src/librustc_ast_passes/feature_gate.rs

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