compiler/rustc_ast_passes/src/feature_gate.rs

   1 use rustc_ast as ast;
   2 use rustc_ast::visit::{self, AssocCtxt, FnCtxt, FnKind, Visitor};
   3 use rustc_ast::{AssocTyConstraint, AssocTyConstraintKind, NodeId};
   4 use rustc_ast::{PatKind, RangeEnd, VariantData};
   5 use rustc_errors::struct_span_err;
   6 use rustc_feature::{AttributeGate, BUILTIN_ATTRIBUTE_MAP};
   7 use rustc_feature::{Features, GateIssue};
   8 use rustc_session::parse::{feature_err, feature_err_issue};
   9 use rustc_session::Session;
  10 use rustc_span::source_map::Spanned;
  11 use rustc_span::symbol::sym;
  12 use rustc_span::Span;
  13
  14 use tracing::debug;
  15
  16 macro_rules! gate_feature_fn {
  17     ($visitor: expr, $has_feature: expr, $span: expr, $name: expr, $explain: expr, $help: expr) => {{
  18         let (visitor, has_feature, span, name, explain, help) =
  19             (&*$visitor, $has_feature, $span, $name, $explain, $help);
  20         let has_feature: bool = has_feature(visitor.features);
  21         debug!("gate_feature(feature = {:?}, span = {:?}); has? {}", name, span, has_feature);
  22         if !has_feature && !span.allows_unstable($name) {
  23             feature_err_issue(&visitor.sess.parse_sess, name, span, GateIssue::Language, explain)
  24                 .help(help)
  25                 .emit();
  26         }
  27     }};
  28     ($visitor: expr, $has_feature: expr, $span: expr, $name: expr, $explain: expr) => {{
  29         let (visitor, has_feature, span, name, explain) =
  30             (&*$visitor, $has_feature, $span, $name, $explain);
  31         let has_feature: bool = has_feature(visitor.features);
  32         debug!("gate_feature(feature = {:?}, span = {:?}); has? {}", name, span, has_feature);
  33         if !has_feature && !span.allows_unstable($name) {
  34             feature_err_issue(&visitor.sess.parse_sess, name, span, GateIssue::Language, explain)
  35                 .emit();
  36         }
  37     }};
  38 }
  39
  40 macro_rules! gate_feature_post {
  41     ($visitor: expr, $feature: ident, $span: expr, $explain: expr, $help: expr) => {
  42         gate_feature_fn!($visitor, |x: &Features| x.$feature, $span, sym::$feature, $explain, $help)
  43     };
  44     ($visitor: expr, $feature: ident, $span: expr, $explain: expr) => {
  45         gate_feature_fn!($visitor, |x: &Features| x.$feature, $span, sym::$feature, $explain)
  46     };
  47 }
  48
  49 pub fn check_attribute(attr: &ast::Attribute, sess: &Session, features: &Features) {
  50     PostExpansionVisitor { sess, features }.visit_attribute(attr)
  51 }
  52
  53 struct PostExpansionVisitor<'a> {
  54     sess: &'a Session,
  55
  56     // `sess` contains a `Features`, but this might not be that one.
  57     features: &'a Features,
  58 }
  59
  60 impl<'a> PostExpansionVisitor<'a> {
  61     fn check_abi(&self, abi: ast::StrLit) {
  62         let ast::StrLit { symbol_unescaped, span, .. } = abi;
  63
  64         match &*symbol_unescaped.as_str() {
  65             // Stable
  66             "Rust" | "C" | "cdecl" | "stdcall" | "fastcall" | "aapcs" | "win64" | "sysv64"
  67             | "system" => {}
  68             "rust-intrinsic" => {
  69                 gate_feature_post!(&self, intrinsics, span, "intrinsics are subject to change");
  70             }
  71             "platform-intrinsic" => {
  72                 gate_feature_post!(
  73                     &self,
  74                     platform_intrinsics,
  75                     span,
  76                     "platform intrinsics are experimental and possibly buggy"
  77                 );
  78             }
  79             "vectorcall" => {
  80                 gate_feature_post!(
  81                     &self,
  82                     abi_vectorcall,
  83                     span,
  84                     "vectorcall is experimental and subject to change"
  85                 );
  86             }
  87             "thiscall" => {
  88                 gate_feature_post!(
  89                     &self,
  90                     abi_thiscall,
  91                     span,
  92                     "thiscall is experimental and subject to change"
  93                 );
  94             }
  95             "rust-call" => {
  96                 gate_feature_post!(
  97                     &self,
  98                     unboxed_closures,
  99                     span,
 100                     "rust-call ABI is subject to change"
 101                 );
 102             }
 103             "ptx-kernel" => {
 104                 gate_feature_post!(
 105                     &self,
 106                     abi_ptx,
 107                     span,
 108                     "PTX ABIs are experimental and subject to change"
 109                 );
 110             }
 111             "unadjusted" => {
 112                 gate_feature_post!(
 113                     &self,
 114                     abi_unadjusted,
 115                     span,
 116                     "unadjusted ABI is an implementation detail and perma-unstable"
 117                 );
 118             }
 119             "msp430-interrupt" => {
 120                 gate_feature_post!(
 121                     &self,
 122                     abi_msp430_interrupt,
 123                     span,
 124                     "msp430-interrupt ABI is experimental and subject to change"
 125                 );
 126             }
 127             "x86-interrupt" => {
 128                 gate_feature_post!(
 129                     &self,
 130                     abi_x86_interrupt,
 131                     span,
 132                     "x86-interrupt ABI is experimental and subject to change"
 133                 );
 134             }
 135             "amdgpu-kernel" => {
 136                 gate_feature_post!(
 137                     &self,
 138                     abi_amdgpu_kernel,
 139                     span,
 140                     "amdgpu-kernel ABI is experimental and subject to change"
 141                 );
 142             }
 143             "avr-interrupt" | "avr-non-blocking-interrupt" => {
 144                 gate_feature_post!(
 145                     &self,
 146                     abi_avr_interrupt,
 147                     span,
 148                     "avr-interrupt and avr-non-blocking-interrupt ABIs are experimental and subject to change"
 149                 );
 150             }
 151             "efiapi" => {
 152                 gate_feature_post!(
 153                     &self,
 154                     abi_efiapi,
 155                     span,
 156                     "efiapi ABI is experimental and subject to change"
 157                 );
 158             }
 159             "C-cmse-nonsecure-call" => {
 160                 gate_feature_post!(
 161                     &self,
 162                     abi_c_cmse_nonsecure_call,
 163                     span,
 164                     "C-cmse-nonsecure-call ABI is experimental and subject to change"
 165                 );
 166             }
 167             "C-unwind" => {
 168                 gate_feature_post!(
 169                     &self,
 170                     c_unwind,
 171                     span,
 172                     "C-unwind ABI is experimental and subject to change"
 173                 );
 174             }
 175             "stdcall-unwind" => {
 176                 gate_feature_post!(
 177                     &self,
 178                     c_unwind,
 179                     span,
 180                     "stdcall-unwind ABI is experimental and subject to change"
 181                 );
 182             }
 183             "system-unwind" => {
 184                 gate_feature_post!(
 185                     &self,
 186                     c_unwind,
 187                     span,
 188                     "system-unwind ABI is experimental and subject to change"
 189                 );
 190             }
 191             "thiscall-unwind" => {
 192                 gate_feature_post!(
 193                     &self,
 194                     c_unwind,
 195                     span,
 196                     "thiscall-unwind ABI is experimental and subject to change"
 197                 );
 198             }
 199             "wasm" => {
 200                 gate_feature_post!(
 201                     &self,
 202                     wasm_abi,
 203                     span,
 204                     "wasm ABI is experimental and subject to change"
 205                 );
 206             }
 207             abi => self
 208                 .sess
 209                 .parse_sess
 210                 .span_diagnostic
 211                 .delay_span_bug(span, &format!("unrecognized ABI not caught in lowering: {}", abi)),
 212         }
 213     }
 214
 215     fn check_extern(&self, ext: ast::Extern) {
 216         if let ast::Extern::Explicit(abi) = ext {
 217             self.check_abi(abi);
 218         }
 219     }
 220
 221     fn maybe_report_invalid_custom_discriminants(&self, variants: &[ast::Variant]) {
 222         let has_fields = variants.iter().any(|variant| match variant.data {
 223             VariantData::Tuple(..) | VariantData::Struct(..) => true,
 224             VariantData::Unit(..) => false,
 225         });
 226
 227         let discriminant_spans = variants
 228             .iter()
 229             .filter(|variant| match variant.data {
 230                 VariantData::Tuple(..) | VariantData::Struct(..) => false,
 231                 VariantData::Unit(..) => true,
 232             })
 233             .filter_map(|variant| variant.disr_expr.as_ref().map(|c| c.value.span))
 234             .collect::<Vec<_>>();
 235
 236         if !discriminant_spans.is_empty() && has_fields {
 237             let mut err = feature_err(
 238                 &self.sess.parse_sess,
 239                 sym::arbitrary_enum_discriminant,
 240                 discriminant_spans.clone(),
 241                 "custom discriminant values are not allowed in enums with tuple or struct variants",
 242             );
 243             for sp in discriminant_spans {
 244                 err.span_label(sp, "disallowed custom discriminant");
 245             }
 246             for variant in variants.iter() {
 247                 match &variant.data {
 248                     VariantData::Struct(..) => {
 249                         err.span_label(variant.span, "struct variant defined here");
 250                     }
 251                     VariantData::Tuple(..) => {
 252                         err.span_label(variant.span, "tuple variant defined here");
 253                     }
 254                     VariantData::Unit(..) => {}
 255                 }
 256             }
 257             err.emit();
 258         }
 259     }
 260
 261     fn check_gat(&self, generics: &ast::Generics, span: Span) {
 262         if !generics.params.is_empty() {
 263             gate_feature_post!(
 264                 &self,
 265                 generic_associated_types,
 266                 span,
 267                 "generic associated types are unstable"
 268             );
 269         }
 270         if !generics.where_clause.predicates.is_empty() {
 271             gate_feature_post!(
 272                 &self,
 273                 generic_associated_types,
 274                 span,
 275                 "where clauses on associated types are unstable"
 276             );
 277         }
 278     }
 279
 280     /// Feature gate `impl Trait` inside `type Alias = $type_expr;`.
 281     fn check_impl_trait(&self, ty: &ast::Ty) {
 282         struct ImplTraitVisitor<'a> {
 283             vis: &'a PostExpansionVisitor<'a>,
 284         }
 285         impl Visitor<'_> for ImplTraitVisitor<'_> {
 286             fn visit_ty(&mut self, ty: &ast::Ty) {
 287                 if let ast::TyKind::ImplTrait(..) = ty.kind {
 288                     gate_feature_post!(
 289                         &self.vis,
 290                         min_type_alias_impl_trait,
 291                         ty.span,
 292                         "`impl Trait` in type aliases is unstable"
 293                     );
 294                 }
 295                 visit::walk_ty(self, ty);
 296             }
 297         }
 298         ImplTraitVisitor { vis: self }.visit_ty(ty);
 299     }
 300 }
 301
 302 impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
 303     fn visit_attribute(&mut self, attr: &ast::Attribute) {
 304         let attr_info =
 305             attr.ident().and_then(|ident| BUILTIN_ATTRIBUTE_MAP.get(&ident.name)).map(|a| **a);
 306         // Check feature gates for built-in attributes.
 307         if let Some((.., AttributeGate::Gated(_, name, descr, has_feature))) = attr_info {
 308             gate_feature_fn!(self, has_feature, attr.span, name, descr);
 309         }
 310         // Check unstable flavors of the `#[doc]` attribute.
 311         if self.sess.check_name(attr, sym::doc) {
 312             for nested_meta in attr.meta_item_list().unwrap_or_default() {
 313                 macro_rules! gate_doc { ($($name:ident => $feature:ident)*) => {
 314                     $(if nested_meta.has_name(sym::$name) {
 315                         let msg = concat!("`#[doc(", stringify!($name), ")]` is experimental");
 316                         gate_feature_post!(self, $feature, attr.span, msg);
 317                     })*
 318                 }}
 319
 320                 gate_doc!(
 321                     include => external_doc
 322                     cfg => doc_cfg
 323                     masked => doc_masked
 324                     notable_trait => doc_notable_trait
 325                     keyword => doc_keyword
 326                 );
 327             }
 328         }
 329     }
 330
 331     fn visit_item(&mut self, i: &'a ast::Item) {
 332         match i.kind {
 333             ast::ItemKind::ForeignMod(ref foreign_module) => {
 334                 if let Some(abi) = foreign_module.abi {
 335                     self.check_abi(abi);
 336                 }
 337             }
 338
 339             ast::ItemKind::Fn(..) => {
 340                 if self.sess.contains_name(&i.attrs[..], sym::plugin_registrar) {
 341                     gate_feature_post!(
 342                         &self,
 343                         plugin_registrar,
 344                         i.span,
 345                         "compiler plugins are experimental and possibly buggy"
 346                     );
 347                 }
 348                 if self.sess.contains_name(&i.attrs[..], sym::start) {
 349                     gate_feature_post!(
 350                         &self,
 351                         start,
 352                         i.span,
 353                         "`#[start]` functions are experimental \
 354                          and their signature may change \
 355                          over time"
 356                     );
 357                 }
 358             }
 359
 360             ast::ItemKind::Struct(..) => {
 361                 for attr in self.sess.filter_by_name(&i.attrs[..], sym::repr) {
 362                     for item in attr.meta_item_list().unwrap_or_else(Vec::new) {
 363                         if item.has_name(sym::simd) {
 364                             gate_feature_post!(
 365                                 &self,
 366                                 repr_simd,
 367                                 attr.span,
 368                                 "SIMD types are experimental and possibly buggy"
 369                             );
 370                         }
 371                     }
 372                 }
 373             }
 374
 375             ast::ItemKind::Enum(ast::EnumDef { ref variants, .. }, ..) => {
 376                 for variant in variants {
 377                     match (&variant.data, &variant.disr_expr) {
 378                         (ast::VariantData::Unit(..), _) => {}
 379                         (_, Some(disr_expr)) => gate_feature_post!(
 380                             &self,
 381                             arbitrary_enum_discriminant,
 382                             disr_expr.value.span,
 383                             "discriminants on non-unit variants are experimental"
 384                         ),
 385                         _ => {}
 386                     }
 387                 }
 388
 389                 let has_feature = self.features.arbitrary_enum_discriminant;
 390                 if !has_feature && !i.span.allows_unstable(sym::arbitrary_enum_discriminant) {
 391                     self.maybe_report_invalid_custom_discriminants(&variants);
 392                 }
 393             }
 394
 395             ast::ItemKind::Impl(box ast::ImplKind {
 396                 polarity, defaultness, ref of_trait, ..
 397             }) => {
 398                 if let ast::ImplPolarity::Negative(span) = polarity {
 399                     gate_feature_post!(
 400                         &self,
 401                         negative_impls,
 402                         span.to(of_trait.as_ref().map_or(span, |t| t.path.span)),
 403                         "negative trait bounds are not yet fully implemented; \
 404                          use marker types for now"
 405                     );
 406                 }
 407
 408                 if let ast::Defaultness::Default(_) = defaultness {
 409                     gate_feature_post!(&self, specialization, i.span, "specialization is unstable");
 410                 }
 411             }
 412
 413             ast::ItemKind::Trait(box ast::TraitKind(ast::IsAuto::Yes, ..)) => {
 414                 gate_feature_post!(
 415                     &self,
 416                     auto_traits,
 417                     i.span,
 418                     "auto traits are experimental and possibly buggy"
 419                 );
 420             }
 421
 422             ast::ItemKind::TraitAlias(..) => {
 423                 gate_feature_post!(&self, trait_alias, i.span, "trait aliases are experimental");
 424             }
 425
 426             ast::ItemKind::MacroDef(ast::MacroDef { macro_rules: false, .. }) => {
 427                 let msg = "`macro` is experimental";
 428                 gate_feature_post!(&self, decl_macro, i.span, msg);
 429             }
 430
 431             ast::ItemKind::TyAlias(box ast::TyAliasKind(_, _, _, Some(ref ty))) => {
 432                 self.check_impl_trait(&ty)
 433             }
 434
 435             _ => {}
 436         }
 437
 438         visit::walk_item(self, i);
 439     }
 440
 441     fn visit_foreign_item(&mut self, i: &'a ast::ForeignItem) {
 442         match i.kind {
 443             ast::ForeignItemKind::Fn(..) | ast::ForeignItemKind::Static(..) => {
 444                 let link_name = self.sess.first_attr_value_str_by_name(&i.attrs, sym::link_name);
 445                 let links_to_llvm =
 446                     link_name.map_or(false, |val| val.as_str().starts_with("llvm."));
 447                 if links_to_llvm {
 448                     gate_feature_post!(
 449                         &self,
 450                         link_llvm_intrinsics,
 451                         i.span,
 452                         "linking to LLVM intrinsics is experimental"
 453                     );
 454                 }
 455             }
 456             ast::ForeignItemKind::TyAlias(..) => {
 457                 gate_feature_post!(&self, extern_types, i.span, "extern types are experimental");
 458             }
 459             ast::ForeignItemKind::MacCall(..) => {}
 460         }
 461
 462         visit::walk_foreign_item(self, i)
 463     }
 464
 465     fn visit_ty(&mut self, ty: &'a ast::Ty) {
 466         match ty.kind {
 467             ast::TyKind::BareFn(ref bare_fn_ty) => {
 468                 self.check_extern(bare_fn_ty.ext);
 469             }
 470             ast::TyKind::Never => {
 471                 gate_feature_post!(&self, never_type, ty.span, "the `!` type is experimental");
 472             }
 473             _ => {}
 474         }
 475         visit::walk_ty(self, ty)
 476     }
 477
 478     fn visit_fn_ret_ty(&mut self, ret_ty: &'a ast::FnRetTy) {
 479         if let ast::FnRetTy::Ty(ref output_ty) = *ret_ty {
 480             if let ast::TyKind::Never = output_ty.kind {
 481                 // Do nothing.
 482             } else {
 483                 self.visit_ty(output_ty)
 484             }
 485         }
 486     }
 487
 488     fn visit_expr(&mut self, e: &'a ast::Expr) {
 489         match e.kind {
 490             ast::ExprKind::Box(_) => {
 491                 gate_feature_post!(
 492                     &self,
 493                     box_syntax,
 494                     e.span,
 495                     "box expression syntax is experimental; you can call `Box::new` instead"
 496                 );
 497             }
 498             ast::ExprKind::Type(..) => {
 499                 // To avoid noise about type ascription in common syntax errors, only emit if it
 500                 // is the *only* error.
 501                 if self.sess.parse_sess.span_diagnostic.err_count() == 0 {
 502                     gate_feature_post!(
 503                         &self,
 504                         type_ascription,
 505                         e.span,
 506                         "type ascription is experimental"
 507                     );
 508                 }
 509             }
 510             ast::ExprKind::TryBlock(_) => {
 511                 gate_feature_post!(&self, try_blocks, e.span, "`try` expression is experimental");
 512             }
 513             ast::ExprKind::Block(_, opt_label) => {
 514                 if let Some(label) = opt_label {
 515                     gate_feature_post!(
 516                         &self,
 517                         label_break_value,
 518                         label.ident.span,
 519                         "labels on blocks are unstable"
 520                     );
 521                 }
 522             }
 523             _ => {}
 524         }
 525         visit::walk_expr(self, e)
 526     }
 527
 528     fn visit_pat(&mut self, pattern: &'a ast::Pat) {
 529         match &pattern.kind {
 530             PatKind::Box(..) => {
 531                 gate_feature_post!(
 532                     &self,
 533                     box_patterns,
 534                     pattern.span,
 535                     "box pattern syntax is experimental"
 536                 );
 537             }
 538             PatKind::Range(_, _, Spanned { node: RangeEnd::Excluded, .. }) => {
 539                 gate_feature_post!(
 540                     &self,
 541                     exclusive_range_pattern,
 542                     pattern.span,
 543                     "exclusive range pattern syntax is experimental"
 544                 );
 545             }
 546             _ => {}
 547         }
 548         visit::walk_pat(self, pattern)
 549     }
 550
 551     fn visit_fn(&mut self, fn_kind: FnKind<'a>, span: Span, _: NodeId) {
 552         if let Some(header) = fn_kind.header() {
 553             // Stability of const fn methods are covered in `visit_assoc_item` below.
 554             self.check_extern(header.ext);
 555
 556             if let (ast::Const::Yes(_), ast::Extern::Implicit)
 557             | (ast::Const::Yes(_), ast::Extern::Explicit(_)) = (header.constness, header.ext)
 558             {
 559                 gate_feature_post!(
 560                     &self,
 561                     const_extern_fn,
 562                     span,
 563                     "`const extern fn` definitions are unstable"
 564                 );
 565             }
 566         }
 567
 568         if fn_kind.ctxt() != Some(FnCtxt::Foreign) && fn_kind.decl().c_variadic() {
 569             gate_feature_post!(&self, c_variadic, span, "C-variadic functions are unstable");
 570         }
 571
 572         visit::walk_fn(self, fn_kind, span)
 573     }
 574
 575     fn visit_assoc_ty_constraint(&mut self, constraint: &'a AssocTyConstraint) {
 576         if let AssocTyConstraintKind::Bound { .. } = constraint.kind {
 577             gate_feature_post!(
 578                 &self,
 579                 associated_type_bounds,
 580                 constraint.span,
 581                 "associated type bounds are unstable"
 582             )
 583         }
 584         visit::walk_assoc_ty_constraint(self, constraint)
 585     }
 586
 587     fn visit_assoc_item(&mut self, i: &'a ast::AssocItem, ctxt: AssocCtxt) {
 588         let is_fn = match i.kind {
 589             ast::AssocItemKind::Fn(box ast::FnKind(_, ref sig, _, _)) => {
 590                 if let (ast::Const::Yes(_), AssocCtxt::Trait) = (sig.header.constness, ctxt) {
 591                     gate_feature_post!(&self, const_fn, i.span, "const fn is unstable");
 592                 }
 593                 true
 594             }
 595             ast::AssocItemKind::TyAlias(box ast::TyAliasKind(_, ref generics, _, ref ty)) => {
 596                 if let (Some(_), AssocCtxt::Trait) = (ty, ctxt) {
 597                     gate_feature_post!(
 598                         &self,
 599                         associated_type_defaults,
 600                         i.span,
 601                         "associated type defaults are unstable"
 602                     );
 603                 }
 604                 if let Some(ty) = ty {
 605                     self.check_impl_trait(ty);
 606                 }
 607                 self.check_gat(generics, i.span);
 608                 false
 609             }
 610             _ => false,
 611         };
 612         if let ast::Defaultness::Default(_) = i.kind.defaultness() {
 613             // Limit `min_specialization` to only specializing functions.
 614             gate_feature_fn!(
 615                 &self,
 616                 |x: &Features| x.specialization || (is_fn && x.min_specialization),
 617                 i.span,
 618                 sym::specialization,
 619                 "specialization is unstable"
 620             );
 621         }
 622         visit::walk_assoc_item(self, i, ctxt)
 623     }
 624
 625     fn visit_vis(&mut self, vis: &'a ast::Visibility) {
 626         if let ast::VisibilityKind::Crate(ast::CrateSugar::JustCrate) = vis.kind {
 627             gate_feature_post!(
 628                 &self,
 629                 crate_visibility_modifier,
 630                 vis.span,
 631                 "`crate` visibility modifier is experimental"
 632             );
 633         }
 634         visit::walk_vis(self, vis)
 635     }
 636 }
 637
 638 pub fn check_crate(krate: &ast::Crate, sess: &Session) {
 639     maybe_stage_features(sess, krate);
 640     check_incompatible_features(sess);
 641     let mut visitor = PostExpansionVisitor { sess, features: &sess.features_untracked() };
 642
 643     let spans = sess.parse_sess.gated_spans.spans.borrow();
 644     macro_rules! gate_all {
 645         ($gate:ident, $msg:literal, $help:literal) => {
 646             if let Some(spans) = spans.get(&sym::$gate) {
 647                 for span in spans {
 648                     gate_feature_post!(&visitor, $gate, *span, $msg, $help);
 649                 }
 650             }
 651         };
 652         ($gate:ident, $msg:literal) => {
 653             if let Some(spans) = spans.get(&sym::$gate) {
 654                 for span in spans {
 655                     gate_feature_post!(&visitor, $gate, *span, $msg);
 656                 }
 657             }
 658         };
 659     }
 660     gate_all!(
 661         if_let_guard,
 662         "`if let` guards are experimental",
 663         "you can write `if matches!(<expr>, <pattern>)` instead of `if let <pattern> = <expr>`"
 664     );
 665     gate_all!(
 666         let_chains,
 667         "`let` expressions in this position are experimental",
 668         "you can write `matches!(<expr>, <pattern>)` instead of `let <pattern> = <expr>`"
 669     );
 670     gate_all!(
 671         async_closure,
 672         "async closures are unstable",
 673         "to use an async block, remove the `||`: `async {`"
 674     );
 675     gate_all!(generators, "yield syntax is experimental");
 676     gate_all!(raw_ref_op, "raw address of syntax is experimental");
 677     gate_all!(const_trait_bound_opt_out, "`?const` on trait bounds is experimental");
 678     gate_all!(const_trait_impl, "const trait impls are experimental");
 679     gate_all!(half_open_range_patterns, "half-open range patterns are unstable");
 680     gate_all!(inline_const, "inline-const is experimental");
 681     gate_all!(
 682         extended_key_value_attributes,
 683         "arbitrary expressions in key-value attributes are unstable"
 684     );
 685     gate_all!(
 686         const_generics_defaults,
 687         "default values for const generic parameters are experimental"
 688     );
 689     if sess.parse_sess.span_diagnostic.err_count() == 0 {
 690         // Errors for `destructuring_assignment` can get quite noisy, especially where `_` is
 691         // involved, so we only emit errors where there are no other parsing errors.
 692         gate_all!(destructuring_assignment, "destructuring assignments are unstable");
 693     }
 694     gate_all!(pub_macro_rules, "`pub` on `macro_rules` items is unstable");
 695
 696     // All uses of `gate_all!` below this point were added in #65742,
 697     // and subsequently disabled (with the non-early gating readded).
 698     macro_rules! gate_all {
 699         ($gate:ident, $msg:literal) => {
 700             // FIXME(eddyb) do something more useful than always
 701             // disabling these uses of early feature-gatings.
 702             if false {
 703                 for span in spans.get(&sym::$gate).unwrap_or(&vec![]) {
 704                     gate_feature_post!(&visitor, $gate, *span, $msg);
 705                 }
 706             }
 707         };
 708     }
 709
 710     gate_all!(trait_alias, "trait aliases are experimental");
 711     gate_all!(associated_type_bounds, "associated type bounds are unstable");
 712     gate_all!(crate_visibility_modifier, "`crate` visibility modifier is experimental");
 713     gate_all!(const_generics, "const generics are unstable");
 714     gate_all!(decl_macro, "`macro` is experimental");
 715     gate_all!(box_patterns, "box pattern syntax is experimental");
 716     gate_all!(exclusive_range_pattern, "exclusive range pattern syntax is experimental");
 717     gate_all!(try_blocks, "`try` blocks are unstable");
 718     gate_all!(label_break_value, "labels on blocks are unstable");
 719     gate_all!(box_syntax, "box expression syntax is experimental; you can call `Box::new` instead");
 720     // To avoid noise about type ascription in common syntax errors,
 721     // only emit if it is the *only* error. (Also check it last.)
 722     if sess.parse_sess.span_diagnostic.err_count() == 0 {
 723         gate_all!(type_ascription, "type ascription is experimental");
 724     }
 725
 726     visit::walk_crate(&mut visitor, krate);
 727 }
 728
 729 fn maybe_stage_features(sess: &Session, krate: &ast::Crate) {
 730     use rustc_errors::Applicability;
 731
 732     if !sess.opts.unstable_features.is_nightly_build() {
 733         let lang_features = &sess.features_untracked().declared_lang_features;
 734         for attr in krate.attrs.iter().filter(|attr| sess.check_name(attr, sym::feature)) {
 735             let mut err = struct_span_err!(
 736                 sess.parse_sess.span_diagnostic,
 737                 attr.span,
 738                 E0554,
 739                 "`#![feature]` may not be used on the {} release channel",
 740                 option_env!("CFG_RELEASE_CHANNEL").unwrap_or("(unknown)")
 741             );
 742             let mut all_stable = true;
 743             for ident in
 744                 attr.meta_item_list().into_iter().flatten().map(|nested| nested.ident()).flatten()
 745             {
 746                 let name = ident.name;
 747                 let stable_since = lang_features
 748                     .iter()
 749                     .flat_map(|&(feature, _, since)| if feature == name { since } else { None })
 750                     .next();
 751                 if let Some(since) = stable_since {
 752                     err.help(&format!(
 753                         "the feature `{}` has been stable since {} and no longer requires \
 754                                   an attribute to enable",
 755                         name, since
 756                     ));
 757                 } else {
 758                     all_stable = false;
 759                 }
 760             }
 761             if all_stable {
 762                 err.span_suggestion(
 763                     attr.span,
 764                     "remove the attribute",
 765                     String::new(),
 766                     Applicability::MachineApplicable,
 767                 );
 768             }
 769             err.emit();
 770         }
 771     }
 772 }
 773
 774 fn check_incompatible_features(sess: &Session) {
 775     let features = sess.features_untracked();
 776
 777     let declared_features = features
 778         .declared_lang_features
 779         .iter()
 780         .copied()
 781         .map(|(name, span, _)| (name, span))
 782         .chain(features.declared_lib_features.iter().copied());
 783
 784     for (f1, f2) in rustc_feature::INCOMPATIBLE_FEATURES
 785         .iter()
 786         .filter(|&&(f1, f2)| features.enabled(f1) && features.enabled(f2))
 787     {
 788         if let Some((f1_name, f1_span)) = declared_features.clone().find(|(name, _)| name == f1) {
 789             if let Some((f2_name, f2_span)) = declared_features.clone().find(|(name, _)| name == f2)
 790             {
 791                 let spans = vec![f1_span, f2_span];
 792                 sess.struct_span_err(
 793                     spans.clone(),
 794                     &format!(
 795                         "features `{}` and `{}` are incompatible, using them at the same time \
 796                         is not allowed",
 797                         f1_name, f2_name
 798                     ),
 799                 )
 800                 .help("remove one of these features")
 801                 .emit();
 802             }
 803         }
 804     }
 805 }