit();
 727         }
 728     }
 729 }